Slotted ground plane technique for mutual coupling reduction of closely MIMO of PIFA elements

This work presents the design of a compact two-element semicircular PIFA MIMO antenna employing a slotted ground plane to reduce mutual coupling. The concept is to introduce simple rectangular slots at the centre of the ground plane, which markedly improve isolation while keeping the antenna footprint compact. Simulation results show a strong reduction in coupling, with S21 enhanced from -19.46 dB to -40.71 dB at 5.75 GHz, together with a wider impedance bandwidth that supports modern wireless applications. Fabricated prototypes validated the design, achieving a measured isolation of -35.4 dB. Key diversity metrics were also examined, including Envelope Correlation Coefficient (ECC), Diversity Gain (DG), Channel Capacity Loss (CCL), Mean Effective Gain (MEG), and Total Active Reflection Coefficient (TARC). The results confirm excellent diversity performance. Overall, the proposed structure offers a practical and low-cost solution for compact devices requiring improved MIMO performance in 5G, Wi-Fi, and IoT systems.