Air Gap Error Compensation for Coaxial Transmission Line Method of Electromagnetic Material Characterization

摘要

This research analyzes material characterization measurements from 50 Mhz to 3.05 GHz where an axially symmetric air gap exists between the sample material and the inner or outer conductor. Higher order fields are excited by the air gap and are accounted for through modal analysis methods. A root search minimizes the difference between the calculated scattering parameters from the modal method and the experimentally measured scattering parameters. The root is the permittivity and permeability of the material. This method is tested with a non-magnetic material and a heavily loaded magnetic material. An error analysis based on dimension measurement uncertainty is performed. The method accurately calculates the permittivity of the non-magnetic material for an air gap to material width ratio of 13.6. For a magnetic material with air gap to material width ratio of 0.02, the method accurately calculates the permittivity and permeability using 10 higher modes, but diverges when using more than 10 modes. Accurate determination of the higher order mode wave numbers is proven critical to the modal method converging.