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

Abstract

A new topology of modified Butler matrix (BM) based on three-way directional coupler (TWDC) is proposed in this brief. The two TWDCs are regarded as two submatrices, by alternately arranging the output ports of the two submatrices and introducing a front network consisting of 3dB/90∘ hybrid couplers, 3dB power divider and phase shifters, a topology of modified five-input six-output (5×6) BM is constructed. In order to verify the design method, a prototype of microstrip 5×6 BM operating at 5.5 GHz is implemented and it is used as a beamforming network (BFN) for multibeam antenna array (MAA) to generate five radiation beams including a boresight beam. The measured and simulated results coincide well with each other. And according to the design method, a topology of extended 9×12 BM is designed based on the 5×6 BMs, which validates the capacity of building a modified BM with a higher number of the input and output ports.