Ultra-low-phase-noise cryocooled microwave dielectric-sapphire-resonator oscillators

摘要

Two nominally identical ultra-stable microwave oscillators are compared. Each incorporates a sapphire resonator cooled to ne,ar 6 K in an ultra-low vibration cryostat using a pulse-tube cryocooler. The phase noise for a single oscillator is measured at - 105 dBc/Hz at 1 Hz offset on the 11.2 GHz carrier. The oscillator fractional frequency stability, after subtracting a linear frequency drift of 3.5 × 10~(-14)/day, is characterized by 5.3 × 10~(-16)τ~(-1/2)+ 9 × 10~(-17) for integration times 0.1 s<τ< 1000 s and is limited by a flicker frequency noise floor near 1 × 10~(-16).