The effects produced on the spatial evolution of gaussian beams diffracted by radial gratings from both experimental and theoretical points of view are shown. The characteristics of the diffracted beams are orthogonal astigmatism and elliptical shape profile oriented 45 degrees with respect to the diffraction plane. Calculations based on the Rayleigh-Sommerfeld diffraction formula in the Fresnel approximation explain these effects well. In particular, we have obtained an accurate result in terms of the complex error function in order to accelerate. In order to accelerate the calculations, another solution has been obtained by means of the stationary phase approximation. We discuss the range of applicability and accuracy of these approximations.