2D Fresnel-Kirchhoff diffraction approach is applied to forward scattering of radar signals at a rotor of a wind turbine (WT). Quasi-static diffraction loss and phase shift as well as instantaneous Doppler shift of the two-way signal due to diffraction at more than one blade of a three blade rotor is investigated which is of particular importance if the rotor axis lies within the radar beam. Comprehensive understanding of such scenario where more than a single blade is illuminated paves way for tracing the worst case in terms of e.g. measured Doppler error.