Improvement of Permittivity Measurement for Materials With Arbitrary Thickness Based on Rectangular Waveguide

In this letter, an improvement of the NRW transmission/reflection method based on the rectangular waveguide is proposed, providing a solution for measuring the material’s complex permittivity with large electrical thicknesses in a waveguide-based system. The proposed method primarily focuses on addressing the issues of half-wavelength divergence and multiple roots by reformulating the calculation equations and compensating for the imaginary part of the propagation constant. A procedure is proposed, and a full-wave simulation is conducted to verify the method’s correctness. A measurement system is fabricated to measure the complex permittivities of three materials with different thicknesses in the frequency range of 8-12 GHz. Compared with existing arts, our proposed method has some advantages, such as avoiding the very low start frequency and initial value prediction, using existing calibration kits, and operating with high accuracy.