| Simulations of electromagnetic wave scattering and propagation involving complex electrically large targets are of great interest. For intermediate-sized homogeneous targets, the multi-level fast multipole algorithm (MLFMA) provides an efficient solution to the problem. However, the conventional MLFMA meets its limitations when multiple targets of different electromagnetic properties are involved. When the operating frequency goes too high to allow a full wave solution, the high frequency asymptotic methods, such as the ray-tracing technique, have to be used. The various approximations used in a ray-tracing technique motive one to have a rigorous numerical method to quantify the accuracy of the model.; To extend the MLFMA to the case of an arbitrary number of dielectric and/or perfectly electric conducting targets in the presence of a half-space, and to provide a benchmark solution for calibrating the ray-tracing method as well, a multi-target MLFMA based on an iterative method is developed. In this multi-target MLFMA, the fields incident on and scattered from each target are updated sequentially by considering each target in isolation. The interactions between the targets are calculated within the MLFMA framework and to make the computation model scalable, each target is analyzed in parallel on a separate computer node, with inter-target interactions addressed via message passing between the processors.; Next, the multi-target MLFMA is used to evaluate the accuracy of the ray-tracing models for the analysis of propagation in complex environments, including forest-like media. The ray-tracing model combines the uniform theory of diffraction (UTD) within an efficient shooting-and-bouncing-ray (SBR) framework. The effects of edge diffraction, creeping-wave propagation, penetration, and multiple bounces between the objects are studied in detail and an efficient ray model for a forest environment is developed. With this ray-tracing model, the wave propagation inside a forest-like environment employing the phase conjugation technique is simulated over a wide band. Results show that the multi-path propagation, a typical propagation phenomenon for a forest environment, contributes positively to the focusing of the energy. |
