LOFAR stations are phased arrays characterized by a large field of view. X/Y polarimetric measurements made with it are therefore nontrivial compared to a radio telescope using dishes: we have to take into account the projection of the dipoles that are generally nonorthogonal on the sky and the fact that this angle varies across the field of view. This figure shows the Mueller matrix corresponding to baseline (01) in a given time and frequency slot, normalized by the Mueller matrix at the phase center (see text). Each pixel in the plot (i,j) shows the amplitude of the (i,j) Mueller matrix element in a certain direction s using a logarithmic scale. Even in this normalized version, the off-diagonal Mueller terms are as high as 10% and cannot be neglected.