# Study of Mesh Pattern for Optically Transparent Flexible Antenna with Feedline
## 1 Introduction  
Optically transparent flexible antennas have attracted great attention in the recent year, as the demand for transparent devices have been increasing in various industrial fields. Since the advantages of transparency and flexibility of the antennas can solve many hardware constraints, they have been widely used in various applications such as integration with satellite solar cell panels, with displays, and with vehicle windshields [1, 2, 3, 4, 5]. In particular, as the Internet of things and machine-to-machine communication are widely commercial, they have become an important alternative in using devices of various shapes and sizes [6, 7, 8]. Transparent conductors are necessary to realize a flexible transparent antenna, for which the most commonly used materials are transparent conductive films and metallic mesh. Antennas integrated on transparent conductive films, such as indium tin oxide (ITO) [9, 10], fluorine-doped tin oxide [11], and silver-coated polyester films [12], obtained high transparency, light weight and flexibility. However, these films exhibit high sheet resistance, which degrades the performance of transparent antennas compared with metal antennas. To overcome this problem, multilayer films was developed. By inserting a metal layer between two transparent conducting oxide (TCO) layers, higher conductivity than TCO is realized, for example, ITO/Cu/ITO configuration [12], indium-zinc-tin oxide (IZTO)/Ag/IZTO configuration [13]. However, they cause difficulty of fabrication and there is a high cost associated with this. Meanwhile, metallic mesh material is a better alternative to overcome these drawbacks. The design principle of implementing a transparent antenna using a metallic mesh is very intuitive. The mesh pattern formed of conductive metal wire guarantee transparency in the visible light region through the open space in the mesh, and the metal mesh has superior conductivity and functions as a suitable radiator. Moreover, in addition to the flexibility of mesh patterns, they can have cost savings and weight reduction [14, 15]. Therefore,transparent flexible antennas using a metal mesh have been studied at various frequencies for various applications in a wide field [15; 16; 17]. However, these studies focused on the antenna implementation by optimizing some parameters by limiting to only a square mesh for the purpose of the antenna. There are also studies comparing the antenna performance by replacing copper with silver, focusing only on the mesh conductor material [18; 19]. To the best of our best knowledge, no work has been performed on detailed studies of the effect of the mesh pattern, which is the most basic design element to implement a metal mesh, on the antenna performance. In particular, comparison of the effect of various types of mesh on antenna performance has not been studied. In this study, we analyze the most commonly used square and diamond mesh patterns by applying them to the feed line and antenna respectively. We analyze the effect of mesh variables and evaluate the trade-off between transmission characteristics and optical transparency (OT) in the case of a feed line and the trade-off between antenna efficiency and OT in the case of an antenna. Although a transparent substrate is an essential element of transparent applications, the core of this study is an analysis of the effect on transmission lines and antennas by focusing on the transparency of the mesh pattern composed of the conductor layer. Therefore, we used an opaque material to minimize errors in the manufacturing process in order to focus on the results according to the change of the mesh pattern. In small-scale manufacturing companies, micro metal mesh film production technology is insufficient, so it is a choice for accurate research.