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.<>