A high stability microwave oscillator based on a sapphire loaded superconducting cavity

By combining the high mechanical rigidity and low loss tangent of cryogenic sapphire with the excellent shielding and low loss properties of a superconducting cavity, the authors have developed a microwave resonator with both high electrical quality factor and very high intrinsic stability even at relatively high power. They have implemented the sapphire-loaded superconducting cavity resonator in a novel phase-stabilized loop oscillator circuit and achieved Allan variances of around 10^-14 for 1 to 1000 s integrating time. This level of stability is competitive with that of the best hydrogen masers, and in fact is superior for integrating times under a few tens of seconds. An overview of the oscillator system is presented and applications and prospects for further improvement in performance are discussed