A Dual-Band Tunable Frequency Selective Surface With Independent Wideband Tuning

In this letter, a dual-band tunable bandstop frequency selective surface (FSS), which is capable of exhibiting independent tuning for the top and bottom layers, has been presented. The proposed design comprises periodic patterns of cross diagonals printed on the opposite sides of a thin substrate, where the varactor diodes are mounted symmetrically. Both the layers use novel biasing circuitries to independently regulate their corresponding responses, thereby resulting in two tunable stopbands. Each of these two stopbands has wide bandwidths (having fractional bandwidths of 110.71%) as well as offers large tuning ranges of 128.21% (with respect to their center frequencies). Furthermore, the geometry is low profile, polarization insensitive, and angularly stable. A prototype has been fabricated, and the varactors have been modulated through parallel biasing. The experimental results show a reasonable agreement with the theoretical responses, thus confirming the proposed concept.