Wideband MIMO handset antenna design based on theory of characteristic modes

A novel multi‐input multi‐output (MIMO) antenna array in a compact mobile handset has been designed to operate in a wide frequency band below 1 GHz. Based on theory of characteristic modes (TCM), a pair of parallel folding metal strips is introduced to make a chassis generate two orthogonal eigenmodes with wideband resonant characteristics. A meander line‐loaded monopole structure is employed to excite higher frequency eigenmode, and a parallel lumped L‐C structure is used to excite lower frequency eigenmode. With two proposed feeding structures, the proposed MIMO antenna array can operate in a wide frequency band covering 745‐960 MHz with an envelope correlation coefficient (ECC) <0.12. Simulation and measurement results demonstrate that the proposed MIMO antenna array has total efficiency better than 40% over the whole operating band.