High-Temperature Superconducting Periodic Transmission Line

In this paper, a high-temperature superconducting transmission line periodically loaded with small insulator gaps is studied in order to investigate its microwave characteristics. We calculate dispersion and impedance equations for both cases of infinite and finite periodic structures. For the infinitely long periodic structure, the method of analysis is based on the ABCD matrix representation of each unit cell in conjunction with the Floquet theorem. In the case of a finite periodic structure, proper boundary conditions are assumed at the ends of the structure, and the complex resonant frequencies of the structure are computed. Band gap formation in this structure is highlighted and its potential applications in the design of passive filters and resonators are discussed. Several devices are fabricated in yttrium barium copper oxide (YBCO) thin films and experimental results are shown to be in fairly good agreement with the numerical simulations.