All-dielectric bilayer angular-selective surface for free-space filtering in W-band

In this work, we demonstrate a fully dielectric bilayer angular-selective surface with large-angle operation in the W band, based on periodically perforated dielectric slabs and validated experimentally under free-space measurement. Whereas the corresponding single-layer structure exhibits only weak angular selectivity, the bilayer architecture converts the incidence angle into an effective tuning parameter that controls the width and sharpness of the transmission band. The modeled, simulated and measured results show a clear evolution from a broad transmission window near normal incidence to a narrower and increasingly selective passband at oblique incidence, while maintaining transmission up to \(θ ≈ 80^∘ \) . Field distributions support a coupled-resonator interpretation in which the air spacer governs interlayer phase accumulation and Fabry–Pérot-like transmission. We experimentally demonstrate that angular dispersion can be engineered as a useful filtering degree of freedom in a metal-free dielectric frequency–selective surface. Our results establish multilayer perforated all-dielectric structures as a simple platform for exploiting angular dispersion in low-loss millimeter-wave free-space filters and quasi-optical systems.