Exercise: Microwave Communication

Questions for: Microwave Communication

Assertion (A): Magnetron is generally used in n mode.

Reason (R): Frequency for p mode can be easily separated from adjacent modes.

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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Assertion (A): A quarter wave transformer is used to match a resistive load to a transmission line.

Reason (R): A quarter wave transformer is a transmission line of quarter wave length.

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: B

A line of length is called quarter wavelength line. Such a line is used for impedance matching.

If

A quarter wave line can match a source impedance Zin with load impedance ZL by selecting a proper value of Z0 so as to satisfy equation.

Such a line is also called transformer.

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To couple a coaxial line to a parallel wire line it is best to use
A:
slotted line
B:
balun
C:
directional coupler
D:
λ/4 transformer
Answer: B

A balun gives 4 : 1 impedance transformation.

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High speed logic circuits use
A:
pulses with very small width
B:
pulses with very large width
C:
pulses whose width is neither small nor large
D:
either (b) or (c)
Answer: A

High speed means time period is small. Therefore pulses should also have small width.

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The total field developed by an antenna array at a distant point is
A:
phasor sum of fields produced by individual antennas of the array
B:
algebraic sum of fields produced by individual antennas of the array
C:
either (a) or (b) depending on type of array
D:
neither (a) nor (b)
Answer: A

Since field is a phasor quantity we have to take phasor sum.

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