Assertion (A): Microstrip is very commonly used in microwave integrated circuits.

Reason (R): Microstrip has an easy access to the top-surface so that active and passive discrete components can be easily mounted.

An Impatt diode has n⁺ - p - i - p ⁺ structure and is used with reverse bias.

It exhibits negative resistance and operates on the principle of avalanche breakdown.

Impatt diode circuits are classified as broadly tunable circuit, low Q circuit and high Q circuit.

The impedance of Impatt diode is a few ohms. The word Impatt stands for Impact Avalanche Transit Time diode.

The features of Impatt diode oscillator are : frequency 1 to 300 GHz, Power output (0.5 W to 5 W for single diode circuit and upto 40 W for combination of several diodes), efficiency about 20%.

Its applications include police radar systems, low power microwave transmitter etc.

It uses a single cavity resonator for generating microwave oscillations.

Its parts are electron gun, resonator, repeller and output coupling.

It operates on the principle of positive feed back.

The repeller electrode is at negative potential and sends the partially bunched electron beam back to resonator cavity.

This positive feedback supports oscillations. Its feature are:

1. Frequency range - 2 to 100 GHz

2. Power output - 10 MW to about 2 W

3. Efficiency - 10 - 20 %

Its applications include radar receivers, local oscillator in microwave devices, oscillator for microwave measurements in laboratories etc.

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.