Analisi di Bloch di strutture periodiche monodimensionali mediante la simulazione di un numero finito di celle

Bloch analyses of periodic electromagnetic waveguides are often obtained by cascading two-port equivalent circuits obtained by simulating a single, isolated cell of the structure, thus neglecting the mutual coupling among cells which occurs in a periodic environment. By simulating truncated structures made of a suitable, finite number of cells such mutual coupling can be correctly modeled; however, spurious solutions are then introduced, that are shown here to be related to the nonuniqueness of certain root-extraction operations in the complex plane. A simple automatic method is proposed to avoid such spurious solutions, while testing the convergence of the analysis by increasing the number of simulated cells. Results for printed periodic structures are validated against those obtained with full-wave MoM simulations which rigorously take into account all mutual-coupling effects through the use of periodic Green’s functions.