In this paper, a compact MIMO antenna with improved isolation is proposed. Elliptical slots and an SRR like structure are employed to improve the isolation. The proposed MIMO antenna structure consists of two semi-circular radiators attached to a rectangular monopole which are mirror images of each other with edge to edge spacing of 0.125 λ0, where λ0 is the free space wavelength corresponding to the lowest operating frequency of the structure. Two square steps are added to the above semi-circular monopole to increase the effective path length to cover the lower frequencies. Thereafter, a semi-annular ring slot is introduced, and square steps above the semi-circular monopole are modified to curved steps to further improve the impedance bandwidth of the antenna. The mutual coupling over the wideband is reduced by placing elliptical slots and SRR like structure in the ground plane. The proposed antenna has impedance bandwidth of 2.1- 12 GHz with |S21| < -20 dB over the entire frequency range. The antenna is designed and fabricated on an FR-4 substrate having overall dimensions of 38 mm × 33.4 mm× 1.6 mm. The measured results show a good correlation with the simulated ones. The envelope correlation coefficient (ECC) of the antenna is less than 0.02 over the entire band. The proposed MIMO antenna is an appropriate candidate for 3G, 4G, Wi-Fi, Bluetooth and UWB applications.
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