DC Extrapolation, S-Parameters

Hello,

I have a set of s-parameters of a two-port network measured with a VNA. The objective is to incorporate the two-port into a Simulink simulation. To generate the Laplace transfer function I used the rationalfit function in Matlab. The frequency range of the measured s-parameters is between 30kHz up to 250MHz. So, my questions is how can I perform a DC extrapolation in Matlab concerning the fitted data. Does somebody have experience with DC extrapolation in Matlab?

Every help would be great.

Thanks, Matthias