Mutual Coupling Suppression Between Two Closely Placed Patch Antennas Using Higher-Order Modes

This article presents a novel method for decoupling two patch antennas. Instead of using the TM $_{\mathbf {10}}$ mode of a conventional patch, TM $_{\mathbf {20}}$ mode is utilized as the operation mode of the antenna. By loading stubs at the radiating edge of the patch, the resonance frequency of the TM $_{\mathbf {20}}$ mode is moved down to the same band as the original TM $_{\mathbf {10}}$ mode. Then, the mutual coupling between two such patch antennas is suppressed simply by physical placement, even when they are placed extremely close to each other. Without using any extra decoupling elements, isolation is improved by up to 20 dB using this method. Furthermore, this method can also be applied to multielement multi-input -multi-output (MIMO) array and dual-antenna system with different operating bands. The proposed method is verified with three different application scenarios, including a two-element MIMO array, a two-antenna system with adjacent operating bands, and a four-element MIMO array. Reasonable agreements between simulated and measured results can be observed, showing the advantages of simple structure, low cost, high isolation, and good radiation performance.