An active phased array multibeam antenna model including the nonlinear model of the amplifiers have been developed and validated experimentally. The amplifier model used is the Shimbo model. A 4-beam C-band array was built and used for the experiments. By comparing predicted and measured patterns it was shown that the model predicts the beams corresponding to the intermodulation products with an accuracy of about 1 dB in power and with a small fraction of a degree in direction. The model can therefore be used as a tool to accurately predict the intermodulation patterns for multibeam satellite array applications, avoiding excessive system margin and reducing dc power consumption. The paper also demonstrates that the model can be incorporated in a hopped multibeam antenna system tool to predict interference, and to optimize traffic capacity and system utilization.