Ultra-low noise microwave phase stabilizer using sapphire ring resonator

The preliminary design details for two sapphire whispering gallery mode phase stabilizers are presented. The sapphire resonators are cooled in individual liquid nitrogen dewars to an operating temperature of approximately 80 K. Each operates to stabilize the phase of an 8.1 GHz signal derived from a quartz crystal oscillator operating at 100 MHz. Ultra-low phase noise (-80 dB/Hz at 1 Hz offset) is projected due to the high resonator Q (3×10⁷ at 80 K). The temperature of the thermally uncompensated sapphire resonators is stabilized by RF heating to a value approximately 3 degrees above that of a liquid nitrogen bath. Oscillator configurations which can further reduce oscillator phase noise are discussed and analyzed. These circuit improvements should provide crystal-oscillator type performance in a room-temperature 10 GHz (X-band) oscillator using a whispering gallery mode sapphire resonator with an intrinsic Q of 2×10⁵. A general description of the oscillator systems and the thermal design considerations together with design details and analysis for the microwave aspects is presented