8. Metamaterials Inspired Frequency Selective Surfaces

Frequency selective surfaces (FSSs) are traditionally formed by two-dimensional periodic arrangement of metallic elements on a dielectric substrate. Depending on the geometry and arrangement of the metallic unit cell, the array might show different functionalities such as band-pass or band-stop spatial filter, absorber, reflect array, and so on. Metamaterials inspired frequency selective surfaces operate based on a different principle that allows superior performance over the traditional structures. For instance, instead of using fully resonant elements as the unit cell of the FSS, nonresonant unit cells with small dimensions are used. The electrical size of the unit cells is decreased to less than l/4 and even in some cases smaller than l/10. These miniaturized elements act as lumped capacitors or inductors and are arranged in a way that they couple to the incident electromagnetic wave. An advantage of this type of FSS is that its frequency behavior can be accurately modelled using lumped element circuit model. Therefore, FSSs with specified functionalities can be designed by the aid of standard circuit-based filter theory. Furthermore, other metamaterials inspired FSSs with different improved functionalities and tunability have also been designed and implemented, such as low-profile second-order band-pass FSS, dual band FSSs with close band spacing, FSS with quasi-elliptical frequency response, and FSSs for high-power microwave and terahertz applications. This chapter will review the progress of the metamaterials inspired FSSs.