**8. Conclusions**

Problems related to scaling in circuits can be solved by introducing auxiliary sources. The coherence of the approach has led to relatively simple models of auxiliary *Multiscale Auxiliary Sources for Modeling Microwave Components DOI: http://dx.doi.org/10.5772/intechopen.102795*

sources. These sources have already been used in the literature, particularly in diffraction, and have been applied here to study the insertion of localized elements in circuits. A simple example has highlighted the limits of the validity of using these sources and has defined a protocol for describing the influence of localized elements in electromagnetism. We have been led to introduce an equivalence relation that allows us to get away from the element's geometry. This last hypothesis, if verified, justifies the intuitive approach, which consists in considering that one must be able to realize an exact electromagnetic calculation by assuming certain parts of the circuit (localized elements) by their "current–voltage" characteristics.

#### **Notes/thanks/other declarations**

The author thanks Mr. Henri Baudrand of the N7 Toulouse for his help.
