Range of validity of transmission line approximations for design of electromagnetic absorbers

Transmission line approximation (TLA) method has been widely used for the d esign of electromagnetic absorbers, because it does not need tremendous cal culations required in numerical analysis methods. But the method has the in trinsic application limits as the low-frequency approximation. In this pape r, we described full-wave analysis on the periodic structure with finite el ement method (FEM) and investigated the accuracy and limitations of TLA by comparing TLA with FEM results for the reflection loss of a dielectric pyra mid, It was found that TLA is valid when lambda > 2p, where lambda is the w avelength of the interested frequency and p is the distance between periodi c cone arrays.