In this paper, a compact I shaped monopole radiator with a dimension of 24 × 22 × 1.6 mm3 is proposed. The monopole radiator achieved an impedance bandwidth of 1.46 GHz (4.06–5.52 GHz) using partial ground plane. Further to cover the sub-6 GHz spectrum (3.4–3.6 GHz) for future 5G communications, a four-element multi-input multi-output (MIMO) antenna configuration is designed by utilizing the single element antenna. The operation bandwidth of 2.27 GHz (3.37–5.64 GHz) is enhanced by using a tapered microstrip feed line. Isolation is increased upto 40 dB over the operating band (3.37–5.64 GHz) by using a modified rectangular stub in the partial ground plane. This stub also provides a decoupling path and consequently limited amount of current couples to the neighbouring element due to surface waves. The modified stub suppress the surface waves and the near fields reducing the coupling between the antennas keeping it below −10 dB for the whole desired frequency range. Therefore, the proposed MIMO antenna achieved wide bandwidth of (3.37–5.64 GHz) and minimum isolation between antenna elements 1 & 4 is −10 dB in 3.4–3.6 GHz frequency band, whereas −15 dB between 3.8 and 5.64 GHz frequency band. The suggested MIMO antenna is designed on a FR4 substrate with a dielectric constant of 4.4 and a loss tangent of 0.02 and a 0.45λ 0 × 0.45λ 0 dimension. In terms of the envelope correlation coefficient (ECC), diversity gain (DG), mean effective gain (MEG), total active reflection coefficient (TARC), isolation between the ports, and channel capacity loss (CCL), the proposed antenna’s diversity performance characteristics are investigated and the obtained values are 0.04, 9.98, ±3, −11, −15 dB, 0.10 bits/s/Hz respectively. The antenna prototypes have been fabricated, and the measurements and simulations have been found to be in close agreement. Therefore, the proposed MIMO antenna covers n77/n78/n79 for 5G (sub-6 GHz) and LTE bands of 42/43/46.

中文翻译：

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用于 LTE/5G（6 GHz 以下）应用的紧凑型四元 MIMO 天线

在本文中，一个紧凑的 I 形单极辐射器，尺寸为 24 × 22 × 1.6 mm3被提议。单极辐射器使用部分接地层实现了 1.46 GHz (4.06–5.52 GHz) 的阻抗带宽。为了进一步覆盖未来 5G 通信的 sub-6 GHz 频谱（3.4-3.6 GHz），利用单元素天线设计了四元素多输入多输出 (MIMO) 天线配置。2.27 GHz（3.37-5.64 GHz）的工作带宽通过使用锥形微带馈线得到增强。通过在部分接地平面中使用改进的矩形短截线，隔离在工作频带 (3.37–5.64 GHz) 上提高了 40 dB。该短截线还提供去耦路径，因此由于表面波而限制了与相邻元件耦合的电流量。修改后的短截线抑制了表面波和近场，减少了天线之间的耦合，使其在整个所需频率范围内保持在 -10 dB 以下。因此，所提出的 MIMO 天线实现了 (3.37-5.64 GHz) 的宽带宽，并且天线元件 1 和 4 之间的最小隔离在 3.4-3.6 GHz 频段为 -10 dB，而在 3.8 和 5.64 GHz 频段之间为 -15 dB。建议的 MIMO 天线设计在 FR4 基板上，介电常数为 4.4，损耗角正切为 0.02 和 0.45λ 0× 0.45λ 0方面。在包络相关系数（ECC）、分集增益（DG）、平均有效增益（MEG）、总有源反射系数（TARC）、端口之间的隔离度和信道容量损耗（CCL）方面，建议天线的分集性能对特性进行了研究，获得的值分别为 0.04、9.98、±3、-11、-15 dB、0.10 bits/s/Hz。天线原型已经制作完成，测量结果和模拟结果非常吻合。因此，建议的 MIMO 天线覆盖 5G（低于 6 GHz）的 n77/n78/n79 和 42/43/46 的 LTE 频段。