A high power millimeter wave TWT amplifier

A coupled cavity traveling wave tube operating at 35 gigahertz has been tested to an output power of 30 kilowatts peak and 9 kilowatts average. This high power millimeter wave amplifier is designed specifically for a coherent millimeter wave radar which is being designed and constructed by Massachusetts Institute of Technology, Lincoln Laboratory, under the sponsorship of the US Army Ballistic Missile Defense Advanced Technology Center. The amplifier was operated at beam voltage of 46.5 kilovolts with a beam current of 4.0 amperes. The tube requirements were 30 kilowatts peak, 3 kilowatts average over 1000 megahertz, 1 dB bandwidth, at a center frequency of 35 gigahertz with 50 dB saturated gain. These requirements were achieved during the development program with 17 percent interaction efficiency. The paper will describe the design concepts used in the development of this milimeter wave TWT amplifier. Design of the electron beam system, which is considered the highest power density electron beam generated to date, and the unique coupled cavity circuit design will be discussed in some detail. Test data for both the beam system and r.f. circuit will be presented. The r.f. performance characteristics of the tube will also be discussed and measured data presented.