Novel butler matrix using CPW multilayer technology

In this paper, a novel 4 times 4 two-layer Butler matrix based on a broad-band two-layer slot-coupled directional coupler is presented and implemented at 5.8 GHz using coplanar waveguide technology. With the slot-coupled directional coupler, the proposed matrix was designed without using any crossovers as used in conventional Butler matrices, which leads to significant size reduction and loss minimization. To examine the performance of the proposed matrix, experimental prototypes of the multilayer directional coupler and the Butler matrix were fabricated and measured. Furthermore, a four-antenna array was also designed and fabricated at 5.8 GHz and then connected to the matrix to form a beamforming antenna system. As a result, four orthogonal beams at -45deg, -15deg, 15deg, and 45deg are produced. Measured results on the entire system agree well with the theoretical predictions, validating the proposed design