## 5 Experimental Results and Discussion  
To provide insight into the properties and working principles of the proposed antenna, with and without the metamaterial, the simulated current distribution is analyzed and discussed. Figure 9 shows the current distribution at each operating frequency. The current path at the lower frequency 0.9 GHz is shown in Figure 9 with a maximum surface current observed strongly around the edges of the slots and a small portion of radiating elements as well as along the T- junction. Figure 9,c shows the current distribution at 2.4 and 3.5 GHz. The intensity is high around the radiating elements and partially so on the slot edges. The radiation at 5.5 GHz is mainly from the radiating elements and the edge of the slots as shown in Figure 9. Furthermore, the power divider also contributes almost at all frequencies. As described in the literature, slots can be used to create a multiband operation [39]. By removing a small width and length of metal area, the antenna operating characteristics will be determined. As a result, the overall antenna performance will be enhanced. Here, it can be seen that multiband operation can be achieved due to the use of slots which strongly perturb the current distribution and increase the current path length as shown in Figure 9.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Para. ** & \begin{tabular}{c} **Value** \\ **(mm)** \\ \end{tabular}  & **Para. ** & \begin{tabular}{c} **Value** \\ **(mm)** \\ \end{tabular}  & **Para. ** & \begin{tabular}{c} **Value** \\ **(mm)** \\ \end{tabular}  & **Para. ** & \ \begin{tabular}{c} **Value** \\ **(mm)** \\ \end{tabular}  & **Para. ** & \begin{tabular}{c} **Value** \\ **(mm)** \\ \end{tabular}  \\ \hline \(l\) & 78.6 & _g1_ & 0.766 & \(l_{2}\) & 5.53 & \(w_{3}\) & 37.1 & \(t\) & 0.42 \\ \(w\) & 42.5 & _g2_ & 1.108 & \(l_{3}\) & 6.506 & \(w_{4}\) & 2.44 & \(s\) & \(1\) \\ \(l_{p}\) & 9.87 & _g3_ & 3.4 & \(l_{4}\) & 11 & \(w_{5}\) & 19.14 & & \\ \(w_{p}\) & 14. The impact of the rectangular slot (SL) is depicted in Figure 10a with a small impedance match at 3.5 GHz when the SL = 20 mm. Furthermore, the optimal benchmark SL value is 25 mm, while two additional resonances are generated at 0.9 and 2.4 GHz as shown in Figure 10b, whereas the two layers of the MTM unit cells are still applied. Figure 11 shows the fabricated two-element antenna array prototype with the metamaterial unit cell. Its reflection coefficient (S11) with and without the MTM is shown in Figure 12. The S11 of the final measured prototype is seen in Figure 13, along with simulated results for the same antenna. It covers the four bands used for the following standards: GSM 900 at 900 MHz, WLAN at 2.3, 2.4, 5, 5.2, and 5.8 GHz, LTE-A at 3.5 GHz, and 5G WiFi centered at 5.5 GHz. The measured results indicate a significant increase in the bandwidth for the highest band, allowing improvement from 9.35% (simulated without unit cell) to 28% (measured with MTM). Moreover, the third band shifted slightly towards high frequencies at 3.5 GHz, with an increment of 27.81%. The lower band frequency at 900 MHz was matched by applying the MTM unit cell. Figure 10: Simulated reflection coefficient for different slot length at: (**a**) SL = 15 mm, SL = 20 mm; (**b**) SL = 25 mm, and SL = 30 mm. Figure 9: Simulated surface current intensity at: (**a**) 900; (**b**) 2.4; (**c**) 3.5; and (**d**) 5.5 GHz. Figure 11: The fabricated prototype of the proposed coplanar waveguide (CPW) antenna: (**a**) 3D view; (**b**) front view; (**c**) back view with MTM; and (**d**) MTM super substrate structure. Figure 12: Simulated reflection coefficient (S11) with and without MTM. The achieved gain of the proposed antenna is shown in Figure 14. The maximum realized gain is increased from 3.4 (without metamaterial) to 6.47 dBi (with metamaterial) at 3.5 GHz. This is a 3 dB improvement and is due to the MTM layers acting as a superstrate which, unlike reflectors, use solid metal that can be placed in close proximity to the radiating elements (here 10 mm).