# Eight Element Wideband Antenna with Improved Isolation for 5G Mid Band Applications
## 4 Proposed Eight-Element Antenna  
### Antenna Design and Decoupling Mechanism  
As seen in Figure 6, the proposed eight-element antenna with an overall dimension of 83 \(\times\) 129 \(\times\) 0.1 mm\({}^{3}\) (1.245A \(\times\) 1.94A \(\times\) 0.0015A) was created by mirroring the four-element antenna at a distance of 3 mm (0.045A) along the \(x\)-axis. The antenna was initially connected with horizontal stubs as shown in Figure 6. This stage (antenna 1) gave an isolation of more than 16 dB throughout the bandwidth as displayed in the scattering parameters plot in Figure 7. To further improve the isolation between the antenna elements, three vertical stubs were connected to the ground plane in the second stage as shown in Figure 6. The scattering parameters of the proposed eight-element antenna are displayed in Figure 8. Incorporating these stubs altered the current path and improved the isolation to more than 24 dB throughout the bandwidth, which is better than that of stage 1.  
Figure 5: Quadelement antenna: (**a**) configuration; (**b**) reflection coefficients; (**c**) transmission coefficients.  
Figure 6: Evolution stages of the proposed eight-element antenna with horizontal stubs (left) and connected ground with vertical stubs (right-proposed).  
The isolation enhancement of the antenna can be further investigated by examining the vector current distribution of the evolution stages. The vector current distribution of the antenna with horizontal stubs (antenna 1) as well as the proposed decoupling structure with vertical stubs is displayed in Figure 9a,b. The current distribution was examined by stimulating the first port (P1) and terminating all the other ports (P2-P8) as given in the figure. From Figure 9a, it is evident that when P1 is stimulated, the current is concentrated on the induced element and a portion of the current is seen on the adjacent elements, indicating mutual coupling between them. However, in Figure 9b, when P1 is excited and all the other ports are terminated, a negligible current appears in the adjacent element indicating better isolation among the antenna elements. The current is intense towards the feedline, radiator edges, and slotted ground plane of the excited element, as well as in the vertical stubs in the ground plane. Incorporating the proposed decoupling structure reduces the coupling current and enhances isolation by creating an out-of-phase current as indicated in Figure 9b. The vector current distribution indicated was calculated at a resonant frequency of 5.03 GHz. The configuration of the proposed eight-element antenna is given in Figure 10.  
Figure 8: Simulated S-parameters of the proposed antenna: (**a**) reflection coefficient; (**b**) transmission coefficients.  
Figure 7: Simulated Parameters of stage 1 (antenna 1): (**a**) reflection coefficient; (**b**) transmission coefficients.  
Figure 10: Configuration of proposed eight-element antenna. Measurements (in mm): Ls = 83, Ws = 129, d1 = 0.5, d2 = 3, d3 = 1, and d4 = 46.  
Figure 9: Vector current distribution at 5.03 GHz: (**a**) Antenna 1; (**b**) Antenna 2 (proposed).