A bi-directional interferometric frequency discriminator for low noise microwave applications

New interferometric frequency discriminators (FD) for frequency stabilization of microwave oscillators are examined. Alternative topologies to the standard interferometric readout are presented. The new readouts are arranged in a bi-directional configuration. In this configuration, microwaves pass in both directions through each arm of the interferometer. The coupling to the resonator is adjusted to maximize the frequency discriminator sensitivity. The sensitivity is compared with that for the conventional interferometric FD and found to be 6 dB greater. No circulator is required within the interferometer, thus eliminating its phase noise contribution.