Circuit effects in second-harmonic tuning of IMPATT diodes

Two-frequency operation of IMPATT diodes is examined in this paper on a conceptual basis. It is shown that a simple interpretation of the "single-frequency" admittances of the diode may be made. An equivalent circuit is presented which shows that the effect of second-harmonic tuning is to introduce a nonlinear resonance into the fundamental input admittance. This occurs when the external circuit admittance is tuned to the neighborhood of the "single-frequency" oscillator admittance of the diode at the second-harmonic. Computer calculations of the tuned-harmonic mode, with the diode embedded in the simplest possible RF circuit, are presented to demonstrate the effect.