# Four-Port MIMO Antenna System for 5G n79 Band RF Devices
###### Abstract  
In this article, a compact four-port MIMO antenna system resonating from 4.7-5.1 GHz on \(-6\) dB criteria is discussed. The proposed antennas are arranged in a perpendicular manner providing diversity with good isolation characteristics. The proposed antenna was fabricated and designed on a commercially available low-cost FR-4 substrate with a relative permittivity of 4.4. The total size of the antenna is \(40\times 40\) mm\({}^{2}\), and a minimum isolation of 25 dB was observed at most nearby resonating elements. The proposed antenna was fabricated and tested at an in-house facility, and the measured results agree well with the simulations. The MIMO antenna characteristics, such as the envelope correlation coefficient (ECC) among any two radiating elements, have been found to be less than 0.1, and the diversity gain (DG) value evaluated showed that the proposed antenna is well designed. Furthermore, the SAR analysis showed that the desired antenna system is safe for users, with a value of 0.94 W/Kg. The channel capacity (cc) was found to be 18.7 bps/Hz, approximately 2.7 times more than SISO systems. Through its robust and reliable performance and its peak gain of 2.8 dBi, the proposed compact antenna is a good candidate for future 5G devices. 5G services; four-port antenna system; handheld devices; spatial diversity; MIMO +
Footnote †: journal: Accepted: 15 December 2021  
the correlation increases [12]. Hence, the basic requirement for an MIMO system is low correlation and high isolation [13]. In the literature, several antennas have been proposed in both mmWave [14] and sub6 GHz for 5G systems [15]. These research studies have included mmWave arrays [16], n77 [17], and n79 [18] and LTE band 42, 43 MIMO systems [19]. In [20] a six element MIMO antenna system is presented in which low correlation has been observed among MIMO elements with a peak gain of 3.1 dBi. The total size of the six-element MIMO system is 136 \(\times\) 68 mm\({}^{2}\). Similarly, in [21] a four-port MIMO DRA system is proposed providing spatial and diversity characteristics. The size of the four-port DRA is 80 \(\times\) 80 mm\({}^{2}\). An eight element MIMO antenna is presented in [22], which shows hybrid transformation comprising both planar- and side-attached resonating elements. Although the isolation among the radiating elements is as good as 15 dB, the hybrid assembly makes the antenna system difficult to fabricate. In [23] an eight-element wideband MIMO antenna is presented with a triband response. The proposed antenna is made on a metal frame and offers low correlation characteristics. In [24] as well as [25], four-element linearly polarized planar structures are presented with simple feeding mechanisms. Although the antenna exhibits well impedance bandwidth and gain characteristics, the isolation among the described structures is low. In [26] a four-port eight-element MIMO antenna array with orthogonal assembly is presented for an mmWave 28 GHz band. The size of the MIMO array system is 30 \(\times\) 35 mm\({}^{2}\), while the peak gain achieved is 3.6 dBi. Similarly, in [27] a two-port orthogonal MIMO configuration is presented for an mmWave band exhibiting approximately 4 GHz bandwidth. A two-port circularly polarized WLAN band antenna system is presented in [28] where the gain of the antenna is increased with the incorporation of a metasurface. Although the relevant approach is good, it makes antenna fabrication a little complicated. This paper presents a four-port inverted-Hook-shaped compact MIMO antenna for the n79 5G band. The overall size of the four-port MIMO antenna is 40 \(\times\) 40 mm\({}^{2}\), and it is fabricated on an FR4 substrate with a relative dielectric constant of 4.4 and a thickness of 0.8 mm. The lowest isolation among the radiating elements is 23 dB and the maximum gain reported is 2.8 dBi. The proposed antenna is positioned in such a way that maximum isolation can be achieved. The paper's layout is as follows.