A method for modeling electromagnetic characteristics of a vehicle having electrical components comprising generating a parallel plate waveguide model and inserting a vehicle model for the vehicle within the parallel plate waveguide model. The vehicle model has a plurality of lumped ports corresponding to on-board electrical components. The method executes an electromagnetic field solver on a first and second waveguide ports and the lumped ports and determines a scaling factor between a first power level configured to excite the first and/or second waveguide ports and a second power level configured to excite the lumped ports. The electromagnetic field solver runs on the first and second waveguide and lumped ports, producing a first output data and the method produces a scattering parameter (S-parameter) model for the vehicle from the first output data that includes a plurality of S-parameter ports.