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The use of directional antennas at the mobile terminal or the base station, and its influence on the observed values of short-term fading depth, is addressed. This influence is modelled through the variation of the Rice factor and the maximum difference in propagation path length among different arriving components, relative to the case when omnidirectional antennas are used. Expressions for the dependence of these parameters on the antenna beamwidth, for different statistical distributions for the angle-of-arrival of arriving waves, and different types of antennas are presented. For illustration, results on the fading depth observed by UMTS and HIPERLAN/2 in different environments are presented and discussed. Globally, when using directional antennas, fading depth reduction is observed in micro-cellular environments; in macro- and pico-cellular ones, fading depth degradation can occur depending on the environment and system characteristics.