## 3 Results and Discussion
### Scattering Parameter Performance
At 4.1 GHz KFSPT result \(S_{11}\) of \(-51.093\) dB. \(S_{21}\) performance of RPT, HFSPT, and KFSPT is declared at the bottom of Figure 4b. At 0.5 GHz the \(S_{21}\) of RPT, HFSPT, and KFSPT are \(-8.311\) dB, \(-14.502\) dB, and \(-15.291\) dB. It can be concluded that the KFSPT has the best \(S_{21}\) performance at low-end frequency. The performance of \(S_{11}\) and \(S_{21}\) for RPT, ESEPT, VWSPT, and HWSPT is shown in Figure 5a. We can see that the best \(S_{11}\) performance is found for RPT. However, ESEPT, VWSPT, and HWSPT have \(S_{11}\) of more than \(-10\) dB in some low frequencies. At 0.5 GHz ESEPT has \(S_{11}-16.859\) dB but at 0.517 GHz to 0.628 GHz. it has an \(S_{11}\) of more than \(-10\) dB as well as the structure of VWSPT and HWSPT. Figure 3: \(S_{11}\) and \(S_{21}\) performance of \(1\times 2\) MIMO (**a**). Regular Palm Tree Coplanar Vivaldi Antenna (RPT-CVA), Front Cut Palm Tree (FCPT-CVA), Middle Cut Palm Tree (MCPT-CVA), and (**b**). \(S_{11}\) and \(S_{21}\) of Regular Palm Tree Coplanar Vivaldi Antenna (RPT-CVA), Back Cut Palm Tree (BCPT-CVA), Complete Cut Palm Tree (CCPT-CVA). The return loss performance of the low frequency will be impacted by the corrugated structure or wave structure. The electric field will be trapped between the corrugated and wave structure. However, the Mutual scattering of HWSPT got the best performance than others. The \(S_{21}\) of RPT, ESEPT, and VWSPT is almost the same. Adding corrugated and wave structures in the vertical direction will affect the \(S_{21}\) performance at low frequencies. The return loss performance of RPT and RLPT is almost the same, likewise the performance of ELPT and MLPT-CVA. It could be shown in Figure 5b that by adding the Ellips and  
Figure 4: \(S_{11}\) and \(S_{21}\) performance of \(1\times 2\) MIMO **(a)**. Regular Palm Tree-Coplanar Vivaldi Antenna (RPT-CVA), Left Tilt Palm Tree (LTPT-CVA), Right Tilt Palm Tree (RTPT-CVA) and **(b)**. Regular Palm Tree-Coplanar Vivaldi Antenna (RPT-CVA), Hilbert Fractal Structure Palm Tree (IFSPT-CVA), Koch Fractal Structure Palm Tree (KFSPT-CVA). Figure 5: \(S_{11}\) and \(S_{21}\) performance of \(1\times 2\) MIMO **(a)**. Regular Palm Tree-Coplanar Vivaldi Antenna (RPT-CVA), Exponential Slot Edge Palm Tree (ESEPT-CVA), Vertical Wave Structure Palm Tree (VWPT-CVA), and Horizontal Wave Structure Palm Tree (HWPTCVA) and **(b)**\(S_{11}\) and \(S_{21}\) of Regular Palm Tree-Coplanar Vivaldi Antenna (RPT-CVA), Elips Lens Palm Tree (ELPT-CVA), and Metamaterial Lens Palm Tree (MLPT-CVA). metamaterial structure in the mouth flared of the two tapered slots, the return loss performance in the low-end frequency becomes worst in the low-end frequency than without adding structure. From Figure 5b, it can also be seen that RPT and RLPT have almost the same return loss at frequencies below 3 GHz, but above 3 GHz there are differences. \(S_{21}\) performance of RPT, RLPT, ELPT, and MLPT can be seen at the bottom of Figure 5b. Even though ELPT and MLPT appear to have \(S_{21}\) below \(-20\) dB at low-end frequency but only a few frequencies are covered. All four antennas have poor mutual catering parameters at low frequencies, even if at 0.895 GHz MLPT has \(S_{21}\) of \(-54.432\) dB. According to the overall scattering parameter simulation findings for the 15 antenna types, BCPT has the best \(S_{11}\) performance at low frequencies, while HWSPT has the most effective \(S_{21}\) performance at low-end frequencies. Adding the structure in the patch will affect the electric field so that it interferes with the scattering parameters.