Prediction of scatter coefficient of buildings at microwave frequencies in site shielding

In assessing the effect of site shielding where multipath interference is a distinct possibility, building scatter is an important factor which could severely defeat shielding. Many measurements made in urban build-up areas showed that strong interference was usually from buildings which cause specular reflections. More purposeful measurements on individual tall buildings with specified geometries were made by Bramely and Cherry (1973). Predictions were also given using Fresnel-Kirchhoff diffraction theory based on plane surfaces. In site shielding situations, distances from possibly scattering buildings are considerably limited by space in urban areas, typically in a range from a few hundred to a few thousand meters. On the other hand at microwave frequencies, buildings are immensely large relatively to the wavelength. This means that the distance is usually only a very small fraction of the Rayleigh far field distance in the order of one hundredth. This paper describes the development of prediction models suitable to assess the scattering behaviour of buildings in site shielding. The validity of the predictions is tested using a reflector and buildings at a frequency of 11.2 GHz.