Citation: Abubakar, H.S.; Zhao, Z.; Wang, B.; Kiani, S.H.; Parchin, N.O.; Hakim, B. Eight-Port Modified E-Slot MIMO Antenna Array with Enhanced Isolation for 5G Mobile Phone. Electronics 2023, 12, 316. https://doi.org/10.3390/electronics 12020316 Academic Editor: Andrea Randazzo Received: 13 December 2022 Revised: 30 December 2022 Accepted: 4 January 2023 Published: 7 January 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). electronics Article Eight-Port Modified E-Slot MIMO Antenna Array with Enhanced Isolation for 5G Mobile Phone Hassan Sani Abubakar 1 , Zhiqin Zhao 1, *, Boning Wang 1 , Saad Hassan Kiani 2 , Naser Ojaroudi Parchin 3, * and Bandar Hakim 4 1 School of Electronics Science and Engineering, University of Electronics Science and Technology of China, Chengdu 610056, China 2 Smart Systems Engineering Lab, College of Engineering, Prince Sultan University, Riyadh 11786, Saudi Arabia 3 School of Engineering and the Built Environment, Edinburgh Napier University, Edinburgh EH10 5DT, UK 4 Electrical and Computer Engineering Department, Faculty of Engineering, King Abdulaziz University, Jeddah 21589, Saudi Arabia * Correspondence: zqzhao@uestc.edu.cn (Z.Z.); n.ojaroudiparchin@napier.ac.uk (N.O.P.) Abstract: An eight-element antenna system operating at sub 6 GHz is presented in this work for a future multiple-input multiple-output (MIMO) system based on a modified E-slot on the ground. The modified E-slot significantly lowers the coupling among the antenna components by suppressing the ground current effect. The design concept is validated by accurately measuring and carefully fabricating an eight-element MIMO antenna. The experimentation yields higher element isolation greater than −21 dB in the 3.5 GHz band and the desired band is achieved at −6 dB impedance bandwidth. The E-shape slot occupies an area of 17.8 mm × 5.6 mm designed on an FR-4 substrate with dimensions of 150 mm × 75 mm × 0.8 mm. We fed the I-antenna element with an L-shape micro-strip feedline, the size of the I-antenna is 20.4 × 5.2 mm 2 , which operates in the (3.4–3.65 GHz) band. Moreover, our method obtained an envelope correlation coefficient (ECC) of <0.01 and an ergodic channel capacity of 43.50 bps/Hz. The ECC and ergodic channel capacity are important metrics for evaluating MIMO system performance. Results indicate that the proposed antenna system is a good option to be used in 5G mobile phone applications. Keywords: antenna systems; 5G; MIMO; ECC 1. Introduction In a communication system, the use of the multiple-input multiple-output (MIMO) antenna technique significantly enhances the channel capacity, spectral efficiency, and reliability link without the additional requirement of increased bandwidth and power [1–3]. As compared to the existing infrastructure of 4G devices which uses at most four radiating elements, the 5G system utilizes a minimum of six to eight elements for efficient transmis- sion [4–7]. The increased demand for faster data rates with exceptionally low latency is outpacing the present LTE advanced technology [8–12]. This results in the adoption of the 5G communication systems, which can deliver data throughput with a much lower latency of <1 ms in comparison to 4G-LTE [13] and intra-band contiguous carrier aggregation to increase the data throughput. Arranging multiple antennas in a size-limited environment is challenging since the radiation among antenna elements disturbs the radiating environ- ment of the neighboring antennas, thus reducing the overall performance of the system. To achieve promising outcomes of such a design, the level of isolation among the elements needs to be greater than 12 dB [14]. Several techniques do exist in most of the recent literature to alleviate the effect of coupling among closely packed antenna elements [15,16]. These isolating structures include neutralization lines [17,18], decoupling networks [19,20], electromagnetic band gap [21], parasitic elements [22], orthogonal modes [23], pattern diversity arrangement [24], and multi-mode decoupling schemes [25]. Electronics 2023, 12, 316. https://doi.org/10.3390/electronics12020316 https://www.mdpi.com/journal/electronics