The design of polygonal patch antennas with a broad-band behavior (e.g. for UMTS applications) is presented in this contribution. The main idea of this work is based on the possibility of changing the electrical antenna features of a standard rectangular patch by means of proper perturbations of its sides (slope, length, etc.). The patch shape resulting from this perturbation is a convex polygonal radiator, which is analyzed through a spectral domain full-wave formulation and a method of moment (MoM) numerical code employing entire-domain basis functions. Some examples of practical UMTS antenna designs are also presented and compared with similar radiators already proposed in the literature in order to show how a proper perturbation of the patch shape can significantly improve the antenna performance.