# A Wideband Eight-Port MIMO Antenna with Reduced Mutual Coupling for Future 5G mm-Wave Applications
## 2 Antenna Design
### Dual-Port MIMO Antenna  
The dual-port novel-shaped antenna was composed of two similar novel-shaped radiating elements with a U-shaped slot and chamfered edges. The dual-port antenna had a common ground, with two vertical half-circle slots, and a neutralization block was added to enhance operating bandwidth and isolation. The front and back sides of the proposed antenna are shown in Figure 3.  
The two elements, slotted rectangular-shaped radiating components of dimension 35 \(\times\) 22.5 \(\times\) 0.8 mm\({}^{3}\), were placed contiguously for better component spacing.  
A slot with width V and D was etched, a square stub with width T \(\times\) S was added, and the lower edges of the rectangular-shaped radiating elements were chamfered by 4.5 mm each to further increase the bandwidth and isolation. A 50 \(\Omega\) microwave strip line (M = 9 \(\times\) N = 1.48) was used for antenna-feeding. The radius of a half circle is given by (R). The antenna resonates from 28 to 46 GHz, as is clear from Figure 4. To achieve an enhanced isolation, a metallic strip (neutralization line) was added between the radiating element. The length of the neutralization line is given by (U) and the width by P. With the use of a neutralization line, 30 dB enhanced isolation was secured without any other complex circuits, as is clear from Figure 4.  
Figure 3: (**a**) Front and (**b**) back sides of the dual-component MIMO antenna.  
Figure 2: S-parameter results for the development stages of the single-port antenna.  
The effect of the neutralization line on the isolation between ports is given in Figure 5, and Figure 5 confirms that the isolation in the lower frequencies is increased from 25 dB to 30 dB.  
The dual-port antenna secures a peak gain of 6.8 to 8.5 dBi with a radiation efficiency of 91 to 97%, as is clear from Figure 6.  
The presented antenna demonstrates a good diversity performance of ECC < 0.0001 and DG < 9.999 dB, as is clear from Figure 7.  
Figure 4: The dual-port MIMO antenna S-parameter’s results.  
Figure 5: Isolation result of dual-port antenna with and without neutralization line.  
Figure 6: Radiation efficiency and gain of the dual-port MIMO antenna.  
The optimization and parametric analysis were carried out in CST Studio for optimum values for the antenna parameters. The dimensions of the lower rectangle (A), the slot (V), the thin slot (D), the length of the stub (S), the radius of the half circle (R) and the ground stub (B) were altered to analyze their effect on the antenna performance, as shown in Figure 8.  
The dimension of the rectangular A was varied from 3 to 3.6 mm in steps of 0.2 mm, and all the other parameters were kept constant. It is clear from Figure 8a that the antenna achieved an improved bandwidth with a 3 mm size. The effect of slot V is studied in Figure 8b. The width of slot V was varied from 4.5 to 6.5 mm in steps of 0.5 mm, and  
Figure 8: Reflection coefficient of the MIMO antenna. (**a**) Rectangular A, (**b**) slot V (**c**) slot D, (**d**) stub S, (**e**) ground slot R and (**f**) ground-stub B.  
Figure 7: ECC and DG of the suggested antenna.  
Figure 8b shows that the designed antenna obtained an improved bandwidth with size 4.5 mm. The effect of stub (S) on antenna reflection coefficient is given in Figure 8c, and it is clear that the antenna demonstrated a good performance with a 7 mm size. The width of the thin slot (D) was varied from 0.5 to 1.25 mm in steps of 0.25 mm, with all other antenna parameters kept constant. Figure 8d clearly shows that the antenna achieved a good performance with size 0.5 mm. The radius (R) of the ground half-circle slot is given in Figure 8e. The size of the radius (R) was varied from 7.7 to 8.6 mm in steps of 0.3 mm, and it is clear from Figure 8e that the antenna achieved a good performance with size 8.6 mm. The ground stub size effect was nominal, as is clear from Figure 8f.  
After analyzing the optimal values for antenna parameters, the suggested antenna's complete dimensions are given in Table 1.