A Simple Multiport Reflectometer using Fixed Probes and an Adjustable Attenuator

A simple microwave multiport network for the determination of complex reflection coefficients is described. It is characterized by the detection of the standing wave pattern generated by the unknown load through an adjustable attenuator, by means of a number of fixed probes. With this attenuator the maximum possible variation of the magnitude of the signals at the probes can be matched to the limited linear range of the power detectors used. To increase both measuring precision and frequency bandwidth, an enlargement of the system is easily possible by the simple insertion of additional probes. A new calibration method has therefore been developed which allows the separate determination of each set of system constants pertinent to a certain detector by means of a nonlinear least-square fitting procedure. The calibration method can also be applied to other types of multiport reflectometers. Experiments with an X-band model are dealt with.