# A Frequency-Selective Reconfigurable Antenna for Wireless Applications in the S and C Bands
## 4 Experimental Results and Discussion
Regarding the truncation of the VSWR plots (Figures 3 and 10), it is important to note that the optimal VSWR value is 1. In practice, real antennas commonly exhibit VSWR values within the range of 1 to 2 at their resonant frequencies. Values exceeding 10 are not displayed in the figures, as they signify a significant portion of the radiation being reflected and not reaching the antenna. This adjustment was made to provide a clearer focus on the region close to 1, which holds greater significance. Next, the radiation patterns for these three modes at 2.07, 4.63, and 6.22 GHz, on both the azimuth and the elevation planes, are illustrated in Figure 11. Like before, the azimuth angle will be referred to as \(\varphi\), while the elevation angle is defined as \(\theta\). Furthermore, the simulation results at 2.04, 4.44, and 6.42 GHz are also included in the figure. Figure 10: Experimental results of the S11 parameter and VSWR for the three modes of operation. While the cross-polarization pattern can offer valuable insights into how the antenna interacts with signals of different polarizations, it is excluded (Figure 11) for the sake of conciseness. The information already presented, including S11/VSWR, radiation pattern, gain, and, now, efficiency for the primary resonances, can adequately convey a comprehensive understanding of the antenna's performance. In turn, according to the 2.07 GHz radiation pattern, the gain of the antenna on the azimuth plane, for elevation angle \(\theta=0^{\circ}\), has a maximum value of 0.45 dBi for an azimuth angle \(\varphi=176^{\circ}\), at the back of the antenna. Figure 11: Measured radiation patterns (in blue) on azimuth (**left**) and elevation (**right**) planes for frequencies: (**a,b**) 2.07 GHz, (**c,d**) 4.63 GHz, and (**e,f**) 6.22 GHz, along with the respective simulated radiation patterns (in red) for frequencies 2.04, 4.44, and 6.42 GHz. As for the forward direction of the antenna, for azimuth and elevation angles \(\varphi=\theta=0^{\circ}\), the gain is \(-0.54\) dBi. By rotating the antenna on the elevation plane at an angle \(\theta=25^{\circ}\), the gain can be improved to the value of \(3.81\) dBi, while \(\varphi=0^{\circ}\). Moreover, the absolute maximum gain is \(5.48\) dBi, which is observed at an elevation \(\theta=140^{\circ}\) at the back of the antenna (\(\varphi=180^{\circ}\)). Similarly, the \(4.63\) GHz patterns indicate that on the azimuth plane (\(\theta=0^{\circ}\) or \(180^{\circ}\)), the highest gain value is \(1.92\) dBi found at \(\varphi=322^{\circ}\). On the forward direction of the antenna, for \(\varphi=\theta=0^{\circ}\), the gain is \(0.58\) dBi. Furthermore, taking both planes into account, a maximum gain could be equal to \(3.97\) dBi at an elevation of \(\theta=152^{\circ}\) and azimuth of \(\varphi=180^{\circ}\). Finally, the \(6.22\) GHz radiation patterns demonstrate a primary lobe with a maximum gain of \(9.12\) dBi, on the azimuth plane at \(\varphi=0^{\circ}\) and \(\theta=0^{\circ}\). In the condition of \(\varphi=0^{\circ}\), and if the antenna is rotated to an angle \(\theta=12^{\circ}\) on the elevation plane, then the gain can be further increased up to \(12.79\) dBi. The experimental results indicate that the antenna operates almost equally well in all three bands of \(2,4\), and \(6\) GHz, at the resonant frequencies of \(2.07\), \(4.63\), and \(6.22\) GHz. However, at \(6.22\) GHz, a much higher gain can be attained. A summary of the results, derived from the network analyzer measurements and the radiation patterns, is shown in Figure 8.0 That includes the resonant frequency, return loss (S11), VSWR, the bandwidth as defined on a \(-10\) dB return loss level, the maximum attainable gain for the three main resonances, as well as the azimuth and elevation angles where observed. As compared to the simulation results, some slight deviations are observed.