An experimental annular reflex klystron

The paper discusses the advantages and disadvantages of the strip and annular forms of klystron. There would appear to be considerable advantages in their application to the high-power and short-wavelength fields. An investigation into the behaviour of these geometries is described, in which an annular reflex klystron operating in the 3 cm band was taken for study. It was expected that problems would arise due to interfering cavity modes, the frequency separation between them and the useful mode being dependent on the size of the cavity. This moding effect would set an upper limit to the cavity size and hence to the power output obtainable, unless steps were taken to suppress the interfering modes. Methods of doing this are discussed, and experimental work on the most promising is presented. The reflex klystron gave a maximum efficiency of 3%, corresponding to an output power of 250 watts, at an operating voltage of 2.5 kV. This agrees well with theoretical predictions.