A Miniaturized 28 GHz 4×4 Butler Matrix using Shielded Ridged Half-Mode SIW

A miniaturized 4×4 Butler matrix using ridged half mode substrate integrated waveguides for operation at millimeter wave frequencies is proposed in this paper. The compact layout of the proposed design and the open side of the waveguides used presents a unique set of challenges due to cross-coupling between components in the system. Structures to reduce undesired coupling are introduced in this paper to ultimately enable the design to function at a 28 GHz 5G band. The paper summarizes the design procedure and presents the measured results. The proposed device achieves a maximum of ±30.7° progressive phase error and an average coupling imbalance of ±1.3 dB between 28.0 and 28.8 GHz in addition to achieving more than 65% miniaturization over a reference SIW based design.