Synthesis of Quasi-Elliptic Bandpass Frequency-Selective Surface Using Cascaded Loop Arrays

A new quasi-elliptic bandpass frequency-selective surface (FSS) is presented by cascading a two-dimensional periodic array of double square loops (DSLs) and an array of gridded square loops (GSLs). The proposed FSS can be systematically synthesized based on microwave filter theory. The synthesized FSS can control not only the passband characteristics, but also transmission-zero frequencies at both ends of the passband, thus resulting in high selectivity and quasi-elliptic filtering response. The operating principle, detailed synthesis procedure, and implementation guidelines for this FSS are presented and discussed. As an example, a prototype of the proposed FSS is designed, fabricated, and tested. Measured results demonstrate that the proposed FSS has a simple structure, high selectivity, and stable bandpass response under a large variation of the incident angle.