Phase noise suppression in frequency comb generators

We propose an idea to suppress the flicker (1/f) noise in radio frequency (RF) multiplier-based frequency comb generators. Comb generators are often used for frequency multiplication in frequency synthesis. In general, comb generators apply high power to a nonlinear element (NLE) such as a step-recovery diode to generate harmonics. Flicker of phase from the NLE causes significant noise to be projected onto the higher-order harmonics of the input signal. The phase noise of the n-th harmonic increases by n² relative to the noise of the input signal; this is also true for the input-referred multiplier phase noise. A system can be constructed that compares the fundamental signal before and after it enters the comb generator. If the phase perturbations between the fundamental and any particular harmonic can be measured in real time, a feedback or feed-forward servo can be implemented to correct the phase noise that is introduced by frequency multiplication. A defective excessively noisy comb generator is used in this experiment to act as the candidate for noise correction. This allows for simplified testing of the proof of principle by measuring the corrected candidate versus a typical comb generator.