One and two-dimensional periodic structures are important in optics and they have numerous applications in the Fourier optics, optical measurements, and metrology. In this paper, diffraction from 2D structures in polar coordinate system having only angular dependency is investigated.  If the dependency to be periodic then the structure so called radial grating. By use of Fresnel integral in the polar coordinate system we will investigate the diffraction of 2D separable structures in the polar system.    The diffraction amplitude is obtained as a series of Henkel transformations. The theoretical approach is implemented to the case of radial phase grating.  In addition, experimental work on the investigation of the diffraction from radial phase gratings having different periods and corresponding simulations are presented. Experimental works have a good consistent with the results of computer simulations and theoretical analyses.