# Design of Wideband Decoupling Antenna Array for 5G Smartphones at N77/N78/N79/WLAN 5 GHz Bands
## 3 Performance of the Eight-Element Antenna System
### Handheld Effects  
We simulate the effect of the user's hand on the antenna performance of an MIMO cell phone when making a phone call or browsing for information, and verify the robustness of the MIMO antenna system. The poses of the simulated handheld antenna model are shown in Figure 18a, with antennas 1, 2, 5, and 6 close to the palm and antennas 3, 4, 7, and 8 close to the fingers. In Figure 18b, we can clearly observe that the reflection coefficient of Ant 7 is slightly larger than \(-10\) dB at 3.6 GHz and 5.5 GHz, and slightly more than \(-10\) dB at 5.6 GHz for Ant 5. This is due to the fact that the human body tissues themselves belong to a kind of conductive material. The thumb portion of the hand model is relatively close to the Ant 5 and Ant 7, which absorbs and scatters the electromagnetic waves radiated by Ant 5 and Ant 7 and scattering. Overall, the reflection coefficients of antennas 1-8 are weakly affected in the frequency band from 3.30 to 5.83 GHz.  
Figure 16: Calculated DG.  
Figure 18c shows that the isolation between Ant 2 and Ant 3 becomes weaker at 3.3 GHz to \(-10\) dB. It is caused by the fact that Ant 2 and Ant 3 are closer to the small thumb of the hand model, so part of the signal is coupled into the human body. Overall, the isolation of each antenna unit is good at the operating frequency. Figure 18d shows the variation of the total efficiency of each antenna unit after adding the human hand model. The influence of the human hand model leads to a slight decrease in the total efficiency, ranging from 30% to 82%. In summary, the constructed MIMO antenna system is less affected by the influence of the human hand model, and the overall performance meets the requirements of 5G mobile terminals.  
Table 1 compares the eight-element MIMO antenna array proposed in this paper with some similar antenna arrays proposed recently. The comparison reveals that most of the design proposals have problems such as larger antenna size or narrower coverage bandwidth. The composite decoupling structure proposed in this paper has significant improvement on the mutual coupling between two antenna pairs, and the design scheme provides a good balance between antenna performance and size.  
Figure 17: Simulated and measured radiation direction plots of ant1 and ant2 at 3.5, 4.5, and 5.6 GHz. (a) xoy plane. (b) xoz plane.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Design** & **Antenna Pairs** & **Decoupling Methods** & **Element Size (mm2)** & **Frequency (GHz)** & **Isolation (dB)** & **Total Efficiency (\%)** & **ECC** \\ \hline
[20] & \(\surd\) & Orthogonal mode & 40 \(\times\) 7.5 & 3.3–5.0 GHz (\(-\)6 dB) & \(<\)\(-\)12 & 31.6–76.7 & \(<\)0.11 \\
[22] & \(\surd\) & Neutralization lines & 35.7 \(\times\) 5 & 4.8–6 GHz & \(<\)\(-\)17 & 60–71 & \(<\)0.06 \\
[23] & - & Neutralization lines & 17.5 \(\times\) 7.5 & 3.3–5.6 GHz (\(-\)6 dB) & \(<\)\(-\)15 & 45–80 & \(<\)0.03 \\
[27] & \(\surd\) & Parasitic elements and DGS & 37 \(\times\) 6 & 3.3–5.95 GHz (\(-\)6 dB) & \(<\)\(-\)15 & 47–78 & \(<\)0.11 \\
[29] & \(\surd\) & DGS & 28 \(\times\) 6 & 3.23–5.24 (\(-\)10 dB) & \(<\)\(-\)11 & 50–89 & \(<\)0.04 \\
[30] & - & DGS & 22 \(\times\) 2 & 3.3–6 GHz (\(-\)6 dB) & \(<\)\(-\)12.1 & 50–61 & \(<\)0.2 \\  & & Parasitic & 3.28–5.85 & & & \\ Proposed & \(\surd\) & elements and DGS & 33.6 \(\times\) 6 & GHz (\(-\)10 dB) & \(<\)\(-\)12.42 & 50–88 & \(<\)0.01 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Comparison with other 5G terminal MIMO antennas.  
Figure 18: (**a**) Model of a user holding a cell phone in the left hand. (**b**) Simulated reflection coefficients. (**c**) Simulated transmission coefficients. (**d**) Simulated total efficiency.