# A Design for a Wide-Band Antenna Pair Applied for Mobile Terminals at the Sub-6 GHz Band
## 2 Geometry of the Antenna  
The structure of the proposed MIMO antenna array and antenna pair is shown in Figure 1. The structures are etched onto an 0.8 mm\({}^{2}\) thick FR-4 substrate with a relative permittivity of 4.3, a relative permeability of 1, and a loss tangent of 0.02. The antenna pair with a size of \(23\times 6\) mm\({}^{2}\) is a symmetrical structure composed of two radiation elements. To obtain a wide band, the coupling feed method is used. For each antenna element, there are two radiating parts. One is \(3\times 5.4\) mm\({}^{2}\) on the inner side of the border, acting as a  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Ref.** & **Antenna Pairs** & **Element Size (mm\({}^{2}\))** & **Decoupling Methods** & **Frequency (GHz)** & **Isolation (dB)** & **ECC** & **Total Efficiency (\%)** & **Ports** \\ \hline
[18] & \(\surd\) & \(39\times 4.2\) & PE & \(\begin{array}{c}3.4-3.6/4.8-5.0\\ (-10 dB)\end{array}\) & \(<\)\(-14.5\) & \(<\)0.04 & - & 8 \\ \hline
[19] & \(\times\) & \(6.78\times 3.8\) & DGS & \(\begin{array}{c}4.4-5.0\\ (-6 dB)\end{array}\) & \(<\)\(-22\) & \(<\)0.049 & 50–73 & 8 \\ \hline
[20] & \(\times\) & \(12\times 14.5\) & - & \(\begin{array}{c}3-4.28\\ (-6 dB)\end{array}\) & \(<\)\(-10\) & \(<\)0.02 & 70–95 & 4 \\ \hline
[21] & \(\times\) & \(8\times 4\) & - & \(\begin{array}{c}3.4-3.6/5.1-5.7\\ (-10 dB)\end{array}\) & \(<\)\(-14\) & \(<\)0.02 & 58–62/68–74 & 8 \\ \hline
[22] & \(\times\) & \(6.5\times 6\) & - & \(\begin{array}{c}3.4-3.6\\ (-10 dB)\end{array}\) & \(<\)\(-10\) & \(<\)0.055 & 65–80 & 10 \\ \hline
[23] & \(\times\) & \(4.6\times 5.6\) & - & \(\begin{array}{c}3.3-3.7\\ (-6 dB)\end{array}\) & \(<\)\(-15\) & \(<\)0.1 & 50–75 & 8 \\ \hline
[24] & \(\times\) & \(14.9\times 7\) & - & \(\begin{array}{c}3.4-3.6/4.8-5.0\\ (-10 dB)\end{array}\) & \(<\)\(-16.5\) & \(<\)0.01 & 74–85/70–82 & 4 \\ \hline
[25] & \(\surd\) & \(20\times 6.2\) & PEs & \(\begin{array}{c}3.4-3.6\\ (-10 dB)\end{array}\) & \(<\)\(-17\) & \(<\)0.1 & - & 4 \\ \hline
[26] & \(\surd\) & \(49.5\times 6\) & NLs & \(\begin{array}{c}2.3-2.4/3.3-3.6\\ (-6 dB)\end{array}\) & \(<\)\(-15\) & \(<\)0.15 & 47–73 & 8 \\ \hline
[27] & \(\surd\) & \(47\times 6\) & \(\begin{array}{c}\text{Pes}\\ \text{and DGS}\end{array}\) & \(\begin{array}{c}3.3-5.95\\ (-6 dB)\end{array}\) & \(<\)\(-15\) & \(<\)0.11 & 47–78 & 8 \\ \hline
**Pro.** & \(\surd\) & \(23\times 6\) & DGS & \(\begin{array}{c}3.4-5.2\\ (-6 dB)\end{array}\) & \(<\)\(-10\) & \(<\)0.1 & 46–84 & 8 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Comparisons of the sub-6G MIMO terminal antenna designs.  
feeding line and major radiation parts. The other part of 10.5 \(\times\) 6 mm\({}^{2}\) on the outer side plays the role of secondary radiation parts and contributes greatly to improving bandwidth. Besides this, the edge-to-edge distance of two antenna elements is only 2 mm, which leads to a serious mutual coupling in terms of radiation characteristics. Thus, three specially arranged strip DGS, located on the ground plane, are added in the middle of the antenna pairs to enhance isolation. The S-parameter results demonstrate that this is effective for wide-band antenna decoupling.