An experimental arrangement for injection locking Ka-band oscillators

Two Ka-band oscillators, which have a free-running frequency difference of 20-50 MHz, can be combined as an injection-locked assembly by inserting a waveguide magic-T, an attenuator and a suitably dimensioned ferrite circulator between their respective multiplier outputs. A waveguide mixer is used to detect the phase difference between the two oscillators. In locked state, the mutual frequency can be fine tuned through the adjustment of one of the supply voltages. Because no synthesizers or frequency dividers are involved, the spectrum is practically free of close-in sidebands. Low-noise coarse frequency adjustment up to 10 ppm can be accomplished through water cooling. The proposed arrangement has been tried in selected test instruments and for short-range radar.