## 3 Results and Discussions
### Simulation Results
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**State** & **Resonance** & **Bandwidth** & **Suitable Communication** \\  & **Frequency** & **Applications** \\ \hline State-1 (ON-ON) & 2.4 GHz & 645 MHz & Wi-Fi, Bluetooth, IoT \\ \hline State-2 (OFF-ON) & 3.33 GHz & 1.31 GHz & Wi-Fi, Bluetooth, IoT \\ \hline State-3 (ON-OFF) & 3.0 GHz & 1.05 GHz & Wi-Fi, Wi-Fi 6, IoT \\ \hline State-4 (OFF-OFF) & 3.45 GHz & 1.53 GHz &
\begin{tabular}{c} 5G mid-bands, Wi-Fi, Wi-Fi 6E, IoT, Cellular bands \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 1: RF performance parameters of the frequency-reconfigurable antenna for each state. Figure 8: _Cont._  
Figure 7: The simulated reflection coefficient (S11) of the proposed frequency–reconfigurable antenna. Another important performance parameter for the proposed antenna is depicted in Figure 10. It is clear from Figure 10 that different radiation efficiencies are observed. For the ON-ON state, the efficiency ranges from 0.3 to 0.48 as the frequency increases. In the ON-OFF state, the radiation efficiency ranges from 0.3 to 0.50 with increasing frequency. The OFF-OFF state has a radiation efficiency ranging from 0.32 to 0.58 as the frequency increases. Finally, the OFF-ON state has a radiation efficiency ranging from 0.35 to 0.5. These results are relevant for sub-6 GHz applications, as they provide information about the radiation efficiency of the frequency-reconfigurable antenna at different frequencies within this range. The ability of the antenna to reconfigure its frequency, pattern, and polarization using PIN diodes makes it suitable for various applications, including WLAN and sub-6 GHz 5G [48]. The antenna design involves proximity-coupling feeding and the use of PIN diode switches to control the excitation of the radiating patch and the length of the feed lines [48]. The experiments conducted by [48] demonstrated that the designed antenna could be switched between two states operating at 2.45 GHz and 3.50 GHz, making it suitable for WLAN and sub-6 GHz 5G applications. The existing literature also highlights the importance of reconfigurable antennas in wireless systems and the different classifications of reconfigurability, including radiation pattern, polarization, and frequency-reconfigurable antennas [48]. While there are only a few preliminary studies on antennas with differential schemes and reconfigurable abilities, the proposed frequency-reconfigurable antenna in this case contributes to the advancement of this research area [48]. In the context of sub-6 GHz applications, ref. [49] discuss the challenges and requirements of future connected and automated driving applications, which may require a larger bandwidth and higher data rates than those currently supported by sub-6 GHz V2X technologies. They propose a sub-6 GHz assisted mm-Wave MAC that decouples the mm-Wave data and control planes, offloading mm-Wave MAC control functions to a sub-6 GHz V2X technology [49]. This highlights the need for innovative solutions to address the challenges of high-frequency bands and high mobility in vehicular communications [49]. In conclusion, the simulated radiation efficiency results of the frequency-reconfigurable antenna in its four states provide \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & & **OFF-ON** & **ON-OFF** & **OFF-OFF** \\ \hline \multirow{3}{*}{3 GHz} & \(\Theta=90^{\circ}\) & **185\({}^{\circ}\)** & **185\({}^{\circ}\)** & **186\({}^{\circ}\)** \\ \cline{2-5}  & \(\Phi=0^{\circ}\) & 180\({}^{\circ}\) & 180\({}^{\circ}\) & 180\({}^{\circ}\) \\ \cline{2-5}  & \(\Phi=90^{\circ}\) & **164\({}^{\circ}\)** & **164\({}^{\circ}\)** & **162\({}^{\circ}\)** \\ \hline \multirow{3}{*}{3.5 GHz} & \(\Theta=90^{\circ}\) & **186\({}^{\circ}\)** & **185\({}^{\circ}\)** & **189\({}^{\circ}\)** \\ \cline{2-5}  & \(\Phi=0^{\circ}\) & **180\({}^{\circ}\)** & **179\({}^{\circ}\)** & **179\({}^{\circ}\)** \\ \cline{2-5}  & \(\Phi=90^{\circ}\) & **164\({}^{\circ}\)** & **164\({}^{\circ}\)** & **162\({}^{\circ}\)** \\ \hline \hline \end{tabular}
\end{table}