Dielectric Characterization for Solids With an Improved NRW Procedure and Uncertainty Estimation

In this work, a modified approach for extraction of dielectric properties of low-loss dielectric materials using two-port transmission-reflection (T/R) measurements is presented. The procedure utilizes Nicolson-Ross-Weir (NRW) method, but without the need for shifting the reference planes. This is done by employing full two-port calibration at the waveguide ports and specially designed sample holders along with precisely machined material under test (MUT) samples. The sample holders can also be cascaded in any order or used independently to perform measurement on MUTs without any adverse effect on results or extraction algorithm. This approach enables repeatable and precise placement of MUTs in sample holder during repetitive measurements and also reduces the errors, which may arise due to improper placement of MUT in the sample holder/guide. This also makes the uncertainty evaluation less complex compared to the traditional NRW approach. Sample holders of different lengths have been fabricated for WR90 waveguide (
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-band; 8.2–12.4 GHz). Experimental measurements are carried out for multiple samples of two of most commonly used low-loss dielectric materials in RF and microwave domain, i.e., poly-tetra-fluoro-ethylene (PTFE or teflon) and poly-propylene (PP). Different lengths of same materials are used and the results are compared with traditional NRW method as well. Combined uncertainty budgets for the proposed procedure have been presented, using the experimentally obtained sensitivity coefficients for the modified dielectric property extraction procedure along with other system uncertainty contributors.