Analysis of multilayer periodic structures with different periodicities using a Hybrid FDTD/GSM method

An efficient algorithm to compute the scattering properties of multilayered periodic structure with different periodicities using a hybrid finite-difference time-domain/generalized scattering matrix (FDTD/GSM) technique is described. In this algorithm the constant horizontal wavenumber approach is used to compute the scattering parameters of each layer. A Floquet harmonic analysis of the periodic structure is presented, where propagation and evanescent behaviors are studied. In addition, guidelines for harmonic selection for specific layer separation is provided. The scattering matrices of different layers including proper harmonics are cascaded to obtain the GSM of the entire structure. The algorithm is verified through numerical examples including frequency selective surface (FSS) with different periodicities. Results showed good agreement with the results obtained from the FDTD simulation of the entire structure, while the new procedure provides significant saving in the computational time and storage memory.