Magnitude Vector Fitting to interval data

Vector Fitting is an effective technique for rational approximation of LTI systems. It has been extended to fit the magnitude of the transfer function in absence of phase data. In this paper, magnitude Vector Fitting is modified to work on inequalities which the magnitude of the transfer function has to satisfy, instead of least squares approximation. The new interval version of the magnitude Vector Fitting is proved valuable for multiband filter design and the fitting of noisy magnitude spectra.