A Novel MIMO Antenna with Compact Structure for 5G Smartphone Applications

A high isolation 8 × 8 multiple-input–multiple-output (MIMO) antenna system is proposed for 5G smartphones with a metal rim. The MIMO antenna system consisting of four identical arranged symmetrically dual-antenna elements. Each dual-antenna element comprises a two-port-fed loop antenna and a single-port-fed T-shaped monopole antenna. The loop antenna is ingeniously designed in an inverted "C" shape to minimize its length and optimize space utilization. To improve the impedance matching of the loop antenna, two protruding branches are employed on the loop antenna. To broaden the bandwidth of the loop antenna, an inductor is added to one end of the differential microstrip line. The two ports of the loop antenna are excited with differential signals for achieving high isolation. The T-shaped monopole antenna is positioned at the center of the loop antenna, making the overall dual-antenna structure more compact. Simulation results show that the dual-antenna element exhibits a −6dB impedance bandwidth ranging from 2.95 to 4.27GHz, and a 15dB isolation bandwidth between 3.3 and 3.8GHz. Subsequently, four such dual-antenna elements are arranged to form an 8 × 8 MIMO antenna system. This configuration achieved a −6dB impedance bandwidth of 3.3–3.8GHz, isolation exceeding 14.5dB, and an envelope correlation coefficient (ECC) below 0.15.