Modelling and Measurement of the Scatter of Microwaves by Buildings
The growing usage and demand for microwave communications has led to the increase in system density, particularly in urban areas, and consequently to the increase in the probability of mutual interference between systems sharing the same frequency band. Satellite and point to point microwave communication systems might have to rely on site shielding to reduce the level of this co-channel interference. In urban areas, there is a great possibility of a building obstructing the interference path, thus providing protection. However, there could be more than one interference path. Scattered interference from other buildings in the vicinity of the site is one which can be found to be almost as harmful as the direct interference. Although site shielding has long been identified as an interference reduction technique, most studies have been devoted to the protection obtained from the obstruction of interference paths, namely diffraction. There is little information available regarding the effects of building scatter in site shielding. The work reported in this thesis was set to carry out theoretical and experimental investigations and characterisation of building scatter. The studies are aimed at the effects of building scatter on site shielding at microwave frequencies. Building scatter prediction models are developed based on Fresnel-Kirchhoff diffraction theory and verified against results obtained from measurement campaigns conducted at a frequency of 11.2 GHz using firstly a perfectly conducting reflector and later a number of buildings in urban environments as the scattering obstacles. Scattering prediction models are developed as extending to that originally applicable to the far field for use in the near and very near field regions of the scattering surface. The very near field model is found to be particularly useful in site shielding applications in urban environments. Furthermore, it has been possible to establish the scattering characteristics in terms of angular and distance dependence of the scattering coefficient using the expansions of the Fresnel integral with appropriate approximations. The effects of building features and surface variations, e.g. protruding and recessed features, windows and surface deviations, are analysed and characterised. These effects are particularly significant in the interpretation of measurement results obtained from buildings in typical urban environments. The thesis provides a prediction procedure which radio system planners and design engineers can use for determining the effects of building scatter on the site shielding factor for specified radio path geometries. The procedure is expected, through UK study group 3, to add considerably to a revised ITU-R (CCIR) procedure and recommendations for building scatter effects in radiowave propagation. The work has also contributed regularly to the technical output of European COST project 235.
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