High-precision temperature stabilization for sapphire resonators in microwave oscillators

In this paper, we propose technical solutions to solve the issue of the thermal stabilization of a room-temperature high-Q whispering gallery mode microwave sapphire resonator. This technology enables the design of very low phase noise microwave sources which can be used as references for phase noise measurements or for high sensitivity radar systems. Nevertheless, the sapphire resonator presents at the ambient temperature a high sensitivity to thermal fluctuations of the order of -70 ppm/K limiting the oscillator stability in the long term. An original resonator thermal configuration has been designed and optimized thanks to finite difference technique simulations. The symmetry of the proposed thermal structure increases the temperature control efficiency. Coupled to a high-resolution electronic temperature controller directly embedded on the microwave cavity, this structure presents a very low sensitivity to the environment thermal fluctuations. This sensitivity is better than -0.05 ppm/K. (c) 2005 American Institute of Physics.