Explicit Permittivity Determination of Medium-Loss Materials From Calibration-Independent Measurements

Calibration-dependent methods, before starting to measurements, require some sort of expensive calibration kits, which could reduce the accuracy of measurements due to the application of imperfect calibration standards. To eliminate such problems and reduce the overall cost of the measurement setup, in this research paper, a novel calibration-independent method has been proposed. Compared with other calibration-independent methods, our method not only extracts the complex permittivity (ε
_r
) uniquely but also removes the need for any numerical method, which generally requires a good initial guess around a global minimum to obtain accurate ε
_r
results. Noniterative and unique ε
_r
is determined by our method using raw (uncalirated) scattering (S-) parameter measurements of four different combinations of two non-reflecting measurement cells (the same length or different lengths) asymmetrically loaded by two identical samples with lengths L and 2L (samples are flushed to the terminals of the measurement cells). X-band waveguide measurements of the polyethylene sample (L = 3.85 mm and 2L = 7.70 mm) were conducted to validate our proposed method and compare its accuracy with other tested methods. An uncertainty analysis was performed to analyze the effect of any inaccurate sample thickness and offset in the position of the shifted sample, which is required by other calibration-independent method, on measured permittivity.