Application of the Kalman Filter/Smoother for accurate material characterization of planar dielectric samples by using free-space measurements at sub-THz

The Kalman Filter/Smoother, as a new post-calibration technique, has been successfully applied for accurate relative complex permittivity e,. extraction of planar dielectric samples using sub-THz free-space transmission scattering parameter S21 measurements. Extracted e,. of the planar polyvinylchloride and polymethylmethacry-late samples without any post-calibration procedure produced non-physical results (violation of the passivity principle) over some frequencies in three frequency bands between 50 and 75 GHz, 75 and 110 GHz, and 110 and 170 GHz, indicating the importance of the application of a post-calibration procedure. It has been demonstrated by S21 measurements and extracted e,. that the Kalman Smoother and the Savitzky-Golay filter, as the other post-calibration technique, produce little offset or deviation in the extracted e,. around the lowest and highest frequencies over the frequency band (or at the intersection of individual frequency bands), as compared with that of the singular spectrum analysis technique, considered as another post-calibration technique.