You can do almost all of what you might do in Simulink or System Modeler in the VHDL-AMS simulator that comes with the Siemens (formerly Mentor) pcb design and layout packages, plus you can directly use SPICE models, VHDL models, and linear s-parameter models. You won’t get the control design tools of Simulink or the filter synthesis tools of a serious RF design package, though. There is a freely accessible web version here, thought, for the curious: