# Compact Quad-Port MIMO Antenna with Ultra-Wideband and High Isolation
## 5 Conclusions  
In this paper, we design a compact four-cell MIMO antenna with high isolation and ultra-wideband capability. The MIMO antenna consists of four rectangular patch antenna units in an orthogonal layout using an encircling ground, with four inclined slits introduced on the ground between the units, and the overall size is 51.2 mm \(\times\) 51.2 mm \(\times\) 1.524 mm. By manipulating the metamaterial structure on the ground and etched patch, the bandwidth of the MIMO antenna is extended to 1-17 GHz, covering multiple bands (L-band, S-band, C-band, X-band and most of Ku-band) with an absolute bandwidth of 16 GHz and a relative bandwidth of 177.78%. Without sacrificing the overall antenna size, the isolation of the proposed UWB MIMO antennas is increased to more than 27.8 dB by using a combination of polarization diversity techniques and introducing gaps in the patches. The measured results show that the proposed antenna has a stable omnidirectional radiation pattern, good gain and efficiency, and is a high isolation and ultra-wideband four-cell MIMO antenna. Meanwhile, the MIMO antenna has good diversity characteristics with acceptable ECC (<0.002), DG (>9.99 dB), MEG (<\(-\)6 dB) and TARC (<\(-\)35 dB), indicating that it is a MIMO antenna with excellent performance for UWB communication, and the excellent broadband  
Figure 18: The TARC curves for the UWB MIMO antenna.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Ref.**} & **Operation** & \multirow{2}{*}{**Isolation/dB**} & **ECC** & **Size/mm\({}^{2}\)** & **Unit No.** &
\begin{tabular}{c} **Unit** \\ **Size/mm\({}^{2}\)** \\ \end{tabular} \\ \hline
[3] & 2.33–6.71 & \(>\)24 & \(<\)0.036 & \(56\times 70\) & 2 & 1960 \\
[4] & 3–11 & \(>\)25 & \(<\)0.004 & \(25\times 35\) & 2 & 875 \\
[5] & 3.1–10.6 & \(>\)31 & \(<\)0.035 & \(47\times 93\) & 2 & 2185.5 \\
[7] & 3–10.7 & \(>\)25 & \(\leq\)0.01 & \(34.9\times 43\) & 2 & 750.35 \\
[10] & 2.1–20 & \(>\)25 & \(<\)0.02 & \(80\times 80\) & 4 & 1600 \\
[11] & 2.8–13.3 & \(>\)18 & \(<\)0.06 & \(72\times 72\) & 4 & 1296 \\
[12] & 3–13.5 & \(>\)15 & \(<\)0.4 & \(40\times 40\) & 4 & 400 \\
[15] & 4.3–11.6 & \(>\)15.8 & \(<\)0.007 & \(41\times 99.4\) & 2 & 2037.7 \\
[16] & 2.7–11.22 & \(>\)20 & \(<\)0.035 & \(30.75\times 37.8\) & 2 & 581.175 \\
[19] & 2.75–16.05 & \(>\)20 & \(<\)0.006 & \(55\times 55\) & 4 & 756.25 \\ Pro. & 1–17 & \(>\)27.8 & \(<\)0.002 & \(51.2\times 51.2\) & 4 & 655.36 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Compares the proposed antenna with other MIMO antennas in the references.  
capability means the antenna can be applied to satellite mobile communication systems and fixed communication systems as well.  
Conceptualization, [PERSON] and [PERSON]; methodology, Z.H.; software, Z.H.; validation, Z.H.; formal analysis, Z.H.; data curation, Z.H.; writing--original draft preparation, Z.H.; writing--review and editing, [PERSON]; supervision, [PERSON]; project administration, [PERSON]; funding acquisition, [PERSON] All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Natural Science Foundation of China (no. 61571320, 62075163).  
Not applicable.  
The authors declare no conflict of interest.