In a microstrip transmission the signal can be easily redirected by changing the centre strip.

The condition for minimum distortion is found by equating The result is .

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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.

Isolation equals coupling plus directivity.

A pure reactance does not absorb any power.

Therefore VSWR is infinite because |r_v| = 1.

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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.

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.

Since all ports matched, input SWR = 1. No power is reflected and P_in = P₄ = 1 W.

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

Printed circuit techniques is used for micro strip line.

For ideal dielectric loss angle is zero. For good quality cables, loss angle is very small, about 1° only.