Electronics and Communication Engineering - Microwave Communication - Discussion

29. 

The frequency of oscillation in a backward wave oscillator can be changed by

[A]. varying the voltage which controls beam velocity
[B]. varying the beam current
[C]. both by varying the beam current and by light varying the voltage which controls beam velocity
[D]. changing the rate of thermionic emission

Answer: Option A

Explanation:

It is somewhat similar to TWT and can deliver microwave power over a wide frequency band.

It has an electron gun and a helix structure. However the interaction between electron beam and RF wave is different than in TWT.

The growing RF wave travels in opposite direction to the electron beam.

The frequency of wave can be changed by changing the voltage which controls the beam velocity.

Moreover the amplitude of oscillations can be decreased continuously to zero by changing the beam current.

It features are:

1. Frequency range - 1 GHz to 1000 GHz.

2. Power output - 10 mV to 150 mW (continuous wave) 250kW (pulsed).

It is used as signal source in transmitters and instruments.


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