Electronics and Communication Engineering - Microwave Communication

46. 

A resistive microwave load with ZL = 150 Ω is connected to 50 Ω coaxial line. SWR is

A. more than 3
B. less than 3
C. equal to 3
D. either (a) or (c)

Answer: Option C

Explanation:


47. 

Which of the following devices uses a slow wave structure?

A. Klystron two cavity amplifier
B. Klystron multicavity amplifier
C. Reflex klystron oscillator
D. TWT

Answer: Option D

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.


48. 

In a turnstile antenna two-half wave resonant wire radiators are placed at 90° to each other in the same plane and are excited

A. in phase
B. in phase opposition
C. 90° out of phase with each other
D. 45° out of phase with each other

Answer: Option C

Explanation:

Since the two wire radiators are at 90° to each other, they have to be excited 90° out of phase with each other.


49. 

A waveguide section in a microwave circuit acts as

A. LP filter
B. Bandpass filter
C. HP filter
D. Band stop filter

Answer: Option C

Explanation:

It allows high frequencies.


50. 

In a klystron amplifier dc electron velocity is v0 and dc electron charge density is r0 the dc beam current is

A. r0v0
B. r0/v0
C. v0/r0
D. (v0/r0)2

Answer: Option A

Explanation:

= coulomb |sec|m2 = current density.


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