Broadband Mutual Coupling Reduction of Multiple Electrical-Current Nulls for Quad-Port Shared-Radiator Slot Antenna Using Characteristic Mode Analysis

A novel quad-port shared-radiator slot antenna with broadband decoupling characteristics is proposed. The proposed slot antenna (PSA) has multiple electrical-current nulls for decoupling, formed by the cancellation of contrary characteristic modes (CMs) currents. The reduction of broadband mutual coupling can be achieved by changing the slot width at the four edges and corners of the original slot antenna (OSA). The −10 dB operating bandwidth is expanded from 28.6% on OSA to 69.7% on PSA. The isolations are only 7–9 dB on OSA but improved to better than 17 dB on PSA, even reaching a maximum of 25 dB. The total efficiency of PSA has a significant improvement compared to the OSA, and the envelope correlation coefficients of PSA are close to zero, far below the OSA. The good coincidence between the simulated and measured results confirms the correctness of the proposed method.