High average power pulsed GaAs LSA oscillators

New State-of-the-Art results are reported in average power and efficiency in high peak power GaAs transferred-electron devices operated at X-band in the LSA mode. Average power of .70W at 13% efficiency with 200W peak power was obtained at high duty cycle, and 16.5% efficiency with 500-600W peak power was obtained at very low duty cycle. These results double the average power, and raise the efficiency by one third, over previously reported results of pulsed X-band LSA devices. The properties of the devices are 10°/W thermal resistance,
2.2 \times 10^{15}
/cm
³
electron concentration and 100 µm thickness in active layer and 1.2Ω low field resistance. Operating voltage is near 260V for low duty cycle operation, and near 170V for high duty cycle operation, both near 9 GHz oscillation frequency. The devices had a ratio of peak bias current to current at high bias voltage (unloaded, but oscillating in a resonator) of 2:1, corresponding: to 18.5% maximum available theoretical efficiency at low duty cycle. The second harmonic is resonated automatically in the circuit used, to obtain the high efficiency with no adjustment except bias voltage. The equivalent circuit parameter values at the fundamental frequency and the second harmonic, and the physical reason for the importance of each, will be given. The general applicability of these results, depending on device parameters, to pulsed and C.W. transit time GaAs transferred-electron devices will also be presented.