# A Frequency-Selective Reconfigurable Antenna for Wireless Applications in the S and C Bands
## 3 Simulation Results
Both are \(0^{\circ}\) at the antenna's front while \(180^{\circ}\) at the back. According to the 2.04 GHz radiation pattern, the maximum gain of the antenna is, in this case, 0.82 dBi, observed at angles \(\theta=355^{\circ}\) and \(\varphi=180^{\circ}\). Furthermore, in front of the antenna, for \(\theta=\varphi=0^{\circ}\), the gain is \(-\)0.78 dBi. Similarly, the 4.44 GHz pattern shows a maximum gain of \(-\)0.31 dBi, at angles \(\theta=310^{\circ}\) and \(\varphi=135^{\circ}\). In front of the antenna, at \(\theta=\varphi=0^{\circ}\), the gain is \(-\)15.74 dBi. However, the gain can be increased to \(-\)3.78 dBi with the antenna's rotation to an angle of \(\theta=34^{\circ}\) on the elevation plane. Finally, the 6.42 GHz radiation pattern shows a maximum gain of 5.68 dBi, at angles of \(\theta=20^{\circ}\) and \(\varphi=0^{\circ}\) while at angles of \(\theta=\varphi=0^{\circ}\), it equals 4.13 dBi. As derived from the simulation, the antenna performs best when operating on mode 3, with a main resonance at 6.42 GHz. It demonstrates the maximum gain, and lowest return loss and VSWR. Figure 3: Simulation results of S11 parameter and VSWR for the antenna’s three modes of operation. Finally, Figure 5 provides a visual representation of the surface current distribution across the antenna for its three primary resonant frequencies: 2.04, 4.44, and 6.42 GHz. It is evident from the figure that, in addition to the patch, the ground plane significantly influences the antenna's radiation characteristics. Although the current is distributed across the entire antenna surface, there is a pronounced concentration behind the patch. Moreover, in all three cases, substantial contributions to the antenna's radiation emanate from the edge of the two segments of the ground plane, which are connected via the PIN diode. There are noticeable differences in the surface current distribution for each frequency. These distinctions in the surface current distribution directly translate into discernible differences in radiation patterns among the three frequencies, as observed in Figure 4.  
Figure 4: Simulated 3D radiation patterns for frequencies (**a**) 2.04 GHz, (**b**) 4.44 GHz, and (**c**) 6.42 GHz. Last but not least, the simulations demonstrate a good radiation efficiency for the antenna across its three primary resonant frequencies. At 2.04 GHz, the radiation efficiency stands at an exceptional 74%, while at 4.44 GHz and 6.42 GHz, it remains notably high at 59% and 54%, respectively. These findings are consistent with typical performance expectations, signifying the absence of significant losses on the antenna. The simulation results for the three resonant frequencies, where the antenna seems to function optimally, are summarized in Table 2. This summary includes the resonant frequencies, their return loss (S11), the VSWR, the bandwidth as defined on a \(-10\) dB level of return loss, the antenna's maximum gain for each case, as well as the azimuth and elevation angles where the maximum gain was observed. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Frequency (GHz)** & **S11 (dB)** & **VSWR** &
\begin{tabular}{c} \(-\)**10 dB** \\ **Bandwidth (MHz)** \\ \end{tabular} & **Max Gain (dBi)** & **Azimuth and Elevation of Max Gain** \\ \hline
2.04 & \(-39.5\) & 1.02 & 211 & 0.82 & \(\varphi=180^{\circ}\), \\
4.44 & \(-22.3\) & 1.17 & 941 & \(-0.31\) & \(\varphi=135^{\circ}\), \\
6.42 & \(-60.6\) & 1.01 & 452 & 5.68 & \(\varphi=0^{\circ}\), \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Simulation results summary for the three primary resonant frequencies in the 2, 4, and 6 GHz bands. Figure 5: Simulated surface current distribution for frequencies (**a**) 2.04 GHz, (**b**) 4.44 GHz, and (**c**) 6.42 GHz.