Synthesis of High-Order Dual-Band Frequency-Selective Surface With Independent Control of Bandwidths and Center Frequencies

In this article, a synthesis technique is proposed for the design of dual-band frequency-selective surfaces (FSSs) with independently controllable center frequencies and bandwidths. The design procedure begins with the analysis of a dual-band Chebyshev bandpass filter prototype, where the effects of input impedance, reactance slope, and impedance inverters on passband characteristics are systematically examined. Based on the insights from the filter model, a novel FSS is proposed, which consists of cascaded stepped impedance patch resonators (SIRs) and coupled apertures. The resonators are designed to provide flexible control over the input impedance and reactance slope, enabling independent adjustment of passband characteristics. An equivalent circuit model (ECM) is subsequently developed to represent the proposed structure. The electrical parameters of the structure are precisely extracted using a numerical short-open-load (SOL) calibration technique, enabling accurate mapping from circuit elements to physical dimensions. Several simulated examples demonstrate the capability of the method to independently control dual-band responses. Furthermore, two fabricated prototypes validate the proposed design framework, achieving both structural compactness and flexible spectral control. Compared to existing empirical or single-band approaches, the presented method provides a systematic and scalable path to dual-band FSS design.