Some Studies on the Effect of the Resonant Cap on the Oscillator Performance of X-Band Gaas and Si Impatt Oscillators

Abstract

X'-band GaAs and Si IMPATT oscillators have been developed using a compact heat-sink cum waveguide cavity arrangement with diodes mounted between a resonant cap and the broad face of the waveguide. In the operating current range, tuned maximum power output and the efficiency at a given dc bias current are strongly dependent on the resonant cap diameter which mainly determines the frequency of oscillation. The maximum efficiency of the GaAs IMPATT oscillator was found to be 19% at a power level of 1.4 W when the device optimum frequency nearly corresponds to freq of oscillation determined by the resonant cap. On the other hand, the maximum efficiency considerably degrades with resultant decrease of tuned maximum power output when the oscillating frequency determined by the cap diameter appreciably differs from the frequency of maximum negative conductance of the diode. Similar investigations have been carried out on Si SDR IMPATT oscillators for various sizes of the resonant cap which show that the power output and efficiency peaks at an optimum size of the resonant cap for a given device.

Indexing Terms:

• Impatt Oscillators
• Resonant Cap Oscillators