Compact MIMO Patch Antenna Design With an Embedded LC Decoupler, Characterized by Tunable Decoupled-Mode

This letter introduces an innovative solution aimed at mitigating mutual coupling in closely spaced multiple-input--multiple-output patch antennas through the deployment of an embedded LC decoupler. Utilizing characteristic mode analysis, it was discovered that the mutual coupling between closely spaced patch elements is significantly influenced by what are termed coupled mode and decoupled mode. A key finding is that mutual coupling can be substantially reduced when the decoupled mode is aligned around the operating frequency, which can be done by integrating tunable inductance and capacitance within the proposed LC decoupler. To verify the feasibility of the decoupling scheme, a set of decoupled two-element patch antennas incorporating a lumped inductor and capacitor were designed, simulated, and experimentally tested. The experimental outcomes demonstrate a significant enhancement in isolation, improving from 4 dB to more than 16 dB across the entire matched bandwidth ranging from 3.4 to 3.6 GHz.