Correlating a multiple measurement system for accurate determination of dielectric properties

Abstract

In this project, two different measurement systems utilising a coaxial transmission line were used to characterise the dielectric properties of lossy materials as a function of frequency, from 100 MHz to 3 GHz. The open-ended coaxial transmission line modelled using an equivalent circuit model developed in-house was used to retrieve the complex permittivity of the material under test from the measured reflection coefficient. Additionally, a closed coaxial transmission line was used to retrieve the complex permittivity of the material under test using a system based on well-known models such as the Nicholson-Ross Weir and the Short-Circuit-line models. The main objective of the project was to conduct measurements using these two methods and compare the results with simulated and standard NPL data. This helps in establishing a benchmark for the closed coaxial transmission in-house developed algorithm which converts from the measured reflection coefficient to the corresponding complex permittivity. A validation process based on comparisons of dielectric measurements of ethanol, methanol, propan2-ol, olive oil and TX100 to simulated data obtained from open-ended coaxial transmission measurements and NPL data was utilised to verify the closed coaxial transmission line. The final part of the project focused on the dielectric measurements of soil.