Electronics and Communication Engineering - Microwave Communication

41.
In mode filter of the given figure which of the following modes is unaffected
TE01
TE10
TE11
all TM
Answer: Option
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
proportional to wavelength
inversely proportional to wavelength
proportional to square of wavelength
inversely proportional to square of wavelength
Answer: Option
Explanation:


43.
A duplexer is used to
couple two antennas to a transmitter
isolate the antenna from the local oscillator
prevent interference between two antennas connected to receiver
use an antenna for reception or transmission without interference
Answer: Option
Explanation:

Same antenna is used for transmission and reception.


44.
A branched duplexer requires
TR tubes
ATR tube
both TR and ATR tube
none of the above
Answer: Option
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
travelling along the line winds itself back and forth
progresses only in forward direction
progresses only in backward direction
either (a) or (c)
Answer: Option
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.