Design of 4 x 4 and 8 x 8 Filtering Butler Matrices Utilizing Combined 90° and 180° Couplers

In this article, a novel design approach for designing 4 x 4 and 8 x 8 filtering Butler matrices is proposed. The matrices, composed of combined 90 degrees couplers and 180 degrees filtering couplers as well as phase shifters, provide incremental phase shifts and a bandpass filter performance. The detailed design process and synthesis method for the Butler matrices are presented. A three-layer symmetrical stripline structure is used to realize the Butler matrix, allowing a fully planar structure without interlayer connections. For experimental verification, two prototype 4 x 4 and 8 x 8 filtering Butler matrices, operating at the center frequency of 2.4 GHz with a bandpass response, are devised, manufactured, and tested. The test results match well with the simulation ones. Based on the measurements, array factors have been calculated, which further indicate the acceptance of the measured results.