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A tri-polarized 12-antenna array working in the 3.5-GHz band (3.4-3.6 GHz) for future 5G (the fifth generation mobile communication) multiple-input multiple-output (MIMO) operations in the smartphone is presented. In order to reduce the mutual couplings and simplify the design process, orthogonal polarization technique is utilized. By combining a quarter mode substrate integrated wave-guide antenna and two open-end slots, a compact 3-antenna tri-polarization block operating in the 3.5-GHz band is achieved within a small volume of 17 × 17 × 6 mm 3 . Thanks to the orthogonal polarization features, the three antennas within the block are able to have good impedance matchings and low mutual couplings between antennas. By integrating four such tri-polarization blocks, a 12-antenna MIMO array is then designed for smartphone applications. It is also due to the tri-polarization feature, the proposed array could attain acceptable isolations and low correlations between antennas with only two additional decoupling structures. The proposed array is fabricated and tested, good antenna performances, such as return loss better than 10 dB, isolation higher than 12.5 dB, and antenna efficiencies higher than 50%, are obtained. The channel capacity of the 12-antenna array is calculated to be about 57 bps/Hz in a 12 × 12 MIMO system with 20-dB signal-to-noise ratio, which indicates the proposed array using tri-polarization technique is a good choice for future 5G terminals.
Li et al. (Mon,) studied this question.