Ultrabroadband 4 × 4 Butler matrix with the use of multisection coupled-line directional couplers and phase shifters

The design of an ultrabroadband 4 × 4 Butler matrix has been presented. The designed Butler matrix utilizes the previously developed 5-section coupled-line symmetrical 3-dB/90° directional coupler compensated with the use of several tuning capacitances as a basic element. The broadband 45° phase shifters have been realized with the use of a tandem connection of two the same couplers and two 2-section Schiffman C-sections. The influence of the coupler´s compensation on the differential phase characteristics of the 4 × 4 Butler matrix is presented, and it is shown that the applied compensation deteriorates differential phase characteristics of the designed Butler matrix. To overcome this problem a method for improving these characteristics is proposed in which an appropriate change to the middle network significantly improves differential phase characteristics of the entire Butler matrix. The measurement results of the developed ultrabroadband 4 × 4 Butler matrix operating in the frequency range 1.8-12 GHz are shown.