## 5 Conclusions  
An ultrathin wideband angularly stable frequency selective surface (FSS) bandpass filter covering the S-C bands was designed and carefully investigated in this paper. The filter structure comprised a multilayer bandpass metasurface obtained by interposing an ultrathin dielectric substrate between two miniaturized FSS layers.  
An analytical synthesis procedure was derived by relying on an equivalent circuit model based on the transmission line theory. A prototype was designed, fabricated, and experimentally characterized for validation of the design procedure. The measured results showed good consistency with the ones obtained from the full wave simulations, thus verifying the effectiveness of the design strategy. The proposed filter exhibited a \(-3\) dB transmission band spanning from 2 to 6.76 GHz (a 108.7% fractional bandwidth), also proving a stable response under incidence angles up to 40\({}^{\circ}\).  
The aforementioned configuration, due to its exceptional attributes of wideband flat bandpass, low profile, polarization insensitivity, and angular stability, holds significant potential in the field of electromagnetic shielding and compatibility. Future work will explore the integration of advanced fabrication techniques, such as screen-printing and physical vapor deposition (PVD), to further reduce the thickness of the proposed shielding structure and enhance its adaptability for application-specific requirements. Its versatility makes it suitable for a large variety of applications and contexts, including wireless communication systems, radar technology, and satellite communication platforms, guaranteeing the instrumentation's safety and efficiency. Given the significance of practical deployment in real-world applications, future research efforts will also focus on systematically investigating and enhancing the mechanical and electromagnetic robustness of the proposed radome. Particular attention will be devoted to its integration as a conformal coating on target platforms operating in complex environments, such as the fuselage of unmanned aerial vehicles (UAVs), thereby ensuring reliable and seamless functionality in mission-critical scenarios.  
\begin{table}
\begin{tabular}{c c c c c} \hline
**Paper** & **Dimension** & **Thickness** & **Fractional BW (\(-3\) dB)** & **Angular Stability** \\ \hline
[31] & \(0.08\lambda_{L}\times 0.08\lambda_{L}\) & \(0.3\lambda_{L}\) & \(10\%\) & \(60^{\circ}\) \\ \hline
[32] & \(0.11\lambda_{L}\times 0.11\lambda_{L}\) & \(0.021\lambda_{L}\) & \(5\%\) & \(60^{\circ}\) \\ \hline
[33] & \(0.15\lambda_{L}\times 0.15\lambda_{L}\) & \(0.025\lambda_{L}\) & \(54\%\) & - \\ \hline
[34] & \(0.04\lambda_{L}\times 5.7\lambda_{L}\) & \(0.21\lambda_{L}\) & \(130\%\) & \(40^{\circ}\) \\ \hline
[35] & \(0.09\lambda_{L}\times 0.09\lambda_{L}\) & \(0.02\lambda_{L}\) & - & \(60^{\circ}\) \\ \hline
[36] & \(0.18\lambda_{L}\times 0.18\lambda_{L}\) & \(0.24\lambda_{L}\) & \(40\%\) & \(45^{\circ}\) \\ \hline
**[this work]** & \(\mathbf{0.16\lambda_{L}\times 0.16\lambda_{L}}\) & \(\mathbf{0.03\lambda_{L}}\) & \(\mathbf{108.6\%}\) & \(\mathbf{40^{\circ}}\) \\ \hline \end{tabular}
\end{table}
Table 3: Comparison of the proposed bandpass FSS filter with previous works in the literature.  
**Author Contributions:** Methodology, F.P. and D.B.; Software, F.P.; Validation, D.B. and A.M.; Investigation, F.P.; Writing--original draft, F.P.; Writing--review & editing, F.P. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research received no external funding.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.  
**Conflicts of Interest:** The authors declare no conflict of interest.