The directive gain of a transmitting antenna is proportional to

A Gunn diode uses GaAs which has a negative differential mobility, i.e., a decrease in carrier velocity with increase in electric field.

This effects is called transferred electron effect. The impedance of a Gunn diode is tens of ohms.

A Gunn diode oscillator has a resonant cavity, an arrangement to couple Gunn diode to cavity, biasing arrangement for Gunn diode and arrangement to couple RF power to load.

Applications of Gunn diode oscillator include continuous wave radar, pulsed radar and microwave receivers.

If line is o.c. |r_v| = 1 and VSWR = ?.

Since reactance does not contribute thermal noise to the circuit, it is a low noise device.

Mode filter suppress modes with lower cutoff frequencies.

Beam width between nulls of a parabolic antenna . Therefore 50° is the nearest value.

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.

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

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

A short-circuited stub is a suitable method of matching.

Oscillator circuits using vacuum tubes (triodes, pentodes) have the following limitations at very high frequencies (microwave region).

The stray capacitances and inductances become important and affect the operation of the circuit.

At low frequencies the transit time between cathode and anode is a small fraction of period of oscillation.

However, at microwave frequencies this transit time becomes comparable to time period of oscillations.