128 Progress In Electromagnetics Research Symposium 2005, Hangzhou, China, August 22-26 Free-Space Electromagnetic Characterization of Materials for Microwave and Radar Applications Habiba Hafdallah Ouslimani, Redha Abdeddaim, and Alain Priou University Paris X, Ville d’Avray, France Abstract Characterization of the electrical material properties ε r , µ r and tan δ is of prime importance for all microwave and antenna design applications. Experimental “S” parameters in wide frequency band are used. Problem related to the calibration elements, calibration references planes and the thickness samples (d) are reported. Problem of calibration can be avoided by using noncontact free space electromagnetic characterization based on the measurement of the insertion transfer function. This method allows spatial correction of the experimental set-up. Problem of the sample thickness (d) is essentially due to the existence of multiple solutions when solving the set of basis equations with S 21 ,S 11 , ε r and µ r . This is the principal reason why some algorithms give spurious solutions or didn’t converge. In this work, we developed a method combining several solutions suggested otherwise based on: - Free-space electromagnetic characterization associated with an adapted wave-guide LRL (“line-reflect- line”) calibration method in the 8-12GHz X band range, - Insertion mode to correct spatial dependence of the transfer function (S 21 ), - An electrical E-wall to correct the phase of the reflection parameter (S 11 ), - A supplementary criterion on loss material is used to obtain a unique solution. We have experimentally characterized a 50mm thick dielectric material and extracted its relative permittivity in the X band. The obtained results are in excellent agreement with the known value. Introduction Recently, there has been intensive research effort in the design, fabrication and characterization of meta materials. These complex materials exhibit new properties which lead to new potential applications in microwave and radar area, increasing at the same time the necessity to develop efficient methods for characterizing these materials. Noncontact free space electromagnetic characterization is well appropriate for such materials. In this paper we present a characterization methods for determining the dielectric properties of materials in the X band frequency range. In order to validate this approach, low loss homogenous dielectric materials with different thickness and different permittivity are studied. In section 1, we present the developed algorithms and their validation. In section 2 we present the experimental results. Developed Algorithms Figure 1: Multi solutions of equa- tion (1) Figure 1 shows at least two minimums for the equation (1) solutions of the permittivity ε ∗ r =(ε r −jε ′ r ) of the studied material. In equation (1) the S 21 parameter is related to the permittivity, the frequency and the sample thickness. For a fixed frequency, existence of multiple solutions is pointed out to be attributed to the rotation of the phase and the increase of the loss coefficient X=e −2αd as a function of ε r and ε ′ r . As a consequence, all the solutions where |X |≪ 1 and |X | > 1 must be eliminated. The following criteria: 0.95 <X ≤ 1 which is naturally available for low loss material is used and the convergence of the iteration process is excellent: the solution is unique. S 21 = (1 − Γ 2 )Z 1 − Γ 2 Z 2 [1 − 4] (1)