Conformal Angularly Stable Quadband Frequency Selective Surface for EMI Shielding

This article presents a miniaturized dual layer angularly stable quad-band frequency selective surface (FSS) for shielding applications. The shield consists of four metallic square rings on a thin FR4 substrate of relative permittivity 4.4 and thickness 0.5 mm with two rings on top layer and other two rings in the bottom layer. The dimension of the shielding unit cell is 0.2 lambda x 0.2 lambda, for the lowest frequency. These shields have been analyzed in both planar and conformal configurations. The equivalent circuit models as well as analytical model are determined. The shield exhibits quad band band-stop characteristics with transmission zeros at 5 GHz (4.3- 5.8 GHz), 6.6 GHz (6.3-6.8 GHz), 8.3 GHz (7-8.8 GHz), and 15 GHz (11-17 GHz). These bands find their application in shielding upper WLAN band, sub-6 GHz 5G band C/Ku band for satellite communication. The proposed FSS prototype is fabricated and tested for shield effectiveness in an anechoic chamber. The proposed FSS design offers stable angular response up to 60 degrees for planar and geometry. Simulated and measured transmission coefficients are in good agreement and hence well suited for shielding applications. As the structure is fourfold symmetric, it exhibits polarization insensitive and angular stability in all four bands.