Non-linearity in a Multicavity Klystron Amplifier

Abstract

Multicavity klystrons are used as power amplifiers in ultra-high frequency television relay transmitters. Here the same amplifier handles the sound, the vision and the chrominance signals. Non-linearity in the amplifier results into inband intermodulation products which interfere with the picture signal.

In the case of klystrons when the bunching parameter is greater than one, the relationship between the input and the output cannot be expressed on an instant to instant basis by means of a power series. Murata analysed the problem of a two-cavity klystron by employing double fourier series and observed that the intermodulation rates obtained agree remarkably well with those obtained by the power series method.

The case of a multicavity klystron involves a large number of parameters thus making a similar mathematical analysis difficult. Therefore, as a practical approach, an attempt was made to decide an appropriate power series from the measured levels of intermodulation products. The intermodulation levels measured for four different input levels were analysed. The first order and the third order coefficients were determined from the first set and checked from the next set. The fifth order coefficient was determined from the third set and the seventh order coefficient from the fourth set. This approach was found to be reasonably successful.