## 3 Results and Discussion
### Radiation Pattern Performance  
#### 3.2.1 Directivity Performance  
The directivity of the element and 1 \(\times\) 2 RPT, 1 \(\times\) 2 of FCPT, MCPT, BCPT, and CCPT is displayed in Figure 6a. At 2 GHz, by arranging the antenna into a MIMO, there is an improvement in RPT directivity of 3.2 dBi. At 2 GHz, the directivity of 1 \(\times\) 2 RPT and 1 \(\times\) 2 FCPT is 8.894 dBi and 11.587 dBi. This means there is an improvement in a gain of 2.693 dBi. However, at a frequency above 2 GHz, the gain decreases. The highest directivity is obtained for 1 \(\times\) 2 BCPT at 4 GHz of 12 dBi.  
Figure 6b shows the directivity comparison between single and 1 \(\times\) 2 RPT, 1 \(\times\) 2 of LTPT, RTP, HFSPT, and KFSPT. It demonstrates that the directivity changes slightly by tilting the antenna. It means there is an improvement in directivity by making the antenna position slightly tilted left and right, in this case, tilted 5 degrees, then the directivity does not change much. But at a frequency below 3.5 GHz, the 1 \(\times\) 2 RTPT has a better performance of directivity than 1 \(\times\) 2 LTPT and 1 \(\times\) 2 RPT. At low frequencies, it can be a  
Figure 6: Directivity of: (**a**). Single and 1 \(\times\) 2 Regular Palm Tree (RPT-CVA), 1 \(\times\) 2 Front Cut Palm Tree (FCPT-CVA), 1 \(\times\) 2 Middle Cut Palm Tree (MCPT-CVA), 1 \(\times\) 2 Back Cut Palm Tree (BCPT-CVA), 1 \(\times\) 2 Complete Cut Palm Tree (CCPT-CVA) and (**b**). Single and 1 \(\times\) 2 of Regular Palm Tree (RPT-CVA), 1 \(\times\) 2 Left Tilt Palm Tree (LTPT-CVA), 1 \(\times\) 2 Right Tilt Palm Tree (RTPT-CVA), 1 \(\times\) 2 Hilbert Fractal Structure Palm Tree (HFSPT-CVA), 1 \(\times\) 2 Koch Fractal Structure Palm Tree (KFSPT-CVA).  
consideration for arranging the antenna with a larger tilt angle outward position so that the electric field coming out of the two tapered slots does not affect each other. Figure 6b shows the directivity of 1 \(\times\) 2 KFSPT of 11.299 dBi while 1 \(\times\) 2 RPT of 8.894 dBi. At Frequency 4 GHz the 1 \(\times\) 2 KFSPT has the best directivity of 12.108 dBi.  
The directivity performance of single and 1 \(\times\) 2 RPT, 1 \(\times\) 2 of ESEPT, VWSPT, and HWSPT can be observed a Figure 7a. 1 \(\times\) 2 ESEPT has better performance of directivity than 1 \(\times\) 2 RPT and 1 \(\times\) 2 VWSPT almost at all frequency ranges. The best directivity is obtained at 4 GHz of 12.877 dBi. Figure 7b shows the directivity performance of single and 1 \(\times\) 2 RPT, 1 \(\times\) 2 RLPT, 1 \(\times\) 2 ELPT, and 1 \(\times\) 2 MLPT. At frequencies, less than 2.5 GHz the 1 \(\times\) 2 ELPT got the best performance of directivity. However, at a frequency of more than 2.5 GHz, 1 \(\times\) 2 MLPT has the best directivity. At 4 GHz, the directivity of 1 \(\times\) 2 RPT, RLPT, ELPT, and MLPT is 12.108 dBi, 14.329 dBi, 15.248 dBi, and 16.561 dBi. It means there is an improvement of directivity of 4.453 dBi. Although the MLPT has a larger substrate size than regular ones, adding a lens and metamaterial structure can trap the electric field in the lens causing the gain increase.  
However, in a wideband antenna, the wider the antenna bandwidth, the greater distance between elements relative to their wavelength (especially at high-end frequencies), and this cause a grating lobe which will reduce the directivity of the antenna. The grating lobe is a side lobe that is enlarged and resembles the main lobe, this thing caused by the effect of changing the distance between the antenna elements further apart. In this case the 1 \(\times\) 2 MIMO has spacing between element is 275 mm and it means that at a frequency of 0.5 GHz, the distance between elements is 0.458\(\lambda\) while at a frequency of 4.5 GHz the distance between elements is 4.125\(\lambda\). The distance between elements rises at 4.5 GHz, causing the grating lobe and antenna directivity to diminish.