Ultra-uniform diffraction patterns in meshed optically transparent antennas

Abstract

State-of-the-art optically transparent antennas used for shared RF/EO/IR apertures typically utilize mesh conductors to simultaneously achieve high optical transmission and low RF resistivity compared to that of transparent conducting oxides (TCOs). Unlike TCOs, however, mesh conductors need to be patterned in a geometric shape – most commonly a square or rectangular periodic grid. As a result, this grid can introduce a diffraction pattern which can degrade the imaging quality of the optical system. It is shown that transmission decreases according to the geometric area covered by the mesh at normal incidence and that transmitted energy is pushed into higher diffractive orders, as expected. These effects are ultimately summarized as a decrease in the signal-to-noise and signal-to-background ratios. Performance tradeoffs in varying the line width and line spacing of a rectangular grid are shown whereas the smaller the line width and spacing, the smaller effects there are from the grid. Furthermore, methods to reduce diffractive effects –improving imaging quality - in structures by randomizing the substructure in which light interacts are presented. Randomizing tiled mesh substructures reduces periodicity to generate ultra-uniform diffraction, while maximizing conductivity of the structure. Increased randomization of a meshed aperture allows for a reduction in higher diffraction orders by 99%. By leveraging the results of this study, shared RF/EO/IR apertures can maximize their performance across the electromagnetic spectrum.