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ECE Objective Questions { Microwave Devices and Circuits }

43. Perodic permanent-manget focussing is used with TVVT's to
A. allow pulsed operation
B. allow coupled-cavity operation at the highest frequencies
C. improve electron bunching
D. avoid the bulk of an electromagnet

44. The reflex klystron is often preferred to the two-cavity ldystron oscillator because the former
A. is more efficient
B. has higher number of modes
C. is easier to tune
D. producess a higher output power

45. Which of the following antenna is best excited from a waveguide?
A. biconical
B. helical
C. horn
D. discone

46. The primary purpose of the helix in a travelling-wave tube is to
A. prevent the electron beam from spreading in the long tube
B. reduce the axial velocity of the FR field
C. ensure broadband operation
D. reduce the noise figure.

47.  Waveguide feeders are pressurised to
A. reduce loss
B. reduce noise
C. prevent ingress of moisture
D. detect faults

48. A helical antenna is used for satellite tracking because of its
A. brod bandwidth
B. maneuverability
C. circular polarization
D. good front-to-back ratio

49. Cassegrain feed is used with a parabolic reflector to
A. increase the gain of the system
B. increase the beamwidth of the system
C. reduce the size of the main reflector
D. allow the feed to be placed at a convenient point

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