A Position-Independent Approach to Accurate Measurement of Broadband Electromagnetic Constitutive Parameters of Magnetodielectric Materials

Magnetodielectric materials have been recently attracting great attention owing to their significant advantages for miniaturization and wide bandwidth of antennas. A precise measurement of broadband permeability and permittivity is crucial to develop and evaluate advanced magnetodielectric materials. The Nicolson-Ross-Weir (NRW) method is widely used to extract electromagnetic constitutive parameters from measured scattering parameters. One of the drawbacks of this method is requiring direct measurement of the actual sample position in the measurement fixture, which leads to uncertainties in the measured permeability and permittivity. In this article, we improve the standard NRW method by removing the need for prior knowledge of sample position. For any isotropic material, the sample position in the measurement fixture can be precisely determined by matching the phasor angles of the reflection coefficients at the sample surfaces. Due to eliminating the error from the direct measurement of sample position, the improved NRW method effectively reduces the uncertainties in the calculated permeability and permittivity. Based on the results from two kinds of magnetodielectric materials measured in two sets of test fixtures of different geometries, this straightforward, explicit, and noniterative method is theoretically and experimentally proven to have a high and position-independent accuracy over a wide frequency range.