A novel four-port MIMO antenna with integrated parasitic elements for 5G NR n78 band applications

• A compact I-shaped 2 × 2 MIMO antenna is proposed for the 5G NR n78 band (3.04–3.80,GHz), offering a space-efficient design. • Innovative parasitic structures, including annular rings, L-shaped stubs, and a hexagonal ring, are employed to enhance isolation without requiring external decoupling networks. • The antenna achieves superior performance with inter-port isolation better than −18dB, resonance at 3.43,GHz, return loss of 24 dB, peak gain of 3.71,dBi, and 93 % radiation efficiency. • Comprehensive MIMO evaluation demonstrates excellent diversity characteristics: DG >9.995dB, ECC 0.010, TARC <-10dB, CCL 0.34,bits/s/Hz, and MEG below −3dB. • Strong agreement between simulated and measured results validates the antenna as a reliable, compact, and high-isolation solution for sub-6,GHz 5G MIMO applications. This paper explores a compact I-shaped 2 × 2 orthogonal multiple-input multiple-output (MIMO) antenna optimized for the 5G New Radio (NR) n78 band (3.04–3.80 GHz). The antenna is implemented on a FR4 substrate ( ε r = 4.4 , tan δ = 0.02 ) with compact dimensions of 0.55 λ × 0.55 λ × 0.018 λ . The design specifically addresses the challenge of achieving high inter-element isolation and minimizing mutual coupling within a compact MIMO configuration. To achieve this without external decoupling networks, parasitic structures including annular rings and L-shaped stubs on the ground plane, along with a hexagonal ring on the top plane are employed to effectively suppress mutual coupling and enhance isolation across the operating band. These elements effectively suppress mutual coupling, resulting in an inter-port isolation over and above − 18 dB across the entire operating band. The antenna resonates at 3.43 GHz with a reflection coefficient of − 24 dB, a peak gain of 3.71 dBi, and a radiation efficiency of 93 %, exhibiting stable radiation characteristics across the entire band. Comprehensive MIMO performance analysis confirms robust spatial diversity, with a diversity gain (DG) above 9.995 dB, an envelope correlation coefficient (ECC) below 0.010, a total active reflection coefficient (TARC) below − 10 dB, and a channel capacity loss (CCL) under 0.34 bits/s/Hz. Additionally, the mean effective gain (MEG) is maintained below − 3 dB. Simulated and measured results demonstrate excellent agreement, validating the proposed antenna as a strong candidate for compact, high-isolation 5G MIMO systems operating in the sub-6 GHz spectrum.