A Wideband Self‐Decoupled Microstrip Patch Antenna Array Using Characteristic Modes of Ground Plane

The reduction of mutual coupling between antenna elements has been a research hotspot in the design of multi‐input multi‐output (MIMO) systems. In this paper, a review of the existing theory of characteristic mode (TCM) based decoupling methods is introduced, and they are summarized and divided into two categories according to mechanisms. The first category consists of the use of the modal properties of the radiator whereas the second one is based on the ground plane to enhance isolation. Moreover, a wideband self‐decoupling method is implemented for the MIMO microstrip patch antenna (MPA) array using the characteristic modes (CMs) of the ground plane. It is found that, by adjusting the dimension of the ground plane, their CMs along with two or three null‐field regions, can be excited by the active MPA. When the feeding position of the adjacent passive MPA is arranged in the null‐field region, the energy cannot be coupled with the receiving port, thereby achieving a good isolation level. For verification, a prototype of the proposed MIMO MPA array has been fabricated and tested. The results show that a wide usable bandwidth of 24.2% has been achieved.