A low-cost millimeter-wave collinear slot phased array enabled by ridge-bent RSIW with high inter-element isolation

This paper presents a low-cost, high-gain 1 × 4 collinear slot phased array for 5G millimeter-wave (mmWave) applications, which is realized on a two-layer standard printed circuit board. The design specifically addresses two key challenges in mmWave phased array design, which are mitigating the strong mutual coupling that limits wide-angle scanning performance and enabling the low cross-polarization radiation structure. A key innovation is the use of a periodically bent ridge within a ridge substrate integrated waveguide to efficiently excite a centerline collinear slot configuration, which minimizes cross-polarization. Furthermore, a compact via-based choke structure is introduced to suppress mutual coupling and thus achieve high inter-element isolation. The fabricated prototype exhibits an impedance bandwidth of 10.7% (26.5–29.5 GHz). The measured results show a peak gain of 14.5 dBi, port isolation better than 19 dB, and a stable 3-dB scanning range of ±50°. These results validate the proposed design as a compelling low-cost solution that achieves an excellent balance of high gain, wide-angle scanning, and high isolation.