Propagation over irregular terrain using a finite-difference time domain/method of moments hybrid approach

A hybrid FDTD/MoM approach was developed to accurately predict the path loss of UHF/VHF signals over irregular terrain and establish a set of bench marks. These bench marks are now available to the general public for validation of propagation codes designed to predict path loss over irregular terrain. The hybrid approach was developed to extend the range between the transmitter and the irregular terrain feature. A near-field transformation was also developed to predict path loss outside the FDTD region.; The derivation of path loss, the FDTD algorithm, the near-field transformation, and the exact solution of near fields around cylinders are presented. Implementation of the MoM, FDTD and near-field transformation algorithms used for the bench marks is also discussed.; Extensive validation was conducted to check individual codes and hybrid approaches. Sample validation cases are presented to justify the approaches. The FDTD code is validated against the exact solution for near fields around perfectly conducting and lossy cylinders. Several comparisons are also presented between FDTD and UTD solutions for various scattering shapes. The FDTD/MoM hybrid approach is also validated against the UTD code. Finally the FDTD near-field transformation hybrid approach is validated against exact and UTD solutions.; Effects of numerical dispersion on the FDTD code are presented in the form of near-field plots around cylinders and large hills. These plots provide insight to significant numerical dispersion errors in FDTD calculations.; Five bench mark scenarios were chosen and predictions of path loss are provided for model comparison. A sample comparison using TIREM and VTRPE propagation models is also presented. These models are based on algorithms significantly different from FDTD.; The validations show the FDTD/MoM approach provides extremely accurate results for path loss predictions. The near-field transformation also provides excellent results and can be used to increase the area over which predictions are made. The combined results from FDTD/MoM and FDTD/near-field transformation approaches verified interference patterns in the shadow region of hills. These effects are not predicted by most propagation codes.