In this paper, we present a method for determining complex permittivity of materials using two different thicknesses of the sample placed in free space. The proposed method is based on the use of transmission having the same geometry with different thicknesses with the aim to determine the complex propagation constant (γ). The reflection and transmission coefficients (S11 and S21) of material samples are determined using a free-space measurement system. | VNU Journal of Science: Comp. Science & Com. Eng., Vol. 33, No. 1 (2017) 57-62 A Novel Method Based on Two Different Thicknesses of The Sample for Determining Complex Permittivity of Materials Using Electromagnetic Wave Propagation in Free Space at X-Band Ho Manh Cuong1,*, Vu Van Yem2 1 Electric Power University Hanoi University of Science and Technology, Vietnam 2 Abstract In this paper, we present a method for determining complex permittivity of materials using two different thicknesses of the sample placed in free space. The proposed method is based on the use of transmission having the same geometry with different thicknesses with the aim to determine the complex propagation constant (γ). The reflection and transmission coefficients (S11 and S21) of material samples are determined using a free-space measurement system. The system consists of transmit and receive horn antennas operating at X-band. The complex permittivity of materials is calculated from the values of γ, in turns received from S11 and S21. The proposed method is tested with different material samples in the frequency range of – GHz. The results show that the complex permittivity determination of low-loss material samples is more accurate than that of high-loss ones. However, the dielectric loss tangent of high-loss material samples is negligibly affected. Received 04 February 2017; Revised 17 May 2017; Accepted 11 July 2017 Keywords: Complex permittivity, Dielectric loss tangent, Complex propagation constant, S-parameters. 1. Introduction* measurements such as printed circuit board (PCB) materials [6-12]. Although the proposed methods are simple, quick, and reliable to use. However, it has drawbacks such as the material samples to determine the complex permittivity require structures the type printed circuit board. The measurement of complex permittivity of material can be made by using the transmission/reflection method developed by Weir [13]. The method for .
