A Self-Decoupling Technique for Isolation Enhancement in Closely-Spaced MIMO Patch Antennas

This letter proposes an effective technique to enhance the isolation in a closely-spaced multiple-input-multiple-output (MIMO) antenna system. In the proposed design, microstrip patches are closely arranged in the H-plane and E-plane configurations with an extremely small edge-to-edge spacing of 0.016$\lambda$ at the center operating frequency. The self-decoupling effect is realized by exciting the coupling patch with a mode that is orthogonal to the operating mode of the radiating element. This is achieved by creating a meander patch edge such that the orthogonal transverse magnetic (TM)$_{02}$ mode has the same resonance frequency of the fundamental TM$_{10}$ mode. Accordingly, very high isolation among MIMO elements is obtained without the use of any decoupling structure. Measurements of a fabricated MIMO antenna demonstrate the feasibility of the proposed concept. The prototype has good matching performance and high isolation of 35 dB at the center operating frequency of 4.8 GHz, which is about 29 dB improvement in comparison with the coupled MIMO antenna. Besides, the proposed self-decoupling method can work effectively in multiport H-plane coupled MIMO array.