Miniature Butler Matrix Design Using Glass-Based Thin-Film Integrated Passive Device Technology for 2.5-GHz Applications

In this paper, miniature branch-line coupler and Butler matrix designs for 2.5-GHz applications are proposed using the glass-based thin-film integrated passive device (TF-IPD) technology. The size reduction is achieved by replacing the quarter-wavelength transmission lines in a conventional branch-line coupler with the bridged-T coil. In this way, the circuit size can be largely reduced without sacrificing the operation bandwidth. The proposed miniature branch-line coupler is then applied to the design of a 4 × 4 Butler matrix centered at 2.5 GHz using the glass-based TF-IPD technology. The measured results show a bandwidth of 2.4-2.6 GHz for better than 13-dB return loss with a maximal dissipation of 4 dB, amplitude imbalance within 1.1 dB, and phase imbalance less than 13^°. Notably, the proposed Butler matrix occupies a chip area of 3.13 mm × 3.3 mm, which is only about 0.026 λ₀ × 0.027 λ₀ at 2.5 GHz.