Harmonic content in solid state microwave oscillators

The harmonic contents of Gunn effect and trapatt oscillators have been experimentally investigated using a lamellar grating far-infrared interferometer and an unusual gated detection system. In order to minimize circuit effects on harmonic content a broad band nonreflecting circuit was devised. In general, only the first few harmonics of the X-band Gunn effect devices were observed and these died off rather rapidly. The experimental results were in fairly good agreement with theoretical predictions and indicate that the relative harmonic content increases with n/f. No definite correlation between harmonic content and bias voltage was found. The highest frequency at which power was observed was 82 GHz, a tenth harmonic. Thus the results do not contradict the predicted upper frequency limit of operation for these devices. Components of a 1.67 GHz fundamental trapatt oscillator were observed up to 40 GHz, a, frequency corresponding to three times the normal transit-time frequency.