Ultra-miniaturized and angularly stable symmetric polarization insensitive frequency selective surface for electromagnetic shielding

This research work presents a miniaturized enhanced angular and polarization stability frequency selective surface (FSS) structure at 660 MHz for electromagnetic (EM) shielding of 4G LTE networks. The vias and spiral-shaped subunit cells are combined to extend the electrical path length corresponding to the lower resonant frequency. The symmetric structure is considered to improve polarization and angular stability. Two symmetric metallic layers are etched on both sides of the FR4 substrate with thickness $h=1.6\mathrm{mm}$ and relative permittivity ${\epsilon }_r=4.4$. Four steps are adopted to improve miniaturization and stability (angular and polarization). The dimension of the unit cell is ${\left(0.016{\lambda }_0\right)}^2$. The figure of merit is also improved to $\frac{{\lambda }_0}{P}=59.49$, where ${\lambda }_0$ is the largest free space wavelength and P is the periodicity of the proposed structure. The proposed band-stop FSS is more angularly stable as a figure of merit for various incidence angles under transverse electric (TE) and transverse magnetic (TM) polarizations. Simulation and measurement have been done to confirm the polarization insensitivity and maximum angular stability of 80°.