# Electronics and Communication Engineering - Microwave Communication

### Exercise :: Microwave Communication - Section 1

31.

In the given figure the time taken by the wave to make one round trip is

 A. 10 ns B. 20 ns C. 30 ns D. 40 ns

Explanation:

32.

For a 50 Ω resistor for 3 GHz application, the stray capacitance should be less than

 A. 1 μF B. 1 nF C. 1 pF D. 0.1 pF

Explanation:

XC should be at least ten times greater than R. Therefore for 50 Ω resistor at 3 GHz, C should be less than 0.1 pF.

33.

In a travelling wave tube distributed interaction between an electron beam and a travelling wave takes place

 A. True B. False

Explanation:

In a klystron the resonant structure limits the bandwidth.

A TWT is a broadband device. Its main components are electron gun (to produce the electron beam) and a structure supporting the slow electromagnetic wave.

The velocity of wave propagation along the helix structure is less than velocity of light.

The beam and wave travel along the structure at the same speed.

Thus interaction occurs between beam and wave and the beam delivers energy to the RF wave.

Therefore the signal gets strengthened and amplified output is delivered at the other end of tube.

The main features of TWT are :

1. Frequency range - 0.5 GHz to 90 GHz

2. Power output - 5 mW at low frequencies(less than 20 GHz) 250 kW (continuous wave) at 3 GHz 10 MW (pulsed) at 3 GHz

3. Efficiency - about 5 to 20%

4. Noise - about 5 dB for low power TWT 25 dB for high power TWT

TWT is used as RF amplifier in broadband microwave receivers, repeater amplifier in broad band communication systems, communication satellites etc.

34.

The fabrication of microstrip line is done by

 A. photo etching B. printed circuit technique C. oxidation D. cladding

Explanation:

Printed circuit techniques is used for micro strip line.

35.

The condition of minimum distortion in a transmission line is

 A. RL = 1 B. R = 0 C. D.