Electronics and Communication Engineering - Microwave Communication
Reflection coefficient 
Assertion (A): A backward wave oscillator has an internal positive feedback.
Reason (R): A positive feedback is necessary for sustained oscillations.
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.
A Microstrip line has a single dielectric substratc with ground plane on one side and a strip on the other face.
Its special feature is easy access to top surface so that minor adjustments can be made after circuit fabrication.
The high dielectric constant of the substrate reduces guide wavelength and circuit dimensions.
A microstrip line is the most commomly used transmission structure for microwave integrated circuits.
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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