Improved performance of a temperature compensated LN/sub 2/ cooled sapphire oscillator

We report on improved stability in a whispering gallery sapphire resonator for which the dominant WGH/sub nll/ microwave mode family shows frequency-stable, compensated operation for temperatures above 77 K. Several modifications during the past year have led to significant improvements in performance. Current tests with improved thermal stability provide Allan Deviation of frequency of 2.6-4/spl middot/10/sup -13/ for measurement times of 1/spl les//spl tau//spl les/100 seconds. We project a frequency stability of 10/sup -14/ for this resonator with stabilized housing temperature and with a mode Q of 10/sup 7/.