Theoretical Limits and Accuracy Improvement of Reflection-Coefficient Measurements in Six-Port Reflectometers

A complete analysis of the influence of six-port reflectometer parameters on the measurement accuracy is presented. A theoretical limit of the reflection-coefficient measurement has been investigated and is derived analytically. Moreover, for a set of six-ports reported in the literature, the numerical analysis of magnitude and phase measurement errors in a wide range of reflection-coefficient magnitude is presented. Furthermore, the modified six-port reflectometer utilizing a 4 × 4 Butler matrix and featuring scalable circle center distribution is proposed, and its advantage is discussed. The impact of power detectors uncertainty on an arbitrary six-port calibration procedure is presented. The performance of the proposed reflectometer has been verified in a wide frequency range of 2-3 GHz by measurements of a reflection coefficient having small magnitude. The obtained results are in agreement with the theoretical predictions, confirming the usefulness of the presented analysis.