Low-noise microwave oscillators based on high-Q sapphire dielectric resonators

Two almost identical 9 GHz oscillators were constructed, each characterised by approximately 500 mW of microwave power dissipated in the sapphire loaded cavity (SLC) resonator. The phase locking of the ´slave´ oscillator to ´master´ required for the phase noise measurements, was accomplished by altering the level of microwave power dissipated in the SLC resonator of the ´slave´ resonator. The spectral density of phase fluctuations of both oscillators was measured with a dual-channel readout system calculating the cross-spectral density of voltage fluctuations between the channels in order to minimise the effect of uncorrelated fluctuations of the each channel on the resolution of spectral measurements.