A loop phase-locked 74 GHz impatt oscillator usable for precise spectroscopy to the 500 GHz region

To examine possible application to spectroscopy and laser frequency measurement, a 74 GHz impatt oscillator was phase-locked to a quartz-crystal oscillator harmonic using a loop employing a digital phase-frequency detector. The maximum frequency multiplication permissible without catastrophic spectral broadening was estimated from the locked-phase spectral-density curve to be about 7 times, to 500 GHz, a factor 3 less than for a good-quality well locked reflex klystron, because of greater phase noise remaining outside the loop bandwidth. The use of wideband loops already existing for solid-state oscillators could suppress this disadvantage.