Accurate measurement of the permittivity of materials is important in the imaging, communication, radar, material analysis and other fields. The method of extracting material parameters under different model conditions of frequency domain continuous wave signal based on quasi-optics vector network analyzer system is realized. It provides reference conditions and practical basis for evaluating the reliability of dielectric parameter measurement and defect detection of terahertz band materials. The process of terahertz wave interaction with the tested sample produces intractable spike noise due to interfacial echo resonance. In the signal transmission, the singularity is due to the wavelength and the sample optical path parameters forming the resonant mode, which is different from other noise signals.We combine wavelet denoising and variational mode decomposition, and introduce frequency expansion, which not only removes frequency-dependent noise, but also avoids frequency curling, which improve the accuracy of the measurement results.
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