Design of Switchable, Polarization-Insensitive, Optically Transparent Window Film for Communication Security

This letter presents the design of a dual-polarization active frequency selective surface (AFSS) on an optically transparent and flexible plastic substrate. The periodic symmetry enables its insensitivity to wave polarization. By configuring the PIN diodes in either the on or off states, this AFSS can be switched between transmission and reflection modes. The fabricated prototype has dimensions of 37 cm x 37 cm, consisting of a total of 1844 diodes. For isolation better than 10 dB, the measured bandwidth for the TE mode spanned from 5.43 GHz to 6.26 GHz over incident angles ranging from 0 degrees to 60 degrees, while the TM mode has a bandwidth of 5.28 GHz to 6.78 GHz. Furthermore, this AFSS can be directly attached to the windows to ensure communication security with maximal optical transparency.