[[EM.Terrano]] is a simulation software tool for modeling radio wave propagation in large scenes like urban canyons, indoor environments and natural terrain. Full-wave numerical methods like the finite difference time domain (FDTD) or the method of moments (MoM) solve differential or integral forms of Maxwellâs equations that require a fine discretization of the physical structure. To ensure the accuray of the simulation results, the resolution of the structureâs mesh must be high enough to accommodate a large number of cells per effective wavelength. Wireless propagation problems, on the other hand, typically involve scenes that may extend by hundreds or thousands of wavelengths. Generating a full-wave mesh in such sccenarios scenarios can easily lead to intractable computational problems demanding terabytes of computer memory. Asymptotic methods such as Shoot-and-Bounce-Rays (SBR) offer a practical solution for large-scale problems of this type. [[EM.Terrano]]âs simulation engine is based on the SBR method, which combines Geometrical Optics (GO) with the Uniform Theory of Diffraction (UTD).
In [[EM.Terrano]], a transmitter (acting as a source) shoots rays in all directions in the 3D space. The simplest source, however, is a short dipole radiator. The rays travel through the free space and are collected at the location of receivers (acting as field observation points). A ray is an electromagnetic energy tube with a triangular cross section that propagates in the channel medium along a certain direction vector. [[EM.Terrano]] models rays as fully polarimetric and coherent spherical waves that emanate from a source point and diverge (or spread) over distance undergoing both attenuation and phase change. In a simple free space channel, the tansmitted rays are directly picked up by the receivers.