# Objective Questions on Microwave Tubes

## Objective Questions on Microwave Tubes

Objective Questions on Microwave Tubes, MCQs on Microwave Tubes, MCQ on Reflex Klystron Amplifier, MCQ on magnetron, MCQ on TWT, MCQ on traveling-wave tube

### Multiple Choice Questions

1. Both axial magnetic field and radial electric fields are used in the following vacuum tube
• magnetron
• a reflex klystron
• Klystron
• traveling-wave tube

2. The following vacuum tube can be used as an oscillator and an amplifier?

• klystron
• BWO
• TWT
• magnetron

3. The transit time can be reduced in microwave tubes,

• if electrodes are brought closer together
• if a higher anode current is used
• if multiple or coaxial leads are used
• none

Answer: if electrodes are brought closer together

4. The modes in a reflex klystron

• give the same frequency but different transit time
• result from excessive transit time across the resonator gap
• are caused by spurious frequency modulation
• are just for theoretical considerations

Answer: give the same frequency but different transit time

5. Vacuum tubes fail at microwave frequencies, because

• noise figure increases
• shunt capacitive reactances become too large
• transit time becomes too short
• series inductive reactances become too small

Answer: shunt capacitive reactances become too large

6. For use as a local oscillator for frequency measurements, the most suitable microwave source would be

• TWT
• double-cavity klystron
• reflex klystron
• magnetron

7. The main advantage of TWT over a multi-cavity klystron is:

• greater bandwidth
• more efficient
• higher number of modes
• higher output power

8. In a travelling-wave tube, the purpose of helix structure is

• to minimise the noise figure
• to minimse the RF field’s axial velocity
• none

Answer: to minimse the RF field’s axial velocity

9. The purpose of attenuator in a travelling-wave tube is

• to prevent saturation
• to increase gain
• to prevent oscillation
• to help bunching

10. The oscillating frequencies of different modes (or cavity resonators ) of magnetrons are not same and are quite close to each other, which results in

• helping focusing
• providing attenuation
• improving bunching
• mode jumping

11. The following is not used as a TWT slow-wave structure

• coupled cavity
• helix
• ring bars
• periodic permanent magnet

12. The phase velocity of RF field’s axial component in the TWT slow-wave structure is

• equal to the velocity of the electrons
• slightly less than the velocity of the electrons
• slightly greater than the velocity of the electrons
• equal to the velocity of light in vacuum

Answer: slightly less than the velocity of the electrons

13. In the following microwave tubes, RF energy travels at nearly the same speed as the electrons that are traveling from the cathode to the collector:

• magnetron
• TWT
• CFA
• Klystron

14. A backward-wave oscillator is based on

• cross-field amplifier
• coaxial magnetron
• traveling-wave tube
• rising sun magnetron

15. Which one of the following can be used for the amplification of microwave energy?

• traveling-wave tube
• magnetron
• reflex klystron
• Gunn diode

16. Strapping is used in magnetrons to

• prevent mode jumping
• ensure bunching
• improve the phase-focusing effect
• prevent cathode back heating

17. The purpose of the slow-wave structure used in TWT amplifiers is

• to increase wave velocity
• to reduce spurious oscillations
• to reduce wave velocity so that the electron beam and the signal wave can interact
• None of the above

Answer: to reduce wave velocity so that the electron beam and the signal wave can interact

18. The following cavity structure is preferred for use in magnetron to overcome problems with strapping at high frequencies is

• slot
• rising sun
• Vane
• all

19. The time taken by the electron to travel into the repeller space and back to the gap in a reflex klystron is referred to as

• transit time, =+ 1/4
• bunching time, + 1/4
• transit time, =+ 3/4
• bunching time, n + 3/4

20. The major advantage of a TWT over a Klystron lies in its

• higher bandwidth
• higher gain
• higher frequency
• higher output