Why do practical Klystron amplifiers generally have more than two cavities ? How can broad band operation be achieved in multicavity Klystrons.

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written 5.8 years ago by

teamques10 ★ 68k

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The bunching process in a two cavity klystron is by no means complete, since there are large number of out of phase electrons arriving at the catcher cavity between bunches. More than two cavities are always employed in practical klystron amplifier.
Four cavities present in klystron amplifier and upto seven cavities have been used in practice.
Partially bunched current pulses will now also excite oscillations in the intermediate cavities, and these cavities in turn set up gap voltages which help to produce more complete bunching. Having the extra cavities helps to improve the efficiency and power gain.
The cavities may all be tuned to the same frequency such synchronous tuning being employed for narrowband operation.
For broadband work, for example with UHF klystrons used as TV transmitter output tubes, or 6 GHz tube used as power amplifiers in some satellite station transmitters, stagger tuning is used.
Here each of the intermediate cavities acts as a buncher with the passing electron beam inducing and enhanced RF voltage than the previous cavity.
With the mult-icavities power gain of around 50 dB can be easily achieved. The cavities can all be tuned to self frequency for narrow band operation.
Bandwidth can be improved by staggered tuning of cavities upto about 80 MHz with reduction in gain(to about 45dB). This staggered tuning is employed in UHF klystron. For TV transmitter output tubes and in satellite earth station transmitter as a power amplifiers at C band.

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