High peak power epitaxial GaAs oscillators

Pulsed epitaxial GaAs Gunn oscillators have been operated in resonant circuits with a power x (frequency)²product of 690 watts (GHz)²and 18.6 percent efficiency. These values represent the highest Pf²product and efficiency reported for Gunn oscillators in the quenched mode. A Gunn oscillator was operated in a resonant cavity at ambient temperatures from -50°C to 170°C with less than ± 2 dB variation in power, less than 10 percent variation in frequency and a 20 percent change in relative efficiency. In a tunable circuit, a device was operated from -85°C to 133°C with essentially constant power output. The stable operation of these devices over an extended temperature range is due to the positive temperature coefficient of resistance of the epitaxial GaAs which provides a built-in protection against thermal runaway. The highest power obtained was 143 watts at 2.20 GHz with 18.6 percent efficiency, from a device 30×30 mils in cross section with an n layer of 100 µm. A pulsed oscillator on life test has so far run 2300 hours with stable output.