COMMUNICATIONS ENGINEERING PART 6ANTENNAS

Multiple Choice. Encircle the letter which corresponds to your answer.

1. An ungrounded antenna near the ground

a. Acts as a single antenna of twice the height

b. Is unlikely to need an earth mat

c. Acts as an antenna arrayd. Must be horizontally polarized

2. One of the following consists of nonresonant antennas:

a. The rhombic antennab. The folded dipolec. The end-fire arrayd. The broadside array

3. One of the following is very useful as a multiband HF receiving antenna. This is the:

a. Conical hornb. Folded dipolec. Log-periodicd. Square loop

4. Which of the following antennas is best excited from a waveguide?

a. Biconicalb. Hornc. Helicald. Discone

5. Indicate which of the following reasons for using a counterpoise with antennas is false:

a. Impossibility of a good ground connection

b. Protection of personnel working underneath

c. Provision of an earth for the antenna

d. Rockiness of the ground itself

6. 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

7. Indicate the antenna that is not wideband

a. Disconeb. Folded dipolec. Helicald. Marconi

8. Indicate which one of the following reasons for the use of an earth mat with antennas is false:

a. Impossibility of a good ground connection

b. Provision of an earth for the antenna

c. Protection of personnel working underneath

d. Improvement of the radiation pattern of the antenna

9. Show which of the following terms does not apply to the Yagi-Uda array

a. Good bandwidthb. Parasitic elementsc. Folded dipoled. High gain

10. An antenna that is circularly polarized is the

a. Helicalb. Small circular loop

c. Parabolic reflectord. Yagi-Uda

11. The standard reference antenna for the directive gain is the

a. Infinitesimal dipoleb. Isotropic antennac. Elementary doubletd. Half-wave dipole

12. Top loading is sometimes used with an antenna in order to increase its

a. Effective heightb. Bandwidthc. Beamwidthd. Input capacitance

13. Cassegrain feed is used with a parabolic reflector to

a. Increase the gain of the systemb. Increase the beamwidth of the

systemc. Reduce the size of the main

reflectord. Allow the feed to be placed at

a convenient point

14. Zoning is used with a dielectric antenna in order to

a. Reduce the bulk of the lensb. Increase the bandwidth of the

lensc. Permit pin-point focusingd. Correct the curvature of the

wavefront from a horn that is too short

15. A helical antenna is used for satellite tracking because of its

a. Circular polarizationb. Maneuverabilityc. Broad bandwidthd. Good front-to-back ratio

16. The discone antenna is

a. A useful direction-finding antenna

b. Used as a radar receiving antenna

c. Circularly polarized like other circular antennas

d. Useful as a UHF receiving antenna

17. One of the following is not an omnidirectional antenna

a. Half-wave dipoleb. Log-periodicc. Disconed. Marconi

18. The polarization of a discone antenna is __________.

a. Horizontalb. Verticalc. Omnid. Directional

19. __________ is the horizontal pointing angle of an antenna.

a. Right angleb. Angle of elevationc. Bandwidthd. Azimuth

20. Which is a properly terminated antenna?

a. Rhombicb. Hertzc. Marconid. Dipole

21. __________ is a device that detects both vertically and horizontally polarized signals simultaneously.

a. Crystalb. Orthomode transducerc. Light transducer d. Optoisolator

22. How much does the radiated power of an antenna increases if its current increased by 3.3 times?

a. 6.6 timesb. 3.3 timesc. 10.89 timesd. 9.9 times

23. What do you call the energy that was not radiated into space or completely transmitted?

a. Incident wavesb. Captured wavesc. Standing wavesd. Modulated waves

24. What is the estimated medium wind loading in the Philippines for antenna tower design?

a. 200 kphb. 250 kphc. 300 kphd. 100 kph

25. The minimum number of turns a helix antenna must have.

a. 4b. 5c. 3d. 6

26. When testing transmitter to prevent interfering with other stations, which type of antenna must be used?

a. Dummy antenna b. Herztian antenna c. Noned. Void antenna

27. A device that radiates electromagnetic energy and/or intercepts electromagnetic radiation.

a. Antennab. Transmitterc. Transmission line

d. Transceiver

28. Determine the gain of a 6 ft parabolic dish operating at 1800 MHz

a. 15.5 dBb. 30 dBc. 11.2 dBd. 28.17 dB

29. Radiation characteristic of a dipole.

a. figure of eightb. omnidirectionalc. bi-directionald. unidirectional

30. An antenna which is not resonant at particular frequencies and so can be used over a wide band of frequencies is called

a. aperiodicb. cassegrainc. top-loadedd. boresight

31. Two wires that are bent 90 degrees apart.

a. Rhombicb. Hertzc. dipoled. log-periodic

32. Harmonic suppressor connected to an antenna.

a. tank circuitb. m-derived filterc. low-pass filterd. high-pass filter

33. Theoretical gain of a Herztian dipole.

a. 0 dBb. 1.76 dBc. 2.15 dBd. 3 dB

34. A helical antenna is used for satellite tracking because of

a. Maneuverabilityb. Good front-to-backc. Circular polarizationd. Broad bandwidth

35. A convenient method of determining antenna impedance.

a. reactance circleb. stub matchingc. Smith chartd. trial and error

36. Unity gain antenna.

a. half-wave dipoleb. rhombicc. dummyd. isotropic

37. EIRP stands for __________.

a. effective isotropic reflected power

b. effective isotropic refracted power

c. efficient and ideal radiated power

d. effective isotropic radiated power

38. Which of the following refers to the smallest beam of satellite antenna’s radiation pattern?

a. Global beamb. Zoom beamc. Spot beamd. Hemispheric beam

39. A region in front of a parabolic antenna.

a. Transmission zone

b. Fraunhoferc. Fresneld. All of these

40. An antenna that can only receive a television signal.

a. isotropic antennab. reference antennac. TVROd. Yagi antenna

41. Radiation pattern of a discone

a. figure of eightb. bi-directionalc. omnidirectionald. unidirectional

42. Radio wave concentration in the direction of the signal emitted by a directional antenna.

a. Back lobe radiationb. Transmitted signalc. Side lobe radiationd. Major lobe radiation

43. The reflector and director of an antenna array are considered as:

a. transcendental elements

b. feed-pointsc. driven elementsd. parasitic elements

44. An electronic equipment used to measure standing wave ratio:

a. Altimeterb. Multimeterc. Reflectometerd. Wavemeter

45. The product of the power supplied to the antenna and its gain relative to a half-wave dipole in a given direction.

a. Rated powerb. ERPc. Peak envelope power d. Carrier power

46. What makes an antenna physically long but electronically short?

a. adding C in seriesb. top loadingc. adding L in seriesd. all of these

47. The capture area of an antenna is directly proportional to the

a. distance between transmitter and receiver

b. power density of the signalc. gain of the antennad. frequency of the received

signal

48. A type of an undergrounded antenna is a/an __________ antenna.

a. Hertzb. Isotropicc. Parabolicd. Marconi

49. What is meant by antenna gain?

a. The ratio of the signal in the forward direction to the signal in the backward direction

b. The ratio of the amount of power produced by the antenna compared to the output power of the transmitter

c. The final amplifier gain minus the transmission line losses (including any phasing lines present)

d. The numeric ratio relating the radiated signal strength of an antenna to that of another antenna

50. 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 arrayb. Yagi antennac. Log-periodic antennad. Broadside array

51. A type of array antenna which consists of one half-wave driven dipole, one reflector and one director.

a. Log periodic dipole arrayb. Yagi-udac. Hertzian dipoled. Broadside collinear

52. It is a measure of the microwave power radiated from an antenna as a function of angular direction from the antenna axis.

a. Polarizationb. Sidelobesc. Beamwidthd. Antenna pattern

53. What is the gain of four identically polarized antennas stacked one above the other fed in phase?

a. 4 dB over the gain of one antenna

b. 10 dB over the gain of one antenna

c. 3 dB over the gain of one antenna

d. 6 dB over the gain of one antenna

54. Gain of an isotropic antenna.

a. 1 dBb. – 1 dBc. 0 dBd. 2 dB

55. A dipole antenna requires to be fed with 20 kW of power to produce a given signal strength to a particular distant point. If the addition of a reflector makes the same field strength available with an input power of 11 kW, what is the gain in dB obtained by the use of the reflector? (Gain referred to this particular dipole)

a. 4.75b. 1.81c. 4.24d. 2.6

56. Top loading is used in an antenna in order to increase its __________.

a. bandwidthb. beamwidthc. input capacitanced. effective height

57. A horizontal antenna is

a. perpendicularly polarizedb. centrally polarizedc. horizontally polarizedd. vertically polarized

58. The frequency of operation of a dipole antenna cut to length of 3.4 m.

a. 42.9 MHzb. 53.5 MHzc. 38.5 MHzd. 61.3 MHz

59. Two or more antennas separated by 9 wavelengths are used.

a. Frequency diversityb. Space diversityc. Hybrid diversityd. Polarized diversity

60. A convenient method of determining antenna impedance.

a. Trial and error

b. Stub matchingc. Smith chartd. Reactance circle

61. Width measured in degrees of a major lobe between end of the lobe at which the relative power is one half (- 3 dB) its value from the peak of the lobe.

a. radiationb. wavelengthc. bandwidthd. beamwidth

62. An increase in the effective power radiated by an antenna in a certain desired direction at the expense of power radiated in other directions.

a. antenna gainb. antenna efficiencyc. antenna total ratiod. antenna back lobe ratio

63. Where does the maximum current and minimum voltage values on a resonant Hertz dipole exist?

a. center of the antennab. ends of the antennac. near the center of the antennad. near the end of the antenna

64. How can the antenna efficiency of a HF grounded vertical antenna be made comparable to that of a half-wave antenna?

a. by isolating the coax shield from ground

b. by installing a good ground radial system

c. by shortening the verticald. by isolating the coax shield

from ground

65. Known as the technique for adding a series inductor at or near the center of an antenna element in order to cancel the capacitive reactance of an antenna.

a. reflectorb. center loadingc. dipoled. loading coil

66. What is meant by the term antenna bandwidth?

a. The angle between the half-power radiation points

b. The angle formed between two imaginary lines drawn through the ends of the elements

c. The frequency range over which an antenna can be expected to perform well

d. Antenna length divided by the number of elements

67. Where does the voltage node of a half-wave antenna exist?

a. at feed pointb. near the feed pointc. near the centerd. at center

68. This is a flexible vertical rod antenna commonly used on mobiles.

a. hertzb. ground planec. whipd. marconi

69. What is a dummy antenna?

a. A non-directional transmitting antenna

b. An antenna used for hand-held ratio

c. One which is used as a reference for gain measurements

d. A non-radiating load for a transmitter used for testing

70. Best description of a collinear and broadside antenna radiation pattern.

a. bidirectionalb. omnidirectionalc. unidirectionald. perfect circle

71. What is a driven element of an antenna?

a. Always the forwardmost element

b. Always the rearmost elementc. The element fed by the

transmission lined. The element connected to the

rotator

72. Antenna which is not properly terminated

a. whipb. non-resonantc. isotropicd. resonant

73. At the ends of a half-wave antenna, what values of current and voltage exist compared to the remainder of the antenna?

a. Minimum voltage and maximum current

b. Maximum voltage and minimum current

c. Minimum voltage and minimum current

d. Equal voltage and current

74. Refers to a type of beam antenna which uses two or more straight elements arranged in line with each other.

a. whip antennab. yagi antennac. rhombic antenna

d. dipole antenna

75. What is meant by the term radiation resistance for an antenna?

a. Losses in the antenna elements and feed line

b. An equivalent resistance that would dissipate the same amount of power as that radiated from an antenna

c. The resistance in the trap coils to received signal

d. The specific impedance of the antenna

76. Which of the following parts of the radio receiver represents the component that extracts the desired RF signal from the electromagnetic wave?

a. detectorb. antennac. crystald. AF amplifier

77. Determine the dB gain of a receiving antenna which delivers a microvolt signal to a transmission line over that of an antenna that delivers a 20 microvolt signal under identical circumstances.

a. - 26 dBb. 26 dBc. 3 dBd. 10 dB

78. What is the term for the ratio of the radiation resistance of an antenna to the total resistance of the system?

a. antenna efficiencyb. radiation conversion lossc. beamwidthd. effective radiated power

79. One of the following prevents a transmitter from emitting a signal that interferes with other station on frequency during the test.

a. use of shielded antenna radiator

b. use of low height antennac. use of dummy antennad. use of grounded antenna

80. In high frequency radio transmission, the lower the radio frequency the __________ of the antenna.

a. longer the lengthb. bigger the diameterc. shorter lengthd. smaller the diameter

81. Which of the following antenna where its beamwidth is determined by the dimensions of its lens or reflector?

a. whip antennab. aperiodic antennac. aperture antennad. long wire antenna

82. What measure will you adopt on the antenna system of a VHF or UHF mobile transceivers that has very low height antenna?

a. increase transmitter to antenna cable

b. use directional antennac. check grounding systemd. provide loading coil

83. In order to have an effective radio antenna, the design of its radiator must have a minimum length equivalent to __________.

a. /10b. /4c. /14d. / 6

84. What is a parasitic element of an antenna?

a. An element dependent on the antenna structure for support.

b. A transmission line that radiates radio-frequency energy.

c. An element that receives its excitation from mutual coupling rather than from a transmission line.

d. An element polarized 90 degrees opposite the driven element.

85. At what position does a maritime ship main antenna have when it is open circuited and that any auxiliary antenna is/are connected to the main receiver?

a. AAb. Emergency transmitterc. Direction finderd. Ground

86. Due to the presence of parallel LC networks in the trap antenna, one of the following is a disadvantage of using this kind of antenna.

a. radiate harmonicsb. reduce powerc. reduce beamwidthd. allow entry of interference

87. How do you compare the length of the reflector element of a parasitic beam antenna with that of its driven element?

a. same lengthb. reflector element is 5% longerc. reflector element is half

shorterd. reflector element is 5% shorter

88. Which of the following statements refers to a reason why intelligence signal cannot be transmitted directly on their frequency?

a. Their frequencies are high and are susceptible to noise

b. Their frequencies are high and need very large antennas

c. Their frequencies are low and need very large antennas

d. Their frequencies are low and need very small antennas

89. What is the purpose of a certain antenna component composed of a parallel LC networks inserted in the antenna called traps?

a. Cancel the capacitive reactance of an antenna

b. Enhance directivityc. Produce resonant system at

specific frequencyd. Provide a multiband operation

90. Refers to the numerical ratio relating to the radiated signal strength of an antenna to that of another antenna.

a. antenna lossb. antenna gainc. antenna bandwidthd. antenna efficiency

91. How much longer or shorter does the length of the director element of parasitic beam antenna compared with that of the driven element?

a. about 5% shorterb. around 10% longerc. one half longerd. around 5% longer

92. Refers to the ratio of radiated to reflected energy.

a. front-to-back ratiob. antenna efficiencyc. radiation efficiencyd. signal-to-noise ratio

93. A half-wave dipole antenna

a. hertzb. marconic. parabolicd. vertical monopole

94. When conductors are spread out in a straight line to a total length of one-quarter wavelength, the antenna is called what?

a. marconib. vertical monopolec. quarter-wave dipoled. all of these

95. What do you call of a polar diagram or graph representing field strengths or power densities at various angular positions relative to an antenna?

a. Venn diagramb. Figure-8 patternc. Lissajous figured. Radiation pattern

96. __________ is the ratio of the front lobe power to the back lobe power.

a. front-to-side ratiob. front-to-back ratioc. back-to-front ratiod. minor-to-major ratio

97. It is defined as the area within a distance D2/ from the antenna, where is the wavelength and D is the antenna diameter in the same units.

a. far fieldb. near fieldc. green fieldd. radiation field

98. What is that ratio of the power radiated by the antenna to the total input power?

a. power gainb. directive gainc. antenna efficiencyd. radiation efficiency

99. __________ of an antenna refers to the orientation of the electric field radiated from it.

a. radiationb. bandwidthc. beamwidthd. polarization

100. Pertains to a wire structure placed below the antenna and erected above the ground. It is a form of capacitive ground system.

a. imageb. counterpoisec. antenna orientationd. antenna polarization