A Miniaturized Metamaterial-Based Dual-Band 44 Butler Matrix With Enhanced Frequency Ratio for Sub-6 GHz 5G Applications

This paper introduces an innovative 4x4 dual-band Butler matrix (BM) characterized by compactness and an enhanced frequency ratio (K). The design employs meandered lines and an interdigital capacitor (IDC) 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 dual-band +/- 45 degrees phase shifters on a single Rogers RT5880 substrate having relative permittivity epsilon(r) of 2.2 and thickness hof 0.787 mm. Simulations and measurement results demonstrate reflection and isolation coefficients exceeding-20 dB at all ports, with obtained insertion loss of-6 +/- 3 dB over the 0.7 GHz and 3.5 GHz frequency bands. The achieved output phase differences of +/- 45(degrees),+/- 135 degrees,+/- 135(degrees), and +/- 45(degrees)at the designed frequencies indicate a maximum average phase tolerance of +/- 4.5 degrees concerning the ideal values. Importantly, the BM's overall dimensions are 143 mmx186 mm, resulting in an impressive 78%size reduction compared to traditional T-shaped BM designs. The proposed configuration is designed and simulated using CST Microwave Studio, with the agreement between simulated and measured parameter shigh lighting 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