## 2 Materials and Methods
Both radiator and ground plane are set as perfect conductors, and the optimized dimensions of each part are shown in Table 1.  
Based on the above dimensions, four types of glass antennas were fabricated with three metallization techniques for top-layer radiators and bottom-layer ground planes. Three metallization techniques include using (1) conductive copper foil (CCF), (2) conductive silver paste (CSP) and (3) ITO conductive film. Table 2 illustrates the structures of these four glass antennas: (1) antenna with CCF as radiator and ground plane, as in case 1; (2) antenna with ITO film as radiator and CCF as ground plane, as in case 2; (3) antenna with CCF as radiator and ITO film as ground plane, as in case 3; and (4) antenna with CSP as radiator and ground plane, as in case 4. The photos of these fabricated samples are shown in Figure 2. The specific processing methods for the three metallization options are described in detail below. The CCF is stuck to the glass substrate through a kind of acrylic adhesive on the back side, and the acrylic adhesive owns the properties of high-temperature resistance and chemical resistance, which is followed by the laser etching process for further treatment of CCF [20]. The laser etching machine used for processing is a picosecond UV laser (Wuhan Hero Optoelectronics Technology Co. Ltd, Wuhan, China) with a minimum focused spot of less than 10 um and with a laser frequency range of 1 Hz-1 MHz at a wavelength of 355 nm. The laser etching machine focuses the laser onto the copper foil and heats it locally to exceed the melting point, then blows the molten metal away with high-pressure gas. The picosecond UV laser adopts the self-developed CCD automatic positioning laser etching technology, which can complete automatic etching by importing CAD data. As the laser moves relative to the copper foil on the glass substrate, the desired shape of the upper radiator can be cut out and realized. As a glass metallization solution, CCF based on laser etching technology owns the merits of high dimension precis \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Structure** & **Length (mm)** & **Width (mm)** & **Thickness (mm)** \\ \hline Glass substrate & 30.00 & 30.00 & 0.70 \\ Rectangular patch & 7.10 & 11.50 & - \\ Quarter-wave length converter & 3.90 & 0.10 & - \\ Feeding line & 7.55 & 1.00 & - \\ Ground plane & 30.00 & 30.00 & - \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Dimensions of the proposed glass antenna. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Case** & **Top Layer** & **Bottom Layer** & **Conductor** \\ \hline case 1 & CCF & CCF & Silicon-boron glass \\ case 2 & ITO & CCF & Silicon-boron glass \\ case 3 & CCF & ITO & Silicon-boron glass \\ case 4 & CSP & CSP & Silicon-boron glass \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Composition of the 4 types of glass antennas. conductivity, while this method should also pay attention to laser control during processing in order to avoid damaging the glass substrate below or burning the required part of CCF. In this study, CCF is used in cases 1, 2, = and 3. ITO conductive film is a semiconductor oxide material with high visible light transmission, high mechanical strength and high chemical stability, which is commonly used in industrial applications [21; 22]. In cases 2 and 3, glass substrates are deposited with ITO films for realizing the radiator and ground plane by magnetron sputtering. In fabrication, ITO thin films are created by using ionized inert gas to bombard the ITO target, causing ITO atoms to be deposited on the glass substrate to form a nanoscale layer. Therefore, ITO films with high visible light transmission were initially applied in the display area, and they now can be used for the implementation of optically transparent glass antennas. The ITO film based top-layer radiator and bottom-layer ground plane are presented in Figure 3 from which we can observe that the fabricated glass sample with ITO film possesses extremely high visible light transparency.