Flanged coaxial material probes: Characterizing exterior CM energy

Small perturbations are commonly visible in complex permittivity data derived from flanged coaxial probe measurements. This was discussed and is associated with waves escaping from the probe and material-under-test (MUT) system. This has not been explicitly considered in published inversion algorithms. To study this exterior wave behavior, we place an open metallic cylinder with closed bottom around the standard SMA flanged probe described. The intention is to impede the common-mode (CM) current coupling onto measurement cabling. The system has been modeled using a commercial finite volume time domain (FVTD) computational package. The simulation results from 1-3 GHz are verified by careful E-field probing techniques. The effects of escaping CM energy, which are tracked from measured reflection data through the inversion process, to perturbations in material property results, are discussed.