Ultra low phase noise C-band oscillators with combined frequency stabilization

In this paper we present the design and preliminary results of an experimental evaluation of C-band microwave oscillators with combined frequency stabilization based on Sapphire Whispering Gallery Resonators (WGR). Design features and phase noise performance of both the main oscillator loop and a frequency stabilization system are presented. The frequency stabilization loop has been implemented using a high sensitivity “noiseless” frequency discriminator based on a traveling wave WGR. The intrinsic phase noise of the oscillator electronics has been minimized utilizing low 1/f-noise silicon and SiGe discrete components and ICs. The single-sideband phase noise of -128 dBc/Hz and -133 dBc/Hz at 1 kHz offset has been measured for free-running oscillators with P_res = 0.15 W and P_res = 0.4 W respectively. An estimate for the phase noise of the stabilized oscillators has been made involving a phase transfer function approach.