Compact Four-Port MIMO Antenna Module With Decoupling Components for 5G Terminal Devices

This study investigated the decoupling mechanism of capacitors in multiple-input–multiple-output (MIMO) antenna designs based on characteristic mode analysis (CMA). First, a two-port single-loop antenna, where shunt capacitor elements were used to obtain high port-to-port isolation properties, was analyzed. CMA revealed that the decoupling capacitors’ mechanism lies in the modal superposition of the original radiation mode (Mode-2) and the manipulated high-order mode (Mode-3) with anti-phase current distributions. Accordingly, a compact four-port MIMO antenna module based on decoupling components (inductors and capacitors) was designed as the first of its kind. Both simulations and measurements were conducted to verify the feasibility of the proposed MIMO antenna module.