In this work, the propagation of short electrical pulse on uniform and non-uniform planar transmission lines is studied by means of computer simulation. As the frequency band associated with electrical pulses with duration of pico-seconds extends up to several hundreds of giga Hertz, the characterization of the transmission lines along which the pulses propagate requires full waves methods. With this purpose the Spectral Domain Approach (SDA) is used to rigorously consider the effects of the line material and geometry, in the frequency band required, to calculate the phase and attenuation constants. A Fourier Transform is used to analyse the transient response in the time domain. It is observed that the tranmission line dispersion is the main cause for distortion fo the pulses, while the losses - due to the materials or mismatching on non-uniform lines - are mainly responsible for signal attenuation. However, in coupled microstrip lines, distortion due to mode coupling was the dominant distortion mechanism. It is also observed that the dispersive nature of the transmission line can be used with advantage, through carefull choice of geometry and composition, to reshape asymetrical pulses. The results fo this study find applications on quasi-optical circuits and optical circuits short pulse generation.