A new termination condition for the application of FDTD techniques to discontinuity problems in close homogeneous waveguide

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Abstract
A general-purpose algorithm such as the finite-difference-time-domain technique would be useful for analyzing discontinuity problems in classical waveguides. Its direct application, however, has been rendered difficult by the absence of exact termination conditions appropriate to the close waveguide environment. A rigorous termination condition specific to homogeneous waveguides is introduced. It is based on the convolution properties of the modal characteristic impedance of the accessible modes. This condition is straightforward to implement, as demonstrated by application to the nontrivial problem of a five cavity inductive post filter. Numerical results are compared to existing analytical and experimental data, showing excellent accuracy.