Complex Permittivity Measurements of Film-Type Materials: Effect of the Waveguide Flange

The flexibility and thinness of most film-type materials make it difficult to use conventional measurement methods such as those in international or organizational standards to accurately measure the complex permittivity of these materials. This led us to develop a novel approach-based on the tip waveguide method and equivalent circuit algorithm-to accurately measure the complex permittivity of film-type materials in the X-band. The tip waveguide method, newly proposed in this paper, allows for a practical and relatively accurate measurement of the s-parameters of film-type materials. The equivalent circuit algorithm is an inversion algorithm that calculates the complex permittivity from the measured s-parameters. To verify the accuracy and validity of this measurement approach, we conducted 3D electromagnetic simulations and various experiments. The 3D electromagnetic simulation tool (CST) was used to analyze the effect of the flange of conventional commercial waveguides. This led to the proposal of the tip waveguide method with a minimized flange size and the validation of its accuracy is presented. A comparison of the results of the complex permittivity measurements from various commercial measurement systems with those of the proposed approach enabled us to confirm that the proposed measurement approach can measure the complex permittivity of film-type materials in a practical and relatively accurate manner.