Optimization and realization of symmetric multilayer cascaded FSSs structure with excellent Butterworth response at large angle incidence

A simple and fast optimization method for symmetric multilayer frequency selective surfaces (FSSs) structure is presented in this paper, based on the mutual admittance approach. To elaborate the proposed method, a symmetric bi-planar FSSs structure is selected to explain the optimizing process. After the optimized analysis, the symmetric bi-planar FSSs structure can achieve good characteristics of flat top and sharp roll-off at 70° angle of incidence, with an optimum coupling layer medium (d 2 = 15 mm, e 2 = 1.15). As it is difficult to obtain the material with e = 1.15 by using traditional technique, we design an array of dielectric cylinders to effectively replace the homogeneous medium, based on the theory of periodic waveguide. To verify the optimization method and design idea, a prototype simple of the symmetric bi-planar FSS is fabricated and measured. The measured results of the prototype well coincided with the simulation results, which further shows the validity of the optimization method and the idea of equivalent substitution.