ANALYSIS OF INFLUENCE OF BUFFER LAYERS ON MICROWAVE PROPAGATION THROUGH HIGH-TEMPERATURE SUPERCONDUCTING THIN-FILMS

Methods of analysis of microwave propagation through superconducting t hin films with buffer layers on dielectric substrates have been discus sed. Expressions describing the transmission coefficient S-21 through the structure and the complex conductivity sigma of a superconductor i n an analytical form have been derived. The derived equations are vali d for microwave propagation in waveguides as well as in free space wit h relevant definition of impedances. Using the obtained solutions, the influences of buffer layers' parameters (thickness, relative permitti vity and loss tangent) on the transmission coefficient has been invest igated using MATLAB. Simulations have been performed for 10 GHz transm ission through YBa2Cu3O7 films on sapphire with SrTiO3 and CeO2 buffer layers and on silicon with CaF2 and YSZ buffer layers. To illustrate the simulations, measurements of the transmission through YBCO film on sapphire with SrTiO3 buffer layer have been performed. It has been sh own that even lossy buffer layers have very little impact (smaller tha n 1% in magnitude and 0.3% in phase) on the transmission coefficient t hrough superconducting thin films, providing their thickness is below 10 mu m.