Recent advances in non re-entrant crossed-field forward-wave amplifiers

Since the late 1940’s when the first significant work was done on crossed-field amplifiers [l], they have generally had the reputation of being relatively low gain devices. Until recently, most of the work or this type of device has been done on tubes of circular format which suffer from problems of gain stability because of the many modes of electromagnetic and electronic feedback from output to input. Recent work on the linear form of the injected-beam forward-wave crossed-field amplifier has greatly reduced the problem and promises to put this device into the high gain class along with klystrons and traveling-wave tubes. Noise on the beam will be the chief limiting factor in the gain attainable in crossed-field amplifiers. Recent tests have shown that at least 40 dB gain can be achieved before such effects become notice-abl e.