A Technique for Measuring Phase at Millimeter Wavelengths

A technique for measuring the phase of millimeter signals in free space is described that uses a reference signal of varying phase. The phase of the reference signal is measured independently and subtracted from the total phase measured to determine the desired phase. The use of a varying reference phase is necessary because flexible or movable waveguide whose phase characteristics can readily be measured are not available at millimeter wavelengths. The theory of the technique described is based upon the interference pattern of slowly varying electric fields.