Strongly nonlinear feedback technique for significant phase noise suppression at microwave harmonic oscillators

Calculations are presented to study the phase noise suppression effects of an additionally introduced highly nonlinear feedback loop in microwave harmonic oscillators. Calculations are done for determining the optimal structure and parameter set of nonlinearly feedbacked harmonic oscillators, with respect to the effects of the nonlinear properties on the behavior of the phase noise characteristics. Using the calculated analytical form 6dB of phase noise suppression was achieved. Experiments have been also performed on a practical setup, specifically on an opto-electronic oscillator structure operating with high harmonic levels. Measurement and simulation results for confirming our theoretical principles are also reported.