Extending the frequency range of the Walfisch-Bertoni (W-B) model, which is a representative theoretical model, was investigated. To extend the W-B model, three changes to the original W-B model were made: (i) re-modeling over rooftop path, (ii) introducing a slant path, and (iii) modeling of multiple reflections between buildings. To validate the proposed model, propagation loss predicted by the model was compared with measurement data. The results of the comparison show that propagation loss predicted by the proposed model agrees well with the measurement results.