Development of a broadband hollow beam, modulating anode L-band klystron at the multi-megawatt level

This paper discusses the development of the L-3707 Klystron at Litton Industries in San Carlos, California. The L-3707 utilizes a hollow electron beam generated by a high perveance magnetron injection gun and delivers a peak rf power of 10 megawatts with a modulating anode voltage of less than 40 kilovolts. This enables video current rise times of less than 500 nanoseconds to be obtained using relatively low voltage hard tube circuitry, and makes the L-3707 particularly adaptable to radar applications requiring extremely small interpulse spacing for pulse coding. In particular, some of the unique characteristics of the high perveance magnetron injection gun in which the accelerator electrode is also employed as the modulating element will be discussed. The first of these is the effect of varying the modulating anode voltage, hence the beam current, on the phase at the output of the klystron. Secondly, the noise performance of magnetron injection guns will be discussed. It will be shown that with properly designed magnetron injection guns, signal to noise ratios which are comparable to signal to noise ratios of conventional solid beam designs can be achieved. The "SKIRTRON" broadbanding technique which is used in the L-3707 to obtain 100 megacycles of instantaneous bandwidth centered at 1300 megacycles will be discussed briefly, and data presented showing typical passband responses and signal to noise ratios under various conditions of beam current, beam voltage and focusing.