## 5 Applications of DRA
### Solar Cells  
The requirement to get power from renewable resources is becoming more challenging owing to the current energy and environmental challenges. The integration of antennas with solar-cell panels offer compact integrated platforms to employ the electromagnetic spectrum in both microwave and optical regimes. Thus, various methods have been implemented to develop antennas with high performance and full compatibility with solar-cell panels. The most common method is to mount an antenna on the bottom side of the solar cells [118]. This method is simple and not affect the solar cells. However, this method has limited applications especially for broadside antennas. By integrating the antenna on top of solar cells, the required coverage will be improved for many applications, but it may reduce solar cell efficiency due to the shadowing effects of the antenna [119]. In order to reduce the shadowing effects, transparent conductive oxides were used [120; 121]. However, transparent conductive oxide has a sheet resistance greater than \begin{table}
\begin{tabular}{c c c c c c c c} \hline
**Ref.** & **Geometry** & \(f_{r}\) **(GHz)** & **BW (\%)** & \(\epsilon_{r}\) & **Gain (dBi)** & **Polarization** & **Applications** \\ \hline \multirow{2}{*}{[104]} & \multirow{2}{*}{Rectangular DR} & 1.7–2.2 & 25.6 & \multirow{2}{*}{9.2} & \multirow{2}{*}{4} & \multirow{2}{*}{LP} & \multirow{2}{*}{LTE automotive} \\  & & 2.5–2.7 & 7.69 & & & & & \\ \hline \multirow{2}{*}{[105]} & \multirow{2}{*}{Cylindrical DR} & 3.3–3.6 & 8.7 & \multirow{2}{*}{10} & \multirow{2}{*}{5.8} & \multirow{2}{*}{LP} & Short-distance vehicle-to-base station and long-distance vehicle-to-satellite communications \\  & & 10–10.5 & 4.88 & & & 12.0 & & \\ \hline \multirow{2}{*}{[116]} & \multirow{2}{*}{Cylindrical DR} & 3.1–5.6 & \multirow{2}{*}{57.5} & 9.8 & \multirow{2}{*}{8.7} & \multirow{2}{*}{LP} & Vehicle-mounted surveillance equipment \\  & & 28.7–29.9 & & & & & \\ \hline \multirow{2}{*}{[52]} & \multirow{2}{*}{Stacked Rectangular DR} & 19.8–20.8 & \multirow{2}{*}{4.92} & 2.2 & \multirow{2}{*}{10.2} & \multirow{2}{*}{6.6-8.2} & \multirow{2}{*}{CP} & UAV \\  & & 28.7–29.9 & & & & & \\ \hline \multirow{2}{*}{[66]} & \multirow{2}{*}{Cylindrical DR} & 3.34–3.54 & 5.8 & 9.8 & 42 & CP & V2V to V2I communications \\ \hline \multirow{2}{*}{[117]} & \multirow{2}{*}{Cross-shaped DR} & 6.26–8.74 & 33.1 & 6.15 & 10.77 & CP & Aerial vehicle \\ \hline \end{tabular}
\end{table} 
Table 11: Comparison between various DRAs for vehicular applications. Figure 28: Conical radiation pattern of the proposed antenna in E-plane at: (a) 33 GHz; (b) 41 GHz [116]. 5 \(\Omega\)/sq with a high optical transmittance and the sheet resistance reduces the radiation efficiency of the antenna. Meshed metallic structures [122] also can be used to improve shadowing effects, as shown in Figure 29. A metal mesh can overcome the drawbacks of conductive films. The open areas guarantee stable optical transparency over the visible light spectrum and the conductive mesh offers a higher sheet conductivity for better radiation efficiency. However, integrating metal-meshed antennas with solar cells might reduce the realized gain and transmission loss, especially at high frequency, due to the loss nature of solar cells and the anisotropy triggered by parallel electrodes on solar cells. To overcome this limitation, transparent dielectrics can be used as resonator antennas and can be mounted on top of solar-cell panels. This method can enhance the performance of the antennas with less shadowing impacts. However, a transparent dielectric usually has a low permittivity, which might affect the antenna design. In [123], a transparent rectangular DRA is integrated on top of a silicon solar cell with glass protection.