Miniaturized 4 × 4 Butler Matrix and Tunable Phase Shifter Using Ridged Half-Mode Substrate Integrated Waveguide

Abstract

A novel 4×4 Butler matrix fabricated on ridged half-mode substrate integrated waveguide (RHMSIW) technology is designed and realized. The integration of the proposed Butler matrix with tunable phase shifters fabricated using the same technology is also demonstrated to achieve semi-continuous beam steering for fifth-generation (5G) applications. This article discusses the design considerations of the various ridged half-mode subcomponents of the Butler matrix in detail and presents two novel interconnects, namely 90° waveguide bends and a half-mode open-edge-to-open-edge transition. This article shows that the capacitive ridge on the open edge of one waveguide can be directly connected to the open edge on another with little compromise on the performance over a reference line of the same length. The simulated and measured results of each Butler matrix component are also presented and are all in good agreement. The proposed Butler matrix has a 5% operational bandwidth centered at 3.51 GHz with less than ±22° error in the progressive differential phase shift and less than ±1.2-dB coupling imbalance. Finally, it is shown that the proposed Butler matrix achieves over 70% board area miniaturization in comparison to a similar design fabricated on half-mode substrate integrated waveguide technology.