Excitation Schemes and Open-End Truncation

According to the first, at the initial time instant, electromagnetic components are defined inside the entire space of the model. This approach is basically used for the analysis of microwave resonators. 

The second type involves the incorporation of a finite-length pulse. Due to its wideband nature, the transmission properties are determined for a prefixed frequency window spanning in one analysis cycle. 

The third and most popular approach defines a harmonic oscillation on a boundary or transverse plane of the structure. Note that the specific scheme is applicable only to the problems where no disturbance from inherent discontinuities affects the function of the source plane. Otherwise, -parameters are erroneously computed and no useful conclusions can be figured out. 

Probing on the separation of incident and reflected waves, a concern still remains two field quantities must be determined on the source plane and updated interactively. For waveguide discontinuities, the regularly implemented scheme of the third case places the source and the near-end terminal plane at the same position, inserts the excitation, and then applies the ABC to the source plane after the pulse has been fully propagated. Nonetheless, before any truncation process is allowed to initiate, DC distortions are induced near the incident waveform by the electric and magnetic boundary conditions. This is another reason why usual techniques cannot be located very close to the discontinuity. An efficient way to alleviate the prior weakness is to 

On the other hand, the truncation of open waveguide ends must be carefully conducted in order to enable the absorption of evanescent waves. These waves decay so abruptly that cannot be sampled by the usual FDTD mesh, especially at low frequencies [24]. The main consequence is a serious numerical reflection from the perfectly matched layer (PML) interfaces, which is larger below a certain cutoff frequency. This defect is confronted by the HO schemes [25] together with a specific category of PMLs, like the one of [26]. Both algorithms provide fairly sufficient simulations, as will be derived from the experimentations. 

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