Mapping of the closure trace phase difference and amplitude ratio of a double source, for different values of the Stokes parameters Q₂ and U₂, taking the trace of the double source with Q₂ = U₂ = 0 (i.e., unpolarized component 2) as the reference trace. The antennas are distributed in the positions {A; B; C; D} → {0; 1; 4; 6}, in units of wave-length λ for a source separation of 1.3 radian. The white cross in the top panel marks the values of Q₂ and U₂ for which we get the maximum closure-trace amplitude ratio. On the other hand, the dashed line in the bottom panel marks the locus of points for which the electric vector position angle (EVPA) of component 1 and component 2 is aligned.