Calibration and performance of an automatic microstrip six-port reflectometer

A six-port reflectometer based on three coupled equal-mode-impedance microstrip lines of improved design was automated. An efficient calibration algorithm which allows the explicit determination of the calibration constants was used. The observed long-term stability of these constants suggested their determination and storage at all frequencies of interest. This drastically reduced the measurement time. Interpolation between the selected calibration frequencies is discussed, and the corresponding performance of the reflectometer is illustrated. The six-port results based on linear interpolation are found to be generally better and faster to obtain than those based on curve fitting using a cubic spline. The overall accuracy and the frequency range of operation can be increased by using a controllable generator with a higher output power