Microwave frequency discriminator with a cooled sapphire resonator for ultra-low phase noise

First results are presented for an X-band frequency discriminator using a cooled sapphire microwave resonator. These results show a lower close-in (1-Hz-1-kHz offset) phase noise measurement floor than any oscillator presently available. This performance is made possible by a sapphire whispering-gallery mode resonator which shows the highest quality factor (with Q's up to 30 million) of any RF microwave, or acoustic resonator at temperatures to 77 K. Performance is increased by use of phase detection circuitry. The sapphire discriminator is used to characterize the phase noise of a single crystal quartz oscillator of the highest quality, without the use of a second similar oscillator as reference.<>