What is the co-simulation workflow between an EM solver and a circuit simulator for amplifier design?

The co-simulation workflow between an EM solver and a circuit simulator for amplifier design combines the electromagnetic accuracy of a full-wave (or 2.5D) simulation for the passive structures (matching networks, bias networks, transmission lines) with the nonlinear device models (transistor models) available in the circuit simulator, producing a more accurate prediction of amplifier performance than either tool alone. The workflow is: design the amplifier circuit schematically (use the circuit simulator (ADS, Microwave Office) to design the matching networks, bias networks, and stability networks using ideal transmission line and lumped element models; optimize the circuit for gain, noise figure, stability, and bandwidth), lay out the PCB/MMIC (translate the schematic design into a physical layout with actual trace widths, lengths, bends, via holes, and component footprints), simulate the passive layout electromagnetically (import the layout into the EM solver (Momentum, Sonnet, HFSS) and simulate the passive structures to generate S-parameter files that capture all parasitic coupling, radiation loss, and discontinuity effects not modeled by ideal circuit elements), replace ideal elements with EM-derived S-parameters (in the circuit simulator: replace the ideal transmission line models with the S-parameter blocks generated by the EM simulation; keep the transistor models (nonlinear device models like the Angelov or Curtice model) as circuit-level components because these cannot be simulated in an EM solver), re-simulate and iterate (run the circuit simulation with the EM-derived passives; the results will differ from the ideal simulation because the EM simulation reveals: parasitic coupling between traces, discontinuity effects at bends and junctions, radiation loss from open structures, and ground return path effects; adjust the matching network dimensions as needed and re-run the EM simulation until the performance meets specification).