Analysis of a low noise tunable oscillator based on a tunable sapphire loaded superconducting cavity

A tunable sapphire-loaded superconducting cavity (T-SLOSC) has been constructed and was used as a high-Q filter in an X -band loop oscillator. It is configured with two cryogenically operational GaAs FET amplifiers. The oscillator is situated in a vacuum can with a two-mode vibration isolation system designed to filter vibrations by 50 dB at 700 Hz from the carrier. By matching theory with measurement, the field patterns of some mode families at room temperature are identified. Calculating frequency shift with temperature enables identification of modes when cooled. Tuning ranges can also be estimated. To measure phase noise, the T-SLOSC was made a voltage controlled oscillator (VCO), and locked to a fixed-frequency SLOSC. The phase noise was measured at room temperature and a range of cryogenic temperatures. The major limitation is the excessive flicker noise exhibited by GaAs FET amplifiers in the feedback loop