A Compact 4×4 Butler Matrix for UWB applications

In this paper, a compact and low cost 4 × 4 Butler Matrix for ultra-wideband applications is presented. Given the extent of the considered frequency band (3.1-10.6 GHz), a multi-layer topology with rectangular slots has been adopted. These matrices avoid using any crossing lines or crossovers, making the design easier and more compact. A spoon-shaped patch for vertical transitions has been proposed to design the 4×4 Butler matrix and good performances have been obtained numerically. A prototype has been fabricated but could not be measured because of the unavailability of 50 Ω loads. Furthermore, a four element UWB antenna array has been connected to the matrix to form a switched-beam antenna system. As a result, four orthogonal beams were obtained, which validates the proposed approach.