An efficient numerical technique called scale changing technique is applied here for the electromagnetic modeling of microstrip reflectarrays. Based on the partition of the array surface into further planar sub-domains at various scale levels, this technique allows the computation of the equivalent multiport from the simple cascade of scale changing networks. Each network models accurately the electromagnetic coupling between the various sub-domains, including the coupling between non-identical cells in arrays. The high flexibility of the approach associated with advantages of the integral equation formulation renders this original technique powerful and rapid for designing antenna arrays. Because the computation of scale changing networks is mutually independent, processing and memory requirements can be reduced enormously by using multiple processing units. Copyright © 2012 John Wiley & Sons, Ltd.