Abstract
This chapter discusses how powerful time‐domain models are based on both the FDTD and the TLM methods. Analytical models are mostly based on mode and ray summations and require eigen‐mode and eigen‐ray extraction. Modes are global wave objects in guiding environments and can be used in representing any kind of excitation. They are confined transversely and propagate longitudinally. Modes and their propagation constants are also called eigen‐functions and eigenvalues, respectively. The vertical beam width and beam tilt can also be adjusted. On the other hand, most of the analytical solutions that may serve as a reference use line‐source excitation. The numerical propagators (SSPE, FEMPE) directly use either a Gaussian beam or an actual planar array distribution as an initial field (antenna) profile. One can use a mode summation approach as an analytical model if the environmental refractivity variations and/or physical transverse boundaries allow EM wave trapping or guiding.
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