Mutual Coupling Mitigation Through Parasitic Structure in a Dual-Band Millimeter-Wave Flexible MIMO Antenna

This paper introduces a dual-band millimeter-wave flexible multi-input multi-output (MIMO) antenna for wearable applications, comprising four identical elements in a cross configuration on a flexible Rogers RT5880 substrate. Each element includes a rectangular microstrip patch with an inverted U-shaped slot, facilitating dual-band operation at 28 GHz and 33 GHz. A parasitic structure was added to the MIMO design to reduce mutual coupling. Results indicate that the antenna achieves a bandwidth of 0.28 GHz (27.98-28.26 GHz) in the lower band and 1.01 GHz (32.24-33.25 GHz) in the upper band, with gains of 6.10 dBi at 28 GHz and 9.05 dBi at 33 GHz, and efficiencies of 0.77 and 0.88, respectively. The parasitic structure reduces the mutual coupling to below −20 dB across both bands. The antenna performed stably under extreme bending conditions. The low envelope correlation coefficient (< 0.05) and high diversity gain (approaching 10 dB) confirmed the effectiveness of MIMO communication. This dual-band MIMO antenna offers a promising solution for wearable applications with high isolation and stable performance.