Frequency selective surface (FSS) is a kind of spatial filter, which is used in wide applications such as radomes, polarizers, and filters due to its capability of controlling electromagnetic waves [1]. Traditional FSSs consist of a two-dimensional periodic array of unit cells, however, such a single-layer surface often suffers from poor filtering characteristics. Furthermore, designing FSSs with a higher-order bandpass response to achieve a wider transmission band has also attracted intensive investigations [2].