In this paper the Uniform Theory of Diffraction (UTD) is used to calculate the electric field strength near perfectly conducting obstacles. In case suppression of an interfering radio wave is wanted, a parameter of interest is the site shielding factor, which expresses the attenuation of an electromagnetic wave that propagates around an obstacle. Site shielding results are presented for a thin screen and a block-type obstacle, and good agreement between theory and experiment is found for both cases. Another application of the site shielding concept is the prediction of the field strength in an urban environment. For this application the use of a versatile block-type obstacle seems more appropriate. To demonstrate the capability of the models presented, the field strength near a cluster of obstacles is calculated. It is explained how communication parameters such as the Doppler and the delay-Doppler spectrum can be derived from the wave analysis. The model proposed can be of use for the planning and analysis of (future) telecommunications systems and the understanding of the behavior of the (mean) signal strength in urban environments.