In the field of high frequency communications, in order to provide better communication bandwidth, a reflectarray antenna is employed to receive and send signals. Large reflectarray geometries analysis demand significant computational resources if one want to use existing full-wave approaches. In this paper, we demonstrate capability of the Scale Changing Technique (SCT) [1] in designing reflectarray antennas having enormous finite number of non-uniform radiating elements with high scale ratios in a given band. We propose the use of parallel advantages of SCT for the electromagnetic simulation of reflectarrays in a grid computing environment. System partitioning and parallel solution methods, as well as parametric studies are described. In order to demonstrate the feasibility and to assess the performance of the proposed techniques, a parallel electromagnetic program for a grid environment has been developed. Tests using arrays of different sizes, executed on Grid'5000 [2] computing nodes, have shown very promising performance indices.