Abstract: A four-diode bridge is positioned within the cavity of a Gunn diode oscillator. A subharmonic signal is applied to the diode bridge and the diode bridge couples an odd harmonic of the injected signal into the cavity. The cavity is thus caused to resonate at the odd harmonic of the injected signal. The injected signal can be changed using a frequency synthesizer in order to provide a microwave oscillator with multiple-channel operation. The diode bridge provides a feedback signal indicative of the phase of cavity oscillation. The feedback signal is applied to a varactor which pretunes the Gunn diode oscillator and thereby provides phase-locked control.