A new absorbing boundary condition structure for waveguide analysis

This paper presents a novel absorbing boundary condition structure for waveguide analysis, which attenuates evanescent waves and waves near cutoff frequencies. The existence of these waves limits the accuracy of the fields computed using the FDTD method, and prompted several researchers to design complicated boundary conditions, including combinations of perfectly matched layer (PML) and Higdon´s higher-order ABCs. Instead, we employ a parallel plate terminating structure in which the lateral walls are made absorbing in addition to the longitudinal walls. The undesirable lateral waves at the normal boundary interface, a dominant source of error, are slowed down and effectively attenuated in the lateral walls, while the propagating waves are absorbed in the longitudinal walls. No lossy materials are employed for absorption.