Large-signal behavior of distributed klystrons

A theoretical large- and small-signal analysis of the behavior of standing-wave-type distributed circuit klystrons, based on a confined flow model, is described. A two-cavity klystron with a π-mode double-gap distributed output circuit and a conventional single-gap input cavity was selected as a specific example for study. The field distribution for the experimental cavities was measured and a conversion efficiency of 52 percent was predicted. The effects of the output cavity position relative to the input cavity, the output cavity gap angle, and the space charge were analyzed theoretically. The theoretical results were compared with measurements made on a precision demountable klystron with identical beam and circuit parameters, but with a Brillouin-focused beam rather than a confined-flow beam. A load efficiency of 35 percent, a conversion efficiency of 42 percent, and small-signal gains up to 15 dB were measured. The corresponding figures for the conventional single-gap output circuit were 24 percent, 28.6 percent, and 9 dB. The measured effects of changes in the tube parameters were in general agreement with the theoretical predicted results. The study indicates that the π-mode double-gap cavity is a very practical output structure yielding high efficiency with a very short interaction length. It should prove useful in medium- and high-power klystrons.