Characterization of Second-Harmonic Effects in IMPATT Diodes

It was found by Swan 2 that the introduction of a trapped resonance at the second harmonic of the oscillation frequency in a 6-GHz Ge I M P A T T diode oscillator provided dramatic increases in the output power and efficiency, as compared with the results obtained with the ordinary single quarter-wave transformer coaxial circuit. Since t h a t time several authors 1 , 3 - s have reported both theoretical and experi1777 1782 T H E BELL SYSTEM T E C H N I C A L J O U R N A L , OCTOBER 15)70 mental examinations of the effect. It appears that the addition of a properly phased second-harmonic voltage improves the phasing of the RF current relative to the fundamental voltage so as to increase the negative conductance and (at least at lower frequencies) give an increase in the power output at the fundamental frequency. The circuit conditions required for the observation of this effect have been incompletely understood. The purpose of this paper is to present the results of an analytical study of the interaction of an I M P A T T diode with a circuit having resonances at two harmonically related frequencies. The analysis is begun by the introduction of an equivalent circuit for the diode by which these two-frequency oscillators may be characterized. A stability theory is then developed along the lines taken by Kurokawa which examines whether a particular circuit, even though matching the impedances required by the diode at both frequencies, will or will not provide a stable oscillation.