A New Technique for the Measurement of Microwave Standing-Wave Ratios

A new microwave standing-wave-ratio (or reflection coefficient) measurement technique, apparently suitable for standards and other high precision work, is described. The technique requires that the phase angle of the unknown reflection coefficient be subjected to arbitrary, known variations-as is possible with a sliding load, for example. Accurate measurement of suitable. sliding loads furnishes standards, and with the aid of comparison techniques, enables indirect measurement of arbitrary unknowns. Generator and detector are connected to two arms of a three-arm waveguide junction. Tuning elements in the junction are (desirably) adjusted for small reflection looking into the third arm, to which the unknown connects. Observation of the detector response vs variation of phase of the unknown yields a curve, similar to a standing-wave pattern, from which the unknown is determinable by procedures that are given. The technique has the advantages of 1) being amenable to rigorous theoretical analysis, 2) enabling the attainment of heavy coupling to the detector without simultaneous severe distortion of the response pattern, and 3) being, in a sense explained in the text, fundamentally simpler than the conventional slotted-line technique.