Exercise: Microwave Communication

Questions for: Microwave Communication

Assertion (A): Impedance matching can be done by using stubs.

Reason (R): A double stub is used for impedance matching when frequency of signal varies.

A:
Both A and R are correct and R is correct explanation of A
B:
Both A and R are correct but R is not correct explanation of A
C:
A is correct but R is wrong
D:
A is wrong but R is correct
Answer: A

Hollow metallic enclosures exhibit resonance behaviour when excited by electromagnetic field.

These enclosures are called cavity resonators.

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The expression HZ = C cos(Bx) cos(Ay)yz is for
A:
TE wave
B:
TM waves
C:
both TE and TM waves
D:
some TE and some TM waves
Answer: A

In TM mode Hz = 0.

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Which of the following is wrong for a magic used to tee?
A:
E and H arms are decoupled
B:
coplanar arms are coupled
C:
all ports are perfectly matched
D:
A signal into coplanar arm splits equally between E and H arms
Answer: B

Coplanar arms are decoupled.

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Assertion (A): In the interaction region of magnetron an electron is subjected to three forces: force due to electric field, force due to magnetic field and centrifugal force.

Reason (R): The mechanism of generation of microwaves, in a magnetron, involves interaction of electromagnetic fields with electrons moving in static electric and magnetic fields oriented at right angles to each other.

A:
Both A and R are correct and R is correct explanation of A
B:
Both A and R are correct but R is not correct explanation of A
C:
A is correct but R is wrong
D:
A is wrong but R is correct
Answer: A

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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For matching over a range of frequencies in a transmission line it is best to use
A:
a balun
B:
a broad band directional coupler
C:
double stub
D:
a single stub of adjustable position
Answer: C

Double stub is useful for matching over a range of frequencies.

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