Experimental Demonstration of High Optically Transparent Reflectarrays Using Fine Metal Line Structure

In this article, we present a novel design method to achieve optically transparent reflectarrays (RAs) with fine metal line (FML) structure. With this design method, an RA element with a peak return loss of 2.8 dB and a phase variation of 360° is achieved during 12.5–14.5 GHz. Compared with the reported transparent RAs, we first realize wide phase variation, high transparency and low return loss simultaneously. The proposed element is composed of FML pattern, quartz glass substrate, and indium tin oxide (ITO) ground. The FML pattern consists of a metal cross and a folded square ring with a linewidth of 50
$\mu $
m made by a photolithographic process. For verification, three
$20 \times 20$
-element RAs with pencil beam and orbital angular momentum (OAM) beam have been arranged, simulated, fabricated, and measured. The measured results agree well with the simulations. The measured optical transmittance of all prototypes is greater than 82% at any position. The proposed FML structure greatly improves the transmittance and has potential for the applications in transparent communication devices.