Predição de cobertura radioelétrica em terrenos irregulares iluminados por fonte de onda esférica: uma abordagem via equações integrais e CBFM

Abstract

This work deals with the forward and backward propagation prediction of electromagnetic fields over irregular terrains in the VHF-UHF bands (30 MHz to 3 GHz) that is necessary in wireless planning. The terrain is modeled as an imperfect electrical conductor with invariant height at the perpendicular direction of propagation and with a punctual source. The scattering fields are determined by solving the Magnetic Field Integral Equation (MFIE) using the Method of Moments. The formulation used to generate the MoM matrix is valid for terrains with smooth profile and far fields. The CBFM - Characteristic Basis Function Method based on macro basis functions is employed to solve the complete linear system arising from the Method of Moments and, as it considers mutual interactions among all segments it can also be used in rough terrains. Here it is used only in smooth terrains since the MoM formulation is for terrains with this characteristic. Theoretical and real situations are analyzed and at regions with significant shadow area the CBFM parameters are chosen with the aim to achieve a more accurate solution. The triangular matrix method (that provides an approximated solution) is compared with the CBFM and the differences in CPU time and accuracy of the results are showed. The use of integral equations in scattering problems over electrically large terrains demands a high computational cost (CPU time and memory requirement). In order to speed up the calculations and to render the model more practical, the acceleration technique called phase extrapolation is implemented and tested.