Modeling of the polarization parameters for the calibrators, 3C48, 3C138, and 3C286. Frequency coverage: from 1 to 50 GHz. For each of the sources, upper panel: the polarized flux density (black line) and the Stokes parameters, Q (blue line) and U (red line); middle panel: the polarization angle variation; and last panel: the polarization degree in percentage variation. The dashed vertical lines mark the frequency ranges used for the modeling.