In this paper, a time domain analysis for the synthesis of antennas suitable for Ultra-Wideband (UWB) communications is presented. Towards this end, a set of time domain requirements that guarantee good impedance matching, distortionless properties, and omnidirectional radiation characteristics are defined. In order to find an antenna configuration fitting these requirements, the structure of the antenna is defined by means of a spline-based geometry. The synthesis problem is then recast as an optimization problem aimed at finding the best values of the antenna descriptive parameters. The effectiveness of the proposed approach is assessed by showing a preliminary and representative result.