Automatic thermal frequency control of microwave oscillator with dielectric disk resonator

Abstract

Microwave oscillators that are stabilized by sapphire disk resonators have good short-term relative frequency stability (σ(τ)=10−10 over averaging time τ∼1 sec) but inadequate long-term stability. This is mainly due to the high temperature coefficient of frequency of the disk resonator. An automatic frequency-control system based on thermal control of the frequency of the disk resonator was developed to improve the long-term frequency stability of the oscillators. The parameters of the automatic frequency-control system were optimized by computer, which involved solution of the nonstationary problem of the temperature distribution in the disk resonator and examination of the stability of the automatic control system for diffuse propagation of the control signal. Recommendations are given for selection of the heater geometry and frequency-control method. An oscillator with the thermal frequencecy-control system had a long-term relative frequency instability of (0.3–1)·10−8 per day, which was determined by the stability of the crystal-controlled reference oscillator. The automatic frequency-control system did not appreciably change the noise characteristics of the oscillator.