High-Q thermoelectric-stabilized sapphire microwave resonators for low-noise applications

Two low-noise high-Q sapphire-loaded cavity (SLC) resonators, with unloaded Q values of 2/spl times/10/sup 5/ and very low densities of spurious modes, have been constructed. They were designed to operate at 0/spl deg/C with a center frequency of 10.000000 GHz. The cavity was cooled with a thermoelectric (TE) Peltier element, and in practice achieved the required center frequency near 1/spl deg/C. The resonator has a measured frequency-temperature coefficient of -0.7 MHz/K, and a Q factor which is measured to be proportional to T/sup -2.5/. An upper limit to the SLC residual phase noise of /spl Lscr/ (100) Hz=-147 dBc/Hz, /spl Lscr/ (1 kHz)=-155 dBc/Hz, and /spl Lscr/ (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 /spl Lscr/(f)/spl sim/-10-30log [f] dBc/Hz between f=10 /Hz and 25 kHz, using the other as a discriminator.<
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