# A Wideband Eight-Element Antenna with High Isolation for 5G New-Radio Applications
## 2 The Design and Simulation of the Presented Antenna  
The geometry and measurements of the wideband eight-element antenna are presented in Figure 1. The MIMO antenna system is made up of a mainboard and two sideboards perpendicular to the mainboard. The sizes of the mainboard and the sideboard are 150 \(\times\) 73.4 \(\times\) 0.8 mm\({}^{3}\) and 150 \(\times\) 7 \(\times\) 0.8 mm\({}^{3}\), respectively. The metal ground surface is in contact with the back of the mainboard and the outside of two sideboards. Eight antenna units are symmetrically placed on the inside of the same two sideboards. In addition, the motherboard and two sideboards are made of an FR4 substrate with \(\varepsilon_{\mathrm{r}}\) of 4.4 and tan6 of 0.02. A microstrip feeder of 50 \(\Omega\) enables the designed antenna to achieve better impedance matching. Every antenna unit consists of a C-shaped strip and two triangle-shaped strips. The structure of a C-shaped strip with two triangle-shaped strips can realize a wideband of 3.3-5 GHz, and the measurement of the antenna elements is only 6.8 \(\times\) 7 \(\times\) 0.8 mm\({}^{3}\). On the bottom of the mainboard and the outside of two sideboards, the isolation structure contains a T-shaped trough with two square strips and a T-shaped groove connected to a T-shaped trough with two square strips on the ground. To understand the theory of the presented wideband antenna, the evolution shapes, reflection coefficients, surface current, optimal parameter analysis, and transmission coefficients of the presented antenna have been analyzed. The layout of the whole antenna structure and the designed antenna simulation results are acquired with HFSS. The evolution and reflection coefficients of the antenna are displayed in Figure 2. The introduction of the rectangular strip on the top of the rectangular groove of Antenna 2 can reduce return loss in the whole frequency band. The two triangle-shaped strips of Antenna 3 are used for achieving \(-\)6 dB S\({}_{11}\) at 3.3 GHz. Finally, the introduction of a rectangular strip of Antenna 4 can achieve a wideband \(-\)10 dB impedance band which can include 3.3-5 GHz. Figure 3 shows the simulation result of the surface current distribution of the presented antenna. The surface current distribution is concentrated on the rectangular strip of the top of the rectangular groove and two triangle-shaped strips at 3.4 GHz. When the frequency is 4.9 GHz, the surface current is mostly focused on the C-shaped strip. In Figure 4, the S\({}_{11}\) simulation results of the designed antenna with dissimilar values of W and H are presented. When W is 3.85 mm, Figure 4a demonstrated that S\({}_{11}\) of \(-10\) dB bandwidth satisfies the frequency band at 3.22-5.6 GHz, which contains 3.3-5 GHz. As shown in Figure 4b, the \(-10\) dB S\({}_{11}\) can meet the requirement of the entire band range when the value of H is 0.8 mm. Figure 3: Simulated surface current distribution at (a) 3.4 GHz; (b) 4.9 GHz. Figure 2: Design development and S-parameters of antenna unit: (a) the design evolution; (b) simulated S\({}_{11}\). The simulated transmission coefficients of the presented antenna with or without the structure reducing the interaction are presented in Figure 5, which demonstrates that the structure of a T-shaped groove can increase isolation between antenna elements. The surface current is retrained and its direction is changed by the T-shaped groove. Accordingly, it expands the gap between each port to attenuate mutual coupling between antenna units. Moreover, as illustrated in Figure 5, the T-shaped groove with two rectangular strips connected to a T-shaped groove forms a parallel structure to achieve better isolation in the lower frequency of 3-4 GHz. The robustness and usefulness of the designed system of MIMO antenna are proved by a study of an application scene of holding MIMO in dual-hand mode (DHM). In Figures 6 and 7, the S-parameter simulation results in DHM are presented, and it shows that the \(-10\) dB bandwidth of Ant. 1 and Ant. 4 cannot cover 3.3-5 GHz.