In this paper, a dual-band 4-, 6- and 8-element multiple-input multiple-output (MIMO) antenna arrays operating at the sub-6-GHz (LTE 42/43 and 46) bands for the fifth-generation (5G) smartphones are proposed. To realize these three MIMO applications in two LTE bands, miniaturized spiral and meander line-shaped strips coupled-fed patch antenna elements are printed on the front side of an FR4 system circuit board and are able to excite two resonance modes. Polarization and spatial diversity techniques are applied to these elements so that the enhanced isolation and reduced coupling effects can be attained. The proposed single antenna element besides 8-element antenna array has been fabricated and experimentally measured. Desirable simulated and measured S-parameters (reflection and transmission coefficients) are obtained for the antenna arrays over the working dual frequency bands. The diversity performance, such as the envelope correlation coefficient (ECC) and diversity gain (DG), has also been simulated and analyzed. Moreover, the performance results, antenna gain and efficiency over the bands, and radiation patterns at the specified resonant frequencies are also presented.
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