An Octave-Band Microwave Phase Comparator

A simple apparatus for measuring the relative phase difference between two signals of identical frequency anywhere within an octave band at microwave frequencies is described. Instantaneous measurements can be performed upon carriers that are periodically 100 percent modulated by narrow pulses since no mechanical contrivances are required. Phase information is converted by detectors into four channels of amplitude information, and these are then combined to yield a relative phase measurement that is unambiguous over a 360° range. In principle, the method is independent of relative signal amplitudes, but in practice it is limited by the useful range of the detectors. Two power dividers, a 90° coupler and a 180° hybrid, four detectors, and an oscilloscope comprise the necessary basic hardware. A derivation of the basic principles of the phase comparator is presented, together with a discussion of calibration test results, for every 10° in phase at each of nine separate frequencies over an octave band. Finally, a processing device for generating a digital indication of relative phase angle is also described.