Phase Stabilization of Microwave Oscillators

A circuit has been developed with which microwave oscillators may be phase-locked to weak but stable reference signals. The circuit was operated with S-band oscillators (707B klystron; 2C37 triode oscillator) and a 2K50 K-band klystron. It is possible to lock a microwave oscillator directly or through a cascade of such circuits to a quartz-stabilized oscillator. The statistical theory of random noise is used to obtain an analysis of the stabilizing effect of the circuit, and the power spectrum of the stabilized microwave source is calculated. The scheme can also be applied in divider operation. Modifications are discussed. A modified circuit that uses carrier-suppressed modulation of the reference signal has also been realized. In another circuit, the oscillator frequency is converted by means of a stable reference, and compared with a second reference that can be of low frequency and tunable. These latter circuits allow elimination of the excess noise introduced by crystal diodes. In the original straight dc circuit this noise cannot be eliminated, but calculation shows that its influence on the output power spectrum is very small.