A low maintenance long-term operational cryogenic sapphire oscillator has been implemented at 11.2 GHz using an ultra-low-vibration cryostat and pulse-tube cryocooler. It is currently the world's most stable microwave oscillator employing a cryocooler. Its performance is explained in terms of temperature and frequency stability. The phase noise and the Allan deviation of frequency fluctuations have been evaluated by comparing it to an ultra-stable liquid-helium cooled cryogenic sapphire oscillator in the same laboratory. Assuming both contribute equally, the Allan deviation evaluated for the cryocooled oscillator is σ-y 1 × 10 -15τ-1/2 for integration times 1 < τ < 10 s with a minimum σy = 3.9 × 10-16 at τ = 20 s. The long term frequency drift is less than 5 × 10-14day. From the measured power spectral density of phase fluctuations, the single-sideband phase noise can be represented by L (f) = 10-14.0/ f4+10-11.6/f3+10-10.0/f 2+10-10.2/f+ 10-11.0 rad2/Hz for Fourier frequencies 10-3 < f < 103 Hz in the single oscillator. As a result, L\approx -97.5 dBc/Hz at 1-Hz offset from the carrier.
|Number of pages||7|
|Journal||IEEE Transactions on Microwave Theory and Techniques|
|Issue number||12 PART 1|
|Publication status||Published - Dec 2010|
- cryogenic sapphire oscillator
- frequency stability
- phase noise