In this paper we present a method to recover electrical parameters of filters embedded in a multiplexer for which scattering measurements are given. Unlike other approaches proposed for this problem, this method does not require a priori knowledge of the scattering parameters of the junction. This feature renders the procedure well suited for tuning purposes or for fault diagnosis. Technically the algorithm starts with a rational approximation step, in order to derive a rational representation of certain scattering parameters of the multiplexer. This representation is then used in a second step to identify the electrical model of each filter. This second step relies on a rational interpolation technique used to extract the filter's responses.