MODELING AND SIMULATION OF ULTRAFAST PULSE-PROPAGATION IN MICROSTRIP LINES

Advances in the electro-optics technology have made possible the generation of pulses of time-duration of the order of a fraction of a picosecond or less; propagation of such pulses in conventional transmission lines is severely affected by both dispersion and attenuation. Since these pulses are finding their application in many fields of science and engineering, it is important to model and simulate their propagation process and to find new ways to overcome these difficulties. In this paper we describe our procedure for modelling and simulation of ultrafast pulses in microstrip transmission lines, both conventional and superconductive. This procedure combines the approximate, curve-fitted expressions for the dispersion characteristics with an analytical approach based on the Taylor-series expansion. In this way, the propagation is described by a cascade of linear filters, each of them related to a well known physical process. The output of the system is then obtained numerically through a Fast Fourier algorithm. The advantage of this method, as compared with entirely numerical methods, is to make it possible for the designer to have a prior estimate of the distortion to be expected in a given situation, and consequently, to be able to manipulate the different variables in search for a better system performance.