• Spectral Decomposition
• Genetic Algorithm
• Mode Matching
• Finite Element Method
• finite phased array
• cascade frequency selective surface

The research activity, illustrated in this work, has been developed in the area of applied electromagnetics and it concerns the development and the improvement of a hybrid numerical method combining the Mode Matching (MM) and the Finite Element (FE) specifically derived for the study of complex microwave devices. Firstly, the optimization problem of unconventional Frequency Selective Surfaces (FSSs), obtained by using NURBS curves, is analyzed. A genetic algorithm is used in order to address the optimization of a multiparametric structure such as the FSS. The hybrid method MM-FE is used to evaluate the frequency behaviour of this kind of structures. The hybrid technique is therefore applied to the study of large finite arrays of open-ended or iris-loaded waveguide apertures or horn antennas. The finite dimensions are taken into account by using a Spectral Decomposition (SD) approach that allows us to reduce the finite problem to a summation of infinite periodic ones. A similar procedure, now based on the Method of Moments (MoM) and the spectral decomposition approach, is applied to the analysis of finite thin frequency selective surfaces. Finally the hybrid methodology MM-FEM-SD, combined with an MoM, is used to study finite arrays of rectangular waveguide cascaded with a finite thin FSS. In order to prove the effectiveness of this methodology, several numerical results are compared with that obtained through a commercial software or available in literature.