# CPW-Fed Transparent Antenna for Vehicle Communications
Reference [20] presents an analysis of the obtained results of a V2V framework developed on VANETs to reduce large amounts of traffic from LTE networks. A relevant element in the design of vehicular communication systems is the antenna, which must satisfy the appropriate radiation specifications [21]. Besides, the antennas must ensure that there is no intervention with the vehicle operation. Usually, antennas are made of metal on dielectric substrates, which can be unattractive for the growing need to optimize spaces and offer better technical and aesthetic performance. Some examples of this are in references [22; 23]--present antennas for 802.11p standard, but are implemented in an opaque substrate. Even in reference [22], the proposed design is a volumetric structure. Furthermore, in [24], a fractal antenna design is presented--this antenna was fabricated using Polyvinyl chloride as a transparent substrate, but it uses copper for the radiation element, making it not completely transparent. Therefore, demand is emerging for research, development, and use of transparent antennas that can be integrated into windshields and windows, solar cell panels, mobile devices, and in the automotive industry, [25; 26]. Finally, it has to be mentioned that there exist other transparent antenna designs for vehicular communications, but they operate within the UHF and VHF bands [27; 28]. Additionally, transparent antennas start to be an option in the application of RF energy harvesting. Some examples of these applications are described by [29; 30]. For the development of transparent antennas, various materials and configurations have been tested to improve efficiency. Some of the transparent conductive films that have been tested for use in this type of antennas include silver-coated polyester film (AgHT-8) [31], indium-tin-oxide (ITO) [32], Indium-zinc-tin oxide (IZTO) [33], Silver grid layer coating (AgGL) [34], and zinc oxide heavily doped with gallium (GZO) [25]. Besides, some transparent antennas designs employ mesh metal films printed on glass substrates--these metal layers present a low sheet resistance [35; 36]. Recently, mesh metal films are applied in transparent antennas at 60 GHz to improve their performance [37]. On the other hand, there are many investigations of transparent antenna geometries. In reference [26] a transparent antenna for WLAN application in 5 GHz is introduced, whose topology is inspired in a flower with six petals built into indium-tin oxide film (ITO) as a transparent radiation element. Several antennas designs use coplanar wave feed [31; 38; 39], because the transparent conductive film is on just one side of the substrate. In [31], a coplanar waveguide-fed transparent antenna for extended ultrawideband applications is presented, using AgHT-8 thin film as conductive material with a staircase-shaped rectangular radiator and a modified partial ground. Moreover, references [38; 39] report a multiband transparent antenna using a coplanar waveguide for 5G applications. Notwithstanding the vast developed area, a remaining problem for designing transparent antennas based on conductive films with sheet resistance over 5 Ohms, (mainly with ITO) [26; 29; 30], is to obtain a multiband behavior with narrow bandwidths. Typically, the transparent antennas with ITO show a fractional bandwidth higher than 20% generating a UWB response. In this work, a multiband operation achieves, and the frequencies bands are well defined. In this work, the design of a fully transparent antenna using ITO-coated glass with a coplanar waveguide (CPW)-fed slot dipole with a multiband operation, IEEE 8002.11p (5.9 GHz), and LTE sub 6 GHz bands, is proposed for future vehicular communications applications. In order to obtain the desired frequencies, a modified ground plane was introduced with symmetrical rectangular stubs [40; 41]. The antenna characterization is performed by considering the measured reflection coefficient and the radiation pattern.