Circuits for High-Efficiency Avalanche-Diode Oscillators (Dec. 1969 [T-MTT])

Absfract—This paper describes and analyzes the circuits which have been used successfully for TRAPATT oscillator studies. The results lead to a better understanding of the TRAPATT oscillator and yield a simple model of the oscillator which is useful for circuit design. The circuit characteristics of ms experimental TRAPATT oscillator are determined from measurements on the circuits and from equivalent circuit model calculations. The following conclusions can be drawn from the analysis. First, the avalanche diode requires sufficient capacitance near the diode to sustain the high-current state required for TRAPATT operation. Seeondly, at a distance from the diode corresponding to approx. inmtely one half-wavelength at the TRAPATT frequency the transmission ~me containing the diode should be terminated by a low-pass filter. The function of the filter is to pass the TRAPATT frequency and to provide a shorting plane for the harmonics of that frequency. Finally, on the load side of the filter, tuning for the TRAPATT frequency is required. The model of the circoit deseribed above suggests a simple explanation of the diode-circuit interaction in a TRAPATT oscillator. SimpliIled waveforms suggested by the model have been used to calculate power output, efficiency, dc voltage change, and RF impedance for the oscillator. The results agree within a few percent with those obtained for an experimental oscillator. An important conclusion of the analysis is that the hlghefliciency operation of avalanche diodes at frequencies in the UHF range can be explained by the TRAPATT theory, even though the trappedplasma or low-voltage state may last only &rth of the oscillation period.