Circuit model for single-layer single-resonant ultra-thin FSS absorbers with wide bandwidth

Electromagnetic absorbers based on frequency-selective surfaces have been explored for many applications. It is often useful to represent these devices using a circuit equivalence, which provides a physical insight into underlying performance capabilities and limitations. Yet, absorbers tend to deviate from their ideal circuit representations for ultra-thin implementations where coupling between layers becomes significant. To date, there has been little investigation into the corrective measures required to compensate for parasitic coupling associated with ultra-thin absorbers. In the paper, a circuit model is proposed for a broadband absorber comprised of a single-resonance FSS cascaded with a PEC-backed substrate. The thin nature of the absorber is shown to introduce undesirable coupling between the FSS and PEC layers, resulting in non-ideal performance. Two corrective measures are outlined with the goal of retuning the absorber for maximum bandwidth.