Indium-Tin-Oxide-Based Broadband Optically Transparent Reflectarray Antenna Using a Multilayer Hybrid Dielectric Substrate and Heterogeneous Elements

In this communication, an optically transparent reflectarray antenna based on indium tin oxide (ITO) material is presented. The reflectarray is composed of a patterned ITO array, two quartz glass substrates, and an ITO ground. By introducing an air gap between the quartz glass substrates, a multilayer hybrid dielectric substrate is formed, reducing the high conductor loss of the ITO material. The heterogeneous single- and combined-resonance elements are jointly utilized to achieve a wider phase variation. At the center frequency of 20 GHz, the reflectarray element owns a reflection loss of less than 1.8 dB and a phase variation of 494°. For verification, a
$15\times15$
-element optically transparent reflectarray with a focus-to-diameter (F/D) ratio of 0.9 is designed, simulated, and measured. The measured results demonstrate good radiation characteristics, showing a measured gain of 24.4 dBi, a 1.5-dB gain bandwidth of 20%, and an overall optical transmittance of 75%. Compared with previously reported ITO-based transparent reflectarrays, this design achieves a wide phase variation, high optical transparency, low return loss, and broad bandwidth simultaneously.