Estimation of frequency response set from interval data of step response

In this paper, a method of estimating a set of frequency response of a stable plant from interval data of step response is given where no parametric model is assumed. The step response is approximated by a piecewise linear function, to which a Fourier transform is applied, and the estimation problem is reduced to a linear programming problem. The result is shown graphically by a vector locus and Bode diagram.