# Dual-Band Single-Layered Frequency Selective Surface Filter for LTE Band with Angular Stability
###### Abstract
The FSS showcases the ability to function effectively regardless of polarization for both X- and Y-polarized fields at normal incidence while also providing consistent performance with angular stability up to 40\({}^{\circ}\), making it dependable across various conditions. The design features a straightforward alteration of a classic square patch, incorporating triangular slots that improve functionality for band stop filtering; hence, the need for a passband persists. The authors in [27] introduce a remarkably thin dual-band FSS tailored for X-band applications, functioning as a band-reject filter at 8.47 GHz and 10.45 GHz, featuring a modest band ratio of 1.23. The FSS boasts a slim design with a thickness of merely 0.021\(\lambda_{\text{l}}\), making it ideal for use in compact electronic devices. In [28], the authors present an innovative single-layer wideband FSS designed for millimeter-wave applications, operating within the 40-70 GHz range and providing an extensive 30 GHz bandwidth. The FSS showcases a compact unit cell size of 0.34\(\lambda\)\(\times\) 0.34\(\lambda\), exhibiting a symmetric structure that ensures polarization independence and effectively minimizes mutual coupling in antenna arrays. In [29], the authors discuss a single-layer FSS that achieves more than 20 dB attenuation across an ultrawide stopband ranging from 6.5 to 14 GHz, demonstrating its effectiveness for EMI shielding. In [30], the authors present a hybrid FSS with an annular ring slot and a slot with a cross-shaped cavity. This structure shows the effect of slots on the frequency shift, where the bandwidth of the second resonance has reduced with the varying slot length. The design in [31], a circular loop geometry, is selected to achieve polarization insensitivity, but the circumference varies the resonance as shown in the parametric study. The authors in [32] propose a dual-layer structure with a circular ring to achieve dual resonance, but for practical applications, a single-layer structure is preferred. Experimental validation showcases its exceptional shielding capabilities, featuring a broad stopband that is unparalleled in EMI shielding technology. A comprehensive parametric analysis reveals adjustable design parameters, including cross dipole and ring dimensions, that influence performance. The study con tracts experimental findings for both normal and oblique incidences alongside numerical simulations, deepening practical insight. The aforementioned design has some limitations, and some key points are as follows:  
* Attaining accurate dual-band filtering at 1.9 GHz and 2.1 GHz, ensuring sufficient bandwidths for LTE applications. * Keeping its angular stability up to 80 degrees, which is far better than the usual stability of designs that are 30-60 degrees. * Simplifying the design while maintaining efficiency, compactness with the unit-cell dimension of \(0.33\lambda_{1}\times 0.33\lambda_{l}\), and a single-layer approach for enhanced scalability and practicality. * Tackling the complexities of PIM in contemporary wireless networks by adopting an FSS framework that minimizes interference and improves communication dependability. This paper aims to analyze and solve the above research problem from the literature on the functions and advantages of FSS in various applications. The application of the FSS should be considered when choosing the size of the structure and bandwidth of the passband. The 2.1 GHz frequency bands give a bandwidth of 60 MHz, which is critically important for a variety of applications ranging from mobile communications to radar systems like surveillance and navigation. Furthermore, 1.9 GHz gives the bandwidth of 40 MHz which is widely adopted for GSM and WiMAX networks. The deployment of the proposed FSS in these bands can significantly reduce unwanted frequencies and interference, thereby sustaining reliable and secure communication. In this paper, the proposed structure resonates at a dual frequency with a single layer and exhibits the in-depth behavior of inductors and capacitors.