Thermal stabilization of microwave sapphire resonator references

Sapphire single crystal, associated with a special mode configuration (whispering gallery mode), is an ideal material for the realisation of high Q microwave resonator. Unfortunately, the frequency sensitivity to temperature fluctuations is relatively high. With such a sensitivity it is impossible to reach high frequency stability over a long time interval without efficient temperature regulation. We implemented original thermal regulation scheme on different sapphire resonators. We report, in this paper, frequency stability measurements of temperature controlled sapphire resonator oscillator at room temperature and at liquid nitrogen temperature