A microwave phase-comparison system and its application to direction-finding

An accurate and stable method of measuring the r.f. phase difference between two microwave signals is described. The measurement is made at radio frequencies by adjusting a reference phase shifter applied to one of two signals entering a waveguide hybrid so that the two output signals are made equal in amplitude. A switching arrangement makes the system insensitive to errors caused by variations in performance of detectors and amplifiers, even when the signal amplitudes are unequal. Equipment operating in the X-band was made which continuously recorded the phase difference between the input signals with an accuracy of one degree, the resolution and stability being one order better than this. By comparing the phases of signals received by two spaced aerials, the direction of arrival of a c.w. signal from a distant source was measured. An angular resolution of one second of arc was readily obtainable, and this has been found sufficient to allow measurement of changes in direction of arrival caused by random variations in the refractive index of the atmosphere.