Wave Propagation

COMMUNICATIONS ENGINEERING PART 7Microwaves

1. Indicate which of the following frequencies cannot be used for reliable beyond-the-horizon terrestrial communications without repeaters:

a. 20 kHzb. 15 MHzc. 900 MHzd. 12 GHz

2. A ship-to-ship communications system is plagued by fading. The best solution seems to be the use of

a. A more directional antennab. A broadband antennac. Frequency diversityd. Space diversity

3. A range of microwave frequencies more easily passed by the atmosphere than are the others is called a

a. Windowb. Critical frequencyc. Gyro frequency ranged. Resonance in the atmosphere

4. Frequencies in the UHF range propagate by means of

a. Ground wavesb. Sky wavesc. Surface wavesd. Space waves

5. Tropospheric scatter is used with frequencies in the following range:

a. HFb. VHFc. UHFd. VLF6. When microwave signals follow the curvature of the earth, this is known as

a. The Faraday effectb. Ductingc. Tropospheric scatterd. Ionospheric reflection

7. Helical antennas are often used for satellite tracking at VHF because of

a. Troposcatterb. Superrefractionc. Ionospheric refractiond. The Faraday effect

8. ________ consists basically of a thin film strip in intimate contact with one side of a flat dielectric substrate, with a similar thin-film ground plane conductor on the other side of the substrate.

a. strip lineb. lecher wirec. microstripd. stub

9. Waveguide is a

a. device used to determine the wavelength of a signalb. hollow metal tube used for transmission of microwave energyc. plastic tubular transmission line for high RF networkd. braided wire used for transmission of HF

10. Transmission lines which can convey electromagnetic waves only in higher order modes are usually called

a. coaxial cableb. twisted pairc. power linesd. waveguides

11. In order to reduce cross-sectional dimensions, the waveguide to use is

a. circularb. ridgec. rectangulard. elliptical

12. A signal propagated in a waveguide has afull wave of electric intensity change between the two farther walls, and no component of the electric field in the direction of propagation. The mode is

a. TE1,1b. TE1,0c. TM2,2d. TE2,0

13. When a particular mode is excited in a waveguide, there appears an extra electric component, in the direction of propagation. The resulting mode is

a. Transverse electricb. transverse magneticc. longitudinald. transverse electromagnetice. none of these

14. The wavelength of a wave in a waveguide

a. is greater than in free spaceb. depends on waveguide dimensions and free space wavelengthc. is inversely proportional to the phase velocityd. is directly proportional to the group velocity

15. When electromagnetic waves are propagated in a waveguide, they

a. travel along the broader walls of the guideb. are reflected from walls but not travel along themc. travel through the dielectric without touching the wallsd. travel along the 4 walls of the waveguide

16. When microwave signals follow the curvature of the earth, this is known as

a. Faraday Effectb. Ductingc. Tropospheric Scatterd. Ionospheric Reflection

17. A waveguide mode in which there is no component of electric field in the direction of propagation given in the British European standards.

a. H-modeb. E-modec. TE moded. M-mode

18. The extra strength needed in order to assure that enough signal reaches the receiving antenna and must be made available to compensate for fades; computed as the difference between the received signal strength and the threshold level

a. Fade Marginb. Threshold Levelc. Noise Figured. RSL

19. The use of redundant system to reduce the effects of multipath fading is

a. combiningb. modulationc. multiplexingd. diversity

20. A profile graph of the microwave energy path

a. shows the cross section of the earths surfaceb. determines LOS or site technical feasibilityc. determines the actual clearance, antenna heights and system reliabilityd. all of the preceding

21. In locating microwave relay stations, the systems designer must consider

a. terrain obstructions and reflection pointsb. site security and navigational hazardsc. availability of power, water source and accessible roadsd. all of the above

22. A microwave path over which radio waves barely touches the obstruction is called

a. Line of Sightb. Obstructed Pathc. Grazing Pathd. Crooked Path

23. What is the function of regenerative repeater?

a. to eliminate bias distortionb. to help in the loading of the telegraph linesc. to reduce required signal levelsd. to reshape the pulses after they have become distorted

24. A situation when there is no net change in attenuation or no gain, no loss occurs when ______ % of the first fresnel radius clears a path obstruction in microwave systems.

a. 45%b. 60%c. 75%d. 85%

25. __________ are concentric circular zones about a direct path of a microwave signal called Huygens radiation center, forming an imaginary solid called an ellipsoid _______.

a. temperature zoneb. skip zonec. fresnel zoned. fraunhoffer zone

26. Waveguides are used mainly for microwave transmission because

a. they depend on straight line propagationb. losses are heavy at lower frequenciesc. they are bulky at lower frequenciesd. no generator is powerful enough to excite them

27. A waveguide assembly that lets the radar transmitter and receiver share an antenna is called

a. translatorb. diplexerc. flip-flopd. duplexer

28. ____________ is a graph wherein the terrain in which the microwave beam should traverse.

a. topographb. radio path profilec. fresnel graphd. net path graph

29. The fresnel zone is the circular zone about the ______ path.

a. reflectedb. directc. LOSd. Refracted

30. The radius in the circular zone is in the first fresnel zone when the reflected path is ________ longer than the direct path.

a. /2b. c. /4d. /8

31. At ______ of the first fresnel zone is a condition where there is no gain and no loss.

a. 0.5b. 0.6c. 0.7d. 0.8

32. The weakest signal the receiver could accept to be considered satisfactory.

a. thresholdb. fade marginc. RSLd. NPL

33. The frequency band from 8 to 12 GHz is known as the ______ band.

a. Cb. Kuc. Xd. Ka

34. The difference between the Received Signal Level and the FM Improvement Threshold

a. System Gainb. Noise Thresholdc. Fade Margind. Reliability

35. A Fade Margin of 28 dB has a reliability of

a. 99%b. 99.9%c. 99.99%d. 99.999%

36. Topographical maps are maps used for microwave communications systems design because ________ are shown, thereby elevations are known.a. latitudesb. longitudesc. contour linesd. scales

37. The dominant mode in a rectangular waveguide.

a. TEMb. TE 1,1c. TE 1,0d. TM 1,1

38. The velocity of a resultant wave as it travels through the waveguide.

a. speed of lightb. group velocityc. phase velocityd. incident velocity

39. The principal mode for a circular waveguide.

a. TE 1,0b. TM 2,0c. TE 1,1d. TEM

40. A type of waveguide that reduces the cutoff wavelength, increases bandwidth and allows for a variation of the characteristic impedance.

a. ridgeb. rectangularc. teed. twisted

41. The subscript which indicates the number of /2s along the waveguide height.

a. mb. nc. ad. b

42. The international equivalent of the TE mode

a. Hb. Ec. Zd. TEM

43. The smallest free space wavelength that is just unable to propagate in the waveguide under given conditions.a. guideb. phasec. cut-offd. group

44. The characteristic wave impedance of a waveguide in the TE mode is _________ that of the TM mode.

a. equal tob. higher thanc. lower thand. NOTA

45. The following are methods of exciting waveguides except

a. slot couplingb. antennasc. flangesd. direct coupling

46. Higher order mode-waveguides are not used in practice because they have _______ cut-off frequencies.

a. lowb. highc. indeterminated. fixed

47. Indicate which of the following cannot be followed by the word waveguide.

a. ellipticalb. flexiblec. coaxiald. ridged48. A piston attenuator is a

a. vane attenuatorb. waveguide below cut-off c. mode filterd. flap attenuator

49. Which of the following waveguide tuning components is not easily adjustable?

a. screwb. stubc. irisd. plunger

50. Which of the following is not a waveguide termination component?a. tapered pyramidb. postc. tapered resistance cardd. stepped resistance card

51. What microwave component can sample part of the power traveling through the waveguide?

a. directional couplerb. magic teec. circulatord. re-entrant cavity

52. The following are gases used for LASERs except

a. heliumb. neonc. argond. ruby

53. Also known as the optical maser

a. ruby maserb. LASERc. quantum mechanicsd. GaAs maser

54. Paramagnetic means _________ magnetic

a. almostb. fullyc. slightlyd. electro

55. Tuning the ruby maser is done by adjusting the _________ to alter the energy level of the ferrous chromium.

a. electric fieldb. magnetic fieldc. pumping of electronsd. electromagnetic field

56. To overcome the very narrow bandwidth in ruby maser, ________ is used.

a. Magnetronb. TWTc. IMPATT dioded. Gunn diode

57. The following are applications of masers except

a. radioastronomyb. radiotelescopec. radar d. ET communications

58. A parametric amplifier is a device which amplifies signal by varying the

a. resistanceb. reactancec. magnetic fieldd. electric field

59. The following are parts of the parametric amplifier except

a. idling circuitb. pump circuitc. tuned circuitd. filter circuit

60. The number of cavities in a magnetron used in practice.

a. 4b. 6c. 8d. 10

61. Changing the anode voltage to change the velocity of the electrons in a magnetron tube

a. frequency pushingb. frequency pullingc. strappingd. pumping

62. The lowest frequency that will propagate through the waveguide while operating in a particular mode.

a. critical frequencyb. cut-off frequencyc. MUFd. UHF

63. The mode of a waveguide where there is no component of magnetic field in the direction of propagation.

a. TEb. TMc. Hd. TEM

64. The following are slow wave structures used to retard the RF field in a TWT excepta. helixb. attenuatorc. waveguide coupled cavityd. NOTA

65. A rectangular waveguide is 5.1 cm by 2.4 cm. The cut-off frequency for the dominant mode is

a. 2.94 GHzb. 6.25 GHzc. 664 MHzd. 57.7 GHz

66. Calculate the cut-off wavelength, the guide wavelength and the characteristic impedance of a circular waveguide whose internal diameter is 4 cm for a 10 GHz signal propagated in it in the dominant mode. (kr = 1.84)

a. 6.83 cm, 3 cm, 420 b. 3 cm, 6.83 cm, 420 c. 6.83 cm, 3.34 cm, 420 d. 6.83 cm, 3.34 cm, 338

67. A wave is propagated in a parallel plane waveguide. The frequency is 6 GHz and the plane separation is 3 cm. The cut-off wavelength for the dominant mode, the group and phase velocities are

a. 5 cm, 166 Mm/sec, 543 Mm/secb. 6 cm, 166 Mm/sec, 543 Mm/sec c. 6 cm, 543 Mm/sec, 166 Mm/secd. 5 cm, 543 Mm/sec, 166 Mm/sec 68. If the MTBF of a communication circuit is 20,000 hours and its MTTR is 5 hours, what is its unavailability?

a. 0.00025b. 99.975%c. 0.25 %d. 00.975%

69. What would be the ERP, in watts if the transmitter output is 30 dBm and the transmission line loss is 20 dB and the antenna connected to it has a power gain of 60 dB?

a. 10,000 wattsb. 1000 wattsc. 100 wattsd. 10 watts

70. Also referred to as the Transferred Electron Device

a. magnetronb. TWTc. Gunn dioded. APD

71. Also known as the Esaki diode

a. gunnb. tunnelc. APDd. TWT

72. The following are negative resistance amplifiers except

a. tunnelb. gunnc. IMPATTd. PIN diode

73. Regarded as the oldest semiconductor device

a. Shottky Barrier diodeb. PIN diodec. point contact dioded. triode

74. Also called the hot electron diode

a. PIN diodeb. ESBARc. APDd. Gunn diode

75. Also called tunnel rectifiers

a. backward diodeb. schottky barrier diodec. APDd. PIN diode

76. Varactors are variable ________ diode.

a. reactanceb. capacitancec. inductanced. resistance

77. Diodes designed to store energy in their capacitance during forward bias and generates harmonics in the reverse bias.

a. step recoveryb. gunnc. APDd. IMPATT

78. A cross between the TWT and the magnetron in its operation

a. CFAb. BWOc. EIAd. Twystron

79. The following are parts of a multicavity klystron except

a. buncher cavityb. catcher cavityc. cathoded. attenuator

80. The very first microwave transistors

a. GaAs FETb. Si BJTc. MICd. NOTA

81. The most common microwave FET which is also known as the MESFET

a. Dual GaAs FETb. Si BJTc. MICd. Schottky Barrier Gate

82. It looks like a shorter, thicker TWT

a. CFAb. BWOc. EIAd. Twystron

83. A Twystron is a hybrid combination of

a. TWT and Magnetronb. TWT and Klystronc. TWT and Ubitrond. TWT and gyrotron

84. A multicavity klystron with interconnected multigap cavities

a. TWTb. Twystronc. EIAd. gyrotron

85. SAW propagate in

a. GaAsb. InPc. Striplined. quartz crystal

86. The output from a laser is monochromatic; this means that it is

a. infraredb. narrow beamc. polarizedd. single frequency

87. The ruby laser differs from the ruby maser in that the former

a. does not require pumpingb. needs no resonatorc. is an oscillatord. produces much lower powers

88. The transmission system using two ground planes

a. microstripb. elliptical waveguidec. parallel wire lined. stripline

89. A BWO is based on the

a. rising sun magnetronb. CFAc. coaxial magnetrond. TWT

90. One of the following is unlikely to be used as a pulsed device

a. multicavity klystronb. BWOc. CFAd. TWT

91. A microwave tube amplifier uses an axial magnetic field and a radial electric field

a. reflex klystronb. coaxial magnetronc. TW magnetrond. CFA92. The attenuator is used in the TWT to

a. help bunchingb. prevent oscillationc. prevent saturationd. increase gain

93. The glass tube of a TWT may be coated with aquadag to

a. help focusingb. provide attenuationc. improve bunchingd. increase gain

94. The cavity magnetron uses strapping to

a. prevent mode jumpingb. prevent cathode back heatingc. ensure bunchingd. improve the phase focusing effect

95. Compared with equivalent transmission lines, 3-GHz waveguides (indicate false statement)

a. are less lossyb. can carry higher powersc. are less bulkyd. have lower attenuation

96. Indicate the false statement. When the free-space wavelength of a signal equals the cutoff wavelength of the guide

a. the group velocity of the signal becomes zerob. the phase velocity of the signal becomes infinitec. the characteristic impedance of the guide becomes infinited. the wavelength within the waveguide becomes infinite

97. A disadvantage of microstrip with respect to stripline circuits is that the former

a. do not lend themselves to printed-circuit techniquesb. are more likely to radiatec. are bulkierd. are more expensive and complex to manufacture

98. In order to couple two generators to a waveguide system without coupling them to each other, one could not use a

a. rat-raceb. E-plane Tc. Hybrid ringd. Magic T

99. A PIN diode is

a. a metal semiconductor point-contact diodeb. a microwave mixer diodec. often used as a microwave detectord. suitable for use as a microwave switch

100. For handling high powers, the best transmission medium is

a. striplineb. microstripc. rectangular waveguided. coaxial line