A comparison between the method based on a rigorous field analysis and the impedance transformation method for the intrinsic surface impedance of superconductor films

Abstract

In obtaining the intrinsic surface resistance (RS) from the effective surface resistance (RS,eff) measured at microwave frequencies by using the dielectric resonator method, the impedance transformation method reported by Klein et al. [N. Klein, H. Chaloupka, G. Muller, S. Orbach, H. Piel, B. Roas, L. Schultz, U. Klein, M. Peiniger, J. Appl. Phys. 67 (1990) 6940] has been very useful. Here we compared the RS of YBa2Cu3O7−δ (YBCO) films on dielectric substrates obtained by a rigorous field analysis based on the TE-mode matching method with those by the impedance transformation method. The two methods produced almost the same RS,eff vs. RS relation in most practical cases of the substrate thickness being less than 1mm and sapphire and rutile used as the materials for the dielectric rod. However, when the resonant frequency of the dielectric resonator became close to that of the resonant structure formed by the substrates and the metallic surroundings, the RS,eff vs. RS relations appeared strikingly different between the two methods. Effects of the TE011-mode cutoff frequency inside the substrate region, which could not be considered in the impedance transformation method, on the relation between the RS,eff and RS of superconductor films are also investigated. We confirmed our arguments by demonstrating a case where existence of evanescent modes should be considered for obtaining the RS of YBCO films from the RS,eff.