Enhanced leakage-current pulse-induced changes in impatt oscillators

Two types of stables changes in c.w. X-band impatt oscillators have been observed after exposure to pulses of enhanced leakage current. The first change is indicated by a change in r.f. power and frequency while maintaining a `clean¿ r.f. spectrum, and is attributed to parasitic circuit-induced instabilities (with changes in oscillator characteristics thought to be influenced by changes in harmonic phasing). The second change is indicated by a modulated r.f. spectrum and oscillations in bias voltage after irradiation, and is clearly attributed to bias-circuit oscillations. These conclusions are supported by experimental results with Si and GaAs diodes in a resonant cap waveguide oscillator circuit. Enhanced leakage-current pulses up to 5 mA in amplitude were obtained using 10 MeV electron pulses from a linear accelerator. The r.f. impedance was adjusted by varying the sliding short-circuit position, while the bias-circuit impedance was varied independently by inserting various length cables between an RC bias network and the diode.