In this paper a method to obtain harmonic transfer matrices (HTM) from simulated or measured values (signature & signature response) is presented. These matrices subserve a description of complex systems (e.g. RF front-ends) with real properties, which can't be specified by simple analytic expressions. They afford to give statements about a systems parameter. That's why HTM are suitable for Built-In-Self-Test (BIST) and opens the option for Built-In-Self-Correction (BISC) for critical function-blocks.