## 3 Results and Discussion  
### Scattering Parameter Performance  
The \(S_{11}\) and \(S_{21}\) performance of RPT, FCPT, and MCPT-CVA are displayed in Figure 3. The best \(S_{11}\) is obtained from MCPT, at the low-end frequency. According to the simulation results displayed in Figure 3a, the low-end frequencies for RPT, FCPT, and MCPT-CVA that got \(S_{11}-\)10 dB are 0.52 GHz, 0.53 GHz, and 0.5 GHz. FCPT experienced poor return loss due to \(S_{11}\) exceeding \(-\)10 dB for frequencies 0.62 GHz to 0.81 GHz. The right side of Figure 1 shows the \(S_{21}\) performance of the RPT, FCPT, and MCPT. As can be observed, in the first low-end frequency at \(-\)20 dB the mutual scattering parameters for RPT, FCPT, and MCPT are 0.769 GHz, 0.848 GHz, and 0.58 GHz respectively. The best \(S_{21}\) is achieved for MCPT at low-end frequencies. However, the best \(S_{21}\) in overall frequency is acquired for FCPT as shown in Figure 3. The mutual scattering parameter has a lesser value at higher frequencies. In this study, an antenna with a substrate element's width of 275 mm was created, with frequencies of 0.5 GHz and 4.5 GHz and equal to the wavelengths of 600 mm and 66.67 mm, respectively. If the antenna has spacing between elements 275 mm so electrically, the antenna has a size of 0.458\(\lambda\) at a frequency of 0.5 GHz and 4.125\(\lambda\) at a frequency of 4.5 GHz. The mutual coupling of the antenna will be large if it has a size of fewer than 0.5\(\lambda\) (at the low-end frequency). Wideband and Ultra Wideband and also Super wideband antennas will experience mutual coupling issues at low frequencies. The greater the frequency, the less mutual coupling. However, it yields the problem of the grating lobe at high frequency. The performance of return loss and mutual scattering characteristics to the RPPT, BCPT, and CCPT in 1 \(\times\) 2 MIMO antenna are assessed in Figure 3b. The best return loss performance is attained for BCPT. At 0.5 GHz, the antenna's \(S_{11}\) is \(-\)10.736 dB. At a frequency of 0.79 GHz, it has an \(S_{11}\) of \(-\)51.094 dB. The worst return loss for CCPT appears at low frequency. It demonstrates that at 0.699 GHz, it exhibits \(S_{11}-\)5.985 dB. Figure 2: The 1 \(\times\) 2 MIMO Coplanar Vivaldi Antenna of (**a**) Koch Fractal Structure Palm Tree (KFSPT-CVA), (**b**) Exponential Slot Edge Palm Tree (ESEPT-CVA), (**c**) Vertical Wave Structure Palm Tree (VWPT-CVA), (**d**) Horizontal Wave Structure Palm Tree (HWPT-CVA), (**e**) Regular Lens Palm Tree (RLPT-CVA), (**f**) Elips Lens Palm Tree (ELPT-CVA), (**g**) Metamaterial Lens Palm Tree (MLPT-CVA). However, CCPT has an \(S_{11}\) of \(-51.359\) dB at 1.628 GHz. The \(S_{21}\) of RPT, BCPT, and CCPT might be visible on Figure 3b's bottom side. The best \(S_{21}\) performance is in BCPT, CCPT, and RPT CVA. Meanwhile, the CCPT CVA received \(S_{21}\) at 0.989 GHz of \(-55\) dB. The CCPT performs well in \(S_{21}\) because it has the largest truncated area without copper on both edges of the patch. Figure 4a shows the comparison of return loss performance and mutual scattering performance of RPT, LTPT, and RTP CVA. From Figure 4a, it could be seen that LTPT has the best performance, due to covering \(S_{11}\) below \(-10\) dB almost in the all-frequency range from 0.5-4.5 GHz. However, the bottom of Figure 4a shows that LTPT has the worst \(S_{21}\) performance. At 0.5 GHz LTPT has \(S_{21}\) \(-11.491\) dB. LTPT has a distance between the feeding point is 0.495\(\lambda\) and RTPT of 0.422\(\lambda\) The distance between the two feeds for LTPT is getting farther away from the distance between the two centers of the tapered slot. RTPT has the best \(S_{21}\) at 0.885 GHz of \(-47.506\). The electric field between two tapered slots will propagate away for RTPT while for LTPT. Figure 4b shows that the HFSPT and KFSPT have better performance of return loss than RPT at low-end frequency. At 0.5 GHz the \(S_{11}\) performance of RPT, HFSPT, and KFSPT are \(-8.311\) dB, \(-12.442\) dB, and \(-14.33\) dB respectively.