Broadband Measurements of $S$-Parameters With the Use of a Single 8 $\times$ 8 Butler Matrix

A novel application of an 8 × 8 Butler matrix in broadband multiport measuring systems has been presented. The proposed measuring system consists solely of a single broadband 8 × 8 Butler matrix and only one isolator allowing for measurements of all S-matrix coefficients of any two-port device. It has been shown that the properties of the applied 8 × 8 Butler matrix allow to obtain high measurement accuracy, which has been estimated with a numerical procedure for a different number of applied power detectors. The improved analytical procedure of calibration necessary for the transmission coefficient measurement has been presented. Performance of the proposed measuring system has been experimentally verified in a wide frequency range of 2-3.5 GHz, by measurements of S-parameters of seven exemplary attenuators and a narrowband bandpass filter. The measurement results are very close to the values obtained with the use of a commercial vector network analyzer.