The condition of minimum distortion in a transmission line is

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.

Therefore VSWR is infinite because |r_v| = 1.

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 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.

Avalanche diode can also be operated in large signal high efficiency mode called Trapped Avalanche Transit Time mode.

The Trapatt oscillations depend on the delay in the current caused by avalanche process.

The avalanche delay makes it possible to increase the diode voltage well above the breakdown voltage.

Therefore a very rapid multiplication of charge carriers occurs. A Trapatt diode is also a negative resistance device.

The features of Trapatt diode oscillator are : Frequency 3 to 50 GHz, Power output 1-3 W, efficiency about 25%.

Its applications are low power doppler radar, microwave beacon landing system etc.

This power splits between ports 1 and 2. Therefore P₁ = P₂ = 0.5 ?, P₃ = 0.