A system level EMC method is proposed in this paper to predict the electromagnetic interference (EMI) from multiple radiators. The problem under test consists of a large network router with 480 optical modules radiating at 10.3 GHz. The proposed method handles the analysis of this system by using different phased array antenna topologies. Systematic conclusions are presented including the effect of same frequency vs. different frequency of radiating subsystems, the possibility of missing the maximum emission (Emax) during horizontal scan and height scan, and the effect of the radiation pattern for different radiators. The results indicate the existence of a 10 Log N (dB) tendency for the Emax parameter in the case of adding a complex electric field (voltage) and random phase distribution over the line cards. It also shows similarity to an 8 Log N (dB) tendency for adding power intensity for different line cards with slightly offset frequencies. The developed method can be extended to other frequency ranges when necessary. The proposed statistical method is useful when it is not practical to assemble a complete system consisting of several radiating subsystems with different frequencies in EMI testing.