Mutual Coupling-Aware Hybrid Beamforming for Densely Packed MIMO Metasurface

The mutual coupling (MC) effect refers to the phenomenon where the voltage on one antenna element induces excitation currents on nearby antenna elements. This paper initially derives precise MC matrices grounded in meticulous circuit and antenna theories, unveiling the asymmetry of MC effects between the transmitter (Tx) and receiver (Rx). This asymmetry arises from the fact that the transmitted signal is the voltage on the antenna elements, whereas the received signal represents the voltage input to the low-noise amplifiers (LNAs). Upon this approach, an MC-aware hybrid beamforming methodology is introduced to mitigate distortions in radiation patterns precipitated by MC effects. Furthermore, we undertake comprehensive performance analysis across various antenna topologies, including rectangular, hexagonal, circular, and concentric circular configurations. Simulation results substantiate the necessity for addressing MC effects and demonstrate the effectiveness of our proposed MC-aware hybrid beamforming methodology. Moreover, these results indicate that MC effects can enhance the capacity under certain antenna separations and topologies, highlighting that MC effects are not merely detrimental but potentially beneficial in densely-packed MIMO.