A Compact 8×8 Dual-Band MIMO Antenna Array with Hybrid Decoupling for Sub-6 GHz and mmWave 5G Smartphone Terminals

Abstract

A compact dual-band Multiple-Input Multiple-Output (MIMO) antenna array comprising eight elements is reported for deployment in 5G handheld terminals. The array simultaneously addresses the n78 band (3.4-3.8 GHz) and the n258 millimeter-wave band (24.5–27.5 GHz), realizing both operating ranges within a single-layer substrate whose overall dimensions are compatible with contemporary smartphone form factors. Each radiating element combines a T-shaped primary branch with two asymmetric C-shaped resonators, a topology that produces independent resonances at the two target bands. Interelement isolation is enhanced through the joint action of defected ground structures (DGS) and a passive neutralization line (NL), which together raise the minimum isolation from approximately 11 dB to 18 dB across the full bandwidth. Cross-validation by CST Microwave Studio and ANSYS HFSS confirms realized gains of 5.7 dBi at 3.6 GHz and 6.4 dBi at 26 GHz, total radiation efficiency in the 85–94 % range, and envelope correlation coefficients (ECC) below 0.04—all confirming suitability for spatial-multiplexing operation in next-generation mobile devices.