In cellular networks, cells are divided into sectors, each containing its own directional antenna. Although localization systems is a major research topic, in all conducted studies, contrary to the existing network structures, the use of omnidirectional antennas is assumed. In this study, an extended received signal strength (RSS) model is proposed to be able to analyze the effects of directional antennas, deviations in angular gain patterns on localization performance. It is shown via various simulations that by using RSS-based fingerprinting technique, the maximum gain direction angle of antennas and angular gain pattern deviations considerably affect the localization accuracy. In addition, the validity of the suggested model is tested by conducting the field measurements in an urban microcellular environment.