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Zones with nonlinear behavior on an object cause intermodulated components in the scattered electromagnetic field. This problem is relevant both for satellite communications and for radio-astronomical applications. Recently, a heuristic model for the passive intermodulation analysis has been derived in a time domain physical optics framework. The heuristic approach proposed requires the determination of few coefficients. Here, a genetic algorithm is introduced for the computation of the optimum values for these coefficients. Index Terms--Genetic algorithms, passive intermodulation, time-domain analysis.

Passive intermodulation (PIM) is a phenomenon which often arises at junctions between different materials. This may be a major issue in tightly packed antenna farms as those typically present on communication satellites. Here, an heuristic nonlinear extension to the time-domain physical optics (TD-PO) is proposed, to take into account electromagnetic scattering at intermodulated frequencies when such a junction is illuminated by two impinging electromagnetic fields at different frequencies. Simulation results are compared with measures to validate the model. Index Terms--Electromagnetic scattering by nonlinear media, physical optics, time-domain analysis.