Abstract-In this paper, we propose a 3D model to characterize the field scattered by an urban area, which is composed of a group of buildings, for both monostatic and bistatic radar configurations. This model is based on a ray-tracing technique combined with the Uniform Theory of Diffraction (UTD). It is useful not only in elucidating mechanisms of ray propagation through the observed area, but also in evaluating the amplitude and the phase of any point in the far-zone scattered field above the ground. In order to validate the model, some comparisons with the commercial software XGTD R are presented. In addition, our model is tested against 33-37 GHz indoor measurements conducted in the anechoic chamber of the "ElectroMagnetic Effects Research Lab" (EMERL) in Singapore. These latter comparisons have shown that the model can predict precisely the location of a target placed between two metallic plates representing walls.