Accurate Bloch Analysis of 1-D Periodic Lines Through the Simulation of Truncated Structures

A common approach to perform dispersive analyses of waveguides periodic along one direction is based on the electromagnetic simulation of a single spatial period of the structure. However, the resulting equivalent two-port network representation of the single cell may lead to inaccurate modal results, since mutual coupling between cells has been neglected. When a finite number of adjacent cells are simulated, with the aim of improving the accuracy of the analysis, spurious solutions are introduced; they are shown here to be related to the nonuniqueness of root-extraction operations in the complex plane. A simple automatic method is proposed to recover the correct solution and to test the convergence of the analysis as the number of simulated cells is increased.