Submillimeter Backward Wave Oscillators

NASA Lewis Research Center is engaged in a program to develop a series of backward wave osci l la tors (BWO's) for the frequency range 500 to 2000 GHz. Generically BWO's are electron beam travel ing wave tubes operating in a dispersive regime in which the group velocity and the phase veloci ty of the induced electromagnetic wave are in opposite direct ions. The osc i l la t ion frequency of a BWO is controlled by the electron beam velocity (anode voltage). Such tubes because of thei r frequency tunab i l l t y , phase locking capabi l i ty, and large bandwidth are ideal local osc i l la tors for heterdyne recelver/spectrometers. The design of the BWO's w i l l be discussed with emphasis on the etched slow wave structure, zero compression electron beam, long l i f e cathode, and moderate operating voltages.