A six-port reflectometer is used to measure the reflection coeficient of the unknown devices. it can measure the magniyude and phase with repeatable measurements and some standards. A six-port reflectometer constructed from a 0°/180° microstrip-ring coupler is presented. Three different constructions are given with their optimum positions of the q-point. One of these constructions is realized on an RT/Duroid 5880 at 3 GHz. Good agreement with the measurements obtained using a vector network analyzer is found.