Novel interferometric frequency discriminators for low noise microwave applications

New configurations of interferometric frequency discriminators (FD) for frequency stabilization of microwave oscillators are examined. The new FDs are arranged in single directional (SD) (patented), bidirectional (BD) (patent pending), and dual reflection (DR) (patent pending) configurations. In the SD configuration, the signals reflected off and transmitted through the resonator separately pass through different arms of the interferometer. In the BD configuration, microwaves pass in both directions through each arm of the interferometer. In the DR configuration, microwaves are reflected from the resonator as well as the compensating arm. The FD sensitivity is compared with that for the conventional interferometric FD and found to be 6 dB greater in the BD configuration. Because no circulator is required within the interferometer in either the BD or the DR FD, the discriminator's phase noise floor is not limited by the circulator contribution.