# A Wideband Eight-Port MIMO Antenna with Reduced Mutual Coupling for Future 5G mm-Wave Applications
## 1 Introduction
An eight-component MIMO antenna setup is recommended to ensure future handsets in article [23]. The 150 \(\times\) 80 \(\times\) 0.5 mm\({}^{3}\)-dimension antenna achieves an efficiency of >62% and an ECC of <0.05. In article [24], an eight-port antenna with CP functionality is presented to operate in 5-6 GHz bandwidth with an isolation of 8 dB. The designed antenna has a 4.9 dBi peak gain and ECC < 0.1. A compact dual-port antenna with wide bandwidth is presented for 38 GHz upcoming 5G applications in [25]. Roger RT/duroid 5880 substrate is used to print 35 \(\times\) 30 \(\times\) 0.8 mm\({}^{3}\) dimension antenna. The antenna achieves an 8.9 GHz operating frequency from 34.8 to 43.7 GHz. The ECC < 0.0002, diversity gain (DG) \(\geq\) 9.999 dB with 10.24 dBi peak gain and isolation \(\leq\) 20 dB. A CPW-fed four-element flexible antenna is printed for future wearable 5G/Wi-Fi 6E applications in [26]. In study [27], a 28/38 GHz crescent-shaped antenna is printed to achieve 5G applications. The 60 \(\times\) 60 \(\times\) 0.508 mm\({}^{3}\)-size antenna is orthogonally placed to obtain an operating bandwidth of 3.05 GHz and 2.41 GHz with good diversity performance. In article [28], a MIMO Vivaldi antenna is fabricated for upcoming mm-waveband applications. In this study, the peak gain is improved by using a bi-axial antistrophic metasurface. A MIMO resonator antenna with 5G applications and improved isolation is presented [29]. The antenna works from 27.25 to 28.59 GHz, located by the FCC for 5G communications. In study [30], a new nature-inspired antenna with a novel MIMO structure is fabricated for 5G communications. An isolation of 17 dB is achieved from 26 to 30 GHz working bandwidth. The antenna also obtains 7.8 dBi gain and 95% efficiency. In [31], a semi-flexible mm-wave dual-port antenna is proposed for wearable applications. The size of the presented antenna is 22.5 \(\times\) 36 mm\({}^{2}\) with a 24-31 GHz secured band. The proposed antenna secures an enhanced isolation of 20 dB. A 4 \(\times\) 4 low-profile circularly polarized, slot-coupled antenna array is presented for emerging mm-wave applications in [32]. The antenna achieves an operating bandwidth of 28-30 GHz. To secure a 26.5-29.5 GHz operating bandwidth, a 1 \(\times\) 8 multimode antenna array is presented for mm-wave terminals in [33]. A helical-inspired MIMO end-fire antenna is presented for 5G diversity applications in [34]. The 15 \(\times\) 25 mm\({}^{2}\) antenna is printed on Roger RO4003. The antenna works from 26.25 to 30.14 GHz. The antenna has ECC \(<\) 0.005 with DG \(>\) 9.95 dB. A novel wideband MIMO patch antenna is fabricated to achieve 28 GHz 5G application in [35]. To obtain 84% radiation efficiency, 26.5-32.9 GHz-wide bandwidth and 5 dBi gain, rectangular slots are defected in the radiator and ground of the antenna. The dual-port antenna has dimensions of 30 \(\times\) 15 \(\times\) 0.25 mm\({}^{3}\) and is printed on ROGER 4003. In the literature discussed above, most of the researchers presented two-port and four-port MIMO antennas with lower frequency ranges, non-connected ground planes, low gain and efficiency, poor diversity performance, large size, complex circuitry and narrow operating bandwidth. To address the above challenges, an 8 \(\times\) 8 MIMO antenna is presented for mm-wave applications. The presented antenna consists of a four-unit cell with connected defected ground structures (DGS). Every unit cell consists of two radiating elements containing a stub inside and a neutralization line block. The radiating elements and neutralization line block is positioned on the front side and DGS on the backside. The antenna secures a wide bandwidth of 28-46, covering 5G mm-wave communications [36; 37]. The neutralization line block and four half-circle ground slots are incorporated for isolation enhancement. The proposed MIMO antenna has secure good radiation performance, with a radiation efficiency of 91-97% and a peak gain of 6.8-8.5 dBi.