In this study, we present a 4-port dual-band multiple-input multiple-output (MIMO) antenna for 5G millimeter-wave (mm-wave) applications operating at 26 GHz and 38 GHz. The design features an asymmetric slot-ring resonator etched in the ground plane, which enables independent tuning of both bands while maintaining high inter-element isolation without requiring decoupling networks or parasitic structures. Fabricated on Rogers RT5880LZ ( \({\in }_{r}\) = 2, tan δ = 0.0021), the antenna achieves wide impedance bandwidths of 24.1–28.5 GHz and 35.1–40.3 GHz. Measured gains reach 5.8 dBi and 6.4 dBi with efficiencies of 96.5% and 88.5%, respectively. Diversity and MIMO performance are validated through key metrics, including isolation greater than 20 dB, an envelope correlation coefficient below 10⁻5, diversity gain of 10 dB, channel capacity loss under 0.3 bits/s/Hz, and mean effective gain within −3 dB to −12 dB. In addition, the total active reflection coefficient (TARC) remains consistently below −10 dB across varying phase excitations, confirming efficient power transmission and minimal mutual coupling. The comparative analysis with recent state-of-the-art antennas shows that the proposed design achieves competitive gain and superior efficiency while eliminating the complexity of decoupling or gain-enhancement techniques. These results demonstrate the antenna’s suitability for reliable high-speed mm-wave 5G MIMO communication, particularly in space-constrained indoor and small-cell environments, with strong potential for extension to outdoor networks.
