# A Dual-Band Flexible MIMO Array Antenna for Sub-6 GHz 5G Communications
## 7 Conclusions  
The proposed dual-band flexible four-element two-port MIMO antenna array designed for the Sub-6 GHz band offers significant advantages in terms of size, flexibility, and performance. The single-element monopole antenna, featuring a modified rectangular radiator with L-strips and a reduced ground plane, is fabricated on a flexible polyimide substrate, achieving a compact size of 57 \(\times\) 50 \(\times\) 0.1 mm\({}^{3}\). It is further demonstrated that extending the single element to a 1 \(\times\) 2 array and subsequently to a four-element MIMO configuration improves the gain (5.2 dBi and 7.7 dBi for the two bands), bandwidth (3.6-3.8 GHz and 5.65-5.95 GHz), and isolation (>22 dB), outperforming many existing designs that often lack flexibility or provide lower isolation.  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Ref.** & **Dimension** & **Impedance** & **I\({}^{\star}\)** & **Ecc** & **DG** & **MEG** & **TARC** & **SAR** (W/kg)** \\ \hline
[2] & 49.09 \(\times\) 25 \(\times\) 1.6 & 3.30–3.85 & 10 & No & \(\sim\)0 & \(\sim\)10 & 0 dB (ratio) & \(<\)\(-\)10 & - \\ \hline
[4] & 150 \(\times\) 75 \(\times\) 0.8 &
\begin{tabular}{c} 3.3–4.2 \\ 4.4-5 \\ 5.15-5.85 \\ \end{tabular} & 14 & No & \(<\)0.05 & - & - & - & - & - \\ \hline
[13] & 160 \(\times\) 70 \(\times\) 0.787 & 5.60–5.67 & 30 & No & \(<\)0.5 & \(\sim\)10 & - & - & (10 g) \\ \hline
[23] & 103.8 \(\times\) 68 \(\times\) 7 &
\begin{tabular}{c} 3.5–4.2 \\ 3.6–4.9 \\ 5.15-5.925 \\ \end{tabular} & 10 & No & \(<\)0.1 & - & - & - & - \\ \hline
[24] & 150 \(\times\) 75 \(\times\) 7 &
\begin{tabular}{c} 3.3–3.8 \\ 4.1–5.8 \\ \end{tabular} & 15 & No & \(<\)0.03 & - & - & \(<\)\(-\)10 & 0.179 (1 g) \\ \hline
**Prop** & **57 \(\times\) 50 \(\times\) 0.1** &
\begin{tabular}{c} **3.6–3.8** \\ **5.65–5.95** \\ \end{tabular} & **22** & **Yes** & **\(<\)0.05** & **\(>\)9.99** & **\(-\)3 dB** & **\(<\)\(-\)10** & **0.25 (10 g)** \\ \hline \hline \end{tabular}  
* I\({}^{\star}\)— isolation.  
\end{table}
Table 3: Comparison between the proposed MIMO configuration and the current literature.  
Figure 28: Electric field and SAR with field exposure estimation.  
The suggested antenna achieves a good MIMO diversity performance, with ECC \(<0.05\), DG \(>9.99\), MEG \(\sim-3\) dB, and TARC \(<-10\) dB, ensuring reliable operation in diverse environments. Furthermore, the low SAR values (0.0702/0.25 W/kg at 3.75 GHz and 0.175/0.507 W/kg at 5.9 GHz) confirm its suitability for wearable and on-body applications, addressing limitations seen in rigid and bulkier counterparts.  
The validation of the antenna through fabrication and measurement shows good agreement with simulations, establishing that this design provides a superior alternative to other MIMO antennas by combining compactness, flexibility, high gain, enhanced isolation, and compliance with safety standards. It is evident that this work addresses critical challenges in MIMO antenna design, offering a practical solution for high-performance Sub-6 GHz 5G communication systems.  
Conceptualization, D.M.J., T.A., S.V., and S.P.; methodology, D.M.J., T.A., S.V., S.P., J.A., and B.V.; software, D.M.J., T.A., S.V., and K.N.; validation, T.A., S.P., R.M.D., K.N., and S.P.G.; formal analysis, D.M.J. and T.A.; writing--original draft preparation, D.M.J.; writing--review and editing, T.A., S.P., J.A., B.V., R.M.D., and S.P.G.; supervision, T.A., S.V., and S.P. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
The data are provided in the manuscript.  
Author [PERSON] was employed by the company Ignion. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.