Influence analysis of dielectric substrate and protective films on the frequency characteristics and scattering of an L-shaped metastructure

<jats:p>The influence of dielectric substrate parameters and protective films on the frequency response and scattering characteristics of a planar L-shaped metastructure operating in the 16–25 GHz range is investigated. The purpose of the study is to determine the configuration providing maximum suppression of backscattering and efficient redistribution of electromagnetic energy into side lobes. Numerical simulations were performed using the finite element method implemented in Ansys HFSS, followed by experimental verification under free-space conditions. The investigated structure consists of a periodic array of metallic unit cells containing four nested L-shaped resonators located on a dielectric substrate backed by a conducting screen. Variations in substrate thickness, dielectric permittivity, and protective coating composition were considered. It was found that increasing the substrate thickness shifts resonance frequencies toward lower values due to changes in the effective electrical length of the resonators. An optimum substrate thickness of 1.5 mm was established, providing resonance maxima at 22.75 and 24.25 GHz and reducing the normal reflection level from 338 to 43 mV. Among the investigated materials, RO3006 with relative permittivity εr = 6.15 demonstrated the best performance, providing backscatter reduction up to 21 dB at 21 GHz. Polymer protective films weakly affect the electromagnetic characteristics, whereas increasing the concentration of graphite filler noticeably deteriorates scattering properties. The obtained results may be used in the design of compact metasurfaces intended for radar cross-section reduction and scattering pattern control.</jats:p>