Common-Loop MIMO Antenna Design With Decoupling Inductors Using Characteristic Mode Analysis

This letter investigates the intrinsic operation principles of the decoupling inductors in multiple-input–multiple-output (MIMO) antenna design using the characteristic mode analysis, in the first of its kind. This work starts with the analysis of a conventional one-wavelength loop antenna and then investigates the MIMO antenna design methods in terminal scenarios. It is revealed that the decoupling inductors introduce a new characteristic mode within the antenna operation band, contributing to the current-mode-canceling effect and responsible for port-to-port isolation. A two-in-one common-loop MIMO antenna design with high-isolation characteristics is proposed for N77/N78/N79 applications. Both simulation and measurement were conducted to verify the feasibility of the proposed MIMO antennas.