# CPW-Fed Transparent Antenna for Vehicle Communications
## 2 Materials and Methods  
In this research, Adafruit commercial indium-tin-oxide (ITO)-coated glass with a thickness of 1850 A was employed to fabricate the proposed antenna. The transparent conductive oxide (TCO) sheet resistance (Rs) was estimated by the well-known method of the four-point probe [42] performed over thirteen positions on a film sample, as can be seen in Figure 1. Table 1 presents those results and the final average for Rs of 7.943 ohm/square that was used for the design and simulations of the antenna. The substrate is glass with relative permittivity and thickness of 5.5 and 1.1 mm, respectively. In the development of antennas, those factors are significant to determine the frequency responses and antenna efficiency [32]. Therefore, it is important to incorporate them into the antenna design and simulation process. Moreover, a coplanar waveguide-fed slot antenna with impedance matching stub was chosen to obtain a multiband response through a crossmatch technique for a proper impedance matching [40; 41], and allowing both the radiator and the ground plane to be on the same side for fabrication ease. High-frequency structural simulator (HFSS, ANSYS, PA, US) was used to design and optimize the chosen topology for the transparent antenna through parametric analysis.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Position** & **Resistance (\(\Omega\))** \\ \hline
1 & 7.831 \\
2 & 7.909 \\
3 & 7.970 \\
4 & 8.008 \\
5 & 8.035 \\
6 & 7.997 \\
7 & 7.914 \\
8 & 7.954 \\
9 & 7.914 \\
10 & 7.900 \\
11 & 7.922 \\
12 & 7.958 \\
13 & 7.950 \\ \hline Average & 7.943 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Rs/Square Measurements Obtained on ITO Film.  
Figure 1: Schematic positions on indium-tin oxide (ITO) film placed on a glass slide for sheet resistance (Rs)/square measurement.  
Through a parametric analysis in the HFSS simulator, the optimized antenna dimensions were obtained, and they are shown in Figure 2 and described in Table 2, respectively. The antenna feedline was calculated to obtain a coplanar waveguide (CPW) with a characteristic impedance of 50 ohms. The proposed transparent antenna is a capacitively coupled CPW-fed slot, dipole antenna with two pairs of protruded slot lines with different lengths, W1 and W2. The resonant frequencies correspond to the two different resonant paths. The two resonance frequencies for the design are 1.9 GHz and 5.9 GHz, which are used in LTE and 802.11p, respectively. Besides, in the parametric analysis, we made variations over the parameters W1, W2, and Wp1, to reach the desired frequency bands performing the matching impedance and observe their impact on the antenna design.  
In [40], it is mentioned that the resonant frequencies are independently controlled by a common aperture and the three pairs of respective thin slots. However, in our design, the variation of the length W1 shift both frequencies, as shown in Figure 3a. Moreover, Figure 3b shows variations in the higher frequency due to change in the length W2, while the lower frequency is fixed. Similar behavior is observed in Figure 3c when varying the width of the central patch, the high frequency is mainly affected, whereas the lower band is minimally changed. The reason is attributable to the fact that lengths of W2 and Wp1 are closer to the shortest wavelength [41]. It is important to mention that in our simulations, the SMA connector was considered.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameter** & **Size (mm)** & **Parameter** & **Size (mm)** \\ \hline W & 50 & L & 17 \\ Wg & 9.5 & Lp1 & 4 \\ Wp1 & 8.5 & Lp2 & 0.4 \\ Wp2 & 1 & L0 & 4 \\ W0 & 3.5 & L1 & 1.5 \\ W1 & 13.5 & L2 & 1.5 \\ W2 & 8.5 & D & 6.5 \\ G & 0.4 & D1 & 0.5 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Dimensions of the Proposed Antenna.  
Figure 2: Antenna configuration with dimensions.