Application of the 4 × 4 Butler Matrix Consisting of Tapered-Coupled-Line Directional Couplers in an Ultra-Broadband Multiport Reflectometer

A novel application of a 4 × 4 Butler matrix consisting of 0/180 ° tapered-coupled-line directional couplers in an ultra-broadband multiport reflectometer is presented. The performed analysis reveals, that such a Butler matrix provide an advantageous inner power distribution, which allows to obtain a good accuracy of complex reflection coefficient measurement. Due to the higher number of available ports in comparison to the classic solutions, the proposed system allows for a great variety of configurations, leading to increase of the measurement accuracy. The proposed multiport reflectometer has been verified experimentally in a frequency range 1 – 8 GHz by measurements of several reflective elements. The results show a good agreement with the ones obtained with the use of a commercial vector network analyzer