A Miniaturized Metamaterial-Based Dual-Band 4×4 Butler Matrix With Enhanced Frequency Ratio for Sub-6 GHz 5G Applications

Abstract

This paper introduces an innovative 4×4 dual-band Butler matrix (BM) characterized by compactness and an enhanced frequency ratio (K). The design employs meandered lines and an interdigital capacitor unit cell based composite right/left-handed transmission-line (CRLH-TL) metamaterial (MTM) structure. The BM integrates compact dual-band 3 dB branch-line couplers (BLC), a 0 dB crossover, and a dual-band 45 • phase shifter on a single Rogers RT5880 substrate (with ε r = 2.2 and h = 0.787 mm). Simulations and measurements results demonstrates reflection and isolation coefficients exceeding −20 dB at all ports, with a obtained insertion loss of −6±3 dB over the 0.7 GHz and 3.5 GHz frequency bands. The achieved phase differences of ±45 • , ±135 • , ±135 • , and ±45 • indicate a maximum average phase tolerance of ±4.5 • . Importantly, the BM's overall dimensions are 140 mm × 192 mm, resulting in a 78% size reduction compared to traditional BM designs. The proposed configuration is designed and simulated using CST Microwave Studio, with the agreement between simulated and measured parameters highlighting design reliability and effectiveness. Additionally, a performance evaluation comparing the proposed BM with existing circuits reveals its suitability for sub-6 GHz 5G dual-band antenna array beamforming networks (BFN) due to its compact size and improved band ratio.