A system and method is disclosed for breaking a feedback loop by replacing at least one component in the feedback loop with a model containing two physically disconnected subnetworks that have terminals that are connected to ground with voltage controlled, voltage sources (VCVSs). Dependent source parameters of the VCVSs control lateral signal transfer though the model allowing the feedback loop to be opened or closed. The model maybe used in a software simulation in which a replicate circuit is used to set and maintain a closed-loop bias on the open-loop circuit. Small-signal analysis of the equivalent open-loop circuit allows extraction of transfer functions that yield a return ratio RR(s) corresponding to the modeled component.