A Microwave Meacham Bridge Oscillator

A microwave analog of the low-frequency Meacham bridge oscillator, long known for its exceptional stability, is described. The incorporation of the resonant element of a feedback oscillator into an appropriate bridge circuit effectively multiplies the Q of the element and consequently the stability of the oscillator. The performance and design of an X-band oscillator consisting of a traveling-wave tube amplifier, a cavity, a microwave Wheatstone bridge, and a bolometer element are described, and experimental results are compared with theory. The application of the principle to ultrastable systems utilizing very high-Q molecular resonators and low-noise amplifiers is also discussed.