This paper presents a practical scheme for threefold stubs etched on the ground plane (GP) to reduce mutual coupling between adjacent patching elements. The multiple input multiple output (MIMO) antenna array consists of two concentric polyhedron annulus patches, a conventional dielectric substrate, threefold fork-shaped stubs (TFSS) and a microstrip line feeder. The equivalent band-stop filtering function of the TFSS suppressing surface wave propagation has been demonstrated in commercial Advanced Design System (ADS) software. The results of previous case studies indicate that the mutual coupling about 5 dB to 47 dB was reduced from 8 GHz to 9.3 GHz (S11 < -10 dB) for antenna arrays. The capabilities of the antenna (in envelope correlation coefficient = 0.018, voltage standing wave ratio = 1.2892, and diversity gain = 20 dB) have been confirmed in a center frequency of 8.97 GHz. An examination of TFSS antennas shows that the side lobes in both the E-plane and the H-plane descends alongside an increasingly broad radiation pattern. The above results demonstrate that the proposed design is highly efficient in MIMO antenna applications.
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