Analysis of Coaxial Soil Cell.

As the research community moves towards research with higher accuracy demands than traditional TDR measurements can provide, the natural evolution of the science will be to transition toward Network Analyzer type measurements in the frequency domain due to the significant improvement in the accuracy and dynamic range the Network Analyzer technique provides over the traditional time domain TDR measurements.  In moving from a measurement of apparent permittivity in the time domain towards a measurement of true permittivity and loss in the frequency domain; of critical need is to remove the response of the cable, instrument and TDR or coaxial probe from the measurement.  In moving toward measurements of true permittivity, of critical need are calibration methods that couple models such as Clarkson and Kraft’s coaxial impedance models, to high quality calibration methods such as are utilized in the microwave engineering field for use in Network Analyzer measurements.  In moving forward, this research reexamines the terminated coaxial cell from a theoretical basis to re-examine underlying assumptions of the Clarkson and Campbell-Kraft models and then applies the developed theory towards confirmation via experimentation.  The results of the findings highlight key areas where the Clarkson and Campbell-Kraft models are not valid along with ways to mitigate the errors that arise due to the standard TDR practice’s deviation from the ideal situation modeled by Clarkson and Campbell-Kraft models.  This paper concludes by utilizing the theory to provide a model for use in through transmission measurements and a new FDT design to perform high accuracy measurements of true complex permittivity.