*Article* **A Dual-Band Eight-Element MIMO Antenna Array for Future Ultrathin Mobile Terminals**

**Chuanba Zhang, Zhuoni Chen, Xiaojing Shi, Qichao Yang, Guiting Dong, Xuanhe Wei and Gui Liu \***

College of Electrical and Electronic Engineering, Wenzhou University, Wenzhou 325035, China **\*** Correspondence: gliu@wzu.edu.cn

**Abstract:** An ultrathin dual-band eight-element multiple input–multiple output (MIMO) antenna operating in fifth-generation (5G) 3.4–3.6 GHz and 4.8–5 GHz frequency bands for future ultrathin smartphones is proposed in this paper. The size of a single antenna unit is 9 <sup>×</sup> 4.2 mm<sup>2</sup> (0.105 λ × 0.05 λ, λ equals the free-space wavelength of 3.5 GHz). Eight antenna units are structured symmetrically along with two sideboards. Two decoupling branches (DB1 and DB2) are employed to weaken the mutual coupling between Ant. 1 and Ant. 2 and between Ant. 2 and Ant. 3, respectively. The measured −10 dB impedance bands are 3.38–3.82 GHz and 4.75–5.13 GHz, which can entirely contain the desired bands. Measured isolation larger than 14.5 dB and 15 dB is obtained in the first and second resonant modes, respectively. Remarkable consistency between the simulated and measured results can be achieved. Several indicators, such as the envelope correlation coefficient (ECC), diversity gain (DG), total active reflection coefficient (TARC), and multiplexing efficiency (ME), have been presented to assess the MIMO performance of the designed antenna.

**Keywords:** 5G; multiple input–multiple output (MIMO); ultrathin; smartphone; dual-band
