The proposed Frequency Selective Surface (FSS) with dual-passband capabilities is presented in this paper for enhanced interference mitigation in 5G n78 and n79 bands. The key contribution of this work is the development of a single-layer, alternating copper-dielectric configuration that integrates circular loops with a decagonal pattern on an FR4 substrate, enabling precise frequency selectivity and efficient suppression of out-of-band emissions. The proposed FSS achieves resonance at 3.5 GHz and 4.8 GHz with a 3 dB fractional bandwidth of approximately 3.5%. The design employs an R-T-R-T-R (reflection-transmission-reflection-transmission-reflection) mechanism, which enhances filtering performance while maintaining angular stability up to 60° for both TE and TM polarizations. Simulation and experimental results validate its robust performance. The low-profile structure, acceptable frequency ratio, and effective out-of-band suppression make it a reliable solution for 5G communication systems.

This study presents an innovative Dual-Band Frequency Selective Surface (FSS) designed for LTE applications, offering an effective solution for minimizing Passive Inter-Modulation (PIM) in contemporary wireless communication systems at the base station. The proposed passband FSS filter is designed to deliver optimal dual-band filtering characteristics with consistent stability over incidence angles up to 80°. Corresponding to antenna systems requirements, the proposed method gives resonant frequencies at 1.9 and 2.1 GHz which operate in the LTE band with bandwidths of 40 and 60 MHz, respectively. Moreover, the proposed design is analyzed to establish the optimal range for each resonant frequency by examining the parametric effects. The suggested FSS-based filter consists of a single-layer structure with the dimension of the unit cell of 0.33${\lambda }_1$ × 0.33${\lambda }_1$ where ${\lambda }_1$ is the wavelength of low frequency, which delivers desired reflection and transmission coefficients using RT/Duroid 5880 with a thickness of 0.508 mm. The designed filter is validated through measurements of a fabricated prototype, demonstrating its practicality and performance. Simulations carried out with Equivalent Circuit Modeling (ECM) are demonstrated by measurements from a constructed 4 × 4 array prototype, showing a robust alignment with experimental findings. This work emphasizes an asymmetric FSS design that improves frequency selectivity and angular stability for the desired LTE dual band and also depicts the future possibilities for tuneable models and broader applications to meet the demands of modern wireless communication.