Backward-Wave Oscillator Experiments at 100 to 200 Kilomegacycles

Electronically tunable oscillations were obtained at wavelengths between 3 and 1.5 millimeters in a demountable backward-wave oscillator whose circuit structure was a ridged waveguide with transverse slots in the broad wall. The slot arrays were formed by tapes wound on suitably dimensioned, interchangeable frames, each giving a tuning range of about 15 per cent. For electron beam velocities between 650 and 2700 volts and current densities between 3 and 10 amperes per square centimeter, probable power outputs of a few tenths of a milliwatt were obtained. One of the goals of the work was to gain insight into the "personality" of traveling-wave tubes at these high frequencies. Among the new concepts to be dealt with are "beam skin effect" and the very strong influence of circuit loss on starting current and power output.