How does mutual coupling affect antenna array performance?

Mutual coupling occurs when nearby antenna elements induce currents in each other, affecting array performance. Effects: Changes element input impedance (active impedance depends on excitation of all elements). Alters individual element patterns, affecting array factor. Can cause scan blindness at certain angles where surface waves are excited. Reduces efficiency due to power coupled to adjacent elements. Modifies array radiation pattern and gain. Analysis/mitigation: Full-wave simulation (MoM, FEM) for accurate modeling. Coupling matrix characterization enables compensation in signal processing. Element spacing >λ/2 reduces coupling but creates grating lobes. Decoupling networks can improve isolation. EBG (electromagnetic bandgap) structures suppress surface waves. Proper calibration accounts for coupling in beamforming weights. Modern massive MIMO systems must include coupling in channel estimation and precoding.