With the objective of obtaining subsidies for the analysis and desing of microwave terrestrial links, under visibility and clear sky conditions, a theoretical model of propagation, based on ray tracing techniques, was developed. This model combines the effects of the radiation pattern of the antennas (amplitude and phase), reflection an refraction from the earth surface and the curvature of the earth. Based on this model, a computer program was generated, that is able to analyze the propagation of signals with the following polarizations: vertical, horizontal, left and rigth circular. To check the validity of the model, and the range of applicability of the computer program, several calculations were made, and the results compared to that obtained from other similar models. A good agreement was achieved. Finaly, measured profiles of refractive index were applied to the determination of cross polarization discrimination (XPD) and cross polarization isolation (XPI) in frequency reuse links. The results are comparable to that resultant from semi-empiric models.