# CPW-Fed Transparent Antenna for Vehicle Communications
## 3 Results and Discussion  
After obtaining the results through numerical simulation, the antenna was manufactured, and measurements of return loss, gain, and radiation diagrams were performed. The transparent antenna was fabricated by using a photolithography process. The transfer of the antenna geometry to the ITO-coated glass was made using a photosensitive film, which was exposed to UV light through a mask with the antenna geometry. Then the area exposed was removed to continue with the etching of the ITO films with a (1:1) solution of hydrochloric acid (HCL). This last process was done at 40 \({}^{\circ}\)C temperature for 2 min. Finally, we remove the photoresistant layer. Besides, an SMA connector was employed to connect the antenna; this connector was soldered to the transparent antenna using indium (In) solder spheres. The fabricated antenna placed onto the BUAP label is shown in Figure 4, where the transmittance of the ITO can be observed. The vector network analyzer (VectorStar, Anritsu) was used to measure the S11 from 0.5 GHz to 12 GHz. The simulated and measured return loss (S11) are shown and compared in Figure 5. The measured S11 at 5.9 GHz is -16.7 dB, which shows a good agreement with the simulated results. Figure 3: Simulated reflection coefficient of the ITO antenna for three parameters variations: (**a**) W1; (**b**) W2; (**c**) Wp1. Although a slightly detuned response is obtained from the measurement, related to fabrication flaws, each fractional bandwidth (FWB) remains, as can be seen in Table 3, showing the FBW for every band in simulation and measurement. The measured FBWs for S11 below \(-10\) dB at the lower band is 31.34% (1.82 to 2.5 GHz), and at the upper band is 87.03% (4.66 to 11.84 GHz), which is large enough to cover the 5.9 GHz required frequency. Thus, experimental results fulfill the communication IEEE 802.11p standard for the required band. Figure 6 shows the simulated and measured 2-D radiation patterns of the proposed antenna at 2.1 and 5.9 GHz. At both frequencies, the H-plane radiation pattern presents omnidirectional behavior, whereas the E-plane radiation pattern is bidirectional. Moreover, to complete the characterization of the antenna, the peak gain of the antenna was simulated and measured at 2.1 and 5.9 GHz--Table 4  
Figure 4: Manufactured antenna photography. Figure 5: Comparison of simulated and measured return loss parameters. \begin{table}
\begin{tabular}{l c c} \hline  & \(\mathbf{f_{range}}\) & **FBW** \\ \hline S & 1.39–1.99 & 36.36\% \\ M & 1.82–2.5 & 31.34\% \\ S & 3.54–7.75 & 71.35\% \\ M & 4.66–11.84 & 87.03\% \\ \hline \end{tabular}
\end{table} 
Table 3: Simulated (S) and Measured (M) Fractional Bandwidth Comparison. FBW: Fractional Bandwidth. summarizes the obtained peak gains. The measured radiation patterns and peak gains are in concordance with the simulate results. Besides, the antenna efficiency at 2.1 and 5.9 GHz was simulated; the obtained values are 10% and 15%, respectively. These gain peaks and efficiency values are in agreement with those reported for other antennas that use ITO as a conductive film [43]. Furthermore, the current distribution for the transparent antenna was obtained by simulation at 2.1 and 5.9 GHz, and it is presented in Figure 7. From Figure 7a, it is observed that the distribution current at 2.1 GHz is more intense on the feedline and, at the bottom of the middle path. Another significant amount of current is around the geometry of the antenna. On the other hand, at 5.9 GHz, the current distribution is mainly on the feedline, and at the middle patch. However, there is a significant amount of current between the resonators and at the largest resonator edges, as shown in Figure 7b. \begin{table}
\begin{tabular}{c c c} \hline  & **2.1 GHz** & **5.9 GHz** \\ \hline S & \(-\)0.167 dB & \(-\)2.12 dB \\ M & \(-\)0.145 dB & \(-\)3.9 dB \\ \hline \end{tabular}
\end{table} 
Table 4: Simulated (S) and Measured (M) Peak Gain.