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Multiple building diffraction loss calculation is often based on the assumption that their dimensions are infinite in the direction perpendicular to the propagation path, even though in reality this assumption is not valid. In this paper, a modified diffraction coefficient model for the calculation of a more realistic diffraction loss caused by a single building with finite dimensions is proposed. The overall diffraction loss is calculated for a group of buildings in a row by using the proposed model. In addition, after carrying out the field measurements, it is shown that for some particular cases where the transmitter and diffracting obstacles are not far away from each other (i.e., microcells or picocells), spherical-wave modeling produces a better accuracy than the plane-wave approximation. It is also demonstrated that the theoretical results can further be improved by considering the higher order terms in the calculation of diffraction coefficients. Lastly, excess path loss obtained for a row of buildings with spherical-wave assumption is compared with our measurement data. This comparison shows reasonable correspondence between our theoretical model and measurements. Therefore, our proposed model can successfully be used for improving the theoretical methods for predicting path loss in urban environments, where diffraction from a number of buildings has to be considered.