# Dual-Band Single-Layered Frequency Selective Surface Filter for LTE Band with Angular Stability
## 6 Performance Comparison of C-FSS  
With the purpose of understanding the unique properties of C-FSS, a comparison is made with the recently designed FSS structures for the LTE band in Table 5 discussed with some parameters such as the substrate, type of FSS, number of layers, number of elements, operating bandwidth, operating frequency, coefficient, analysis method, and incident angle. It is found that the proposed C-FSS is resonating at dual frequencies with a single layer and single element. The asymmetric property makes it distinctive from other dual-band FSSs.  
The proposed C-FSS presents significant benefits compared to the recently developed FSS. The proposed FSS achieves dual frequency bands at 1.9 and 2.1 GHz, featuring bandwidths of 40 and 60 MHz, respectively, with reflection coefficients around \(-29.59\) and \(-31.11\) dB. This performance surpasses other designs, such as [42], which show a reflection coefficient of \(-25\) dB at 2.11 GHz and a stability restricted to \(30^{\circ}\). In comparison to [20], the active FSS operates in a single band at 2.1 GHz with a bandwidth of 0.86 GHz, exhibiting a reflection coefficient of \(-20\) dB and angular stability limited to \(60^{\circ}\), the proposed C-FSS offers enhanced efficiency and improved stability, reaching up to \(80^{\circ}\). Moreover, in contrast to the tri-band designs in [43; 44], which function across various bands yet fall short in the precision and focus necessary for dual-band LTE applications, the C-FSS offers a customized solution with its asymmetric structure. For instance, Ref. [43] offers a wider operational range but sacrifices some angular stability, whereas [44] utilizes textile substrates that emphasize flexibility rather than performance metrics such as reflection coefficients. The proposed design distinguishes itself from [45; 46], which emphasizes multi-functional or band-stop applications at the expense of the simplicity and compactness found in single-layer structures. Furthermore, the C-FSS outperforms the multi-layered FSS in [41] regarding material efficiency and ease of manufacturing, all while maintaining exceptional performance. In [47], the authors proposed a dual-band WIFI filter using a 6 \(\times\) 6 array unit cell with a Pyrex glass substrate. Utilizing an RT/Duroid 5880 substrate along with an asymmetric configuration, the proposed design guarantees excellent angular stability and precise frequency filtering, positioning it as an exceptional option for LTE applications that require high-performance standards.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline
**Ref.** & **Application** & **Design Type** & **Substrate** & **Dimension (mm)** & **N1** & **N2** & **Band** & \begin{tabular}{c} **Operating** \\ **Bandwidth** \\ **(CH)** \\ \end{tabular} & \(t_{s}\) **(CH)** & \begin{tabular}{c} **Coefficient** \\ **(dB)** \\ \end{tabular} & **Analysis** & \(\theta\) \\ \hline \multirow{3}{*}{[43]} & SC and UMTS energy-saving glass & \multirow{3}{*}{Apperture type} & FR4 & \(40\times 40\) & \(1\) & \(3\) & \begin{tabular}{c} (0.64-0.99), \\ (1.71-1.96), \\ (4.43-3.79) \\ (at \(-3\) dB) \\ \end{tabular} & \(0.7,19,3.6\) & - & - & - & - \\ \cline{2-13}  & & & & & & & & & & \\ \hline \multirow{3}{*}{[44]} & \multirow{3}{*}{\begin{tabular}{c} technology–integrated into \\ edding or extending veto to \\ reduce radar cross-section \\ \end{tabular} } & \multirow{3}{*}{\
\begin{tabular}{c} Aperture type \\ \end{tabular} } & \multirow{3}{*}{
\begin{tabular}{c} F164 and full