The Design and Performance of a 150-MW Klystron at S Band

Design considerations and performance characteristics of a 150-MW pulsed klystron amplifier at S band are described. One of the main problems encountered in generating such high power at microwave frequencies is the extremely high-voltage gradients developed across the output gap of the klystron which may cause RF breakdown. A double-gap 2¿-mode output cavity is used successfully in the present case to generate a peak output power of 150 MW at a frequency of 2870 MHz with an efficiency of 51 percent, saturation gain of 59.3 dB, and a pulsewidth of 1 ¿s. A reduction in gap voltage of at least 25 percent as compared to a similar klystron with a conventional single-gap output cavity at the same voltage and at their respective maximum efficiency points is theoretically predicted. Examination of the gaps after an extended period of operation shows that they are smooth and without signs of erosion, indicating that the fields were uniform and not excessive. Extrapolating from the gradient which exists in this present tube, it appears feasible to generate still higher powers (of the order of 700 MW) efficiently with a single klystron at S band with a pulsewidth of 1 ¿s, if the need arises.