In the context of ground based Radar or wireless communications, non line of sight situations occuring in suburban type built environments are particularly demanding regarding the accuracy of field simulations. This communication presents new developments of the frame-based Gaussian beam shooting method to address some of the diffraction problems encountered in the presence of buildings. The presentation is focused on the problem of back-scattering by the bottom and the top of a building, which is addressed through incident beam selection, image frame and frame redecomposition. Numerical results obtained with this algorithm are compared to results obtained with the Parabolic Equation and with reference results.

Frame-based Gaussian Beam Shooting is presented as an alternative to ray-based methods, when reliable and accessible knowledge of propagated electromagnetic fields is required at all points in built-up environments. This communication presents a general Gaussian Beam Shooting algorithm based on paraxial beam tracking complemented with the use of "image" frames and with frame redecomposition on reflecting surfaces, to account for the presence of ground and buildings. Numerical results obtained in the case of a "single wall" and of a "parallelipedic building" are compared to Parabolic Equation and FEKO software results.

Abstract-In spite of well-known limitations, ray based methods are the quasi-unique tool for modelling the electromagnetic propagation in urban areas. As an alternative to these methods, two models based on the resolution of the Parabolic Wave Equation, and on Gaussian Beam Shooting, are proposed. Both are specifically adapted to meet the challenges of urban areas propagation: three-dimensional, wide angle approximation and considering the backscatter propagation for the first one; taking into account ground and grazing angles for the second one. A preliminary test case is presented and configurations of interest under processing are detailed.