Resonant-circuit operation of Gunn diodes: a self-pumped parametric oscillator

Theory and experiments are reported which show that a key to understanding the resonant-circuit behaviour of a Gunn diode lies in the impedance presented to the diode at the second harmonic of oscillation. This leads to an interpretation of the device as a parametric oscillator, and allows one to develop useful microwave circuits with an octave continuous-tuning range.