Litton folded-waveguide high-power millimeter-wave TWTs

Summary form only given, as follows. Litton EDD is developing a new class of PPM-focused, narrowband, high average power, millimeter-wave TWTs that utilize a novel integral-polepiece folded-waveguide circuit. The first of these TWTs produced over 250 watts of average power at Ka-band despite construction errors that degraded tube performance. This paper describes the third of such tubes built and tested under Litton's internal research and development program. This TWT is similar to that mentioned above in several ways. They both utilize 20 kV 0.75 A beams formed with a beam convergence of only 36 to minimize beam thermal effects. They both have gain levels of 10 dB/inch, bandwidths of about 350 MHz at Ka-band, and peak power levels between 800 and 1400 watts. However, additional development has resulted in significantly improved performance. By improving the beam optics, the DC transmission was raised above 99% and the minimum RF transmission raised above 98%. By increasing the depression of the single stage collector, the total efficiency was raised to values between 20% and 28%. By increasing the duty to 75%, average output powers were raised above one kilowatt. Specific test results are presented along with their impact on Litton's development of a 250 watt average power W-band TWT. >