Nonlinearities of multicavity klystron amplifiers

The nonlinearities of a five-cavity klystron for wide-band operation are investigated by making use of the large signal analysis and experiments. The variations of frequency-response characteristics with respect to the input signal level, and the amplitude and phase nonlinearities are presented in detail for two typical tunings. It is shown that the nonlinearities are affected by the tuning of the intermediate cavity. The amplitude nonlinearity at saturation is about -3 to -6 dB within a frequency range of 80 MHz at the 14-GHz band. There exists some discrepancy between the calculated and measured phase nonlinearities. The nonlinear mechanisms are discussed to explain the results obtained by categorizing them into four parts. In the discussions, an emphasis is placed upon the velocity modulation of the beam by the intermediate cavity which introduces the frequency dependence into the nonlinearities.