A comparison between discrete-time and vector fitting representations of S-parameter data

Given an S-parameter description of an arbitrary microwave network up to a specified frequency, this paper addresses the problem of finding an equivalent time-domain description suitable for transient simulation. Two approaches are compared: a novel discrete-time impulse response (DTIR) method and an exponential-form response using standard vector fitting (VF) along with the inverse Laplace transform (iLT). Transient simulation examples are given to show that compared with the VF-iLT method, the DTIR approach is more straightforward mathematically while also being efficient to implement due to its compact representation.