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.