MIMO Antenna Mutual Coupling Reduction Using Modified Inverted-Fork Shaped Structure

This article presents, a mutual coupling reduction technique between a very closely spaced (1.8 mm) two-element microstrip-based multiple-input multiple-output (MIMO) antennas using a modified inverted-fork-shaped decoupling (m-IFSD) structure. The m-IFSD structure consists of an inverted fork and a cross-shaped structure with a shorted via. The combined effect of inverted-fork and shorted cross-shaped structure results in mutual coupling reduction below −35 dB between adjacent antenna elements. The decoupling technique is analyzed using an approximate transmission-line model and field distribution. Furthermore, the two-element MIMO antenna design is extended to an eight-element MIMO configuration to improve the MIMO diversity. To verify the proposed isolation technique a two-element MIMO antenna prototype is fabricated and measured. The proposed MIMO antenna exhibits a low mutual coupling (<−35 dB) with good impedance matching (<−10 dB) at 5.45 GHz. The MIMO antenna provided a total active reflection coefficient (TARC) less than −10 dB and envelop correlation coefficient (ECC) (for isotropic propagation scenario) less than 0.5. Finally, the ECC of the proposed MIMO antenna system is analyzed for a realistic Gaussian/uniform propagation scenario for various incidence angles and angular spreads to better understand the effect of the mutual coupling reduction technique.