A Transparent Artificial Periodic Structure for Beam-Tilting Antenna

A transparent anisotropic artificial periodic structure (APS) based on indium tin oxide (ITO) and its application in a beam-tilting antenna are proposed in this letter. The proposed APS is composed of double split-ring structures printed on both sides of a glass substrate. By tuning the size of the double split-ring structure, a refractive index variation ranging from 1.8 to 3.3 can be obtained. In the meantime, high optical transparency is achieved using a transparent conductor, ITO, with moderate surface resistance. To validate the proposed design, a transparent medium composed of the proposed APS unit cell is constructed to realize beam tilting in an endfire antenna. Simulation and measurement results show that the main beam direction of the entire antenna in E-plane is tilted by 13° and 17° with respect to the original endfire direction at 8.5 and 9.5 GHz, respectively. Compared with the initial feeding source antenna, the proposed beam-tilting antenna shows a gain enhancement of 2.2 dB at 9.5 GHz. The results show that the performance of the periodic structure using the low-conductivity ITO as the conductive layer is comparable with that using high-conductivity metal. This proposed technology can find potential applications in the internet-of-things, vehicular communications, and navigation systems.