0.054 x 8.68 = 0.47 dB/m.

A Klystron is a vacuum tube used for generation/amplification of microwaves.

An electron beam is produced by oxide coated indirectly heated cathode and is focussed and accelerated by focussing electrode.

This beam is transmitted through a glass tube. The input cavity where the beam enters the glass tube is called buncher.

As electrons move ahead they see an accelerating field for half cycle and retarding field for the other half cycle.

Therefore, some electrons are accelerated and some are retarded. This process is called velocity modulation.

The velocity modulation causes bunching of electrons. This bunching effect converts velocity modulation into density modulation of beam.

The input is fed at buncher cavity and output is taken at catcher cavity.

In a two cavity klystron only buncher and catcher cavity are used. In multi cavity klystron one or more intermediate cavities are also used.

The features of a multicavity klystron are :

1. Frequency range - 0.25 GHz to 100 GHz

2. Power output - 10 kW to several hundred kW

3. Power gain - 60 dB (nominal value)

4. Efficiency - about 40%.

A multicavity klystron is used in UHF TV transmitters, Radar transmitter and satellite communication.

Hollow metallic enclosures exhibit resonance behaviour when excited by electromagnetic field.

These enclosures are called cavity resonators.

A balun gives 4 : 1 impedance transformation.

Power handling capacity ? (voltage)² and is inversely proportional to f² max.

The quantities required to be measured in microwave circuits are frequency, power and impedance.

Microwave frequency measurement is done by slotted line, resonant cavities and transfer oscillator.

Microwave power measurement uses bolometers and micromave power meters.

A self balancing bridge working on the principle of power substitution is commomly used.

Microwave impedance measurement is done by measurement of reflection coefficient and VSWR.

A slotted line and probe is a basic tool for these measurements.' Network analyser enables rapid impedance measurement over a broad frequency range.

A PIN diode has an intrinsic (i) layer between p and n layers. When reverse bias is applied depletion layers are formed at p-i and i-n junctions.

The effective/width of depletion layer increases by the width of i layer. It can be used as a voltage controlled attenuator.

At high frequencies the rectification effect ceases and impedance of diode is effectively that of i layer.

This impedance varies with the applied bias. It is used in high frequency switching circuits, limiters, modulators etc.

PIN diode is not used in oscillators.

Time required for microwave cooking is much less than the time required for conventional cooking.

Coplanar arms are decoupled.