In this paper, the synthesis of a triple-band planar antenna working in the GSM (900 and 1800 MHz) and UMTS frequency bands is presented. As reference geometry, a hybrid pre-fractal shape has been adopted by integrating a Sierpinski and a Meander-line structure. The synthesis of the antenna has been performed by optimizing the descriptive geometrical parameters of the reference shape by means of a customized Particle Swarm strategy to comply with the electrical and geometrical requirements.