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 end-fire 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 end-fire direction at 8.5 GHz 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.