Impact of Stabilizing Networks on Phase Noise in Microwave Bridge Oscillators

The microwave oscillator utilizing a bridge-type network as a positive feedback loop filter (MBoS) opens a possibility to increase an oscillator effective g-factor by many times thus improving its frequency stability and phase noise. This paper develops the previous analysis taking into account impact on MBoS phase noise of auxiliary stabilizing networks (SNs) used in practical design to prevent parasitic oscillations. The SNs under analysis are presented with a classic transmission resonator (SN1), a new non-minimal-phase circuit of the second order having two pairs of complex conjugate zeros and poles (SN2) and their combination. As expected, the optimized MBoS could provide as low phase noise as approximately -(140... 145) dBc/Hz at 1 kHz offset in the case of a room temperature X-band oscillator utilizing sapphire whispering-gallery resonator