A new computer-based mathematical model has been designed to calculate the effects of scattering, signal blockage (or shadowing), and scatterer interactions on the course structure of the Instrument Landing System (ILS) localizer. This model uses the Ohio State University ElectroScience Laboratory Near Zone Basic Scattering Code (NZBSC) along with a pre-processor and a post-processor interface which were designed at Ohio University Avionics Engineering Center as a part of this work. No current localizer model has the capability to predict the effects on the localizer course structure produced by shadowing. This model using NZBSC has been developed for the purpose of evaluating the effects of scatterers such as hangars, closely spaced power lines, and vehicles on the localizer course structure. The theoretical bases of this model for calculation of the scattered fields are Geometrical Optics and the Uniform Theory of Diffraction. The pre-processor and post- processor were designed to implement the NZBSC appropriately for analyzing localizer course structures in a multipath environment where reflections, signal blockage, and scatterer interactions exist.