Improving modal analysis of ID-periodic lines based on the simulation of finite structures

The numerical analysis of 1D-periodic waveguides and antennas can be performed through both approximate and rigorous methods. The latter ones are based on the full-wave solution of the electromagnetic problem in the minimal spatial period of the structure (the "unit cell") with Floquet conditions at its boundaries. On the other hand, a well-known approximate method is based on the description of the periodic waveguide as a cascade of cells, each characterized as a two-port network. Only one mode is assumed to be propagating along the unperturbed uniform waveguide, and a voltage and a current associated to it are defined at the boundary of each cell, i.e., at the ports of the relevant network. Since the Bloch waves propagating along the waveguide are modified simply through a complex factor between two adjacent ports, the associated voltage and current can be regarded as eigenvectors of the transmission matrix of each two-port network.