In this letter, the design of a planar antenna compliant with FCC requirements for ultra-wideband (UWB) transmission systems is described. With reference to a planar geometry on a dielectric substrate, the shape of the antenna is described by means of a spline-based representation and it is determined by means of an optimization process aimed at finding the optimal descriptive parameters that allow to fit the user-defined electrical and dimensional requirements. The reliability and effectiveness of the antenna prototype are assessed through simulations as well as experimental measurements.