A novel symmetric cascaded frequency selective surface wtih butterworth response in X-band

In this letter, a new technique for designing symmetric cascaded frequency selective surfaces with arbitrary bands of operation, with Butterworth band-pass responses at band of operation, is presented and experimentally verified. The technique is based on utilizing mutual admittance to represent transmission coefficient and getting a Butterworth response numerically through optimum parameter of the coupling layer. The result is a low-profile planar structure composed of two metal and three dielectric layers that acts as a spatial version of the Butterworth type microwave filter.