A Low Phase Noise Microwave Sapphire Loop Oscillator

Abstract

A tuneable 10.24 GHz microwave oscillator based on a sapphire-loaded cavity (SLQ resonator operating in a "whispering gallery"-mode has been built. Extremely low phase noise of -130 dBc/Hz @ 1 kHz and -179 dBc/Hz floor has been measured, without the need for any form of noise reduction. This level of performance is made possible by the high Q factor of the SLC resonator, together with the low phase noise of a commercially-available sustaining amplifier based on a parallel combination of heterojunction bipolar transistors (HBTs). This paper presents the results for the performance of this low phase noise, sapphire resonator based loop (SLOOP) oscillator. The SLOOP has an SLC resonator with a significantly improved start-up time over previous sapphire-based resonators, coming to temperature lock within 2 minutes over the operating temperature range 0 to +55degC