Precise Active Frequency Stabilization of a Microwave Cavity

In this paper, a system for precise frequency stabilization of a microwave cavity is presented. A cavity mode is probed in transmission, and a phase comparison scheme is used to measure its frequency fluctuations. In this way, shifts are corrected not only if temperature induced, but also if induced by mechanical stress, inasmuch as the latter effect is similar for the target mode and for the mode used to implement the stabilization system. A servo loop is then realized, which locks the cavity resonance to an external reference set to the nominal value by thermal actuators driven by a proportional-integral compensator