Isolated Ground-Radiation Antenna With Inherent Decoupling Effect and its Applications in 5G MIMO Antenna Array

This paper studies an isolated ground-radiation antenna (iGradiANT) that has inherent isolation with another closely-located antenna element and demonstrates its applications in 5G multiple-input multiple-output (MIMO) antenna array. The proposed iGradiANT is accomplished by merely employing a small out-of-ground loop into a traditional ground-radiation antenna (GradiANT). Hence, in contrast to the traditional GradiANT, the proposed iGradiANT can simultaneously support an in-ground loop-type current mode and an out-of-ground loop-type current mode, responsible for far-field radiation and near-field energy cancellation, respectively. In this way, the proposed iGradiANT can exhibit an intrinsic decoupling effect with the adjacent antenna element. Hereby, a typically used inverted-F antenna (IFA) and a normal loop antenna are adopted to separately validate the functionality and versatility of the proposed iGradiANT in establishing $2\times 2$ MIMO antenna sets without any separation. Furthermore, an $8\times 8$ MIMO antenna array is demonstrated for the usage of 5G terminal devices; both simulation and measurement are conducted to verify its radiation performance and diversity performance.