Cryo-cooled sapphire oscillator for the Cassini Ka-band experiment

We present design aspects of a cryogenic sapphire oscillator which is being developed for ultra-high short term stability and low phase noise in support of the Cassini Ka-band Radio Science experiment. With cooling provided by a commercial cryocooler instead of liquid helium, this standard is designed to operate continuously for periods of a year or more. Performance targets are a stability of 3/spl times/10/sup -15/ (1 second/spl les//spl tau//spl les/100 seconds) and a phase noise of -73 dB/Hz @ 1 Hz measured at 34 GHz. Test results are reported for several subsystems; including cryocooler, vibration isolation system, and ruby compensating element.