Reducing Mutual Coupling in 2x2 MIMO Circularly Polarized Patch Antenna Array Using Reflecting Polarization Conversion Metasurface

The 2x2 MIMO circularly polarized (CP) patch antenna is presented with an effective technique for reducing mutual coupling. The Reflecting Polarization Conversion Metasurface (RPCM), featuring symmetrically X-shaped patches, enables this enhancement by generating an additional neutralization wave strategically placed over the CP array. The proposed decoupling structure employs circular-to-circular polarization conversion to counteract this effect. Circular polarization involves the rotation of the electric field, and the decoupling structure utilizes this characteristic to isolate fields from each antenna, mitigating interference and improving the array's overall performance. The 2×2 MIMO CP patches are placed at a narrow separation distance of 4.05mm, leading to a notable reduction in mutual coupling at 3.5 GHz. Sii consistently remains below -25 dB, and overall mutual coupling within the 2.28-4.02 GHz band remains higher than -26 dB. The evaluation of key diversity parameters like ECC and DG underscores the potential of this antenna array for 5G applications.