An Improved NRW procedure for Dielectric Characterization for solids and Uncertainty Estimation

We present a modified approach for extraction of dielectric properties of low-loss dielectric materials using two port T/R measurement. The procedure utilizes NRW method, but without the need for shifting the reference planes. This is done by employing full two-port (TOSM) calibration at the waveguide ports and specially designed sample holders along with precisely machined MUT samples. This approach enables repeatable and precise placement of MUTs in sample holder, during repetitive measurements and reduces the errors due to improper placing 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 (X-band; 8.2 GHz to 12.4 GHz). Experimental measurements are carried out for multiple samples of two of most commonly used low-loss dielectric materials in RF & microwave domain i.e. Poly-Tetra-Fluro-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.