Efficiency-Improved UWB Transparent Antennas Using ITO/Ag/ITO Multilayer Electrode Films

In this paper, a transparent antenna made with a new structure of ITO/Ag/ITO is proposed. Overcoming the physical limitations of transparency and conductivity is an important problem with transparent materials. By studying and comparing previously reported transparent materials, a transparent electrode with thin film Ag inserted between two layers of ITO instead of a single layer is selected for a highly efficient transparent antenna. This electrode has low sheet resistance (
$3.1~\Omega $
/sq) relative to its high transparency (88 % at 550 nm), which is a factor that can increase the efficiency of the antenna. In general, it is difficult to measure sheet resistance (SR) using a 4-point DC probe for very thin films (thickness of transparent material is less than the skin-depth). Therefore, a form of reverse engineering that can estimate DC sheet resistance using RF SR was presented and verified. As a result, it was possible to predict and design the performance of the transparent antenna with the new material structure. The selected transparent material is applied to design the wideband transparent antenna and the design process for wideband performance is covered in the paper. The proposed antenna with ITO/Ag/ITO was implemented for verification. The peak efficiency of the fabricated antenna was 66 %, and the measured bandwidth was 123 % (from 2.5 GHz to 10.6 GHz), which is the best performance than previously reported transparent antennas.