Wideband Optically Transparent Low-Profile Holographic Impedance Metasurface for Multimode OAM Generation

Conventional holographic impedance metasurfaces with large apertures usually have extremely narrow bandwidths, limiting their applications for broadband orbital angular momentum (OAM) waves. In this article, a new wideband, optically transparent low-profile holographic impedance metasurface is proposed for launching multimode OAM vortex waves. To enhance the bandwidth, a metasurface cell composed of materials with high optical transparency (indium tin oxide, polyethylene glycol terephthalate (PET), and borosilicate glass) is put forward for the first time. The design process is presented for wideband OAM implementation based on the distinctive dispersion properties of the devised cell. Moreover, the multimode multiplexed impedance distributions are exhibited. Simulation and measurement results show that the proposed metasurface can effectively generate dual-mode OAM waves from 17 to 21.5 GHz (BW
$=$
22.5%) with a high isolation of over 40 dB. The proposed method provides a comprehensive solution for wideband, optically transparent, easy fabrication, low profile, and multimode OAM launching.