A compact quad-port multiband MIMO antenna with CSRR-engineered ground for high isolation and low correlation in radar, IoT, and S and C-band applications

This manuscript presents a compact quad-port MIMO antenna array featuring an innovative multiband structure for S-and C-band applications. The proposed design achieves high compactness and cost-effectiveness by integrating Complementary Split-Ring Resonator (CSRR) structures on the ground plane of an FR-4 substrate, effectively suppressing unwanted surface-current flow between radiating elements and significantly reducing inter-element mutual coupling. An orthogonal arrangement of antenna elements, combined with λ/4 spacing, ensures enhanced port-to-port isolation. Experimental results reveal peak isolation levels of 23, 31, and 38 dB at 2.7, 6.5, and 7.9 GHz, respectively. The design also exhibits excellent diversity performance, with an Envelope Correlation Coefficient (ECC) of 0.0015, Diversity Gain (DG) of 9.99 dB, and Channel Capacity Loss (CCL) below 0.38 bits/s/Hz. With its strong diversity characteristics and multiband operation, the proposed MIMO antenna is well-suited for 5G, WLAN, and Internet of Things (IoT) applications.