Microwave Engineering Practical File
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Practical No. 1 Aim: Introduction to various component of microwave workbench and measuring equipment Theory: 1] Klystron Power Supply; Klystron Power supply is a state of art solid state regulated power supply for operating low power klystron such as 2k25, 723 MB. 2] VSWR meter The meter indicates the signal level in propogation to the i/p which is calibration directly in VSWR and db 3] Klystron mount These are mount for mounting corresponding klystron,. These consist of a section of waveguide flanged on one end and transmitted with a movable sport on the other end. 4] Isolator: This port circular may be converted into isolator by terminating one of its port in\to momental load. 5] Frequency motor: It gives directfrequencyon the dial provided These are recommended for used Whgenever quick determination of frequency and easy reading are desired. 6]Variable attenuator Waveguide This is provided atleast 20db of continous variable attenuator. This Consist of movable loosywave inside the section of a guide by means of a micrometer 7] Slotted line Section: It consists of two parallel plane strips and central conductor with N(m) connection on one end and N(f) connector on the other end. 8] Magic Tee: TEE consist of a section of waveguide wiuth both series and shunt wave guide arms mounted at the exact midpoint of main arm. 9] Fixed attenuator: These are used for inserting a known attenuator to a waveguided. These of a attenuation to a waveguide. These of a loosy inserted in a section flanged on the b oth ends. 10] Movable Short: This consist of a sectiono f waveduide, flange on one end and tranmitted with a movable shorting plunger oin the other end.
11] Side Screw Tunner: This consist of a section of waveguide flinged on both ends and a thin slot is providedin the board wall of the waveguide. 12] H and F plane Tee: Tee and series the type T junction and consist of three section of wave guide joined together in order to divide and compare power levels. E plane: The signal entering the first port of this junction will be equally divided of second and third ports of the some magnitude but in \opposite phase H Plane: the signal fed through the first port of h plane tee will be equally divided in waveguide at 2nd and 3rd ports but in some phase. 13] Multiple Directional Coupler: These are useful for Sampling a port of microwave energy for monitoring purpose and for measuring reflections and impedence. 14] Waveguide Stand: Waveguide stands are meant to accept the component of respective bands for setting up a waveguide test bench.
Practical No. 2 Aim: To study the characteristics of reflex klystron. Apparatus: Klystron power supply, microwave bench, klystron tube oscillator, isolator, detector, frequency meter variable attenuator, CRO, CRO probes, etc. Theroy: Reflex Klystron uses only a single cavity resonator andoperates as an oscillator. The various part included as electron gunn; Resonato, repeller and o/p coupling. The repeller electrode is at a (-ve) potential and sends the partially bunched electrode beam back to the resonator cavity. This provides a (+ve) feedback mechanism which supports oscillation . If the voltage difference between resonator and repeller is V and the distance is ‘d’, the retardation experienced by the electron beam may be obtained as A= Force/Mass = e/m Bunching in reflex Klystron: Bunching phenomena in a reflex klystron can be utilized by studying electron trajectories in the region between the resonator and repeller. The bunches formed would deliver power to t h resonator at an instant. When the field retards the bunch. This value corresponding to various mode of reflex klystron. A particular mode of operation may be selected by choice of repeller voltage. Procedure: • Connect the equipments and components as shown in figure. • Set variable attenuator to around zero position. • Set mode Selector switch to AM mode position. • Keep beam voltage fully anticlockwise and reflector voltage knb to fully clockwise and beam switch of OFF position • Switch on the klystron power supply to beam voltage of 300 V by voltage control knobe. • Keep the amplitude knobe of AM mode to max. position and rotate the reflector voltage anticlockwise to get the modes a shown in fig. • •
The horizontal axis represents reflector voltage and vertical axis represents o/p power. By changing the reflector voltage measure the o/p power
Conclusion: In this practical, by performing we conclude that reflex klystron tube is used for high power and amplitude and output is as shown in figure.
Practical 3: Aim: To measure the frequency of Carrier wave and wavelength of the wave. Apparatus: Microwave bench, klystron power supply, klystronosci CRO, DMM Theory: Frequency is the most fundamental quantity required in almost all microwave calculation. Anyone of the frequency or the core is calculated directly and other is calculated from it. Frequency Measurement: The primary frequency standard Image may be a Cesium automatic clock or a gas mser with a accuracy of 1 part in 10^-4 or better. The more common standard is a highly stable temp. compensated crystal oscillator whose accuracy is of the order of 0.8 part in 10^-10. The microwave stability to few parts if 10^-9. This may be used to calibrate a good generator at a single point. Wavelength Measurement: One method is to calculate it from measure directly using c=(f )*(lambda). Another method is to S.C. the far end of the standing wave detector and moving the probe away from the S.C. unit position of first Vmin is reached Distance from the point to S.C is equal to ½ (lambda) of signal. This method has high accuracy of the order of 0.1mm. and is done by taking avg. after many reading W/g, W/g is given as
Where l/lc and lg are frequency space, cut off and waveguide wavelengths for TE10 mode lc=2a where a is broad dimension of w/g Procedure: • Set component and equipments as shown in figure. • Set variable attenuator at min. attenuation position • Keep the control knobs of VSWR meter range =50db • Vp Switch = crystal low impedance meter = normal position, gain= mid-position. • Keep the control knob of klystron P.S. as below Beam volt off, AM beam volt knob fully anticlockwise reflector volt, fully anticlockwise reflector volt:fully anticlockwise. • Switch on klystron supply, VSWR and fun • Witch on beamvolt and set it to 300V, Adjust the reflector volt to get some deflection is VSWR meter
Practical No. 4 Aim: To study V-I Characteristics of Gunn Diode.
Apparatus: Gunn power supply, gun oscillator, isolator, PIN modulator, VSWR meter variable attenuator, Detector mount, cables, etc. Theory: The Gunn Oscillator is based on negative differential conductivity effect in bulk semi-conductor, which has two conductor bands minima separated at cathode give rise to high field region, which travels towards anode. It disappears and another domain is formed at catho\de and starts moving towards anode and so on. The time required for domain to travel from cathode to anode gives oscillation. In a given oscillator, gunn diode is place din a resonant cavity. In this case the oscillator frequency is determined by cavity dimension than by diode itself. Procedure: • Set the components and equipments as shown in fig. • Initially set variable attenuator for maximum attenuation. • Keep control knob of gunn diode supply at meter switch off. Gunn bias knob-Fully anticlockwise • Keep control knob of VSWR meter as meter switch-Normal. Input Switch – low impedance, Range db switch – 40 db, Gain control knob – Fully clockwise • Set the micrometer of Gunn oscillator for required frequency of operation. • Switch ON the Gunn power supply, VSWR meter and celling Fan. • Turn the meter switch of Gunn power supply to voltage position. • Measure Gunn diode current corresponding to various voltages through panel meter and meter switch. Donot exceed 9 volt. • Plot the voltage vs. current reading on graph as shown in fig. • Measure the threshold voltage which corresponds to Max. Current. Conclusion: From this practical, as we shift the S.S, tuner to left side, our VSWR increases, hence we can conclude hat on shifting SS tuner to left side, discontinuity on the line increase.
Practical 5: Aim:
To find out coupling and directivity of MHDC ( Multi Hole Directing Coupling) Apparatus: Microwave source, isolators, frequency meter, variable attenuator, slotted line, tunable probe, magic tee, matened terminations, MHD coupler, waveguide stand, detector mount Theory: A directional coupler is a device with which it is possible to measure the incident and reflected wave separately. It consists of two transmission line, the main arm and auxiliary arm, electromagnetically coupled to each other. The power entering port 1 in the main arm divides between two port 2 and 3 and almost no power comes in port 4. The coupling factor is defined as = 10 log10(p1/P2). The directivity of coupler is a measure of separation between incident wave and the reflected wave. It is measured as the ratio of the power output from auxiliary line. When a give amount of power is applied to each terminates of the main lines with other port terminated by material load. Observation Table: i/p Port 1 i/p Port 2
P1 mW 23 18.4
P2 mW 18.4 23
P3 mW 5.75 0
V1(v) 1 0.8
V2(v) 0.8 1
V3(v) 0.25 0
Procedure: 1. Connect the multihole DC to the micro wave bench and give beam voltage – 300 Volt. 2. Keep current constant at 23mA. 3. Give Repeller voltage 154 V 4. Set the frequency knob on frequency meter at 3 db. 5. Measure various power, i.e.:P1, P2 and P3 by calculating voltages at corresponding ports P1, P2 and P3. 6. Calculate coupling factor and directivity. Conclusion: From this practical we can calculate that the directivity is infinity, coupling factor C= 14.4 dB and Insertion loss =0.139 dB.
Practical 6: Aim: To Study about power division of magic tee.
Apparatus: Microwave source, isolator, variable attenuator frequency meter, slotted line, magic tee, tunable probe, matched termination, waveguide stand detector mount and accessories. Theory: Magic Tee: A magic tee is a 4 port device. It consists of two collinear arms, one E Plane and H Plane tee. But exhibits property different from either. Characteristics of magic Tee: If two waves of equal magnitude and some phase are fed into two collinear arms, the output is in H arm and no output at E arm. If two waves of equal magnitude and but 180 degree are fed into two collinear arms the output is in E arm and no output at H arm. If a wave is fed in Harms the output is equal in phase in the two collinear arms and no output in E arms. If a wave is fed in E Arm, the output is equal but 180 degree out of phase in the two collinear arms and no output in the H arms. Procedure: • Connect the magic tee to the microwave bench and give beam voltage=300 volt. • Using klystron power supply which give repeller voltage=163 volt. • Apply power at H arm and measure output at E arms with collinear arms matched terminate. • Calculate coupling factor by C=10-(alpha)/20 where alpha= 10 log (P3/P4), base 10. Conclusion: We conclude by the performance of the experiment that the isolation factor is more than the coupling factor hence the signal is attenuated while traveling from port 3 to port 4. i.e. H arm to E arm in Magic Tee.
Aim: To study about E plane tee. Apparatus: Microwave source, isolator, frequency meter, variable attenuator, slotted line, matched termination E plane tee, waveguide stand, detector mount, CRO probes. Theory: An E plane tee is a waveguide tee in which the axis of its side arm is parallel to the E filed of the main guide. If the collinear arms are symmetric about the side arm, there are two different transmission characteristics. If the E plane tee is perfectly matched with the aid of screw tuners or inductive or capacitive windows at the junction, the diagonal components of the scattering matrix S11, S22 and S33 are zero because there will be no reflection. When the waves are fed into the side arm (port 3). The waves appearing at port 1 and port 2 of the collinear arm will be in opposite phase an in the same magnitude. Procedure: • Connect the E plane tee to the microwave bench and give beam voltage= 300 volts. • Using klystron power supply which give repeller voltage 163 volt. • Apply power at port 3 and measure output at port 1 and port 2 of the collinear arm. Conclusion: By performing this experiment we can conclude that if we give input to port 3 and measure output from port 1 and port 2 it will equally divided of input and opposite in phase.
Practical 8 Aim: To study about the H plane Tee. Apparatus: Microwave source, Isolator, variable attenuator, freq. meter, slotted line, tunable probe, H plan Tee, etc. Theory: A H plane Tee junction is formed by cutting a rectangular slot along the width of a main waveguide, the side arm is called as H arm. The port 1 and port 2 of the main waveguide are called as collinear ports and port 3 is called as side arm. H plane Tee is so called because the axis of side arm is parallel to the plane of the main transmission line. As there are three arms of the H plane Tee lie on the plane of magnetic field, the magnetic field divides itself into the arms it is called as current junction. The properties of H plane Tee can be completely defined by its [S] matrix. As no. of port=3, there are three possible inputs and three possible outputs Procedure: 1] Set up the components, remove the tunable probe and H plane Tee from slotted line and connect the detector mount. 2] Energize the microwave source for particular frequency of operation and tune the detector mount for maximum output. 3] Remove detector mount and connect H plane Tee and H arm to slotted line 4] Now measure output at port 1, keeping port 2 shorted. 5] Now measure output at port 2, keeping port 1 shorted. 6] Note down the power levels. Conclusion: We conclude that the power which is fed to port 3 of H arm is equally divided into port1 and port 2 of H arm.
Practical 9 Aim: Study the isolator and circulator. Apparatus: Microwave source, isolators, circulators, frequency meter, variable attenuator, slotted line, tunable probe, detector mount, VSWR meter, test isolation, circulation and accessories. Theory: Isolator: The isolator is a two port device with small insertion loss in forward direction and a large in reverse attenuation. Circulator: The circulator is a multi-part junction that permits transmission in different ways. A wave incident in port 1 is coupled to port 2 only; a wave incident at port2 is couple to port 3 only and so on. Insertion loss: The ratio of power supplied by a source to the i/p port to the power detected by a detector in the coupling arm. i.e. o/p arm with other port terminated in the matched load is defined as insertion loss or forward loss. Isolation: It is the ratio of power fed to i/p arm to the power detected at not coupled port with other port terminated in the matched load. Input VSWR: The i/p VSWR of an isolator or circulator is the ration of voltage maximum to voltage minimum of the standing wave existing on the line, when port of it terminates the line and others have matched termination. Procedure: A] Input VSWR Measurement: • Connect the equipments as shown in the figure • Energize the microwave source for maximum power at any frequency of operation. • Measure the VSWR with the help of tunable probe, slotted line and VSWR meter as described in the experiment as measurement of low and medium VSWR. • Repeat the above step for a frequency if required. B] Measurement of insertion loss in isolation. • Remove the tunable probe, isolator or circulator from the slotted line and connect the detector mount to the slotted section. The o/p of the detector mount should be connected with VSWR meter. • Energize the microwave source for maximum o/p for a particular frequency of operation. Tune the detector mount for maximum o/p in the VSWR meter. • Set any reference level on the VSWR meter with the help of variable attenuator and gain control knob of VSWR meter, Let it be P1.
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Carefully disconnect the detector mount from the slotted line, without disturbing any position on the set up. Insert the isolator or circulator between the slotted line and detector mount. Keeping i/p port to slotted line and detector as its o/p port matched termination should be place at 3rd port in case of circulator. Record the reading in the VSWR meter. If necessary change range switch to high or lower position and taking 10 db change for one step change of switch position. Let it be P2. Compute insertion loss on P1-P2 in dB. For measurement of isolation or circulator has to be connected reverse. i.e. o/p port to slotted line and detector to i/p port with other port terminated by matched termination after setting a reference level without isolator or circulator in the setup as described in insertion loss measurement. Let same P2 level is set. Record the reading of VSWR meter inserting the isolator or circulator as given in step7. Let it is P3. Compute isolation as P1- P3 in dB. The same experiment can be done for other ports of circulator. Repeat the above experiment for other freq. if needed.
Conclusion: From this practical, we can conclude that in circulator, when we give i/p in 1, we get o/p at port 2 and zero o/p at port 3 and it rotate circulatory. i.p. input in port 3 and it rotate circulatory i.e. input in port 3 give o/p at port 3 and So on. In Isolator, when we give i/p in port 1 we get o/p in port 3 but reverse is not possible.
Practical 10 Aim: To study fixed and variable attenuator. Apparatus: Microwave source, isolator, freq. meter, variable attenuator, slotted line, tunable probe, detector mount, matched termination, VSWR meter, fixed and variable type attenuator and accessories. Theory: The attenuator is two port bi directional devices which attenuates some power when inserted into transmission line. Attenuation A(dB)=10log(base 10) P1/P2 where P1 is power absorbed or detected by load without the attenuator in the line. P2 is power absorbed / detected by the load line with attenuation in the line. The attenuation consists of a rectangular waveguide with resistive vane inside it to absorb microwave power according to their positions with respect to side wall of the waveguide. As electric field is maximum at centre in TE10 mode, the attenuation will be maximum if the vane side wall, attenuation decreases in the fixed attenuator. The vane position is fixed where as in variable attenuator; its position can be changed by help of micrometer or by other methods. Procedure; A] i/p VSWR Measurement • Remove the tunable probe attenuator and matched termination form the slotted section in the above set up. • Connect the detector mount to the slotted line and tune the detector mount also for maximum deflection on VSWR meter. • Set any reference Level on the VSWR meter with the help of variable attenuation and gain control knob of VSWR meter. Let it be P1 • Carefully disconnect the detector mount from the slotted line, without disturbing any postion on the set up. Place the test variable attenuator to the slotted line and detector mount to other port of test variable attenuator. • Keep the micrometer reading of test variable attenuator to zero and record the reading of VSWR meter. Let it be P2. then the insertion loss or test attenuator will be P1-P2 dB. • For measurement of attenuation of step 4 of above measurement. Carefully disconnect the detector mount from the slotted line without disturbing any position obtained up to step 3. • Place the est attenuator to the slotted line and detector mount to the other port of test attenuator. • Record the reading of VSWR meter • Let is be P3. Then the attenuation value of fixed attenuator for particular position or micro meter reading will be P1-P3 dB.
In case of variable attenuator, change the micro meter reading and record the VSWR meter reading. Find out Attenuation value for different position of microwave reading. Now change the operating frequency and whole step should be repeated for finding frequency sensitivity for fixed and variable attenuator.
Conclusion: From the observation made we can conclude that the attenuation (in dB) calculated is nearly equal to the standard mentioned value on the attenuator.