Cuong Manh Ho, Yem Van Vu

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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 8.0 – 12.0 GHz. The results show that the dielectric loss tangent of low-loss material samples, the more accuracy of complex permittivity. However, the complex permittivity is slightly effected by the dielectric loss tangent of high-loss of material samples.