The coupling to the fast wave of an ICRH antenna is principally determined by its distance to an optimum plasma density correlated to the cutoff one and by the density gradient between this optimum density and the bulk plasma. This explains the differences in coupling for the various heating and current drive phasings as predicted for different plasma edge profiles considered for ITER. For a given electron density edge profile the ion mix, the steady magnetic field and the frequency have also a significant effect on the coupling performances. These quantities affect the coupling mainly by influencing the position of the optimum density in the profile. A marked perturbation of the coupling leading to a large edge power deposition can occur when the Alfvén resonance lies in the edge profile. The results are applied to different ICRF scenarios considered for ITER at full and half toroidal field.