Modeling and design of superconducting microwave passive devices and interconnects

A spectral-domain volume-integral-equation method is developed for analyzing superconducting planar transmission lines. This method rigorously accounts for the complex conductivity, the finite metallization thickness, and the anisotropy of superconductors. Calculated effective dielectric constants and quality factors for microstrip lines and coplanar waveguides show good agreement with measured data. The effects due to the anisotropy of high-temperature superconductors are found to be negligible for c-axis oriented films. The characteristics of a microstrip line with a thin buffer-layer and a stripline with a small air gap are also analyzed. Based upon the current distribution, a quantitative analysis is made of the power-handling capability of superconducting non-TEM resonators. Among several commonly used planar transmission lines, microstrip lines are found to have the largest power-handling capability. A more efficient full-wave method is developed based upon an equivalent surface impedance concept. In the formulation, the superconducting strips are transformed to infinitely thin strips. A full-wave integral equation method is then used to solve the problem with infinitely thin strips. This method reduces the computation time by nearly two orders of magnitude compared to the volume-integral-equation method. The validity of the equivalent surface impedance approach is verified by measurements and by the volume-integralequation method. This method is extended to model single and coupled microstrip lines on anisotropic substrates with a rotated optic axis. In the development of the equivalent surface impedance method, a closed-form expression for the current distribution in isolated superconducting strips is obtained. This closed-form expression is valid for strip thicknesses less than a few penetration depths. The equivalent surface impedance method is used to develop a set of computer routines for modeling and designing superconducting edge-coupled bandpass filters. In the design procedure and the simulation, the secondary coupling effects are neglected. A sensitivity analysis is performed on a 4-pole 1% bandwidth microstrip filter centered at 10 GHz and a 4-pole 0.05% bandwidth shielded microstrip filter centered at 2 GHz. The analysis shows that the filters remain well matched with a shift in center frequency when the superconducting