Low noise, microwave signal generation using cryogenic, sapphire dielectric resonators: an update

Abstract

X-band Q factors of IO5 to lo9 have been obtained for sapphire dielectric resonators operated at temperatures in the range 4K to 77K. Based on considerations of exceptionally high Q and moderate signal handing capability, resonator use as a microwave signal generator reference element should allow realization of short-term frequency stabilities unattainable using alternative technologies.In this paper, we will report on recent results obtained at Westinghouse using sapphire dielectric resonators for AFC stabilization of an X-band, SAWR VCO-based source. The resonators are operated on a low order (%I) mode and employ high temperature superconducting films in the metal enclosure covers in order to obtain unloaded Q-factors of 3X105 to 5X105.Signal source flicker-of-frequency noise characterized by Sy(100H~)=SXlO-~~/f or L( 100Hz)=-96dBc/Hz and noise floor levels of -165dBckIz have been measured at X=band.While these results constitute state-of-the art performance, the measured values for flicker-of frequency noise is lOdB poorer than anticipated, based on the large value (72uVMz) of discriminator sensitivity obtained. Possible causes for current limitations in signal near-carrier spectral performance include resonator short-term frequency fluctuations resulting from environmentally-induced effects and/or frequencydrive (AM-to-FM) effects. Resonator vibration sensitivities (force ap lied parallel to enclosure covers) on the order of 1x10-5 per g have been measured.

Superconducting modulators for high dynamic range delta-sigma analog-to-digital converters

“…Clock jitter does not limit performance [2] at 10 GHz where a radar system would use a stable local oscillator like that of [7]. The effects of cross talk are negligible in this design because of the continuous nature of the feedback.…”