Limits of a scalar reflectometer using branch-line coupler and power detector LT5581

The design of a four-port scalar reflectometer operating at center frequency 2.4 GHz is presented in this paper. The proposed reflectometer is constructed from two 10 dB branch-line couplers, which are produced in microstrip line technique. Parameters of the realized device are in good agreement with simulation results. Directivity of the two couplers is over 22 dB at the center frequency. The reflection coefficient is below −20 dB for a bandwidth of 1 GHz. Power detector Linear Technology LT5581, which has 40 dB dynamic range at frequencies from 0.8 to 2.6 GHz, is installed to measure the scalar reflection coefficient of a Device Under Test (DUT). Since both used components have their limitations, this paper discusses the process of determining the restricted accuracy of such a scalar reflectometer for applications relating to microwave amplifiers. The reflectometer was tested at a single frequency of 2.4 GHz. The final result points out that −18 dB is the reachable limit of this reflectometer and a method is proposed to predict the scalar reflection coefficient.