Impact of SRR and CSRR placement strategies on microstrip antenna array performance: a comprehensive numerical and experimental investigation

Abstract This work presents a comprehensive numerical and experimental investigation of metamaterial-based split-ring resonator (SRR) and complementary split-ring resonator (CSRR) unit-cell placement strategies in a 2-element microstrip antenna array operating at 10 GHz. Unlike prior studies that focus on limited configurations, this research systematically evaluates eight distinct placement configurations incorporating square- and circular-shaped SRR and CSRR structures to establish clear performance trends and design guidelines. The impact of these configurations on mutual coupling, gain, radiation efficiency, and sidelobe suppression is rigorously analyzed. The optimized circular CSRR configuration achieves a 50.72% reduction in mutual coupling compared to the reference array, along with a 5.63% gain improvement, a 6.37% improvement in radiation efficiency, and a 10.72% improvement in the sidelobe-to-mainlobe level ratio. The broader significance of this work lies in its demonstration that metamaterial placement is not merely a passive decoupling technique but an active mechanism for shaping the electromagnetic field. By establishing that CSRR-based ground-plane integration consistently outperforms SRR-based approaches across multiple performance metrics, this study provides antenna designers with a clear, evidence-based methodology for achieving simultaneous improvements in isolation, gain, and efficiency without increasing structural complexity or fabrication cost. The systematic evaluation of 160 distinct configurations yields actionable design guidelines that can be directly applied to larger arrays, different frequency bands, and emerging applications such as 5G massive MIMO, millimeter-wave systems, and compact IoT devices, where high isolation and radiation efficiency are critical for reliable system performance.