# Dual-Band Single-Layered Frequency Selective Surface Filter for LTE Band with Angular Stability
###### Abstract
The construction uses ring resonators to maximize the transmission band by considering strip length, width, gap width, and periodicity. However, this study does not focus on magnetic excitation and works only for TM mode. This constraint of single mode is resolved in [18]; it gives polarization for TE and TM modes. The design is accomplished by duplicating the fractal patterns to make it appropriate for filtering the LTE, Wi-Fi, X band which exhibits enhancement of bandwidth. The angular stability is demonstrated up to 60\({}^{\circ}\) for TE mode and up to 45\({}^{\circ}\) for TM mode. More work is required to control the mechanism of resonance while maintaining the miniaturization. The technique of miniaturization is presented in [19], where a miniaturized wide-band supercell FSS is created. The proposed design features two SRRs with gaps on opposite sides which show resonance at 3.7 GHz and another design with two identical SRRs, which resonate at 3.54 GHz. Active FSS in [20] employs PIN diodes for EM switching and polarization selection. This improves the intended active FSS. It has four modes and a two-PIN-diode switch. Similar PIN diodes are EM switches, while opposite ones are polarization selectors. The design was angular stable in the 2.1 GHz LTE band across incident angles and wave polarizations. Its multifunctionality prevented our study from testing its use in electrically changing devices. The authors propose in [21] a developed modular antenna that combines a Fabry-Perot cavity, a Partially Selective Surface (PSS), and an Artificial Magnetic Conductor (AMC), which produces a significant increase in realized gain of 4-8 dB within the 1.7-2.5 GHz frequency range. The antenna's bandwidth is 30.9% at 2.16 GHz, and its highest gain is 8.2 dBi. It is ideal for Multiple LTE Radio communication due to its inherent characteristics. The proposed design in [22] introduces an FSS that employs an interdigital slot structure to optimize its compatibility with LTE systems. Using a slot structure reduces the FSS size to \(\lambda/8\) and yields an 8.43 dB gain at 1.8 GHz. In [23], the authors present a miniaturized design utilizing a knitted construction to create a passband that ranges from 5.5 GHz to 10.3 GHz and has a bandwidth of 3 dB. The authors propose in [24] a metamaterial structure shaped like a Swastika, featuring interconnected resonators that demonstrate single negative permeability and permittivity within the microwave frequency range of 1-10 GHz. The research further explores the mechanisms of energy decay through the examination of evanescent EM waves within the structure. Moreover, the Swastika-shaped FSS demonstrates absorption over an extensive frequency range, showcasing impressive performance at key frequencies that display negative characteristics. The significance of material composition and structural design in realizing customized EM responses elucidates the understanding and application of metamaterials. The proposed Swastika-shaped FSS is made as an absorber; hence, it is not appropriate as a band-pass filter. The authors introduce in [25] a compact FSS featuring a unit cell size of 0.095\(\lambda\)\(\times\) 0.095\(\lambda\), employing a complex Swastika-shaped design to minimize physical dimensions while maintaining performance. The proposed FSS exhibits stop band features at 5.12 GHz, rendering it suitable for indoor WLAN signal protection. It effectively filters signals with a fractional bandwidth of 9.0% at the center frequency. The balanced design of the unit cell guarantees consistent performance, regardless of the angle of incidence or polarization state, ensuring reliability across various conditions. The suggested FSS has strong angular stability; however, the study notes that performance may vary at extreme angles of incidence, which may limit its use in some applications. The authors present in [26] a single-layer band stop FSS tailored for WLAN applications, featuring an extensive bandwidth of around 3.80 GHz (ranging from 2.25 to 6.05 GHz) and a resonance frequency set at 5.25 GHz.