Design of Broadband 9×9 Butler Matrix and its Extension for Multibeam Application

In this brief, a broadband 9×9 Butler Matrix (BM) and its extension for multibeam antenna array (MAA) application are presented. Based on the configuration of 3×3 beamforming network (BFN) comprised of three couplers and two 90° phase shifters, the topology of 9×9 BM is built, which can provide in-phase signals at output ports. And a broadband 9×9 BM is implemented to verify the design by adopting broadband components. The results indicate that the designed broadband 9×9 BM achieves equal power division and 9 uniformly distributed progressive phases (PPs) between output signals in a relative bandwidth of 40% when the 9 input ports are excited, respectively. And the fabricated 9×9 BM is applied in MAA for producing 9 beams including a boresight beam. In addition, according to the design method of 9×9 BM, the topology of the extended 27×27 BM is built and presented, which validates that an extended BM with higher order can be realized by the design method, and the extended BM can also provide in-phase signals at output ports.