The coaxial wire method is a common and appreciated choice to assess the beam
coupling impedance (BCI) of an accelerator element. Nevertheless, the results
obtained from wire measurements could be inaccurate due to the presence of the
stretched conductive. The aim of this work is to establish a solid technique to obtain
the BCI from electromagnetic simulations, without modifications of the device
under test. In this framework, we identified a new relation to get the resistive wall
beam coupling impedance of a circular chamber directly from the scattering
parameters. Furthermore, a possible generalization of the method to arbitrary cross
section geometries has been studied and validated with numerical simulations
