High-Isolation and Compact 4 × 4 Butler Matrix Feed Network for C-Band Switched-Beam Arrays

This article presents the design, simulation, fabrication, and measurement of a compact 4 × 4 Butler matrix beamforming network for C-band applications. The proposed feed network is based on a standard topology of branch-line couplers and crossovers, realized on a single-layer Rogers RT5880 substrate to ensure low loss and high integration. The core novelty of this work lies in successfully breaking the traditional trade-off between miniaturization and electrical performance in planar networks. Full-wave simulations in CST Studio Suite predict a return loss better than 28 dB at the center frequency of 4.0 GHz and the generation of four orthogonal beams steered to ±14° and ±42°. A prototype was fabricated and characterized using a 4-port vector network analyzer. Measurement results confirm the simulated performance, showing a −15 dB impedance bandwidth of approximately 470 MHz and a remarkable port isolation of better than 20.2 dB (often exceeding 30 dB within the band). By simultaneously achieving these state-of-the-art metrics within a highly compact footprint of 0.41λ0 × 0.33λ0 on a purely single-layer substrate, the design eliminates the need for complex, costly multi-layer or substrate integrated waveguide technologies. The combination of these advanced features makes the proposed Butler matrix a highly competitive, cost-effective, and volume-manufacturable beamforming solution for switchedbeam antenna systems in satellite communication, radar, and next-generation wireless networks.