Spherical Vector Wave Approach for MIMO Antenna Decoupling

In this letter, mutual coupling between multiple-input-multiple-output (MIMO) antenna elements are expressed in terms of spherical vector waves (SVWs). Orthogonality of SVWs in the near-field region inspires the idea of exciting different SVWs by different MIMO antenna elements to minimize the mutual coupling. Since coplanar electric and magnetic current sources do not excite the same type of SVW, it is proposed to use them as MIMO antenna elements. Using the proposed approach, the simulation and measurement results show that the closely spaced MIMO antennas with very low mutual coupling can be implemented.