Design and implementation of a compact planar 4 × 4 microstrip Butler matrix for wideband application

Abstract

A compact planar 4 × 4 microstrip Butler matrix is proposed in this paper. It is a wideband beam-forming network with the advantages of compact size, low cost and ease of fabrication. Three-branch line couplers with lumped-distributed elements are adopted to reduce the size, and multi-U-shaped coupled-line Schiffman phase shifters are designed to get good transmission and phase performances. The Butler matrix is fabricated and measured, and a good agreement is found between the simulated and measured results, which makes it very attractive for wideband multi-beam antenna applications.