Left panel: spectral energy distribution of the Stokes parameters (I, Q, U, V, where I ≡ I_ν is the specific intensity in cgs units [ergs s⁻¹ cm⁻² ster⁻¹ Hz⁻¹]) computed with the static background jet model described in Sect. 3.1 and the corresponding fractional linear and circular polarizations. Middle panel: same as the left panel, but assuming no emission/absorption in Stokes V (j_V = a_V = 0). Right panel: same as the left panel, but assuming no Faraday conversion (ρ_Q = 0). The flux in Stokes V (left panel) in the optically thick part of the spectrum is mainly produced by Faraday conversion. In the optically thin part of SED, Stokes V is due to intrinsic emission. In this jet model the spectra of fractional linear and circular polarization have steep and nearly flat spectral slope, respectively. When the values of Q, U, and V are negative, −Q, −U, and −V are plotted here.