Bel Project & Training Report

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BHARAT ELECTRONICS LIMITED INTRODUCTION India, as a country, has been very lucky with regard to the introduction of telecom products. The first telegraph link was commissioned between Calcutta and Diamond Harbor in the year 1852, which was invented in 1876. First wireless communication equipment were introduced in Indian Army in the year 1909 with the discovery of Radio waves in 1887 by Hertz and demonstration of first wireless link in the year 1905 by Marconi and Vacuum Tube in 1906. Setting up of radio station for broadcast and other telecom facilities almost immediately after their commercial introduction abroad followed this. After independence of India in 1947 and adoption of its constitution in 1950, the government was seized with the plans to lay the foundations of a strong, self-sufficient modern India. On the industrial front, Industrial Policy Resolution (IPR) was announced in the year 1952. It was recognized that in certain core sectors infrastructure facilities require huge investments, which cannot be met by private sector and as such the idea of Public Sector Enterprises (PSE) was mooted. With telecom and electronics recognized among the core sectors, Indian Telephone Industry, now renamed as ITI Limited, was formed in 1953 to undertake local manufacture of telephone equipment, which were of electro-mechanical nature at that stage. Hindustan Cable Limited was also started to take care of telecom cables.

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L - 51504061/ECE/2K5 Bharat Electronics Limited (BEL) was established in 1954 as a public Sector Enterprise under the administrative control of Ministry of Defence as the fountainhead to manufacture and supply electronics components and equipment. BEL, with a noteworthy history of pioneering achievements, has met the requirement of state-of-art professional electronic equipment for Defence, broadcasting, civil Defence and telecommunications as well as the component requirement of entertainment and medical X-ray industry. Over the years, BEL has grown to a multi-product, multi-unit, and technology driven company with track record of a profit earning PSU. The company has a unique position in India of having dealt with all the generations of electronic component and equipment. Having started with a HF receiver in collaboration with T-CSF of France, the company’s equipment designs have had a long voyage through the hybrid, solid-state discrete component to the state of art integrated circuit technology. In the component arena also, the company established its own electron value manufacturing facility. It moved on to semiconductors with the manufacture of germanium and silicon devices and then to the manufacture of Integrated circuits. To keep in pace with the component and technology, its manufacturing and products assurance facilities have also undergone sea change. The design groups have CADD facility; the manufacturing has CNC machines and a Mass Manufacture Facility. QC checks are preformed with multi-dimensional profile measurement machines, Automatic testing machines, environmental labs to check extreme weather and other operational conditions. All these facilities have been established to meet the stringent requirements of MIL grade systems. Today BEL’s infrastructure is spread over nine locations with 29 production divisions having ISO-9001/9002 accreditation. Product mix of the company are spread over the entire Electro-magnetic (EM) sp 3ectrum ranging from tiny audio frequency semiconductor to huge radar systems and X-ray tubes on the upper edge of the spectrum. Its manufacturing units have special focus towards the products ranges like Defence Communication, Rader’s, Optical & Opto-electronics, Telecommunication, sound and Vision Broadcasting, Electronic Components, etc. Besides manufacturing and supply of a wide variety of products, BEL offers a variety of services like Telecom and Rader Systems Consultancy, Contract Manufacturing, Calibration of Test & Measuring Instruments, etc. At the moment, the company is installing GTBKIET.Six Months Training 2

L - 51504061/ECE/2K5 MSSR radar at important airports under the modernization of airports plan of National Airport Authority (NAA). BEL has nurtured and built a strong in-house R&D base by absorbing technologies from more than 50 leading companies worldwide and DRDO Labs for a wide range of products. A team of more than 800 engineers is working in R&D. Each unit has its own R&D Division to bring out new products to the production lines. Central Research Laboratory (CRL) at Bangalore and Ghaziabad works as independent agency to undertake contemporary design work on state-of-art and futuristic technologies. About 70% of BEL’s products are of in-house design. BEL was among the first Indian companies to manufacture computer parts and peripherals under arrangement with International Computers India Limited (ICIL) in 1970s. BEL assembled a limited number of 1901 systems under the arrangement with ICIL. However, following Government’s decision to restrict the computer manufacture to ECIL, BEL could not progress in its computer manufacturing plans. As many of its equipment were microprocessor based, the company, Continued to develop computers based application, both hardware and software. Most of its software requirements are in real time. EMCCA, software intensive navel ships control and command system is probably one of the first projects of its nature in India and Asia. BEL has won a number of national and international awards for Import Substitution, Productivity, Quality, Safety, Standardization etc. BEL was ranked No. 1 in the field of Electronics and 46th overall among the top 1000 private and public sector undertakings in India by the Business Standard in its special supplement “The BS 1000 (1997-98)”. BEL was listed 3rd among the Mini Rattan’s (Category II) by the Government of India, 49th among Asia’s top 100 worldwide Defence Companies by the Defence News, USA.

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CORPORATE MOTTO , MISSION AND OBJECTIVES: The passionate pursuit of excellence at BEL is reflected in a reputation with its customers that can be described in its motto, mission and objectives:

CORPORATE MOTTO “Quality, Technology and Innovation.”

CORPORATE MISSION To be the market leader in Defence Electronics and in other chosen fields and products.

CORPORATE OBJECTIVES  To become a customer-driven company supplying quality products at competitive prices at the expected time and providing excellent customer support.  To achieve growth in the operations commensurate with the growth of professional electronic industry in the country.  To generate internal resources for financing the investments required for modernization, expansion and growth for ensuring a fair return to the investor.  In order to meet the nations strategic needs, to strive for self-reliance by indigenization of materials and components.  To retain the technological leadership of the company in Defence and other chosen fields of electronics through in-house research and development as well as through Collaboration/Co-operation with Defence/National Research Laboratories, International Companies, Universities and Academic Institutions.  To progressively increase overseas sales of its products and services.  To create an organizational culture which encourages members of the organization to real and through continuous learning on the job

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MANUFACTURING UNITS BANGALORE (KANARATAKA) BEL started its production activities in Bangalore on 1954 with 400W high frequency (HF) transmitter and communication receiver for the Army. Since then, the Bangalore Complex has grown to specialize in communication and Radar/Sonar Systems for the Army, Navy and Air-force. BEL’s in-house R&D and successful tie-ups with foreign Defence companies and Indian Defence Laboratories has seen the development and production of over 300 products in Bangalore alone. The Unit has now diversified into manufacturing of electronic products for the civilian customers such as DoT, VSNL, AIR and Doordarshan, Meteorological Dept., ISRO, Police, Civil Aviation and Railways. As an aid to Electorate, the unit has developed Electronic Voting Machines that are produced at its Mass Manufacturing Facility (MMF).

GHAZIABAD (UTTER PRADESH) The second largest Unit at Ghaziabad was set up in 1974 to manufacture special types of radar for the Air Defence Ground Environment Systems (Plan ADGES). The Unit provides Communication Systems to the Defence Forces and Microwave Communication Links to the various departments of the State and Central Govt. and other users. The Unit’s product range included Static and Mobile Radar, Tropo scatter equipment, professional grade Antennae and Microwave components.

PUNE (MAHARASHTRA) This Unit was started in 1979 to manufacture Image Converter Tubes. Subsequently, Magnesium Manganese-dioxide Batteries, Lithium Sulphur Batteries and X-ray Tubes/Cables were added to the product range. At the present the Laser Range Finders for the Defence services.

MACHILIPATNAM (ANDHRA PRADESH) The Andhra Scientific Co. at Machilipatnam, manufacturing Optics/Opto-electronic GTBKIET.Six Months Training

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L - 51504061/ECE/2K5 equipment was integrated with BEL in 1983. the product line includes passive Night Vision Equipment, Binoculars and Goggles, Periscopes, Gun Sights, Surgical Microscope and Optical Sights and Mussel Reference Systems for tank fire control systems. The Unit has successfully diversified to making the Surgical Microscope with zoom facilities.

PANCHKULA (HARYANA) To cater the growing needs of Defence Communications, this Unit was established in 1985. Professional grade Radio-communication Equipment in VHF and UHF ranges entirely developed by BEL and required by the Defence services are being met from this Unit.

CHENNAI (TAMIL NADU) In 1985, BEL established another Unit at Chennai to facilitate manufacture of Gun Control Equipment required for the integration and installation and the Vijay anta tanks. The Unit is now manufacturing Stabilizer Systems for T-72 tanks, Infantry Combat Vehicles BMP-II; Commander’s Panoramic Sights & Tank Laser Sights are among others.

KOTDWARA (UTTER PRADESH) In 1986, BEL STARTED A unit at Kotdwara to manufacture Telecommunication Equipment for both Defence and civilian customers. Focus is being given on the requirement of the Switching Equipment.

TALOJA (MAHARASHTRA) For the manufacture of B/W TV Glass bulbs, this plant was established in collaboration with coming, France in 1986. The Unit is now fully mobilized to manufacture

HYDERABAD (ANDHRA PRADESH) To coordinate with the major Defence R&D Laboratories located in Hyderabad, DLRL, DRDL and DMRL, BEL established a Unit at Hyderabad in 1986. Force Multiplier Systems are manufactured here for the Defence services 20’’ glass bulbs indigenously.

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BEL GHAZIABAD UNIT Formation In the mid 60’s, while reviewing the Defence requirement of the country, the government focused its attention to strengthen the Air Defence system, in particular the ground electronics system support, for the air Defence network. This led to the formulation of a very major plan for an integrated Air Defence Ground Environment System known as the plan ADGES with Prime Minister as the presiding officer of the apex review committee .At about the same time, Public attention was focused on the report of the Bhabha committee on the development and production of electronic equipment. The ministry of Defence immediately realized the need to establish production capacity for meeting the electronic equipment requirements for its plan ADGES. BEL was then inserted with the task of meeting the development and production requirement for the plan ADGES and in view of the importance of the project it was decided to create additional capacity at a second unit of the company. In December 1970 the Govt. sanctioned an additional unit for BEL. In 1971, the industrial license for manufacture of radar and microwave equipment was obtained, 1972 saw the commencement of construction activities and production was launched in 1974. Over the years, the unit has successfully manufactured a wide variety of equipment needed for Defence and civil use. It has also installed and commissioned a large number of systems on turnkey basis. The unit enjoys a unique status as manufacture of IFF systems needed to match a variety of primary raiders. More than 30 versions of IFF’s have already been supplied traveling the path from vacuum technology to solid-state to latest Microwave Component based system.

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PRODUCT RANGES The product ranges today of the company are:

RADAR SYSTEMS  3-Dimensional High Power Static and Mobile Radar for the Air Force.  Low Flying Detection Radar for both the Army and the Air force.  Tactical Control Radar System for the Army.  Battlefield Surveillance Rader for the Army.  IFF Mk-X Radar systems for the Defence and export.  ASR/MSSR systems for Civil Aviation.  Radar & allied systems Data Processing Systems.

COMMUNICATIONS  Digital Static Tropo scatters Communication Systems for the Air Force.  Digital Mobile Tropo scatters communication System for the Air Force and Army.  VHF, UHF & Microwave Communication Equipment.  Bulk Encryption Equipment.  Turnkey communication Systems Projects for Defence & civil users.  Static and Mobile Satellite Communication Systems for Defence.  Telemetry /Tele-control Systems.

ANTENNA  Antennae for Radar, Terrestrial & Satellite Communication Systems.  Antennae for TV Satellite Receive and Broadcast applications.  Antennae for Line-of-sight Microwave Communication Systems.

MICROWAVE COMPONENT  Active Microwave components like LNAs, Synthesizer, and Receivers etc.  Passive Microwave components like Double Balanced Mixers, etc.

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SERVICES OF BHARAT ELECTRONICS LIMITED (BEL):-

DEFENCE PRODUCTS: Naval System  Military Communication Equipment  Radars  Tele Communication & Broadcasting Services  Opto Electronics  Electronic Warfare  Tank Electronics

NON-DEFENCE PRODUCTS: Electronic Voting Machine  Solar Products  Simputer  DTH

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ROTATION PROGRAM Under this students are introduced to the company by putting them under a rotation program to various departments. The several departments where I had gone under my rotational program are: 1.

Test Equipment and Automation

2.

P.C.B. Fabrication

3.

Quality Control Works-Radar

4.

Work Assembly- Communication

5.

Magnetics

6.

Microwave lab Rotation period was to give us a brief insight of the company’s functioning and

knowledge of the various departments. A brief idea of the jobs done at the particular departments was given. The cooperative staff at the various departments made the learning process very interesting , which allowed me to know about the company in a very short time.

TEST EQUIPMENT AND AUTOMATION This department deals with the various instruments used in BEL. There are 300 equipments and they are of 16 types. Examples of some test equipments are:  Oscilloscope(CRO)  Multimeter  Signal Analyzer  Logical Pulsar  Counter  Function Generator etc. Mainly the calibration of instruments is carried out here. They are compared with the standard of National Physical Laboratory (NPL). So, it is said to be one set down to NPL. As every instrument has a calibration period after which the accuracy of the instrument falls from the required standards. So if any of the instruments is not working properly, it is being GTBKIET.Six Months Training 10

L - 51504061/ECE/2K5 sent here for its correct calibration. To calibrate instruments software techniques are used which includes the program written in any suitable programming language. So it is not the calibration but programming that takes time .For any industry to get its instrument calibrated by NPL is very costly, so it is the basic need for every industry to have its own calibration unit if it can afford it.

Test equipment and automation lab mainly deals with the equipment that is used for testing and calibration .The section calibrates and maintains the measuring instruments mainly used for Defence purpose. A calibration is basically testing of equipment with a standard parameter. It is done with the help of standard equipment should be of some make, model and type. The national physical laboratory (NPL), New Delhi provides the standard values yearly. BEL follows International Standard Organization (ISO) standard. The test equipments are calibrated either half yearly or yearly. After testing different tags are labeled on the equipment according to the observations. 1. Green –O.K , Perfect 2. Yellow – Satisfactory but some trouble is present. 3. Red – Can’t be used, should be disposed off. The standard for QC, which are followed by BEL are: 1. WS 102 2. WS 104 3. PS 520 4. PS 809 5. PS 811 6. PS 369 Where, WS = Workmanship & PS = Process Standard After the inspection of cables, PCB’s and other things the defect found are given in following codes. GTBKIET.Six Months Training

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L - 51504061/ECE/2K5 A

--- Physical and Mechanical defects.  B

--- Wrong Writing

 C

--- Wrong Component / Polarity

 D

--- Wrong Component / Mounting

 E

--- Bad Workmanship/ Finish

 F

--- Bad Soldering

 G

--- Alignment Problem

 H

--- Stenciling

 I

--- Others (Specify)

 J

--- Design & Development

After finding the defect, the equipment is sent to responsible department which is rectified there.

P.C.B. FABRICATION P.C.B. stands for Printed Circuits Board. It’s an integral part of the Electronics equipment as well as all the components are mounted on it. It consists of the fiberglass sheet having a layer of copper on both sides.

TYPES OF PCBs 

Single Sided Board

: Circuits on one side.



Double Sided Board

: Circuit on Both side.



Muti-layer Board

: Several layers are interconnected through hole metallization.

Raw material for PCB’s Most common raw material used for manufacturing of PCBs is copper cladded glass epoxy resin sheet. The thickness of the sheet may vary as 1.2, 2.4 and 3.2mm and the standard size of the board is 610mm to 675mm.

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Operation in process Following steps are there for PCB manufacturing:

CNC Drilling



Drill Location



Through Hole Plating



Clean Scrub and Laminate



Photo Print



Develop



Cu electroplate



Tin electroplate



Strip



Etching and cleaning



Tin Stripping



Gold plating



Liquid Photo Imageable Solder Masking (LPISM)



Photo print



Develop



Thermal Baking



Hot Air leaving



Non Plated Hole Drilling



Reverse Marking



Sharing & Routing



Debarring & Packing P.C.B. is a non-conducting board on which a conductive board is made. The base

material, which is used for PCB plate are Glass Epoxy, Bakelite and Teflon etc.

Procedure for through hole metallization Loading-Cleaner-Water Rinse-Spray Water-Rinse-Mild Etch-Spray Water-RinseHydrochloric Acid-Actuator-Water Rinse-Spray Water-Rinse-Accelerator Dip-Spray Water-

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L - 51504061/ECE/2K5 Rinse- Electrolyses Copper-Plating-Plating- Spray water-Rinse-Anti Tarnish Dip-Hot Air Drying- Unloading.

After through hole metallization, photo tool generation is done which is followed by photo printing. In this the PCB is kept b/w two blue sheets and the ckt. is printed on it. A negative and a positive of a ckt. are developed. To identify b/w the negative and positive, following observation is done. If the ckt. is black and the rest of the sheet is white, it is positive otherwise negative.

Next, pattern plating is done. The procedure for pattern plating follows:

Loading- Cleaner- Water rings- Mild etch- Spray- Water Rinse-Electrolytic- Copper plating- Water rinse- Sulfuric acid-Tin plating- Water rinse- Antitarnic dip- Hot air dryUnloading. To give strength to the wires so that they can not break. This is done before molding. Varnishing is done as anti fungus prevention for against environmental hazard.

After completion of manufacturing proceeds it is sent for testing. This is followed by resist striping and copper etching. The unwanted copper i.e. off the tracks is etched by any of the following chemicals. After this, tin is stripped out from the tracks.

After this solder marking is done. Solder marking is done to mark the tracks to get oxidized & finally etch. To prevent the copper from getting etched & making the whole circuit functionally done.

There are three types of solder marking done in BEL: Wet solder mask: Due to some demerits this method is totally ruled out. The demerit was non- alignment, which was due to wrong method applied or wrong machine. Dry pin solder mask: Due to wastage of films about 30% this method is also not used now. Liquid photo imaginable solder mask (LPISM): In this first presoaking is at 80 degree Celsius for 10 to 20 minutes. Next, screen preparation is done. The board is covered by a silk cloth whose mesh is T-48. The angle to tilt of the board is 15 degree to 22.5 degree. GTBKIET.Six Months Training

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The next is ink preparation:

Ink + Hardener 71 %: 29 % (150 gms.)

: (300gms.)

+ Butyrate solo solve 50gms/kg.

Ink preparationIt uses:Ink-----100gm Catalyst----10% of total weight

Reducer-----10% of total weight

The catalyst is used as binder and prevents the following, while reducer is used as thinner. The three things are then fully mixed.

For wash out, following procedure takes place.

Water-Lactic acid-Water-Bleaching power-Water-caustic Soda-Water-Air dry-TCE.

After wash out, final baking for one hour at the temp. Of 20degree C is done. After this shearing or routing is done which is followed by debarring and packing.

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QUALITY CONTROL According to some laid down standards, the quality control department ensures the quality of the product. The raw materials and components etc. purchased and inspected according to the specifications by IG department. Similarly QC work department inspects all the items manufactured in the factory. The fabrication department checks all the fabricated parts and ensures that these are made according to the part drawing, painting , plating and stenciling etc are done as per BEL standards.

The assembly inspection departments inspects all the assembled parts such as PCB , cable assembly ,cable form , modules , racks and shelters as per latest documents and BEL standards .

The mistakes in the PCB can be categorized as: 

D & E mistakes



Shop mistakes



Inspection mistakes

The process card is attached to each PCB under inspection. Any error in the PC is entered in the process card by certain code specified for each error or defect.

After a mistake is detected following actions are taken: 1. Observation is made. 2. Object code is given. 3. Division code is given. 4. Change code is prepared. 5. Recommendation action is taken

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WORK ASSEMBLY This department plays an important role in the production. Its main function is to assemble various components, equipments and instruments in a particular procedure.

It has been broadly classified as:



WORK ASSEMBLY RADAR e.g. INDRA –II, REPORTER.



WORK ASSEMBLY COMMUNICATION e.g. EMCCA, MSSR, MFC.



EMCCA: EQUIPMENT MODULAR FOR COMMAND CONTROL APPLICATION.



MSSR: MONOPULSE SECONDARY SURVEILLANCE RADAR.



MFC: MULTI FUNCTIONAL CONSOLE.

The stepwise procedure followed by work assembly department is: o Preparation of part list that is to be assembled. o Preparation of general assembly. o Schematic diagram to depict all connections to be made and brief idea about all components. o Writing lists of all components. In work assembly following things are done :

Material Receive: Preparation- This is done before mounting and under takes two procedures. Tinning- The resistors ,capacitors and other components are tinned with the help of tinned lead solution .The wire coming out from the components is of copper and it is tinned nicely by applying flux on it so that it does not tarnished and soldering becomes easy. Bending- Preparation is done by getting the entire documents , part list drawing and bringing all the components before doing the work. GTBKIET.Six Months Training

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L - 51504061/ECE/2K5 Mounting- It means soldering the components of the PCB plate with the help of soldering tools. The soldering irons are generally of 25 W and are of variable temperature, one of the wires of the component is soldered so that they don’t move from their respective places on the PCB plate. On the other hand of the component is also adjusted so that the PCB does not burn. Wave Soldering- This is done in a machine and solder stick on the entire path, which are tinned. Touch Up- This is done by hand after the finishing is done.

Cleaning: Inspection- This comes under quality work. Heat Ageing- This is done in environmental lab at temperature of 40 degree C for 4 hrs and three cycles.

Testing: Lacquering- This is only done on components which are not variable. Storing- After this variable components are sleeved with Teflon. Before Lacquering mounted plate is cleaned with isopropyl alcohol. The product is then sent to store.

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MAGNETICS In this department different types of transformers and coils are manufactured , which

are used in the various Defence equipments

i.e. radar , communication

equipments. This department basically consists of three sections : 1.) PRODUCTION CONTROL :- Basic function of production control is to plan the production of transformer and coils as per the requirement of respective division (Radar and Communication). This department divided into two groups : (a) Planning and (b) Planning store . 2.) WORKS (PRODUCTION) :- Production of transformers and coils are being carried out by the works departments. 3.) QUALITY CONTROL :- After manufacturing the transformer/coils the item is offered to the inspection department to check the electrical parameters(DCR , No load current , full load current , dielectric strength , inductance , insulation resistance and mechanical dimension as mentioned in the GA drawing of the product. The D&E department provides all the information about manufacturing a coil and the transformer. The various types of transformers are as follows : 1. Air cored transformers 2. Oil filled transformers 3. Moulding type transformers 4. P.C.B Mounting transformers :(a) Impedance matching transformers (b) RF transformers (c) IF transformers GTBKIET.Six Months Training

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L - 51504061/ECE/2K5 The various types of cores are as follows : 1. E type 2. C type 3. Lamination 4. Ferrite core 5. Toroidal core Steps involved in the process of manufacturing of transformer/coils: 

Preparation of former : Former is made of plastic bakelite comprising a

male

and female plates assembled and glued alternately to form a hollow rectangular box on which winding is done. 

Winding : It is done with different material and thickness of

wire. The

winding has specified number of layers with each layer’s having a specified number of turns. The distance between the two turns should be maintained constantly that is there should be no overlapping. The plasatic layer is inserted between two consecutive layers. The various types of windings are as follows : 

Layer Winding



Wave Winding



Bank Winding



Insulation : For inter-winding and inter layer , various types of insulation sheets viz. Craft paper , paper , leather , oil paper , polyester film are being used.



Protection : To protect the transformer from the external hazards , moisture , dust and to provide high insulation resistance , they are impregnated.

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MICROWAVE LABORATORY Microwave lab deals with very high frequency measurements or very short wavelength measurements. The testing of microwave components is done with the help of various radio and communication devices. Phase and magnitude measurements are done in this section. Power measurements are done for microwave components because current and voltage are very high at such frequencies. Different type of waveguides is tested in this department like rectangular waveguides, circular waveguides. These waveguides can be used to transmit TE mode or TM mode. This depends on the users requirements. A good waveguide should have fewer loses and its walls should be perfect conductors. In rectangular waveguide there is min. distortion. Circular waveguides are used where the antenna is rotating. The power measurements being done in microwave lab are in terms of S- parameters. Mainly the testing is done on coupler and isolators and parameters are tested here. There are two methods of testing: a.) Acceptance Test Procedure(ATP) b.) Production Test Procedure(PTP) Drawing of various equipments that are to be tested is obtained and testing is performed on manufactured part. In the antenna section as well as SOHNA site various parameters such as gain ,bandwidth ,VSWR , phase ,return loss, reflection etc. are checked. The instruments used for this purpose are as follow: i)

Filters

ii)

Isolators

iii)

Reflectors

iv)

Network Analyzers

v)

Spectrum Analyzers GTBKIET.Six Months Training

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Amplifiers and Accessories

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RADAR History of RADAR Nobody can be credited with "inventing" radar. The idea had been around for a long time--a spotlight that could cut through fog. But the problem was that it was too advanced for the technology of the time. It wasn't until the early 20th century that a radar system was first built. One of the biggest advocators of radar technology was Robert Watson-Watt, a British scientist.

Great Britain made a big effort to develop radar in the years leading up to World War Two. Some people credit them with being pioneers in the field. As it was, the early warning radar system (called "Chain Home") that they built around the British Isles warned them of all aerial invasions. This gave the outnumbered Royal Air Force the edge they needed to defeat the German Luftwaffe during the Battle of Britain.

While radar development was pushed because of wartime concerns, the idea first came about as an anti-collision system. After the Titanic ran into an iceberg and sank in 1912, people were interested in ways to make such happenings avoidable

Introduction The term RADAR was coined in 1941 as an acronym for Radio Detection and Ranging. This acronym of American origin replaced the previously used British abbreviation RDF (Radio Direction Finding). Radar is a system that uses radio waves to detect, determine the distance or speed, objects such as aircraft, ships, rain and map them. Speed detection is measured by the amount of Doppler Effect frequency shift of the reflected signal. A transmitter emits radio waves, which are reflected by the target, and detected by a receiver, typically in the same location as the transmitter. Although the radio signal returned is usually very small, radio signals can easily be amplified, so radar can detect objects at ranges where other emission, such as sound or visible light, would be too weak to detect. Radar is used in many contexts, including GTBKIET.Six Months Training

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L - 51504061/ECE/2K5 meteorological detection of precipitation, air traffic control, police detection of speeding traffic, and by the military.

Several inventors, scientists, and engineers contributed to the development of radar. The use of radio waves to detect "the presence of distant metallic objects via radio waves" was first implemented in 1904 by Christian Hülsmeyer, who demonstrated the feasibility of detecting the presence of ships in dense fog and received a patent for radar as Reichspatent Nr. 165546. Another of the first working models was produced by Hungarian Zoltán Bay in 1936 at the Tungsram laboratory

BASIC PRINCIPLE Echo and Doppler Shift Echo is something you experience all the time. If you shout into a well or a canyon, the echo comes back a moment later. The echo occurs because some of the sound waves in your shout reflect off of a surface (either the water at the bottom of the well or the canyon wall on the far side) and travel back to your ears. The length of time between the moments you shout and the distance between you and the surface that creates the echo determines the moment that you hear the echo. Doppler shift is also common. You probably experience it daily (often without realizing it). Doppler shift occurs when sound is generated by, or reflected off of, a moving object. Doppler shift in the extreme creates sonic booms (see below). Here's how to understand Doppler shift (you may also want to try this experiment in an empty parking lot). Let's say there is a car coming toward you at 60 miles per hour (mph) and its horn is blaring. You will hear the horn playing one "note" as the car approaches, but when the car passes you the sound of the horn will suddenly shift to a lower note. It's the same horn making the same sound the whole time. The change you hear is caused by Doppler shift.

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HOW RADAR WORKS A radar system, as found on many merchants’ ships, has three main parts: 1. The antenna unit or the scanner 2. The transmitter receiver or ‘transceiver’ and 3. the visual display unit The antenna is two or three meter wide and focuses pulses off very high frequency radio energy into a narrow vertical beam. The frequency of the radio waves is basically about 10,000 Mhz. The antenna is rotated at the rate of 10 to 25 rpm so that radar beam swaps through 300degree Celsius all around the shiout to a range of about 90 kms. In all radar it is vital that the transmitting and the receiving in a transceiver are in close harmony. Every thing depends on accurate measurement of the time that passes between the transmission of pulse and the return of the echo. About 1000, pulses per second are transmitted. Though it is varied to suit the requirements. Short pulses are best for shortrange work, longer pulses are best for longer-range work. An important part of transceiver circuit is ‘modular circuit’. This

‘keys’ the

transmitter so that it oscillates, or pulses for the right length of time. The pulses so designed are ‘video pulses. These pulses are short range pulses hence can’t serve out the purpose of long range work .In order to modify these pulses to long range pulses or the RF pulses, we need to generate the power. The transmitted power is generated in a device called the “magnetron” which can handle all these short pulses and very high oscillations. The display system usually carried out the control necessary for the operation of whole radar .It has a cathode ray gun, which consists of a electron gun in its neck. The gun shouts electron to the phosphorescent screen at the far end. Phosphorescent screen glows when hit by an electron and the resulting spot can be seen through the glass face. The basic idea behind radar is very simple: a signal is transmitted, it bounces off an object and some type of receiver later receives it. They use certain kinds of electromagnetic waves called radio waves and microwaves. This is where the name RADAR comes from (Radio Detection And Ranging). Sound is used as a signal to detect objects in devices called GTBKIET.Six Months Training

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L - 51504061/ECE/2K5 SONAR (Sound Navigation Ranging). Another type of signal used that is relatively new is laser light that is used in devices called LIDAR (Light Detection And Ranging). Once the radar receives the returned signal, it calculates useful information from it such as the time taken for it to be received, the strength of the returned signal, or the change in frequency of the signal.

Basic Radar System:

A basic radar system is spilt up into a transmitter, switch, antenna, receiver, data recorder, processor and some sort of output display. Everything starts with the transmitter as it transmits a high power pulse to a switch, which then directs the pulse to be transmitted out an antenna. Once the signals are received the switch then transfers control back to the transmitter to transmit another signal. The switch may toggle control between the transmitter and the receiver as much as 1000 times per second. Any received signals from the receiver are then sent to a data recorder for storage on a disk or tape. Later the data must be processed to be interpreted into something useful, which would go on a Pulse Width and Bandwidth: Some radar transmitters do not transmit constant, uninterrupted electromagnetic waves. Instead, they transmit rhythmic pulses of EM waves with a set amount of time in between each pulse. The pulse itself would consist of an EM wave of several wavelengths with some dead time after it in which there are no transmissions. The time between each pulse is called the pulse repetition time (PRT) and the number of pulses transmitted in one GTBKIET.Six Months Training

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L - 51504061/ECE/2K5 second is called the pulse repetition frequency (PRF). The time taken for each pulse to be transmitted is called the pulse width (PW) or pulse duration. Typically they can be around 0.1 microseconds long for penetrating radars or 10-50 microseconds long for imaging radars (a display. microsecond is a millionth of a second). In math language, the above can be said... PRT = 1 / PRF or PRF = 1 / PRT And for all you visual learners out there, this is what it looks like...

RT means repetition time. However, the above diagram is not quite realistic for several reasons. One reason why it is not realistic is that the frequency in waves of the pulses is the same. In real life the frequency of the waves are not the same and they change as time goes on. This is called frequency modulation, which means the frequency changes or modulates. It looks something like this...

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L - 51504061/ECE/2K5 Think of this as one pulse. All the pulses will look something like this. On the above diagram, the frequency of the wave is low on the left and it slowly increases, as you look right. The different frequencies of the wave will lie in a range called bandwidth. Radars use bandwidth for several reasons regarding the resolution of a data image, memory of the radar and overuse of the transmitter. For instance, a high bandwidth can yield a finer resolution but take up more memory. When an EM wave hits a surface, it gets partly reflected away from the surface and refracted into the surface. The amount of reflection and refraction depends on the properties of the surface and the properties of the matter, which the wave was originally traveling through. This is what happens to radar signals when they hit objects. If a radar signal hits a surface that is perfectly flat then the signal gets reflected in a single direction (the same is true for refraction). If the signal hits a surface that is not perfectly flat (like all surfaces on Earth) then it gets reflected in all directions. Only a very small fraction of the original signal is transmitted back in the direction of the receiver. This small fraction is what is known as backscatter. The typical power of a transmitted signal is around 1 kilowatt and the typical power of the backscatter can be around 10 watts.

TYPES OF RADAR Based on function radar can be divided into two types: 1. PRIMARY RADAR 2. SECONDRY RADAR Primary radar or the simple radar locates a target by procedure described in section. But in cases as controlling of air traffic, the controller must be able to identify the aircraft and find whether it is a friend or foe. It is also desired to know the height of aircraft. To give controller this information second radar called the secondary surveillance radar (SSR) is used. This works differently and need the help of the target aircraft it séance out a sequence of pulses to an electronic BLACK BOX called the TRANSPONDER, fitted on the aircraft. The transponder is connected to the aircrafts altimeter (the device which measures the planes altitude) to transmit back the coded message to the radar about its status and altitude. Military aircrafts uses a similar kind of radar system with secrete code to make GTBKIET.Six Months Training

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L - 51504061/ECE/2K5 sure that it is friend or foe, a hostile aircraft does not know what code to transmit back to the ground station for the corresponding receiver code.

IFF UNIT IFF is basically a radar bacon system employed for the purpose of general identification of military targets .The bacon system when used for the control of civil air traffic is called as SECONDARY SURVEILLANCE RADAR (SSR). Primary radar locates an object by transmitting signal and detecting the reflected echo. A secondary radar system is basically very similar to primary radar system except that the returned signal is radiated from the transmitter on board the target rather then by reflection, i.e. it operates with a cooperative ‘active’ target while the primary radar operates with “passive target’.

Secondary radar system consists of an interrogative and a transponder. The interrogator transmitter in the ground station interrogates transponder equipped aircraft, providing two way data communication on different transmitter and receiver frequency .The transponder on board the aircraft on receipt of a chain of pulses from ground interrogator, automatically transmit the reply, coded for the purpose of identification, is received back to the ground interrogator where it is decoded and displayed on a radar type presentation.

RADAR EQUATION The amount of power Pr returning to the receiving antenna is given by the radar equation:

where •

Pt = transmitter power

•

Gt = gain of the transmitting antenna

•

Ar = effective aperture (area) of the receiving antenna

•

σ = radar cross section, or scattering coefficient, of the target

•

F = pattern propagation factor GTBKIET.Six Months Training

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L - 51504061/ECE/2K5 •

Rt = distance from the transmitter to the target

•

Rr = distance from the target to the receiver. In the common case where the transmitter and the receiver are at the same location, Rt

= Rr and the term Rt2 Rr2 can be replaced by R4, where R is the range. This yields:

This shows that the received power declines as the fourth power of the range, which means that the reflected power from distant targets is very, very small. The equation above with F = 1 is a simplification for vacuum without interference. The propagation factor accounts for the effects of multipath and shadowing and depends on the details of the environment. In a real-world situation, pathloss effects should also be considered.

RADAR SIGNAL PROCESSING Distance measurement Transit time

Principle of radar distance measurement using pulse round trip time. One way to measure the distance to an object is to transmit a short pulse of radio signal, and measure the time it takes for the reflection to return. The distance is one-half the product of round trip time (because the signal has to travel to the target and then back to the GTBKIET.Six Months Training

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L - 51504061/ECE/2K5 receiver) and the speed of the signal. Range =

cτ where c is the speed of light in a vacuum, 2

and τ is the round trip time. For radar, the speed of signal is the speed of light, making the round trip times very short for terrestrial ranging. Accurate distance measurement requires high-performance electronics. The receiver cannot detect the return while the signal is being sent out – there is no way to tell if the signal it hears is the original or the return. This means that a radar has a distinct minimum range, which is the length of the pulse multiplied by the speed of light, divided by two. In order to detect closer targets one must use a shorter pulse length. A similar effect imposes a specific maximum range as well. If the return from the target comes in when the next pulse is being sent out, once again the receiver cannot tell the difference. In order to maximize range, one wants to use longer times between pulses, the inter-pulse time. These two effects tend to be at odds with each other, and it is not easy to combine both good short range and good long range in a single radar. This is because the short pulses needed for a good minimum range broadcast have less total energy, making the returns much smaller and the target harder to detect. This could be offset by using more pulses, but this would shorten the maximum range again. So each radar uses a particular type of signal. Long range radars tend to use long pulses with long delays between them, and short range radars use smaller pulses with less time between them. This pattern of pulses and pauses is known as the Pulse Repetition Frequency (or PRF), and is one of the main ways to characterize a radar. As electronics have improved many radars now can change their PRF.

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DIFFERENT TYPES OF RADARS 1. 3D Mobile Radar (PSM 33 Mk II) 3-D mobile radar employs monopulse technique for height estimation and using electronic scanning for getting the desired radar coverage by managing the RF transmission energy in elevation plane as per the operational requirements. It can be connected in air defence radar network. The Radar is configured in three transport vehicles, viz., Antenna, Transmitter cabin, Receiver and Processor Cabin. The radar has an autonomous display for stand-alone operation.

FEATURES  Frequency agility  Monopulse processing for height estimation  Adaptive sensitivity time control  Jamming analysis indication, pulse compression, plot filtering / tracking data remoting  Comprehensive BITE facility

2. Low Flying Detection Radar (INDRA II) The low-level radar caters to the vital gap filling role in an air defence environment. It is a transportable and self-contained system with easy mobility and deployment features. The system consists mainly of an Antenna, Transmitter cabin and Display cabin mounted on three separate vehicles. GTBKIET.Six Months Training

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SYSTEM CHARACTERISTICS  Range up to 90 km (for fighter aircraft)  Height coverage 35m to 3000m subject to Radar horizon  Probability of detection: 90% (Single scan)  Probability of false alarm: 10E-6  Track While Scan (TWS) for 2D tracking  Capability to handle 200 tracks  Association of primary and secondary targets  Automatic target data transmission to a digital modem/networking of radars  Deployment time of about 60 minutes

FEATURES

 Fully coherent system  Frequency agility  Pulse compression  Advanced signal processing using MTD and CFAR Techniques  Track while scan for 2-D tracking  Full tracking capabilities for maneuverings targets  Multicolor PPI Raster Scan Display, presenting both MTI and Synthetic Video  Integral IFF

3. Tactical Control Radar This is an early warning, alerting and cueing system, including weapon control functions. It is specially designed to be highly mobile and easily transportable, by air as well GTBKIET.Six Months Training

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L - 51504061/ECE/2K5 as on the ground. This radar minimizes mutual interference of tasks of both air defenders and friendly air space users. This will result in an increased effectiveness of the combined combat operations. The command and control capabilities of the RADAR in combination with an effective ground based air Defence provide maximum operational effectiveness with a safe, efficient and flexible use of the airspace.

FEATURES

 All weather day and night capability  40 km ranges, giving a large coverage  Multiple target handling and engagement capability  Local threat evaluation and engagement calculations assist the commander's decision making process, and give effective local fire distribution  Highly mobile system, to be used in all kinds of terrain, with short into and out of action times (deployment/redeployment)  Clutter suppression

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RADAR APPLICATION

 Air traffic control uses radar to track planes both on the ground and in the air, and also to guide planes in for smooth landings.  Police use radar to detect the speed of passing motorists.  NASA uses radar to map the Earth and other planets, to track satellites and space debris and to help with things like docking and maneuvering.  The military uses it to detect the enemy and to guide weapons.

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RADAR TRANSMITTER The radar transmitter produces the short duration high-power of pulses of energy that are radiated into space by the antenna. The radar transmitter is required to have the following technical and operating characteristics: •

The transmitter must have the ability to generate the required mean RF power and the required peak power

•

The transmitter must have a suitable RF bandwidth.

•

The transmitter must have a high RF stability to meet signal processing requirements

•

The transmitter must be easily modulated to meet waveform design requirements.

•

The transmitter must be efficient, reliable and easy to maintain and the life expectancy and cost of the output device must be acceptable. The radar transmitter is designed around the selected output device and most of the

transmitter chapter is devoted to describing output devices therefore:

Picture: transmitter of P-37

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L - 51504061/ECE/2K5 •

One main type of transmitters is the keyed-oscillator type. In this transmitter one stage or tube, usually a magnetron, produces the rf pulse. The oscillator tube is keyed by a high-power dc pulse of energy generated by a separate unit called the modulator. This transmitting system is called POT (Power Oscillator Transmitter). Radar units fitted with an POT are either non-coherent or pseudo-coherent.

•

Power-Amplifier-Transmitters (PAT) are used in many recently developed radar sets. In this system the transmitting pulse is caused with a small performance in a waveform generator. It is taken to the necessary power with an amplifier flowingly (Amplitron, klystron or Solid-State-Amplifier). Radar units fitted with an PAT are fully coherent in the majority of cases. o

A special case of the PAT is the active antenna. 

Even every antenna element



or every antenna-group is equipped with an own amplifier here.

Pictured is a keyed oscillator transmitter of the historically russian radar set P-37 (NATO-Designator: „Bar Lock”). The picture shows the typical transmitter system that uses a magnetron oscillator and a waveguide transmission line. The magnetron at the middle of the figure is connected to the waveguide by a coaxial connector. High-power magnetrons, however, are usually coupled directly to the waveguide. Beside the magnetron with its magnetes you can see the modulator with its thyratron. The impulse-transformer and the pulse-forming network with the charging diode and the high-voltage transformer are in the lower bay of this rack.

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BRIEF DESCRIPTION OF THE RADAR SUBSYSTEM Main Circuit of Radar Subsystem  High Tension Unit  Transmitter Unit  Lo+Afc Unit  Receiver Unit  Antenna  Video Processor

High Tension UnitThe high tension unit converts the 115v 400Hz 3 Phase mains voltage into a d.c supply voltage of about 4.2kv for the transmitter unit. The exact value of the high voltage depends on the selected PRF(low,high or extra)to Prevent the dissipation of the magnetron from becoming too high PRF the lower the supplied high voltage

Transmitter Unit – The transmitter unit Comprises •

Submodulator

•

Modulator

•

Magnetron

•

Afc control Unit The magnetron is a self – oscillating RF Power generator. It supplied by the

modulator with high voltage Pulses of about 20kvdc, whereupon it Produces X-band Pulses with a duration of about 0.35us. The generated RF Pulses are applied to the receiver unit. The Pulse repetition frequency of the magnetron pulses is determined by the synchronizations circuit in the video Processor, Which applies start pulses to the sub GTBKIET.Six Months Training 38

L - 51504061/ECE/2K5 modulator of the transmitter unit. This sub modulator issues start Pulses of suitable amplitude to trigger the thyraton in the modulator. Which is supplied by the high tension unit, Produces high voltage Pulses of about 20kvDC.As a magnetron is self- oscillating some kind of frequency control is required. The magnetron is provided with a tunning mechanism to adjust the oscillating frequency b/w certain limits. This tunning mechanism is operated by an electric motor being part of the Afc control circuit. Together with circuits in the Lo+Afc units, a frequency control loop is created thus maintaining a frequency of the SSLO and the magnetron output frequency.

LO+AFC Unit The Lo+Afc unit determines the frequency of the transmitted radar pulses. It comprises•

Lock Pulses mixer

•

Afc discriminator

•

Solid state local oscillator(SSLO)

•

Coherent oscillator(COHO)

The Afc lock Pulses are Pulses are also applied to the COHO. The COHO outputs signals with a freq. of 30Hz, and it is synchronized with the pulse of each transmitter Pulse. In this way a phase reference signal is obtained, required by the Phase sensitive detector in the receiver unit.

Receiver unit The Rx unit converts the received RF echo signal to IF level and detects the IF signals in two different ways, two receiver channel are obtained, called MTI channel and linear channel. The RF signal received by the radar antenna pass the circulator and are applied to a low noise amplifier. The image rejection mixer mixes the amplified signals with the SSLO signals, to obtain a 30MHz IF signal is split into two branches.viz, an MTI channel and a linear channel.via directional coupler, a fraction of the low noise amplifier output is branch offer and applied to the broadband jamming detector. The BJD is a wideband device, which amplifies and detects the signal applied. The resulting signal is passed on the SJI-STC circuit (Search jamming indication sensitivity time control) in the video Processor , if jamming GTBKIET.Six Months Training

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L - 51504061/ECE/2K5 occurs, it is used to prevent a polar diagram of a jamming on the PPI Screen, Which shows the direction of the jamming source. In the MTI channel, the IP signal is amplified again by the MTI main amplifier and applied to the phase sensitive detector. The second signal applied to the phase sensitive detector PSD is the phase reference signal from the COHO. The output signal of the PSD consists of video pulse, the amplitudes of which are a function of the phase difference between the two input signal of the PSD. The polarity of the video pulse indicate whether the phase difference is positive or negative. The phase differences between the corlo signal and if echo signals from a fixed target are constant whereas those between the COHO signal and if echo signals from a moving target are subject to change. The PSD output signal is applied to the canceller in the video processor. The linear detector outputs positive video signals which are passed on to the colour PPI drive unit.

Antenna The antenna is a cosecant square parabolic reflector, rotating with a speed of about 48 r.p.m. in the focus of the reflector is a radiator, which emits the RF pulses from the circulartor and which receives RF echo Pulses. In the waveguide is Polarisation shifter, which causes the polarization of the RF energy to the either horizontally or circularly. The polarization shifter is controlled by the system operator.

Video Processor The video processor processes the MTI receiver channel, to make the video suitable for presentation on the colour PPI screen and for use by the video extractor. The main circuit comprised by the video processor are :  Synchronization circuit.  Canceller  Floating level circuit  Correlator Synchronization circuit GTBKIET.Six Months Training

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L - 51504061/ECE/2K5 The synchronization circuit develops the start pulse for the sub modulator in the transmitter unit, and accordingly it generates the timing pulses required by the canceller. The repetition time of the start pulses depends on the PRF is staggered Pseudorandomly : 32 point stagger is used for low and high PRF and 64 point stagger is used for extra PRF. The 64 point stagger for extra PRF is actually is compound of a 32 point staggered short PRT and 32 point staggered long PRT and a 32 point staggered long PRT. Canceller The canceller is a circuit used to suppress the echo’s of fixed targets or very slow moving targets. The canceller makes use of the difference in phase behavior moving and fixed targets with moving target and phase differs from pulse to pulse, but with fixed targets the phase is constant (i.e. the PSD output is constant). The suppression by the canceller is limited. The higher the PRF of the radar pulses, the better the suppression factor; a further cancellation improvement can be obtained by using a triple canceller instead of a double canceller; here a compromise is to found. The operation of the canceller depends on the selected PRF : Low and high PRF ; The canceller is swithched as double canceller. Extra PRF : The PRF jumps from pulse to pulse between low PRF and high PRF. The canceller switched to double is a digital three pulse comparison canceller. Video’s are : 

Undelayed video (V0)



Video delayed by one PRT (V1)



Video delayed by two PRT’s (V2)

By addition, multiplication and subtraction these video are combined to obtained a canceller output according to the following formula. V out (double) = 2 V1 – (V 0 + V 2) The canceller switched to triple is digital four pulse comparison canceller. This circuit the following video’s are obtained : 

Undelayed Video (V0) GTBKIET.Six Months Training

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L - 51504061/ECE/2K5 

Video delayed by one PRT (V1)



Video delayed by two PRT (V2)



Video delayed by three PRT’s (V3)

Canceller output according to the following formula : V out (triple) = V0 – 3 V1 + 3 V2 – V3

SIGNAL PROCESSING UNIT INTRODUCTION The signal processing unit constitutes a very important functional block with vital roles to perform in overall system configuration of receiver radar returns under normal operating conditions are initially processed by the analogue processing stages (such as LNA, IF, VIDEO DETECTOR etc.) and then processed by signal processor. This type of signal processor is known as MOVING TARGET DETECTOR. To improve the radar resolution in range, without the need for transmitting narrow pulse, a technique called PULSE COMPRESSION is employed. This will avoid the need for the transmission of a narrow pulse with high peak power, thus simplifying the transmitter chain.

PRINCIPLE OF OPERATION The signal processor consists of Digital Pulse Compression system followed by the prewhitening clutter cancellation filter in the form of three pulses in MTI. The MTI output is then processed by a sixteen point FFT processor with frequency domain windowing feature. Final stage of data processing is detection. In detection block Cell Averaging (CACFAR) with programmable threshold setting features in range/Doppler domain is used. The MTI, FFT and CFAR are collectively known as MTD. Similarly, in order to enable detection of tangentially moving (or low Doppler ) targets under noise limited, and weak to moderate ground clutter conditions, the Zero GTBKIET.Six Months Training

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L - 51504061/ECE/2K5 Velocity Filter (ZVF) and its associated clutter map are used. PRF staggering scheme on scan-to-scan and CPI-to-CPI basis is employed to ensure better performance against blind speed conditions. Signal Processor receives digital data from if processor. The data is received and offset corrected (if AUTO OFFSET is ON SP control panel) and passed on to Digital Pulse Compression (DPC) block. The Digital Pulse Compression block carries out the matched filtering and correlation of the returns with the transmitted phase codes. However, to enable the detection of weak signals under noise and clutter backgrounds, and extraction of signal parameters such as Doppler content, strength, range and azimuthal positions etc. further processing needs to be carried out using clutter cancellation, filtering and integrations, and detection techniques. Moving Target Detector (MTD) technique, facilitate optimal detection under conditions of heavy clutter especially in Radars used for low looking surveillance role. Keeping in view, the environment under which the INDRA-II is expected to perform its role for the given specifications, the MTD technique naturally turns out to be the ideal choice of its implementation. Timing and control signals required by various functional blocks of the Signal Processor and also the transmitter system are catered for as part of the Signal Processor design feature. To facilitate the validation and testing of the signal processor, a swept Doppler BITE is also provided. Similarly, to monitor on Oscilloscope outputs of MTI, FFT and ZVF blocks, the necessary circuits in the form of D/A converters are also provided. Interface circuits for MTD processed video on PPI as well for MTD data transfer to centroid/RDP processor also form part of the design features.

HARDWARE ORGANISATION The Signal Processor is realized on multiple, multilayer PCBs. The PCBs are grouped into functions are packed into a single card cage. Each card cage is capable of housing up to 15 PCBs, along with a power supply module. The power supply takes ac input and caters for the +5V, +15V and -15V supply needs of that card cage. GTBKIET.Six Months Training

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Two such card cages are put together in a card enclosure called Card Panel. Two such card panels are being used to realize total signal processing hardware. Each of the card panel is mounted on rails, to be able to pull out for maintenance purpose.

FUNCTIONAL ORGANISATION All the functions performed by Signal Processor can be organized under following groups:

SIGNAL PROCESSING FUNCTIONS: These are the main functions that process the radar echo, and hence form the main functional chain. •

DIGITAL PULSE COMPRESSION

•

AUTO OFFSET CORRECTION

•

MATCHED FILTER

•

MOVING TARGET INDICATOR

•

FFT PROCESSING

•

ZERO VELCITY FILTER (ZVF)

•

ADAPTIVE THRESHOLDING (CFAR)

INTERFACE FUNCTIONS: These are the functions enabling the signal processor to communicate with other units in the radar. Following are realized as dedicated interface on separate PCBs. Other interfaces are part of their respective hardware. •

DISPLAY INTERFACE

•

CENTROIDER INTERFACE

SYSTEM FUNCTIONS: GTBKIET.Six Months Training

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L - 51504061/ECE/2K5 These functions receive controls (if any), and generate control for some functions performed by other units of radar. •

SYSTEM TIMING (also contain circuits for internal timing requirements of SP).

•

SYSTEM BITE – Generates control for simulated target generation by Receiver.

•

ADAPTIVE MSC (AMSC) – Adaptive map generation and transfer to receiver for Adaptive Microwave Sensitive Control.

•

ECCM – Analyze and generate control for optimum frequency selection and jammer indication on PPI.

MONITORING FUNCTIONS: For parameter control and quick check on health of Signal Processor following functions are performed:  RPM monitoring.  SP output monitoring.  Control Panel Function.

FUNCTIONAL DESCRIPTION The following are detailed description of each functional block.

DIGITAL PULSE COMPRESSION (DPC) BLOCK DPC card module performs the following functions:  I/Q channel Digital Matched Filtering.  Automatic DC offset correction for I/Q ADC data.  Adaptive Microwave Sensitivity Control.  Online JAM sensing with real – time ECCM controls.  Systems BITE control for generation of simulated targets for on-line injection at RF & IF levels.  PD /Pfa / Antenna RPM monitoring & Indication. The Digital Card Module houses 13 nos. of extended double Euro Multi-layer PCBs as part of the Signal Processing Rack of INDRA-PC RADAR. GTBKIET.Six Months Training

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This card module receives the INPHASE and QUADRATURE channel ADC data (12+12 bits) from the 30 MHz IF processor. Automatic DC offset correction is applied to this data and inputted to the digital matched filter. The I & Q channel pulse compressed signal is then fed to the corner turning memory of the MTD processor in the next card module. The received ADC data also goes after buffering to the Adaptive Microwave Sensitivity Control (AMSC) card and ECCM control card.

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MATCHED FILTER FUNCTION BLOCK DPC CONTROL CARD # 1, DPC CONTROL CARD # 2, I-CH matched filter and Q-CH matched filter together constitutes the matched filter block. I/Q ADC data from IF unit, offset corrected in Auto Offset Correction Card enters DPC CNTL CARD # 1.Here I/Q ADC data is added to I/Q clutter BITE (CLUT). The clutter BITE is initiated with the help of CLUT PULSE trigger when needed only. I/Q ADC + CLUT data is multiplexed with I/Q SIM data and the selected data goes to I/Q matched filters. SIM data is used for on-line diagnostics and fault indication. Under normal operating conditions, ADC data is present during radar operational range and DPC SIM data is injected during the dead range of the radar. There is an overriding switch control DPC BITE ON/OFF by which only DPC SIM data can be selected as input to I/Q matched filters for diagnostics purposes. I and Q matched filters look for the correlation in the code between the transmitted pulse and that of received echo pulse. The peaking of the signal occurs whenever the correlation exists. There are two banks in the matched filter performing the similar filtering operation and the selection of a particular bank for operation is decided by the signature analysis circuit in DPC CNTL CARD # 2. Signature analysis is carried out on-line during the dead range. The matched filter output patterns for I & Q DPC SIM data are stored in EPROMs. A signature analysis gate is opened during which the on-line matched filter outputs are compared with the signatures stored and the error condition if any is detected With BANK # 1 selected, I-DPC data is selected for signature analysis for 8 sweeps and then Q-DPC data for the next 8 sweeps. The same sequence is followed when BANK # 2 is selected. If there is any error in BANK # 1 or BANK # 2 of I-MF or BANK # 1 or BANK # 2 of Q-MF, an appropriate LED is switched on. The signature analysis logic automatically switches to alternate bank when one bank is found faulty.

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L - 51504061/ECE/2K5 The codes used in operation are stored in a PROM band can be selected manually using DIP-switch on the card or automatically when code agility mode is selected. DPC CONTROL CARD # 1 generates the various control signals for signature analysis. Code generation and distribution to the other subunits/subsystems, is done, in DPC CONTROL CARD # 2. This card also receives various signals and distributes them. DPC output analog video is generated for monitoring purposes in DPC CONTROL CARD # 1 & # 2.

AUTO OFFSET CORRECTION FUNCTION Auto offset correction block comprises – •

Auto offset correction hardware card, and

•

AMSC- Master Card. The estimation of offset value in I/Q ADC data is done on-line every scan using

ADSP processor in AMSC-Master Card. This offset data is subtracted (with proper sign) from the real time I/Q data for every range cell in following scan. During the dead CPI period, when there is no transmission, I/Q samples are taken at 3microsec. interval over several range cells. This way samples are collected over several dead CPIs in a scan. The mean of these samples is computed to get the offset value in each of the channels. These I/Q offset values are passed on to the Auto Offset Correction Card, where the hardware corrects the offset in the two channels on-line in the following scan. Auto Offset Correction Card receives I-ADC and Q-ADC data from IF processor unit corrects the offset in the two channels and passes on to DPC CONTROL CARD # 1. It also buffers and distributes the I-ADC and Q-ADC data to AMSC and ECCM CARD #1.

BULK MEMORY FUNCTION BLOCK As the processing requirement is in the batch mode for MTD, the radar real time data has to be reordered and to processing block. This reordering is done in the bulk memory. This GTBKIET.Six Months Training

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L - 51504061/ECE/2K5 circuit consists of two PCBs. The first PCB is the Bulk Memory Control Card. In this PCB, the address generations for both read and write operations; control generation and BITE generation are implemented. In the second card mainly the memory and the corresponding switching buffer is available. The memory in the second board is organized in such a way that while DPC output data is written in one of the memories called bank ‘A’, the other memory called bank ‘B’, outputs the previous CPI data for processing block. The clock used for the read operation is gated Rck, generated in system timing card. The bank switching is done after every CPI.

MOVING TARGET DETECTOR PROCESSOR BLOCK MTD is an example of an MTI processing system that takes the advantage of the various capabilities offered by digital techniques to produce improved detection of moving targets. Infact, The MTI, FFT and CFAR are collectively known as MTD.

MOVING TARGET INDICATOR FUNCTION BLOCK It is possible to remove from the radar display the majority of clutter, that is, echoes corresponding to stationary targets, showing only the moving targets. This is often required, although of course not in such applications as radar used in mapping or navigational applications. One of the methods of eliminating clutter is the use of MTI, which employs the DOPPLER EFFECT in its operation.

DOPPLER EFFECT The apparent frequency of electromagnetic sound waves depends on the relative radial motion of the source and the observer. “If source and observer are moving away from each other, the apparent frequency will decrease, while if they are moving towards each other, the apparent frequency will increase. The Doppler effect is observed only for radial motion, not for tangential motion. Thus no Doppler effect will be noticed if a target moves across the field of view of radar.

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L - 51504061/ECE/2K5 A Doppler shift will be apparent if the target is rotating, and the resolution of the radar is sufficient to distinguish leading edge from its trailing edge.

FUNDAMENTALS OF MTI Basically, the moving-target indicator system compares a set of received echoes with those received during the previous sweep. Those echoes whose phase has remained constant are then cancelled out. This applies to echoes due to stationary objects, but those due to moving targets do show a phase change; they are thus not cancelled-nor is noise, for obvious reasons. The fact that the clutter due to stationary targets is removed makes it easier to determine which targets are moving and reduces the time taken by an operator to ‘take in’ the display. It also allows the detection of moving targets whose echoes are hundreds of times smaller than those of nearby stationary targets and which would otherwise have been completely masked. The phase difference between the transmitted and received signals will be constant for fixed targets, whereas it will vary for moving target. The advantage offered by digital MTI processing:  Compensation for “blind phases”, which cause a loss due to the difference in phase between the echo signal and the MTI reference signal. This is achieved by use of I & Q processing, something that was always known to be of value for MTI processing, but which was not convenient to implement with analog methods.  Greater dynamic range can be obtained than was possible with acoustic delay lines.  Digital processor can be made reprogrammable.  Digital MTI is more stable and reliable than analog MTI, and requires less adjustments during operation in the field.

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FFT PROCESSOR FUNCTION BLOCK FAST FOURIER TRANSFORM (FFT) Digital filtering involves the use of Fourier transform. The FFT requires less computational effort, and it has been popular for many applications. It has some limitations, however compared to. The number of samples has to be expressed as 2 n if a filter bank is being generated, all filters have identical responses, they will be uniformly spaced frequencies, and the weighting coefficients are not optimum since they cannot be chosen independently for each filter. The filters possible with a non-FFT filter bank also can achieve greater attenuation of moving clutter (such as rain or chaff) because of the greater flexibility available in their design. There are times, therefore, when the classical Fourier transform may be more advantageous than the FFT even though the FFT might be quicker and require less complexity.

HARDWARE FFT processor has been realized on 12 multilayer PCBs. The PCBs are as follows:  FFT Timing and Control  Cascade Buffer for FFT  Processor 1 ALE  Processor 1 Feedback  Processor 1 Feed forward  Complex multiplier  Processor 2 ALE (Architecture same as Processor 1 ALE)  Processor 2 Feedback (Architecture same as Processor 1 Feedback)  Processor 2 Feed forward (Architecture same as Processor 1 Feed forward)  Frequency Domain Window (Real)  Frequency Domain Window (Imag.)  Magnituder

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ZERO VELOCITY FILTER FUNCTION The MTD also uses a new concept of Zero Velocity filter (ZVF) to overcome the probability of missing the targets which have a velocity falling in the zero Doppler zone. This will be the case of targets which are flying tangential radar and low velocity radial targets, who’s Doppler is such hat they fall in zeroeth filter. Also since the response of the DMTI is rather poor for low Doppler targets, there is every chance that these targets may go under. ZVF performs its function by forming a clutter map. Clutter map: A conventional MTI processor eliminates stationary clutter, but it also eliminates aircraft moving on a crossing trajectory (one perpendicular to the radar line of sight) which causes the aircraft’s radial velocity to be zero. This is unfortunate since the radar cross-section of an aircraft is relatively large when viewed at the broadside aspect presented by a crossing trajectory. The MTD took advantage of this large cross-section to detect the targets that normally would be lost to a simple MTI radar. It did this with the aid of a clutter map that stored the magnitude of the clutter echoes in a digital memory. The clutter map established the thresholds used for detecting those aircraft targets which produce zero radial velocity. There may be many range cells which may not contain clutter, or contain low clutter, but due to the poor response of MTI. These may be the implementation of the ZVF will allow the detection of targets whose return exceeds that of the clutter in that particular range – azimuth cell. The ZVF is implemented by integrating all the 18 returns of a CPI, and whose response extends to the frequency band covered by the zeroeth filter. In the zeroeth Doppler cell, the clutter is generally due to the ground echoes. To estimate the average backscatter signal level, the entire range – azimuth space is divided into fine grain resolution cells and the returns are stored in the form of a map. To build up the map accurately, each antenna resolution is broken into 256 CPIs and there are 2560 range cells. The ZVF is made up of magnitude of 18 samples, which are formed by first adding 9 samples and then adding the next 9 samples coherently and non-coherently adding up the sums.

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CFAR PROCESSOR BLOCK CFAR is used in radars to maintain effectiveness when there are too many extraneous crossings of a fixed threshold caused by clutter or noise. Automatic tracking of targets can be seriously degraded if excessive false alarms occur. CONSTANT FALSE ALARM RATE (CFAR) processor block is one of the major functional blocks of digital signal processor. The output of the FFT filtering block is further processed to facilitate the following  Generation of adaptive threshold levels using Moving Window concept.  Detection of signals and extraction of primitive (primary) data information pertaining to the detected signals. The output of the FFT magnituder forms the main data input to the CFAR Processor block. Functional sub-blocks such as the running sum computation, Pipeline memory storage, Mode Selection Multiplier and threshold detection constitute the hardware blocks of the CFAR processor. In the CFAR processor block, the threshold levels are so found, so as to enable the detection of the signals with the constant false alarm rate under conditions of mainly thermal noise and also under jamming and interference backgrounds. In order to achieve this Newman Person detection criterion, with adaptive thresholding in all the Doppler channels using moving window concepts is implemented. In case of Non-Gaussian clutter dominated Doppler channels designed features have been provided to selectively apply higher threshold levels, so as to restrict the false alarm to the acceptable level. The CFAR Processor block functions with its own timing and control signals. The master source for these timings however is from the system timing circuit. CFAR BITE facility has also been provided to test and validate the CFAR processor block in stand-alone mode.

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DISPLAY VIDEO INTERFACE FUNCTION This function is to generate trigger and videos for two Display consoles. The raw video from IF processor is mixed with Jammer video and is then buffered to generate RAW video for Display Consoles. Mixing CFAR output with Jammer video and AMSC video generates the MTD video for Display Consoles. The triggers are suitably delayed Radar Trigger (RT), they are also buffered before sending to Display Consoles.

CENTROID INTERFACE FUNCTION The data packet to be sent to the centroider from CFAR Processor, basically, contains the information such as signal strength, Doppler bin number (velocity bin), Range cell number, CPI number, PRF code and data pertaining Jam to strobe, Tx blanking flag, carrier frequency code, etc. This data packet needs to be tagged to the threshold crossing pulse to facilitate centroiding and subsequent data processing. The Threshold Crossing decision on sample-tosample basis is carried out at real time processing rate of 250ns per report. However the centroider accepts the information asynchronously. This necessitates the use of hardware buffering devices such as FIFOs. The information needs to be passed to a 16-bit data bus. Hence various sets of information indicated above need to be generated, edited, formatted and sequenced before data-transfer. The required hardware design was carried out in two PCBs. The first PCB consists of timing and control circuits and a part of data editing. The next PCB consists of sequencing, FIFO store and data interface.

SYSTEM TIMING FUNCTION GTBKIET.Six Months Training

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L - 51504061/ECE/2K5 This is the function that generates all the basic timing signals required for use within the Signal Processor as well as other units of the radar. It generates necessary synchronization signals for Transmitter and Sampling clock for IF Processor. The signals thus generated are described below. •

20 MHz GENERATOR

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20 KHz GENERATOR

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PRF GENERATOR

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CPI PAIR GATE

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NM AND ACP GENERATION

BITE FUNCTION BLOCK The interactive BITE sub-system provides comprehensive test facilities. Two target pulses can be generated using commands from a keyboard. The commands have been chosen in a way that it is easy to remember and consists of two alphabets followed by suitable functional parameters. The following are the BITE controls that can be used for signal processing and RDP checks.  BITE pulses can be positioned in any range (distance – wise or range cell – wise) and in any azimuth.  BITE pulses can be moved along range and / or along azimuth at any speed (0 to 9999 Kms per Hr).  Any Doppler shift (0 to 100 %) in terms of percentage of PRF can be given.  Target straddling can be introduced.  Asynchronous interference can be introduced along with BITE pulse.  BITE pulse can be fed at RF of IF stages.  Primary and secondary BITE pulses can be switched on/off individually.

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L - 51504061/ECE/2K5  BITE pulses can be introduced continuously (in a ring mode) or once a scan.  Multiple BITE pulses can be generated for each of the primary target pulses along range as well as along azimuth. A maximum of 16 pulses can be generated along range and 32 along azimuth. Also, the separation between these multiple pulses can be varied in multiples of 1.8 Km along range and in multiples of 7.5 degree along azimuth. Apart from these, BITE subsystems can be used to generate programmable ECCM sector controls. They are •

To selectively blank radar transmission in a sector (up to 8 such sectors).

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To selectively effect data blanking for centroids in any sector (up to 8 such sectors).

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To selectively choose random frequency or Least Jammed Frequency operating in any sector (up to 8 such sectors).

The BITE subsystem is distributed in three PCBs. BITE control card #1 contains  BITE Processor.  Keyboard interface.  Boot memory and data memory PROMs.  Clock generation circuitry.  Decoders for various registers.  Sector control registers.  Circuit for generating scan interrupts. Apart from these serial interface circuits and spare input registers and output registers have been provided. BITE Control Card # 2 is identical for target _ 1 and target – 2. This card consists of: •

Range registers.

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Azimuth registers. GTBKIET.Six Months Training

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L - 51504061/ECE/2K5 •

Circuit for Doppler control.

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Circuit for antenna modulation.

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Circuit for multiple target pulse generation along range and azimuth.

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Circuit for pulse width control along range and azimuth.

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Decoders for various registers.

AMSC FUNCTION BLOCK Transportable and mobile tactical radar systems which need to operate with coverage extending over hilly and mountainous terrain have to cope with heavy volumetric clutter even at distant ranges. Under such conditions STC circuit which is widely used to reduce large echoes from close-in clutter will not be effective. **Hence an adaptive microwave sensitivity control is employed which has the capability to intelligently self-program the receiver sensitivity in each range–azimuth cell in an accurately and optimum fashion. This is done by deriving a coarse clutter map from a zero-velocity (low-pass) filter, built up over a few scans for each range-azimuth cell, operating on the I & Q channel ADC data. The clutter map is built after applying a constant attenuation of 30dB uniformly in the total range-azimuth plane. Then the relative clutter level w.r.t. the saturation point is computed for each range-azimuth bin and the corresponding attenuation accurately worked out to bring the clutter everywhere into the linear dynamic range. The adaptive attenuation programming is a one time operation initiated under full power transmission by the radar operator with the push of a button. This may be done whenever the radar site is changed or whenever required. AMSC block is configured as AMSC-MASTER & AMSC-SLAVE. AMSCMASTER is housed in SPU-Rack & AMSC-SLAVE housed in Receiver-Rack. The two are connected through the serial line. The function of AMSC-MASTER is to derive the clutter map built up over 8 scans from I & Q ADC data and to transfer this map data to AMSC-SLAVE processor through a GTBKIET.Six Months Training

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L - 51504061/ECE/2K5 serial channel. AMSC-SLAVE receives the map data, stores in its memory as a replica of map memory of MASTER, transfers the map data from RAM to the EEPROM and starts outputting map values every PRT to RF CONTROL card for generating attenuation values.

The derivation of coarse clutter map from zero-velocity filter is done as follows. In every CPI 210 range samples of I & Q data are taken starting with every PRT. The range samples are taken at 3 µ sec interval. The I & Q samples for each range cell are integrated over 16 PRTs in a CPI. The magnitude of I & Q data is computed for each range cell using 7/8 L + 1/2 S algorithm and stored in external memory. This way magnitude for all the range azimuth cells in a scan is computed and stored in a memory. The computation and accumulation of magnitude is done for over 8 scans and the action is stopped. Since we have256 CPIs in a scan and 200 range cells per CPI, the number of range azimuth cells per scan will be 256 * 200 =51,200 i.e., 51K of external memory is required for storing the map information. External RAM used in the circuit is of 128K words capacity and 8 pages are used to store the map information. The processor selects the memory page using the MSB 3 bits of CPI number. The locations in each page are addressed by the processor using LSB 5 bits of CPI number and 8 bits of range cell address.

The data is send to AMSC-SLAVE on a serial port of the processor. The MASTERto-SLAVE communication is synchronous (same serial clock is used for both the processors). Mode of communication is duplex mode, where in the word sent by MASTER is echoed back by SLAVE. The MASTER processor checks for the correctness of the received word before sending the next word. If there is any error, the word is repeated. The AMSC block operates in three modes.  MODE # 1: No clutter map generation and no transfer of data in this mode the slave has to only output the map values stored in RAM every PRT. This is normal mode of GTBKIET.Six Months Training

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L - 51504061/ECE/2K5 operation.  MODE # 2: No clutter map generation, only data stored in AMSC-MASTER EEPROM is transferred to AMSC-SLAVE.  MODE # 3: Clutter map generation and transfer of data to SLAVE by MASTER. Slave processor has to receive the data and store in its external memory. Once the data transfer is completed, the data is outputted with every PRT. For each word of data to be transferred, three 16-bit words are sent to slave. First word gives the page number of the memory, second word gives the address of the memory where data has to be stored and the third word is the data which has to be stored in the address location given by the second word. The MSB three bits of each word are used to code the word as page number, address and data. The slave has to decode the three bits and take appropriate action like selecting memory page number or forming address pointer to load the data or load the data into specific location of the memory. The process of derivation of clutter map has to be done with full transmitter power ON and a 30dB uniform attenuation applied to the front end, which is done by the slave processor. AMSC action is initiated by AMSC-INIT switch on the display front panel. AMSCINIT switch resets both MASTER and SLAVE processors. If AMSC-INIT switch is held pressed for one scan, MASTER processor should go in for derivation of clutter map. If this facility is not given, any accidental pressing of the switch during Radar operation causes 30dB front end attenuation being applied by the SLAVE processor and the detection will suffer for 8 scans. The hardware in AMSC card senses whether the AMSC-INIT switch is pressed for one scan and set a flag. After initialization with reset, the MASTER processor waits for one scan time and polls the flag. If the flag is active, it starts with MODE # 3. If not it will go to MODE # 2.

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L - 51504061/ECE/2K5 Sampling of data for map generation starts with the first CPI encountered after initialization with reset. This first CPI number read from counter is stored. The functions of processor in each CPI are:  Read the CPI number.  Read current I/Q values of each range cells ; accumulate will previous I/Q values stored in internal memory.  Compute the magnitude of accumulated I and Q values of previous CPI.

ECCM CONTROL FUNCTION BLOCK In every pulse repetition time [PRT] interval during the dead range (beyond 94 Kms), the receiver is switched through all the 11 frequencies, in two batches and A/D, I-Q samples corresponding to these frequencies is collected. This is repeated for a total of 15 PRTs in every coherent pulse interval (CPI). Hence in all 660 samples of ADC data (or 330 complex I/Q samples) are colleted and stored in the internal data memory of the processor. An MTI operation is done on this data and then magnituding and hence the magnitude for each frequency is found out. The MTI operation is done to cancel noise due to clutter if any, occurring in the dead range corresponding to the Transmitted frequency thus avoiding erroneous estimation of least jam frequency. The Σ magnitudes obtained for each of the frequencies in a CPI is obtained as well as sum of all the Σ magnitudes. The magnituded data is used for analyzing and to compute the different functions to be performed by this processor and outputted. These different functions are described below:

LEAST JAMMED FREQUENCY The Σ magnitudes obtained for each frequency are compared and the frequency corresponding to minimum Σ magnitude gives the LJF. This is done in every CPI. Also the Σ magnitude corresponding to the present CPI-LJF, is compared with that of the previous CPI-LJF and if it is less than 5 times that of previous one, only then the current LJF is putout, else the previous LJF itself is output as the LJF for the next CPI.

AUTO THRESHOLD BITS 3 Bits are generated by comparing the Σ magnitude for the LJF in a CPI with some constant value of expected jamming noise and after weighting, are sent out to the CFAR GTBKIET.Six Months Training

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L - 51504061/ECE/2K5 processor. This is done in every CPI. 2 bits of data are generated to indicate the jam level corresponding to the LJF and sent to frequency indication panel unit on display console.

AUTO ATTENUATION CONTROL Once again depending upon the value of the sum of Σ magnitudes, like auto LJF, auto STC off and also 24 dB dead range RF attenuation ON are generated and sent to appropriate units.

JAM STROBE PRESENTATION Using the sum of all the Σ magnitudes of all frequencies as a basis and an algorithm, the digital logarithm and hence what is called a LOAD NUMBER is arrived at each CPI. The load numbers in two adjacent CPIs are interpolated and a load pulse is generated every PRT to load a 3-stage counter, the terminal count of the third stage after strobing is used as the video pulses for jam strobe. This is sent to PPI for presentation. The interpolation gives the presentation of a smooth strobe. A fixed IF attenuation of 30dB is introduced during the dead range, in order to obtain distinct main lobe and side lobes for the jammer strobe indication.

JAMMER CLASSIFICATION Jammer duty ratio count and jammer bandwidth count are generated using certain algorithms comparing the Σ magnitude (after MTI operation) over a 8 CPI bracket. Depending on the values of these counts the jammer is classified as Low, Medium or High duty as well as Narrow bandwidth, Medium bandwidth or Wide bandwidth. In each case 2 bits of data are generated and the classification is indicated on the frequency indication panel (in system control unit), using LEDs.

RPM MONITORING CIRCUITS This circuit can monitor in either test mode (local diagnostics) or in operate (i.e. system) mode, the following parameters being indicated for two sets of numeric displays. Set 1 indicates while the values for a single scan while Set 2 dispays the values averaged over the past 8 scans. The parameters monitored are:  Probability of detection, percentage-indicated as a number in the form-(ZZZ)-with BITE (targets) only. GTBKIET.Six Months Training

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L - 51504061/ECE/2K5  Probability of false alarms, a No. (x 106)-indicated as a number-for all 16 filters in the form-(XX.YY).  Probability of false alarms, a No. (x 106)-indicated as a number 4 single filter in the form-(XXX.Y). With the help of DIP switches the above operation is selected.

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OUTPUT MONITORING FUNCTIONS This card is mainly to see the D/A converted output of 3 types of the signal channels of the signal processor on an oscilloscope. The card is designed to take 16 bits of data of any 3 channels, as the signal processor (MTD) hardware has got 3 main channels namely MTI, FFT, ZVF.

CONTROL PANEL FUNCTIONS Each of the cards has its card panel mounted on the front side. The control panel.

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Fully Coherent Radar

Figure 1: an easy block diagram of a fully coherent radar The block diagram on the figure illustrates the principle of a fully coherent radar. The fundamental feature is that all signals are derived at low level and the output device serves only as an amplifier. All the signals are generated by one master timing source, usually a synthesizer, which provides the optimum phase coherence for the whole system. The output device would typically be a klystron, TWT or solid state. Fully coherent radars exhibit none of the drawbacks of the pseudo-coherent radars, which we studied in the previous section.

Duplexer The duplexer alternately switches the antenna between the transmitter and receiver so that only one antenna need be used. This switching is necessary because the high-power pulses of the transmitter would destroy the receiver if energy were allowed to enter the receiver.

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Mixer Stage The function of the mixer stage is to convert the received rf energy to a lower, intermediate frequency (IF) that is easier to amplify and manipulate electronically. The intermediate frequency is usually 30 or 60 megahertz. It is obtained by heterodyning the received signal with a local-oscillator signal in the mixer stage. The mixer stage converts the received signal to the lower IF signal without distorting the data on the received signal.

IF-Amplifier After conversion to the intermediate frequency, the signal is amplified in several IFamplifier stages. Most of the gain of the receiver is developed in the IF-amplifier stages. The overall bandwidth of the receiver is often determined by the bandwidth of the IF-stages.

Power Amplifier In this system the transmitting pulse is caused with a small performance in a waveform generator. It is taken to the necessary power with a Power Amplifier flowingly. The Power Amplifier would typically be a klystron, Travelling Wave Tube (TWT) or solid state.

Stable Local Oscillator (StaLO) The StaLO is also very stable CW RF oscillator, which generates the local RF frequency simultaneously for up-conversion in the transmitter and down-conversion in the receiver. Minimum FM noise (or phase noise) of the StaLO is an important characteristic. This is because such noise would limit the overall MTI improvement factor, as fixed clutter would inherit a Doppler component from the transmission. Similar arguments apply to FM noise added by the output device.

Coherent Oscillator The COHO is a very stable CW (Continuous Wave) oscillator locked to the IF frequency (The COHO frequency is generally derived from a master crystal oscillator) and constitutes the internal phase reference. The COHO provides the coherent reference signal to the Phase Sensitive Detector and also through a frequency divider generates the system PRF in the Synchronizer. GTBKIET.Six Months Training

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Mixer / Exciter The function of this mixer stage is to convert the StaLO- Frequency and the COHOFrequency upwards into the phase-stabile continuous wave transmitter-frequency.

Waveform-Generator The Waveform-Generator generates the transmitting pulse in low- power. It generates the transmitting signal on an IF- frequency. It permits generating predefined waveforms by driving the amplitudes and phase shifts of carried microwave signals. These signals may have a complex structure for a pulse compression.

Phase Sensitive Detector The IF-signal is passed to a phase sensitive detector which converts the signal to base band, while faithfully retaining the full phase and quadrature information (I & Q- processing) of the Doppler signal.

Signal Processor The signal processor is that part of the system which separates targets from clutter on the basis of Doppler content and amplitude characteristics.

Radarscope / Monitor The indicator presents to the observer a continuous, easily understandable, graphic picture of the position of radar targets. In recently radars the indicator would be a computer display.

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cathode L - 51504061/ECE/2K5 filament leads

pickup loop

MAGNETRON

Figure 1: Magnetron МИ 29Г of the Radar „Bar Lock” In 1921 Albert Wallace Hull invented the magnetron as a powerful microwawe tube. Magnetrons function as self-excited microwave oscillators. Crossed electron and magnetic fields are used in the magnetron to produce the high-power output required in radar equipment. These multicavity devices may be used in radar transmitters as either pulsed or cw oscillators at frequencies ranging from approximately 600 to 30,000 megahertz. The relatively simple construction has the disadvantage, that the Magnetron usually can work only on a constructively fixed frequency.

Physical construction of a magnetron The magnetron is classed as a diode because it has no grid. The anode of a magnetron is fabricated into a cylindrical solid copper block. The cathode and filament are at the center of the tube and are supported by the filament leads. The filament leads are large and rigid enough to keep the cathode and filament structure fixed in position. The cathode is indirectly heated and is constructed of a high-emission material. The 8 up to 20 cylindrical holes around its circumference are resonant cavities. The cavities control the output frequency. A narrow slot runs from each cavity into the central portion of the tube dividing the inner structure into as many segments as there are cavities.

Figure 2: Cutaway view of a magnetron The open space between the plate and the cathode is called the interaction space. In this space the electric and magnetic fields interact to exert force upon the electrons. The GTBKIET.Six Months Training

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L - 51504061/ECE/2K5 magnetic field is usually provided by a strong, permanent magnet mounted around the magnetron so that the magnetic field is parallel with the axis of the cathode.

Figure 3: forms of the plate of magnetrons The form of the cavities varies, shown in the Figure 3. The output lead is usually a probe or loop extending into one of the tuned cavities and coupled into a waveguide or coaxial line. a) slot- type b) vane- type c) rising sun- type d) hole-and-slot- type

Basic Magnetron Operation As when all velocity-modulated tubes the electronic events at the production microwave frequencies at a Magnetron can be subdivided into four phases too: 1. phase: Production and acceleration of an electron beam 2. phase: Velocity-modulation of the electron beam 3. phase: Forming of a „Space-Charge Wheel” 4. phase: Dispense energy to the ac field

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Figure 4: the electron path under the influence of the varying magnetic field. 1. Phase Production and acceleration of an electron beam When no magnetic field exists, heating the cathode results in a uniform and direct movement of the field from the cathode to the plate (the blue path in figure 4). The permanent magnetic field bends the electron path. If the electron flow reaches the plate, so a large amount of plate current is flowing. If the strength of the magnetic field is increased, the path of the electron will have a sharper bend. Likewise, if the velocity of the electron increases, the field around it increases and the path will bend more sharply. However, when the critical field value is reached, as shown in the figure as a red path, the electrons are deflected away from the plate and the plate current then drops quickly to a very small value. When the field strength is made still greater, the plate current drops to zero. When the magnetron is adjusted to the cutoff, or critical value of the plate current, and the electrons just fail to reach the plate in their circular motion, it can produce oscillations at microwave frequencies. 2. Phase: Velocity-modulation of the electron beam The electric field in the magnetron oscillator is a product of ac and dc fields. The dc field extends radially from adjacent anode segments to the cathode. The ac fields, extending between adjacent segments, are shown at an instant of maximum magnitude of one alternation of the rf oscillations occurring in the cavities. GTBKIET.Six Months Training

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Figure 5: The high-frequency electrical field Well, the electrons which fly toward the anode segments loaded at the moment more In the figure 5 is shown only the assumed high-frequency electrical ac field. This ac field work in addition to the to the permanently available dc field. The ac field of each individual cavity increases or decreases the dc field like shown in the figurepositively are accelerated in addition. These get a higher tangential speed. On the other hand the electrons which fly toward the segments loaded at the moment more negatively are slow down. These get consequently a smaller tangential speed. 3. Phase: Forming of a „Space-Charge Wheel” On reason the different speeds of the electron groups a velocity modulation appears therefore.

Figure 6: Rotating space-charge wheel in an eight-cavity magnetron The cumulative action of many electrons returning to the cathode while others are moving toward the anode forms a pattern resembling the moving spokes of a wheel known as GTBKIET.Six Months Training

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L - 51504061/ECE/2K5 a „Space-Charge Wheel”, as indicated in figure 6. The space-charge wheel rotates about the cathode at an angular velocity of 2 poles (anode segments) per cycle of the ac field. This phase relationship enables the concentration of electrons to continuously deliver energy to sustain the rf oscillations. One of the spokes just is near an anode segment which is loaded a little more negatively. The electrons are slowed down and pass her energy on to the ac field. This state isn't static, because both the ac- field and the wire wheel permanently circulate. The tangential speed of the electron spokes and the cycle speed of the wave must be brought in agreement so. 4. Phase: Dispense energy to the ac field

Figure 7: Path of an electron Recall that an electron moving against an E field is accelerated by the field and takes energy from the field. Also, an electron dispense energy to a field and slows down if it is moving in the same direction as the field (positive to negative). The electron spends energy to each cavity as it passes and eventually reaches the anode when its energy is expended. Thus, the electron has helped sustain oscillations because it has taken energy from the dc field and given it to the ac field. This electron describes the path shown in figure 7 over a longer time period looked. By the multiple breaking of the electron the energy of the electron is used optimally. The effectiveness reaches values up to 80%.

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L - 51504061/ECE/2K5 Modes of Oscillation The operation frequency depends on the sizes of the cavities and the interaction space between anode and cathode. But the single cavities are coupled over the interaction space with each other. Therefore several resonant frequencies exist for the complete system. Two of the four possible waveforms of a magnetron with 8 cavities are in the figure 8 represented. Several other modes of oscillation are possible (3/4π, 1/2π, 1/4π), but a magnetron operating in the π mode has greater power and output and is the most commonly used.

Strapping

Figure 9: cutaway view of a Figure 8: Waveforms of the magnetron (Anode segments are represented „unwound”) magnetron, showing the strapping rings and the slots.

So that a stable operational condition adapts in the optimal pi mode, two constructive measures are possible: •

Strapping rings: The frequency of the π mode is separated from the frequency of the other modes by strapping to ensure that the alternate segments have identical polarities. For the pi mode, all parts of each strapping ring are at the same potential; but the two rings have alternately opposing potentials. For other modes, however, a phase difference exists between the successive segments connected to a given strapping ring which causes current to flow in the straps.

•

Use of cavities of different resonance frequency E.g. such a variant is the anode form „Rising Sun”. GTBKIET.Six Months Training

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Magnetron coupling methods Energy (rf) can be removed from a magnetron by means of a coupling loop. At frequencies lower than 10,000 megahertz, the coupling loop is made by bending the inner conductor of a coaxial line into a loop. The loop is then soldered to the end of the outer conductor so that it projects into the cavity, as shown in figure 10, view (A). Locating the loop at the end of the cavity, as shown in view (B), causes the magnetron to obtain sufficient pickup at higher frequencies.

Figure 10: Magnetron coupling, view (A) and (B) The segment-fed loop method is shown in view (C) of figure 11. The loop intercepts the magnetic lines passing between cavities. The strap-fed loop method (view (D), intercepts the energy between the strap and the segment. On the output side, the coaxial line feeds another coaxial line directly or feeds a waveguide through a choke joint. The vacuum seal at the inner conductor helps to support the line. Aperture, or slot, coupling is illustrated in view (E). Energy is coupled directly to a waveguide through an iris.

Figure 11: Magnetron coupling, view (C), (D) and (E)

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L - 51504061/ECE/2K5 Magnetron tuning A tunable magnetron permits the system to be operated at a precise frequency anywhere within a band of frequencies, as determined by magnetron characteristics. The resonant frequency of a magnetron may be changed by varying the inductance or capacitance of the resonant cavities. Tuner frame

addition al inductiv e tuning element s

anode block

Figure 12: Inductive magnetron tuning An example of a tunable magnetron is the M5114B used by the ATC- Radar ASR910. To reduce mutual interferences, the ASR-910 can work on different assigned frequencies. The frequency of the transmitter must be tunable therefore. This magnetron is provided with a mechanism to adjust the Tx- frequency of the ASR-910 exactly.

Figure 13: Magnetron M5114B of the ATC-radar ASR-910

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Figure 13: Magnetron VMX1090 of the ATC-radar PAR-80 This magnetron is even equipped with the permanent magnets necessary for the work.

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Pulse Compression This is a method which combines the high energy of a long pulse width with the high resolution of a short pulse width. The pulse is frequency modulated, which provides a method to further resolve targets which may have overlapping returns. The pulse structure is shown in the figure 1.

Figure 1: separation of frequency modulated pulses

Since each part of the pulse has unique frequency, the returns can be completely separated. This modulation or coding can be either •

FM (frequency modulation)

o

linear (chirp radar) or

o

non-linear or

•

PM (phase modulation). Now the receiver is able to separate targets with overlapping of noise. The received

echo is processed in the receiver by the compression filter. The compression filter readjusts the relative phases of the frequency components so that a narrow or compressed pulse is again produced. The radar therefore obtains a better maximum range than it is expected because of the conventional radar equation.

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Figure 2: short pulse (blue) and a long pulse with intrapulsemodulation (green) The ability of the receiver to improve the range resolution over that of the conventional system is called.0 the pulse compression ratio (PCR). For example a pulse compression ratio of 50:1 means that the system range resolution is reduced by 1/50 of the conventional system. Alternatively, the factor of improvement is given the symbol PCR, which can be used as a number in the range resolution formula, which now becomes: Rres = c0 · Pw · ( 2 · PCR)

The compression ratio is equal to the number of sub pulses in the waveform, i.e., the number of elements in the code. The range resolution is therefore proportional to the time duration of one element of the code. The maximum range is increased by the PCR. The minimum range is not improved by the process. The full pulse width still applies to the transmission, which requires the duplexer to remained aligned to the transmitter throughout the pulse. Therefore Rmin is unaffected.

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Table 1: Advantages and disadvantages of the pulse compression Disadvantages Advantages lower pulse-power high wiring effort therefore suitable for Solid-State-amplifier higher maximum range bad minimum range good range resolution time-sidelobes better jamming immunity difficulter reconnaissance

Pulse compression with linear FM waveform At this pulse compression method the transmitting pulse has a linear FM waveform. This has the advantage that the wiring still can relatively be kept simple. However, the linear frequency modulation has the disadvantage that jamming signals can be produced relatively easily by so-called „Sweeper”. The block diagram on the picture illustrates, in more detail, the principles of a pulse compression filter.

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Figure 3: Block diagram (an animation as explanation of the mode of operation The compression filter are simply dispersive delay lines with a delay, which is a linear function of the frequency. The compression filter allows the end of the pulse to „catch up” to the beginning, and produces a narrower output pulse with a higher amplitude. As an example of an application of the pulse compression with linear FM waveform the RRP-117 can be mentioned. Filters for linear FM pulse compression radars are now based on two main types. GTBKIET.Six Months Training

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L - 51504061/ECE/2K5 •

Digital processing (following of the A/D- conversion).

•

Surface acoustic wave devices.

Figure 4: View of the Time-Side-Lobes

Time-Side-Lobes The output of the compression filter consists of the compressed pulse accompanied by responses at other times (i.e., at other ranges), called time or range sidelobes. The figure shows a view of the compressed pulse of a chirp radar at an oscilloscope and at a ppi-scope sector. Amplitude weighting of the output signals may be used to reduce the time sidelobes to an acceptable level. Weighting on reception only results a filter „mismatch” and some loss of signal to noise ratio. The sidelobe levels are an important parameter when specifying a pulse compression radar. The application of weighting functions can reduce time sidelobes to the order of 30 db's.

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Pulse compression with non-linear FM waveform The non-linear FM waveform has several distinct advantages. The non-linear FM waveform requires no amplitude weighting for time-sidelobe suppression since the FM modulation of the waveform is designed to provide the desired amplitude spectrum, i.e., low sidelobe levels of the compressed pulse can be achieved without using amplitude weighting.

Phase-Coded Pulse Compression

Figure 8: diagram of a phase-coded pulse compression Phase-coded waveforms differ from FM waveforms in that the long pulse is subdivided into a number of shorter sub pulses. Generally, each sub pulse corresponds with a range bin. The sub pulses are of equal time duration; each is transmitted with a particular phase. The phase of each sub-pulse is selected in accordance with a phase code. The most widely used type of phase coding is binary coding. The binary code consists of a sequence of either +1 and -1. The phase of the transmitted signal alternates between 0 and 180° in accordance with the sequence of elements, in the phase code, as shown on the figure. Since the transmitted frequency is usually not a multiple of the reciprocal of the sub pulse width, the coded signal is generally discontinuous at the phase-reversal points. The selection of the so called random 0, π phases is in fact critical. A special class of binary codes is the optimum, or Barker, codes. They are optimum in the sense that they provide low sidelobes, which are all of equal magnitude. Only a small number of these optimum codes exist. They are shown on the beside table. A computer based study searched for Barker codes up to 6000, and obtained only 13 as the maximum value. It will be noted that there are none greater than 13 which implies a maximum compression ratio of 13, which is rather low. The sidelobe level is -22.3 db. GTBKIET.Six Months Training

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Radar complexity Radar — an old acronym for radio detection and ranging — has always been a demanding technology, but at no time more so than today. Essentially, it works by emitting radio frequency (RF) signals at particular frequencies, and then listening for the signal's return — or "bounce" — off of targets of interest. At it simplest theoretical level, this does not sound like a big deal, but putting the theory into useful practice is where advanced technology — and designers headaches — come in. Several different kinds of radar systems are in use today, including continuous wave (CW), pulsed, pulsed-Doppler, phased array, and synthetic aperture.

The Mercury RACE++ Series PowerStream 510 system is used in applications such as advanced radar, sonar, imaging, and inspection.

CW radar continually transmits energy toward the desired target and receives a reflection of this "continuous wave." These kinds of radar are useful for determining a target's velocity by using the Doppler effect to compare differences in the transmitted and received signals. These radar systems, however, have difficulty determining the target's range, or how far way it is.

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L - 51504061/ECE/2K5 Pulsed radar, on the other hand, sends out a series of short RF pulses. By measuring how long it takes to receive the returns from these pulses, system operators can estimate the range to the target. Pulse Doppler radar, in addition, uses Doppler shifts with radar pulses to determine the velocities of moving targets. These systems can determine the velocities, angles, and ranges of targets. These added capabilities, however, make pulse Doppler radar much more compute-intensive than simple pulsed radar. Phased array radar systems, meanwhile, arrange large numbers of transceiver modules arranged on flat or curved surface. The system controls the phase — or a slight variation in the transmit and receive time of groups of transceiver modules — with computer commands, and in essence "steers" the radar beams quickly, enabling the phased array radar to scan specific areas quickly, "stare" at targets of interest, or do a variety of other tasks, all without the need to move the transceiver array mechanically. The ability of phased array radar systems to manipulate their groups of transceivers also gives this system an "adaptive array" capability, which not only can steer beams quickly, but also enables the system to shift the focus of radar beams to "null out" electronic interference or jamming. Precise radar images most often come from synthetic aperture radar systems. These so-called "side-looking" aircraft-mounted systems — such as the U.S. Joint Surveillance and Target Attack Radar System known as Joint STARS — produce two-dimensional images, where one dimension is the range, or distance from the radar to the target using Doppler processing, and the other dimension is the azimuth, which requires a physically large antenna to focus the transmitted and received RF signal into a sharp beam. Synthetic aperture radar, better known as SAR — collects data over a long distance, and processes the data as if it came from a physically long antenna. SAR requires extremely fast processing and very fast signal sampling rates. After all this, the way in which a radar system processes information also can change the nature of the radar system itself. Take radar pulse compression, for example. This is a technique that makes the most of the radar's sensitivity and resolution by balancing the effects of radar pulse duration, radar pulse power, and radar pulse bandwidth.

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L - 51504061/ECE/2K5 Pulse compression uses Fast Fourier Transform (FFT) processing to massage the signal as it comes in from the A-D converters. "With pulse compression, you need to take an FFT of the radar signal to remove as much stuff that doesn't belong to the return signals as possible," explains Rodger Hosking, vice president of Pentek Inc. of Upper Saddle River, N.J., which supplies single-board processors to radar designers. "So they send out a 'chirp', or a unique signal that doesn't exist in nature," Hosking continues. "You convert what comes back into frequency domain, and take the frequency domain of your outgoing pulse and correlate the two. You extract only the part of the signal coming back that has to do with the outgoing pulse. Then you do an inverse FFT, and you get a very nice 'blip'." Until recently, Hosking explains, that kind of processing has been done in analog, and in DSPs. "It's a very demanding problem to do in real time."

Processing challenges One of the first and most serious problems confronting radar systems involves noise and clutter in the return signal. After all, RF energy bounces off a lot more than simply the target of interest; it bounces off trees, buildings, mountains, vehicles, and about anything else in its path, and in various degrees of intensity depending on the reflecting materials. One of the most important tasks of modern radar systems is to reject, or "filter-out," return signals that are not of interest. Next, radar users today want far more from their systems than simply the proverbial "blip on the screen." Many modern radar systems are able to filter their return signals so finely that these signals produce an actual image of the target. Finally, most radar systems — particularly those for military and aerospace applications — must operate in real time. All these factors combine to produce a challenge of staggering computational intensity for all but the simplest radar systems. Today's radar systems digitize their signals very quickly after receiving them. After analog-to-digital conversion, advanced algorithms process the signals to eliminate noise by filtering out unwanted portions of the signal, perform Doppler calculations to help determine range, and do many other operations to prepare the data for further processing later that will do tasks like enter radar signatures into databases and display the information on graphical screens.

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L - 51504061/ECE/2K5 In the front-end "pre-processing" stage, the processor of choice increasingly is the field programmable gate array (FPGA) from companies such as Xilinx Inc. in San Jose, Calif., and Actel Corp. in Sunnyvale, Calif. This is primarily a move away from DSPs on the front end, experts say. At the same time, systems designers rely more heavily than ever before on high-end general-purpose processors such as the Altivec on the back end.

The rise of FPGAs FPGAs only recently have achieved the kinds of densities necessary for fast and demanding radar front-end processing, experts say. "FPGAs are now so much bigger and so much faster than they were years ago," says Jane Donaldson, president and chief executive officer of Annapolis Micro Systems Inc. a radar processing firm in Annapolis, Md. "Normally you can have 30 million gates in a single VME slot, while five years ago you would struggle to get a million gates. You have enough processing power now to solve the problem." This fast expansion in number of gates per device has made all the difference for radar systems integrators and their signal processing systems providers. "Over the past year we have been seeing a swing to more FPGA processing, particularly at the front end of radar and sonar processing, for repetitive math functions, filtering, and things that go on at the front end of the processor," says Stuart Heptonstall, product marketing manager for DSP products at Radstone Technology, a single-board radar processor supplier in Towcester, England. "FPGAs you can code exactly how you want, to keep them chunking away at that front-end data," he says, and enable designers to change the front-end processor for different platforms. "Our customers, the prime contractors, all are looking to put FPGAs as close to the radar sensing elements as possible — the antennas, transmitters, and receivers — to do preprocessing," says Philip Lindsay, northeast regional sales manager at Thales Computers Inc. in Raleigh, N.C. FPGAs, he says, are valuable for "massaging the data and lining it up so it is amenable to quick-corner turns, or quick FFTs, or quick FIRs [finite responses] so it can be processed almost immediately by the CPUs. They get the data as they need it, and you reduce latency." The radar signal-processing challenge is not fundamentally different today from how it was decades ago; what is changed is the processing approaches, which is where FPGAs GTBKIET.Six Months Training

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L - 51504061/ECE/2K5 come in today, says Larry Nork, director of radar business development at Mercury Computer Systems in Chelmsford, Mass.

The Lockheed Martin Medium Extended Air Defence System (MEADS) uses a UHF surveillance radar and X-band Multifunction Fire Control Radar. "In radar signal processing. What you needed in the past you need today, but you might do it more efficiently today," Nork explains. "You take channel equalization, phase compensation, and follow that up with pulse compression done with convolution processing where you have an FFT and a complex multiply, then do a inverse FFT, and that allows you to match filter processing on the radar return. Those are data-independent functions that are performed in a streaming fashion no mater what is coming into the input of the radar receiver, where the same function is repeated time after time, with no need for programmability. So you can add efficiency to the processing by using FPGAs, as opposed to using a programmable RISC processor." Still, Radstone's Heptonstall cautions that the necessary investment in FPGAs is relatively high, and implementers also must invest a lot of time providing the FPGA function. The FPGA programmer must write his own VHDL FFT code to engineer that solution, while today's DSPs often are easier to program than are FPGAs. Many systems designers insist that DSPs still have a role in radar processing; the trick is to determine the niche that FPGAs and DSP processors serve, says Bernard Pelon, director GTBKIET.Six Months Training

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L - 51504061/ECE/2K5 of product research at CSPI Inc., a radar processing supplier in Billerica, Mass. Either the FPGA or DSP might do better on some classes of problems, but might be more difficult to use, he says. "That may be why we begin to look at FPGAs and specialized processors. We need to understand where each applies and balance them out." No matter the choice of the FPGA or DSP, Pelon points out that both represent a step away from trends toward general-purpose processors that are not application specific, although he says FPGAs are farther away from the general-purpose ideal than are today's DSPs. "In both cases you lose generality; there is no question that they are not generalpurpose hardware," he says. "What we are facing is a non-standard world. The FPGA inside is a profusion of non-standard things, such as how you connect your gates, so with the specialized DSP there is an advantage. Now we need to define a standard internal FPGA bus, and we are nowhere close to that." As far as CSPI is concerned, "we lean to FPGA and specialized DSP; there is space for both, Pelon says. They are both in the spatial function side." He points to new generations of DSPs, such as the Analog Devices TigerSHARC, and the FastMATH and FastMIPS architectures from Intrinsity Inc. in Austin, Texas, that might cause radar designers to take another look at DSPs — either for front- or back-end processing.

The PowerPC Altivec On back-end radar processing, meanwhile, "two to three years ago we started seeing a shift away from dedicated DSP chips over to the PowerPC processors," Heptonstall says. The DSP chips required coding in low-level languages, such as assembler, "which is great if you know how to do it, and have the time, but we need to get to market quicker today," he says. "It's too much of a pain and an investment to program in assembler all the time." Rapid increases in the PowerPC Altivec's clock speed and other performance parameters started gaining the attention of radar systems integrators about three years ago when Motorola first introduced the Altivec version of the venerable PowerPC microprocessor, CSPI's Pelon says. "Before Altivec, PowerPC was not judged to be very attractive, but after Altivec it was judged to be a very good solution," Pelon says. It was significant because you were GTBKIET.Six Months Training

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L - 51504061/ECE/2K5 bringing DSP into a scalar architecture. You increased by a factor of four the operations you could run. It was fantastic news for anyone who had chosen the PowerPC architecture." Six years ago, for example, the most advanced PowerPC processors ran at clock speeds of 200 MHz, "but then, with the Altivec, you had 400 MHz — four times the operations, plus the processor's L2 cache was improved. So overall you had a factor of 20 improvement for FFT processing" Pelon says. PowerPC Altivec processors soon will be available that run at clock speeds as fast as 1 GHz. Software issues also make up an attractive aspect of general-purpose processors such as the Altivec, experts say. Radstone's Heptonstall says he believes the Motorola suite of advanced PowerPC Altivec processors "have much more easy user interfaces and support for off-the-shelf real-time operating systems such as Wind River VX Works, Linux, LynuxWorks LynxOS, and the OSE real-time operating system," than do the industry's DSP offerings. "The processors have a lot of momentum for these operating systems and have commonality with slot-1 single-board computers, which are predominantly the PowerPC processor. It makes the whole thing easier and more user friendly," he says. Aside from its advantages in speed, the PowerPC Altivec also offers designers the benefits of a standard off-the-shelf architecture that is well understood throughout the industry. "The benefit of standard hardware and software is concurrent engineering," says CSPI's Pelon. "If I have a piece of software that you can run on any workstation, then you can have several players doing concurrent engineering, and that couldn't be done in the past. That translates into minimizing development time, which is very important in terms of effective results and solutions and quality." Another factor running in the Altivec's favor is the new crop of fast switched-network architectures, such as RapidIO, Infiniband, and StarFabric, which promise to boost the Altivec's power when many processors combine on a network. In terms of fabric, none of this can work without a very fast fabric to connect general-purpose processor nodes with some of the more specialized nodes," Pelon says. "We need more than ever a high-speed interconnect."

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Architectural considerations Often the type of radar system under development will help determine the signalprocessing architecture. Large fixed-site radar systems with virtually unlimited capacity for space, weight, and power, for example, might accommodate a processing architecture heavy on general-purpose processors. Yet fighter aircraft radar, which places a premium on small size, lightweight, and low power consumption, might require a processor architecture heavy on FPGA and DSPs, and might not accommodate general-purpose processors at all. "The requirements for small-volume and low weight in advanced applications rely heavily on FPGAs. Other areas where we are not as restricted is where we can use the offthe-shelf processors," explains Kam Insky, manager of radar engineering project management at Lockheed Martin Naval Electronics & Surveillance Systems in Syracuse, N.Y. Lockheed Martin Syracuse provides a wide variety of radar systems, from large ground-based air traffic control systems, to space-constrained airborne systems.

The AN/TPS-77 Tactical Transportable Radar can be operational in less than one hour.

"In our advanced ground and airborne systems, where we not only deal with volume and weight, but also in advanced technologies such as digital advanced beamforming, we use GTBKIET.Six Months Training

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L - 51504061/ECE/2K5 a hybrid — or FPGA — approach, primarily on the front end," Insky explains. "For backend data processing, we use general-purpose processors" such as the PowerPC. "There are niches," Insky points out. "I see an evolution to more use of FPGAs than the dedicated DSPs, but we still have a product that relies heavily on DSPs" — an airborne system that uses the Analog Devices SHARC, he says. It is primarily driven by application — and in our applications now, we see continued use of FPGAs."

Popularity of the Altivec helps designers re-invent the DSP Although some radar systems designers may be writing off the digital signal processor (DSP) as a thing of the past in radar processing systems, proponents of the DSP say word of their passing is premature. The recently released TigerSHARC DSP from Analog Devices in Norwood, Mass., is perhaps the strongest argument against the demise of the DSP in radar applications. Yet the TigerSHARC and other new DSPs are competing head-to-head with the PowerPC Altivec microprocessor, not field programmable gate arrays (FPGAs), in radar applications, experts say. The TigerSHARC is an ultra high-performance static superscalar architecture for computationally demanding applications, and combines elements of RISC, VLIW, and standard DSP processors for 1-, 8-, 16-, and 32-bit fixed and floating-point processing. The original Analog Devices SHARC 21060 DSP — short for Super Harvard Architecture — dominated radar and sonar signal processing applications throughout the 1990s, yet gradually gave way to fast Altivec processors as the new century dawned. DSP proponents say the new TigerSHARC will give a big boost not only to the Analog Devices DSP product line, but also to DSP architectures across the board. "We've seen with the introduction of the TigerSHARC, our competitive environment changed 180 degrees; historically when we introduced the SHARC, we competed with Texas Instruments [DSPs}. Now with the introduction of the TigerSHARC, we are competing with the Altivec," says Darren Taylor, vice president of sales and marketing at BittWare Inc., a single-board DSP designer in Concord, N.H. GTBKIET.Six Months Training

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L - 51504061/ECE/2K5 "The TigerSHARC serves very well in some of these radar applications; we are seeing it across the board for radar systems," particularly for air traffic control, over-the-horizon, and 3D-based radar applications, Taylor says. The European radar manufacturer Alenia Marconi, for example, is using the TigerSHARC as their processor of choice for next-generation 3D air traffic control radar systems, Taylor says. "They did this because of the ability to do the continuous data movement and processing." Taylor admits that the Altivec G4 general-purpose processor can crunch data faster than the TigerSHARC can, "but you need to get the data in and the data out," he says. "That is where the TigerSHARC does much better in the real world." In addition, Taylor says, the TigerSHARC is more attractive in terms of power consumption. "The G4s are huge consumers of power" from five to 20 watts per chip, he says. "You are limited to the number of processors you can get on a board."

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