Electronics and Communication Engineering - Microwave Communication
A balun gives 4 : 1 impedance transformation.
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 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.
Assertion (A): Magnetron is generally used in n mode.
Reason (R): Frequency for p mode can be easily separated from adjacent modes.
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.
Turn ratio is so selected as to give low SWR at both ports.
Assertion (A): The velocity factor of a line is the ratio of wave velocity on the line to speed of light.
Reason (R): If the conductors of a line are immersed in a non magnetic insulating liquid, the wave velocity increases.
R is wrong because wave velocity decreases.