Broadband Decoupling for Antenna Arrays Using Multiple Decoupling Nulls

In order to mitigate the mutual coupling problem in antenna arrays, a new concept of broadband decoupling using multiple decoupling nulls is proposed in this article. First, the principle of decoupling between antennas is explained through the field analysis. It demonstrates that the essence of the decoupling of loaded metal structures is that the field is transferred between the antenna and the metal structure, with the metal structure acting as a resonator. The isolation of the antenna array generates a decoupling null when the resonator resonates with the excited antenna. Moreover, these resonators can independently control the corresponding decoupling nulls on the isolation. Therefore, broadband decoupling in the antenna array can be achieved by introducing multiple resonators within the operating frequency band of the antenna. The design method of the decoupling structure in the antenna array is also elucidated in this article, which provides significant computational resource savings. Finally, three examples are designed and tested to verify the proposed method. The simulation and test results demonstrate its effectiveness and its high potential for application to fifth-generation (5G) multiple-input–multiple-output (MIMO) antenna arrays deployed in base stations and wireless routers.