The Frequency Response Function of a Linear Time-Varying System

Abstract Although linear time-varying systems can be represented in terms of a frequency domain type representation based on the Zadeh system function, a well-known problem with the application of this formalism is that the system function is usually irrational, even in the case when the given system is finite dimensional. In this paper, the focus is on the problem of constructing rational approximations of the Zadeh system function for linear time-varying discrete-time systems. Rational approximations are constructed by generalizing the procedure for matching the combined sequences of Markov parameters and moments developed by Jonckheere and Ma for time-invariant systems. An example is given which illustrates the improvement in the approximation that can be gained in comparison to that of the frozen-time approximation. The use of rational approximations in system analysis is also briefly considered.