A system for automatic suppression of signals picked up by a sensitive receiver from a nearby oscillator

In a great variety of applications, a microwave signal is used to remotely probe a physical object, the modulation of the reflected signal being analysed by a receiver placed close to the oscillator. Limited isolation between the oscillator and receiver may cause serious problems. This paper describes a method to cancel the leakage signal by injecting a compensating signal derived from the oscillator, which is automatically adjusted. Adjustment is performed for the in-phase and quadrature components separately by a pair of independent feedback loops, using a sample of the oscillator signal as a reference. The theory, a number of salient points in the practical realisation, and the performance obtained are discussed.