Estimation methods to extract complex permittivity from transmission coefficient in the terahertz band

In this paper, the characteristics of the transmission coefficient (S$$_{21}$$ 21 ) measured in free-space at terahertz frequencies are analyzed. The analysis results are used to estimate the permittivity of the material under test, and the estimated permittivity is adopted as an initial-value for the iterative algorithm to extract the complex permittivity of the material from the S$$_{21}$$ 21 . The iterative extraction technique based on the estimation is efficient, while the iterative extraction technique without the estimation is inefficient. Various known materials in the literature are used to validate the technique in the terahertz band.