HIGH-Q THERMOELECTRIC-STABILIZED SAPPHIRE MICROWAVE RESONATORS FOR LOW-NOISE APPLICATIONS

Two low-noise high-Q sapphire-loaded cavity (SLC) resonators, with unl oaded Q values of 2 x 10(5) and very low densities of spurious modes, have been constructed. They were designed to operate at 0-degrees-C wi th a center frequency of 10.000000 GHz. The cavity was cooled with a t hermoelectric (TE) Peltier element, and in practice achieved the requi red center frequency near 1-degrees-C. The resonator has a measured fr equency-temperature coefficient of -0.7 MHz/K, and a Q factor which is measured to be proportional to T-2.5. An upper limit to the SLC resid ual phase noise of L (100) Hz = -147 dBc/Hz, C (1 kHz) = -153 dBc/Hz, and L (10) kHz = -160 dBc/Hz has been measured. Also, we have created a free-running loop oscillator based on one of the SLC resonators, and measured a phase noise of L(f) approximately -10-30log [f] dBc/Hz bet ween f = 10 /Hz and 25 kHz, using the other as a discriminator.