Broadband 4 × 4 butler matrix for K- and Ka- bands

Design of microstrip 4 × 4 Butler matrix for millimeter-wave (mm-Wave), K and Ka-bands beam-steering applications, is presented in this paper. The proposed design utilizes multilayer printed circuit board (PCB) technology. The proposed 4 × 4 Butler matrix configuration consists of four hybrid couplers and two phase shifters without using crossovers. The design is based on coupled transmission lines that use ringshaped broadside-coupled patches and an elliptical-shaped slot etched in a common ground layer. The proposed design shows good return loss and acceptable insertion loss with minimum transmission phase imbalance across the frequency band of interest.