PHASE NOISE-REDUCTION OF A 19 GHZ VERACTOR-TUNED GUNN OSCILLATOR FOR ELECTRON-PARAMAGNETIC RESONANCE SPECTROSCOPY

Klystrons are being replaced with solid-state microwave oscillators by designers of microwave bridges for electron paramagnetic resonance (EPR) spectroscopy. Veractor-tuned Gunn oscillators have a number of advantages, but phase noise 100 kHz from the carrier is excessive. A Pound-type dc automatic frequency control (AFC) circuit is described that reduces phase noise of a Hughes veractor-tuned 19 GHz Gunn osillator by 23 dB, resulting in a value of -117 dBc/Hz. This value is typical for a good quality external-cavity reflex klystron at this frequency. It is concluded that the oscillator with AFC exhibits sufficiently low phase noise for normal EPR spectroscopy.