Design of wide band SIW based Reflective Mode FSS with Angular Stability for X-band application

• This paper presents the design of Substrate Integrated Waveguide (SIW) based Frequency Selective Surface (FSS) operating in a wide-band reflective mode, specifically tailored for X-band applications. • The conventional unit cell gives a center frequency of 8.90 GHz in a narrow band with a relative bandwidth of 3.71 %. To improve the bandwidth, a square loop with a slot in the FSS, has been combined with an SIW cavity, which creates resonance. • The SIW-based FSS structure provides a resonant frequency of 11.5 GHz with bandwidth of (9.05–14.50 GHz) and relative bandwidth of 46.28 %. To validate the design, a comprehensive Equivalent Circuit model was implemented. • The proposed work achieved angular stability by varying the different angles of incidence from 0° to 70° and maintains the stable resonant frequency. • The SIW-based FSS design is optimized for the applications in radar, electromagnetic shielding, and satellite communication particularly to facilitate the uplink and downlink frequency in the X-band range. This paper presents a design of Substrate Integrated Waveguide (SIW) based reflective mode Frequency Selective Surface (FSS) that operates in wide-band tailored for X-band applications. The design is implemented on FR4 substrate, which has a dielectric constant (ε r ) of 4.3, chosen for its favorable electrical properties and compatibility with the intended frequency range. Regarding physical dimensions, FSS is highly compact, featuring unit cell dimensions of 11 × 11 × 1.57 mm 3 , making it suitable for space-constrained applications. The SIW-based FSS structure gives a wide bandwidth of 9.05–14.50 GHz with a relative bandwidth of 46.28 %. To validate the design, a comprehensive equivalent circuit model is implemented, providing a theoretical foundation for the FSS performance. Furthermore, hardware fabrication of the proposed design is undertaken to verify the model's predictions empirically. The experimental results support the theoretical findings, demonstrating the FSS effectiveness in real-world scenarios. This FSS design is optimized for critical applications in radar and electromagnetic shielding within the X-band frequency range, offering a significant advancement in developing high-performance, compact, and wideband FSS technologies.