Polarisation Insensitive Active FSS for EM Shielding

This paper proposes a narrowband polarisation insensitive transmissive/reflective frequency selective surface (FSS). The FSS comprises unit cells with square and circular metallic loops connected by PIN diodes controlled by a biasing source. In contrast to typical wideband FSSs, the structure provides 0.55 GHz of narrow stopband (a fractional bandwidth of 22%) at 2 GHz in the OFF state bias. The bandstop response can be adjusted by varying the reverse bias voltage. The FSS alternates between its functionalities and, in forward bias, provides a passband at the operational frequency. The structure is compact and operates as a transmissive/reflective surface under two different bias conditions (ON and OFF). The design is angularly stable and polarization-insensitive for both TE and TM polarisation. A prototype of the designed structure is developed and the measured results correlate well with the simulated responses.