A deterministic approach to the modelling of electromagnetic wave propagation in urban environments

This thesis treats the development of a deterministic model for the electromagnetic (EM) field-strength prediction in built-up areas. The model uses Geometrical Opties (GO) together wi th various diffraction contributions based on the Uniform Theory of Diffraction (UTD) to determine the interaction of the EM wave with the environmental objects. Two applications of the model are discussed in this dissertation. The first one concerns the determination of the effeetiveness of placing an obstacle on the propagation path of an interfering signal in order to raise the signa.l-to-interference ratio of an earth-space link. Results of this intentional signal obstruction are presented for various obstacle types and positions of the observation point. Attention is also paid to the case where a receiving antenna is vcry close to the obstacle. In that case, a separate far-field treatment of obstacle and antenna diffraction is no longer allowed and a combined analysis should be carried out. This near-field analysis is performed for two types of parabolic reflector antennas, and results for the shielding effectiveness of obstacles are presented and compared. Also the validity of applying spatial far-field antenna weighting functions in field-strength prediction models based on ray methods is discussed. The second application of the model described in this thesis is the prediction of the EM field strength of a Land Mobile Satellite (LMS) signal in an urban environment. Due to its deterministic character the model developed is capable of analysing effects such as specular refiection and st rong shadowing. The lat ter are not taken into account in conventional statistical LMS field-strength prediction modeIs. Because the GO j UTD model accepts a detailed description of the urban environment, it can be used to analyse an arbitrary environment, whereas conventiona.l statistical models a.re suited for one specific geometry only. To demonstrate the capability of the model, it was used for the determination of the field strength along two trajectories at the campus of Eindhoven University of Technology. Not only the field strength, but also the Doppier spectrum, the time-delay profile and the delay-Doppler spectrogram were derived. The deterministic model is expeded to be a. valuable complement to existing statistical LMS field-strength prediction modeIs, especially if detailed digital databases of towns and cities are available.

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