Novel Filtering 180° Hybrid Coupler and Its Application to 2 x 4 Filtering Butler Matrix

In this paper, a novel filtering 180° hybrid coupler is proposed and used to design a 2 x 4 filtering Butler matrix. The filtering 180° hybrid coupler can provide power division and phase shift together with a second-order bandpass transfer function, and is based only on coupled resonators. The 2 x 4 filtering Butler matrix is easily realized by utilizing several hybrid couplers. The analytical synthesis procedures for the hybrid coupler and Butler matrix are presented in this paper. Finally, broadside and end-fire arrays are realized by using the Butler matrix. To illustrate the concept experimentally, a filtering 180° microstrip hybrid coupler and a 2 x 4 filtering microstrip Butler matrix are designed, fabricated, and measured. Simulation and measured results are found to be in good agreement with each other.