Investigation of Magnitude and Phase Errors in Waveguide Samples for the Nicolson-Ross-Weir Permittivity Technique

The Nicolson-Ross-Weir (NRW) technique is a commonly-used method for measuring the electromagnetic properties of low-loss materials. The technique entails placing the material under test in a waveguide, and then inferring the electromagnetic properties of that material from the reflection and transmission coefficients measured at the ends of the guide. While NRW technique generally provides reliable and accurate results, there are conditions where errors can arise. Some of the known errors are attributed to sample preparation, although errors have been observed even with perfectly-prepared samples. Those errors generally result in an overestimation of loss and unrealistic values for permeability, and they are shown to be associated with phase errors in the reflection and transmission coefficients. The work reported here shows the relationship between measurement phase errors and how they impact estimated electromagnetic property values. Further, an approach to correct for those errors when evaluating non-magnetic materials is given