A Miniaturized Ultrawideband Dual-Bandpass Frequency-Selective Surface With High Selectivity

This article presents an ultrawideband dual-bandpass frequency-selective surface (FSS) that exhibits outstanding transmission characteristics and a miniaturization feature in the required frequency band. In order to obtain a dual-band filtering response, initially, a specific topological structure of a dual-band bandpass microwave filter is theoretically investigated, and using periodic structures with capacitive, inductive, or resonant-type surface impedances synthesizes its components. Subsequently, employing a compact cascaded hybrid resonant element to construct the FSS, which is composed of convoluted strip grids (CSGs), convoluted square rings (CSRs), and square rings arranged on different layers. In addition, an accurate equivalent circuit model (ECM) is constructed to analyze the working mechanism of the proposed FSS. Finally, the designed FSS is made and measured. The results indicate that the designed FSS achieved −3-dB bandwidths of 105.4% from 1.01 to 3.26 GHz and 47.8% from 3.75 to 6.10 GHz, respectively. At the center frequency of the first passband, the FSS’s size is as compact as
$0.056\lambda _{0} \times 0.056\lambda _{0}$
. The test results obtained are in good agreement with the results of the full-wave simulation and show excellent resonant stability with respect to different polarizations and incident angles up to 45°.