High-temperature superconductor microwave circuits

• Main Author: Liang, Guo Chun
• Format: Dissertation
• Language: English
• Subjects: engineering, electronics and electrical; engineering, materials science

Microwave properties of superconductors are discussed from the electromagnetics point of view, treating a superconducting material as a dielectric with a negative real part of the permittivity. A superconductive surface wave is predicted and discussed. Maxwell's equations for dispersive media and the formulation of a time-domain simulation of dispersive boundary problems are given. A parallel-plate superconductive transmission line is analyzed by treating the superconductor as a negative dielectric material. The design of a Josephson sampling circuit for measuring pulse propagation on superconductive transmission lines is proposed. From that measurement, the surface impedance of a superconducting material suitable for planar transmission lines can be found.
Various high-T$\sb{\rm c}$ superconductive resonators, filters, and hybrid superconductor/semiconductor phase shifters were made and tested. The superconductor straight-line resonator, which uses silver as its ground plane, has a high Q and an electromagnetic feedthrough level below $-$65 dB up to 10 GHz. A novel design for a band-pass filter (alternating parallel-coupled filter), which uses much less chip area than other filter structures and is suitable for superconducting high-order filters, is demonstrated. Direct-coupled, parallel-coupled, and alternating parallel-coupled types of bandpass filters were analyzed and experimental data are compared with simulation results, showing reasonably good agreement. The properties, performance, and limitations of the hybrid phase shifter are discussed in detail. The first realization of a YBCO/semiconductor hybrid phase shifter employs YBCO as the main circuit structure with semiconductor PIN diodes as switches. The measured phase shifter performance agrees reasonably well with the simulation over about 5% bandwidth. A four-bit high-T$\sb{\rm c}$ phase shifter was also designed. In addition, a loaded-line-type low-T$\sb{\rm c}$ superconductive digital phase shifter is proposed. It uses superconductive microstrip lines as the main circuit structure and tunnel junctions with suppressed-supercurrent as switches. The supercurrent of the Josephson junction is suppressed by applying a dc current in the vicinity of the junction. Simulation shows that this wholly superconductive phase shifter has a lower insertion loss, broader bandwidth, faster switching speed, and better reproducibility than conventional phase shifters of similar type. Partial experimental results are shown, indicating successful bias circuit operation and supercurrent suppression.