Six-Port Reflectometer Using Edge-Coupled Microstrip Couplers

Abstract

This letter presents the design of a six-port reflectometer (SPR), which makes use of edge-coupled, coupled-line microstrip couplers. By designing the couplers to have coupling slightly larger than the isolation, good Q-point placement on the complex Gamma-plane is obtained. The SPR Q-points are obtained by a proposed two-step process using two standard terminations-a matched load and an open circuit load. The designed SPR has been tested using various loads and the computed load reflection coefficients have been compared against those of a standard commercial Vector Network Analyzer. The raw dynamic range is 21-39 dB in the frequency range from 1.6 to 2.2 GHz and the uncalibrated load reflection coefficients follow the expected values closely, with average phase error spread of only about 2.7%-7.7%. The designed SPR is fabricated on FR4 substrate. It achieves a reduction in size due to lesser number of components and is ideal for narrowband and low cost use.