Design of Modified Butler Matrix Based on N-Way Directional Coupler and Its Multibeam Application

In this article, a new approach to designing a modified N2 × N2 Butler matrix (BM) based on an N-way directional coupler (NWDC) is presented. First, by introducing phase shifters and ingeniously arranging the input and output ports, the topologies of 9 × 9 BM based on a three-way directional coupler (3WDC) and 16 × 16 BM based on a four-way directional coupler (4WDC) are built. Next, according to the design method of 9 × 9 BM and 16 × 16 BM, the topology design of modified N2 × N2 BM based on NWDC is developed. Considering whether there are progressive phase differences (PPDs) of 0° at output ports, the two cases in which N is odd and even are discussed. Finally, in order to verify the design method, a prototype of microstrip 9 × 9 BM working at 5.5 GHz is designed, fabricated, and measured. The results show that the designed microstrip 9 × 9 BM achieves equal power division and nine different PPDs among the output signals when the nine input ports are excited, respectively, which meets design expectations. And it is used as a beamforming network (BFN) for a multibeam antenna array (MAA) to generate nine radiation beams. And then, the design method of modified N2 × N2 BM is validated by the implementation of microstrip 9 × 9 BM. And the design method of the modified N2 × N2 BM provides a novel approach for BFN technology when massive input and output ports are required.