# Frequency Selective Surfaces: Design, Analysis, and Applications
## 12 Conclusions  
This study provides an analysis of frequency selective surfaces (FSSs), a rapidly evolving area in modern electromagnetism. Traditional FSS structures are systematically categorized into four primary groups based on their geometries: center-connected elements like dipoles and Jerusalem crosses, loop types including various legged elements and loops, solid interior or plate types, and combinations of these forms. The operational mechanisms of these traditional FSSs are fundamentally reliant on structural-based resonances, which are briefly discussed along with methods of characterization and numerical simulations.  
The research presented in this paper extensively details various design techniques, array element structures, frequency ranges, bandwidths, and polarization characteristics through comparative tables. This valuable information serves as a resource for microwave researchers and the MEFSS design community, aiding in the development of new methods and facilitating comparative analysis. The study highlights the potential of FSS designs in enabling numerous practical applications across different frequency bands, including microwave, millimeter, terahertz, and optical modes.  
By bridging the gap between theoretical foundations, structural parameters, and performance characteristics, this study is anticipated to advance the state-of-the-art design of FSS devices. Additionally, the research discusses innovative approaches to tuning and switching FSS, particularly the mechanical tuning method that eliminates the need for DC biasing and the novel embedded bias network designed for varactor-based FSS, which minimizes interference issues and simplifies the implementation.  
Our work summarizes significant advancements in the field of frequency selective surfaces (FSSs) through several approaches. Firstly, we investigate tunable and reconfigurable FSS designs that incorporate active components, enabling dynamic control over frequency responses, which is crucial for applications in mobile communication and radar systems. Additionally, we explore the use of flexible substrates and novel geometries, such as fractal and hexagonal shapes, to enhance bandwidth and reduce beamwidth, thereby improving signal directionality. Our research also addresses fabrication challenges by proposing single-layer FSS configurations that maintain performance while simplifying manufacturing processes. Furthermore, we emphasize the importance of miniaturizing unit cell sizes to achieve higher angular stability, which is vital for applications in close proximity to radiation sources. Lastly, we highlight the potential of dual-band and multi-band FSS designs, which can effectively operate across multiple frequency bands, thus broadening their applicability in modern communication systems.  
Conceptualization, W.A. and W.R.; methodology, W.A.; software, W.A.; validation, W.A., M.R.R., A.E. and W.R.; formal analysis, W.A. and W.R.; investigation, W.A.; resources, M.T.A.R., M.Z.B. and W.A.; data curation, M.Z.B.; writing--original draft preparation, W.A.; writing--review and editing, A.E. and M.R.R.; visualization, M.T.A.R. and M.Z.B.; supervision, W.R. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
The authors declare no conflicts of interest.