10 GHz cryocooled sapphire oscillator with extremely low phase noise

The phase noise characterisation of two 10 GHz cryogenic sapphire oscillators exhibiting frequency stability higher than 3×10−15 is reported. One of these oscillators developed for the deep space navigation ground stations of the European Space Agency, incorporates a closed cycle cryocooler as cold source. Near the carrier, the measured phase noise is limited by a flicker frequency noise: Sϕ(f)=−30log(f)−98 dBrad2/Hz.