Group Study - Antennas Answer Key

GROUP STUDY - ANTENNAS 1. The direction at which radiation intensity is zero. a. Major lobe b. Minor lobec. Null d. Side lobe 2. Type of antenna that radiates equally in all directions along the horizontal plane. a. Fan beam b. unidirectional c. omnidirectional d. bidirectional 3. A resonant half wave dipole in free space has a feed line current of 1 amp. How much power appears at the input to the feedpoint? a. 73 w b. 146 w c. 219 w d. 292 w. 4. What would be the physical size of a Herts antenna operating at 74.784 MHz? (k=0.95) a. 71 in b. 75 in c. 79 in. d. 150 in 5. The efficiency of an antenna is 82%. Its radiation resistance is 30 ohms. What is the value of its loss resistance? a. 75 ohms b. 15 ohms c. 12 ohms d. 6.58 ohms 6. The power gain of a half wave dipole with respect to an isotropic radiator. a. 3 dB b. 6 dB c. 5 dB d. 2.15 dB 7. Antennas commonly used for microwave links are a. Loop b. parabolic c. log periodic d. rhombic 8. A loop antenna is commonly used for a. Radar b. direction finding c. satellite comm d. SONAR 9. An antenna that is circularly polarized a. Parabolic b. log periodic c. Yagi Uda d. helical 10.In a Yagi Uda Antenna, antenna maximum direction of radiation is towards the a. Director b. Reflector c. Driven Element d. Array 11.System of buried conductors that improves ground conductivity a. Counterpoise b. Antenna Coupler c. Earth Mat d. Top Load 12.Ratio of the power density of an antenna to the power density of an isotropic radiator a. Directive gain b. ERP c. Power Density d. Power Gain 13.What is the power gain in dB for an antenna with directive gain of 40 dB and an efficiency of 65%? a. 38.13 dB b. 31.83 dB c. 65 dB d. 40 dB 14.A paraboloid is to have a power gain of 41.55 dB. If the frequency of operation is 8GHz, what is the diameter of the parabolic reflector? a. 10 ft b. 6 ft c. 2.3 ft d. 1.4 ft. 15.What is the beamwidth for the previous problem? a. 3 degrees b. 5.4 degrees c. 8 degrees d. 1.4 degrees 16.The end impedance of a half wave dipole is a. Resistive and low c. inductive b. Resistive and high d. capacitive 17.Find the higher optimum frequency of a Marconi antenna if the distance between the feedpoint and the antenna trap is 2.5 m. a. 11.54 MHz b. 11 MHz c. 30 MHz d. 12.2 MHz 18.The antenna property of interchangeability for transmitting and receiving electromagnetic energy under the same radio frequency is referred to as a. Back to back b. maximum energy c. retransmission d. reciprocity

19.It consists of a number of dipoles of equal size, equally spaced along a straight line with all dipoles fed in the same phase from the same source. a. End Fire Array b. Yagi Uda c. Log Periodic d. Broadside Array 20.A type of antenna that has a physical length equivalent to one half wavelength of the radio frequency being used. a. Yagi Uda b. Hertz c. Rhombic d. Marconi 21.It is a measure of the microwave power radiated from an antenna as a function of angular direction from the antenna axis. a. Polarization b. Sidelobes c. Beamwidth d. Antenna Pattern 22.Which is the Non-resonant antenna? a. Folded dipole b. End fire array c. long wire antenna d. rhombic antenna 23.How much does the radiated power of an antenna increase if its current increases 3.3 times? a. 3.3. times b. 9.9 times c. 10.89 times d. 6.6 times 24.Radio wave concentration in the direction of the signal emitted by a directional antenna. a. Transmitted signal b. side lobe c. back lobe d. major lobe 25.A region in from of a paraboloid antenna a. Fresnel b. transition zone c. fraunhoffer d. all of these 26.An ungrounded antenna near the ground a. acts as a single antenna of twice the height c. is unlikely to need a ground screen b. acts as an antenna array d. must be horizontally polarized 27.One of the following consists of nonresonant antennas: a. rhombic antenna b. folded dipole c. end-fire array d. broadside array 28.Which of the following antennas is best excited from a waveguide? a. Biconical b. Horn c. Helical d. Discone 29.One of the following is not a reason for the use of an antenna coupler: a. To make the antenna look resistive b. To provide the output amplifier with the correct load impedance c. To discriminate against harmonics d. To prevent reradiation of the local oscillator 30.Which one of the following terms does not apply to the Yagi-Uda array? a. Good bandwidth b. Parasitic elements c. Folded dipole d. High gain 31.An antenna that is circularly polarized is the a. Helical b. small circular loop c. parabolic reflector

d. Yagi-Uda

32.The standard reference antenna for the directive gain is the a. infinitesimal dipole b. isotropic antenna c. elementary doublet d. half-wave dipole 33.Top loading is sometimes used with an antenna in order to increase its a. effective height b. bandwidth c. beamwidth d. input capacitance 34.A helical antenna is used for satellite tracking because of its a. circular polarization c. maneuverability

b. broad bandwidth

d. good front-to-back ratio

35. One of the following is not an omnidirectional antenna: a. Half-wave dipole b. Log-periodic c. Discone Marconi

d.

36. In a Yagi antenna, a. The director is shorter than the driven element b. The elements are spaced at least one wavelength apart c. The reflectors are shorter than the driven element d. There are usually more reflector than directors 37.Antenna polarization is determined by____. a. The direction of the magnetic field vector c. The direction of the electric field vector b. The frequency of the radiated wave d. The direction of the radiated wave 38.The length of a half-wave dipole for 28 MHz is approximately____. a. 17.6 feetb. 23.6 feet c. 30.6 feet d. 34.6 feet 39.One kilowatt is supplied to a rhombic antenna resulting to 20 microvolts per meter at the receiving station. In order to produce the same field strength at the receiving station, a half-wave antenna, properly oriented and located near the rhombic, must be supplied with 16.6 kilowatts. What is the gain (in dB) of the rhombic referred to isotropic antenna? a. 12.2 b. 6.5 c. 14.35 d. 10.25 40.The amount of voltage induced in a wire by an electromagnetic wave is determined by the wave’s a. Field Strength b. Direction of Travel c. Velocity d. Frequency 41.An antenna supported by insulators appears electrically longer than its physical length due to a. End Effect b. Reflection c. The Ionosphere d. The Troposphere 42.Where do the maximum current and minimum voltage values on a resonant Hertz dipole exist? a. Center of the antenna c. Near the end of the antenna b. Near the center of the antenna d. Ends of the antenna 43.What is meant by the term antenna efficiency? a. Efficiency = (effective radiated power /transmitted output) x 100% b. Efficiency = (radiation resistance / transmission resistance) x 100% c. Efficiency = (total resistance / radiation resistance) x 100% d. Efficiency = (radiation resistance / total resistance) x 100% 44.A convenient method of determining antenna impedance. a. reactance circle b. stub matching c. Smith chart

d. Trial and

error 45.Unity gain antenna. a. half-wave dipole b. rhombic

c. dummy

46.A region in front of a parabolic antenna. a. Transmission zone b. All of these d. Fresnel

d. isotropic c. Fraunhoffer

47.Radiation pattern of a discone a. figure of eight b. bi-directional unidirectional

c. omnidirectional

d.

48.Radio wave concentration in the direction of the signal emitted by a directional antenna. a. Back lobe radiation b. Transmitted signal c. Side lobe radiation d. Major lobe radiation 49. The reflector and director of an antenna array are considered as: a. Transcendental elements b. Feed-points c. Driven elements d. Parasitic elements 50.The product of the power supplied to the antenna and its gain relative to a half-wave dipole in a given direction. a. Rated power b. ERP c. Peak envelope power d. Carrier power 51.What makes an antenna physically long but electronically short? a. Adding C in series b. All of these c. Top loading Adding L in series

d.

52.Determine the field strength at 1 mile for a vertical antenna ¼ wavelengths high when power is 1 kw and antenna loop resistance is 8 ohms. a. 0.4 V/m b. 5 mV/m c. 1 mV/m d. 0.2 V/m 53.The ability of an antenna to radiate more energy in one direction than in other directions is called: a. directivity b. active antenna c. selectivity d. resonance 54.An antenna's beamwidth is measured: a. from +90dB to –90dB c. between half-power points b. from front to back d. between the minor side-lobes 55.ERP stands for: a. Equivalent Radiation Pattern b. Effective Radiation Pattern

c. Equivalent Radiated Power d. Effective Radiated Power

56.The polarization of plane waves received from a satellite is changed by: a. gamma rays b. helical rotation c. Faraday Rotation d. the distance traveled 57.An antenna can be matched to a feed line using: a. a shorted stub b. an LC network c. a loading coil above 58.Arrays can be: a. phased b. parasitic

c. driven

d. all of the

d. all of the above

59.An array with one driven element, a reflector, and one or more directors is called a: a. Marconi b. Log-Periodic Dipole c. Yagi d. stacked array 60.The energy picked up by a parabolic antenna is concentrated at the: a. center b. focus c. edges d. horn 61.An antenna is the interface between the transmission line and ____________________.

a. space

b. coupler

c. impedance

d. electromagnetic

waves 62.The length of a half-wave dipole is about _________________% of a half-wave in free space. a. 100 b. 90 c. 95 d. 99.95 63.The ____________________ resistance is the portion of an antenna's input impedance due to transmitted radio waves leaving the antenna. a. load b. loss c. antenna d. radiation 64.Input impedance at the center feed point of a resonant half-wave dipole is about _____ ohms. a. 250 b. 300 c. 377 d. 73 65.Input impedance at the center feed point of a resonant folded dipole is about ____ ohms. a. 150 – 200 b. 280 – 300 c. 200 – 270 d. 377 66.The ____________________ of a directional antenna is the angle between its half-power points. a. directivity b. maximum directive gain c. beamwidth d. a or b 67.A horizontally mounted dipole will radiate waves with ____________________ polarization. a. vertical b. linear c. horizontal d. random 68.A monopole antenna is typically mounted in the ____________________ direction. a. vertical b. horizontal c. any d. none of these 69.The length of a typical monopole antenna is ____________________ wavelength. a. one half b. full c. one quarter d. 3/4 70.A monopole antenna mounted high on a tower typically uses a _______________ plane. a. vertical b. horizontal c. ground d. mounted 71.A vertical antenna has a/n ______________ radiation pattern for groundbased receivers. a. unidirectional b. bidirectional c. omnidirectional d. cardiod 72.The number of driven elements in a Yagi antenna is typically ____________________. a. one b. two c. three d. more than 3 73.All the waves that hit the surface of a parabolic antenna merge at the ______. a. Focus b. feedpoint c. a or b d. a and b 74.A microwave ____________________ antenna is essentially an extension of a waveguide. a. parabolic b. lens c. loop d. horn 75.Calculate the physical length of a half-wave dipole for use at 300 MHz. a. 475 m b. 475cm c. 475mm d. 475 um

76.How much power will a 95% efficient antenna radiate if driven with 100 watts? a. 90w b. 95w c. 100w d. 105w 77.If an antenna has 10.14 dB of gain compared to a point source, how much gain does it have compared to a half-wave dipole? a. 9dB b. 2.15 dB c. 1.76 dB d. 8dB 78.A resonant antenna has an input impedance of 100 ohms and is driven by 100 watts. What is the RMS current in the antenna? a. 2 amp b. 3 amp c. 100 amp d. 1 amp 79.A resonant antenna has an input impedance of 100 ohms and is driven by 100 watts. What is the RMS voltage at the feed-point of the antenna? a. 1 v b. 10 v c. 100 v d. 1000 v 80.A dipole antenna has a radiation resistance of 67 ohms and a loss resistance of 5 ohms, measured at the feedpoint. Calculate the efficiency. a. 95% b. 98% c. 93% d. 97% 81. The efficiency of an antenna is 82 %. Its radiation resistance is 30 Ω. What is the value of its loss resistance? a. 10 ohms b. 6.58 ohms c. 8 ohms d. 12 ohms 82.________________ means that the characteristics and performance of an antenna are the same whether the antenna is radiating or intercepting an electromagnetic signal. a. antenna reciprocity b. antenna polarization c. antenna grounding d. tower sway 83.Which of the following methods is used to lower the resonant frequency of a shortened vertical antenna? a. loading coil b. top hat loading c. drooping radials d. grounding 84.Calculate the gain (relative to an isotropic) of a parabolic antenna that has a diameter of 3 m, an efficiency of 60% and operates at a frequency of 4 GHz. a. 39.8 dBi b. 41.94 dBi c. 37.66dBi d. 79.53 dBi 85.It is a phenomenon caused by any support insulators used at the ends of the wire antenna. a. skin effect b. end effect c. faraday effect d. miller effect 86.The shape of the electromagnetic energy radiated from or received by an antenna is called the a. signal shape b. electromagnetic pattern c. radiation pattern d. antenna pattern 87.Antennas that transmit an equal amount of energy in the horizontal direction are called a. bi-directional b. unidirectional c. omnidirectional d. unilateral 88.The ability of an antenna to send or receive signals over a narrow horizontal directional range is referred to as

a. focal factor d. horizontal range

b. permittivity

c. directivity

89.A basic antenna connected to a transmission line plus one or more additional conductors that are not connected to the transmission line form a a. parasitic array b. bi directional array c. half wave dipole d. counterpoise 90.An antenna made up of a driven element and one or more parasitic elements is generally referred to as a a. Hertz antenna b. Marconi antenna c. collinear antenna d. Yagi antenna 91.A stacked collinear antenna consisting of half-wave dipoles spaced from one another by one-half wavelengths is the a. broadside array b. end-fire array c. wide-bandwidth array d. parasitic array 92.A half-wave dipole is sometimes called: a. Marconi antenna b. Yagi Antenna

c. Hertz Antenna d. none of

these 93.An antenna can be matched to a feed line using a. a shorted stub b. a loading coil c. an LC network

d. all of

these 94.As the length of a "long-wire" antenna is increased a. the directive gain increases c. efficiency decreases c. the number of nodes decreases d. none of these 95.LPDA stands for a. Low-Power Dipole Array

b. Log-Periodic Dipole

Array c. Low-Power Directed Array

d. Log Power Dipole Array

96.A receiving antenna with a built-in preamplifier a. active antenna b. passive antenna c. coil antenna

d. LC

97.Refers to the direction in space of electric vector of the electromagnetic wave radiated from an antenna and is parallel to the antenna itself. a. Propagation b. Coordinates c. Polarization d. Azimuth 98.Placing a metallic array on the antenna effects to increase the current at the base of the antenna, and also to make the current distribution more uniform. What is this called? a. Reflector b. Grounding c. Top Loading d. Feeding 99.Calculate the beam width between nulls of a 2-m paraboloid reflector used at 6GHz. Note: such reflectors are often used at that frequency as antennas outside broadcast television microwave links. a. 14 degrees b. 7 degrees c. 3.5 degrees d. 0.875 degrees 100. A structure-generally metallic and sometimes very complex-designed to provide an efficient coupling between space and the output of a transmitter or input to a receiver. a. Stub b. Antenna c. Transmission Line d. Waveguide