Application of moving window FDTD to predicting path loss over forest covered irregular terrain

A new wave oriented approach to modeling radiowave propagation based on an extended finite difference time domain (FDTD) method has been developed. The new approach takes advantage of the fact that when a pulsed radio wave propagates over a long distance, the significant pulse energy exists only over a small part of the propagation path at any instant of time. This allows the use of a relatively small FDTD computational mesh that exists only over a portion of the propagation path and moves along with the pulse. At the leading edge of the FDTD mesh, inside the moving window, the appropriate terrain and foliage parameters are added to the mesh. At the trailing edge, the terrain and foliage that have been left behind by the pulse are removed. The moving window FDTD (MWFDTD) method has previously been applied to propagation over different types of irregular terrain. This paper extends this approach to forest covered terrain by treating the foliage as a lossy dielectric layer. Comparisons with path loss measurements show good accuracy and illustrate the advantages of a full wave method.