This is the Multiple Choice Questions in Chapter 11: Microwave Tubes and Circuits from the book Electronic Communication Systems by George Kennedy. If you are looking for a reviewer in Communications Engineering this will definitely help. I can assure you that this will be a great help in reviewing the book in preparation for your Board Exam. Make sure to familiarize each and every questions to increase the chance of passing the ECE Board Exam.
Start Practice Exam Test Questions
Choose the letter of the best answer in each questions.
1. A microwave tube amplifier uses an axial magnetic field and a radial electric field. This is the
- a. reflex klystron
- b. coaxial magnetron
- c. traveling-wave magnetron
- d. CFA
2. One of the following is unlikely to be used as a pulsed device. It is the
- a. multicavity klystron
- b. BWO
- c. CFA
- d. TWT
3. One of the reasons why vacuum tubes eventually fail at microwave frequencies is that their
- a. noise figure increases
- b. transit time becomes too short
- c. shunt capacitive reactances become too large
- d. series inductive reactances become too small
4. Indicate the false statement. Transit time in microwave tubes will be reduced if
- a. the electrodes are brought closer together
- b. a higher anode current is used
- c. multiple or coaxial leads are used
- d. the anode voltage is made larger
5. The multicavity klystron
- a. is not a good low-level amplifier because of noise
- b. has a higher repeller voltage to ensure a rapid transit time
- c. is not suitable for pulsed operation
- d. needs a long transit time through the buncher cavity to ensure current modulation
6. Indicate the false statement. Klystron amplifiers may use intermediate cavities to
- a. prevent the oscillations that occur in two-cavity klystrons
- b. increase the bandwidth of the device
- c. improve the power gain
- d. increase the efficiency of the klystron
7. The TWT is sometimes preferred to the multicavity klystron amplifier, because it
- a. is more efficient
- b. has a greater bandwidth
- c. has a higher number of modes
- d. produces a higher output power
8. The transit time in the repeller space of a reflex klystron must be n + ¾ cycles to ensure that
- a. electrons are accelerated by the gap voltage on their return
- b. returning electrons give energy to the gap oscillations
- c. it is equal to the period of the cavity oscillations
- d. the repeller is not damaged by striking electrons
9. The cavity magnetron uses strapping to
- a. prevent mode jumping
- b. prevent cathode back-heating
- c. ensure bunching
- d. improve the phase-focusing effect
10. A magnetic field is used in the cavity magnetron to
- a. prevent anode current in the absence of oscillation
- b. ensure that the oscillations are pulsed
- c. help in focusing the electron beam, thus preventing spreading
- d. ensure that the electrons will orbit around the cathode
11. To avoid difficulties with strapping at high frequencies, the type of cavity structure used in the magnetron is the
- a. hole-and-slot
- b. slot
- c. vane
- d. rising sun
12. The primary purpose of the helix in a traveling-wave tube is to
- a. prevent the electron beam from spreading in the long tube
- b. reduce the axial velocity of the RF field
- c. ensure broadband operation
- d. reduce the noise figure
13. The attenuator is used in the traveling-wave tube to
- a. help bunching
- b. prevent oscillations
- c. prevent saturation
- d. increase gain
14. Periodic permanent-magnet focusing is used with TWTs to
- a. allow pulsed operation
- b. improve electron bunching
- c. avoid the bulk of an electromagnet
- d. allow coupled-cavity operation at the highest frequencies
15. The TWT is sometimes preferred to the magnetron as a radar transmitter output tube because it is
- a. capable of a longer duty cycle
- b. a more efficient bandwidth
- c. more broadband
- d. less noisy
16. A magnetron whose oscillating frequency is electronically adjustable over a wide range is called a
- a. coaxial magnetron
- b. dither-tuned magnetron
- c. frequency-agile magnetron
- d. VTM
17. Indicate which of the following is nota TWT slow-wave structure:
- a. Periodic-permanent magnet
- b. Coupled cavity
- c. Helix
- d. Ring-bar
18. The glass tube of a TWT may be coated with aquadag to
- a. help focusing
- b. provide attenuation
- c. improve bunching
- d. increase gain
19. A backward-wave oscillator is based on the
- a. rising-sun magnetron
- b. crossed-field amplifier
- c. coaxial magnetron
- d. traveling-wave tube
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