# Electronics and Communication Engineering - Microwave Communication

### Exercise :: Microwave Communication - Section 2

41.

In mode filter of the given figure which of the following modes is unaffected

 A. TE01 B. TE10 C. TE11 D. all TM

Explanation:

TE01 mode is unaffected because its horizontally oriented electric field is every where perpendicular to the conducting strips.

42.

The directive gain of a transmitting antenna is

 A. proportional to wavelength B. inversely proportional to wavelength C. proportional to square of wavelength D. inversely proportional to square of wavelength

Explanation:

43.

A duplexer is used to

 A. couple two antennas to a transmitter B. isolate the antenna from the local oscillator C. prevent interference between two antennas connected to receiver D. use an antenna for reception or transmission without interference

Explanation:

Same antenna is used for transmission and reception.

44.

A branched duplexer requires

 A. TR tubes B. ATR tube C. both TR and ATR tube D. none of the above

Explanation:

A branched duplexer funds use in narrow bandwidth applications.

TR tube stands for transmit-receive tube and ATR tube stands for antitransmit receive tube.

Both these tubes are used in branched duplexer.

45.

In a backward wave oscillator the wave

 A. travelling along the line winds itself back and forth B. progresses only in forward direction C. progresses only in backward direction D. either (a) or (c)

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.