In this work we show a new technique for sub-structured Ronchi rulings generation and the calculation of the irradiance profile produced by this ruling. Commonly, these rulings are used to increase the spatial resolution in the Ronchi test and allow us to observe smaller surface defects. To generate the sub-structured Ronchi ruling we propose a combination of several classical Ronchi rulings with different frequency, in order to calculate the irradiance profile generated by the substructured Ronchi ruling, we propose a combination of the irradiance profile generated by each combined classical Ronchi ruling. The comparison of synthetic and experimental Ronchigrams of spherical surfaces are shown. We found that the proposed method can reproduce reliably the experimental irradiance profile.