Preliminary design steps for thin-film superconducting filters

Techniques which aid in the design and development of microstrip filters on high-dielectric-constant substrates are presented. While the procedures are valid for most types of coupled-line filter structures, they are particularly useful as the initial steps in designing superconducting MIC filters. Numerical examples are given for both Chebyshev and elliptical designs. Measurements of the substrate properties of lanthanum galate and aluminate at ambient and liquid-nitrogen temperatures are presented. These measurements were used to design a C-band, four-pole hairpin filter. A technique to improve the prediction accuracy of commercial CAD programs for high-dielectric constant substrates was introduced and successfully tested with the prototype.<>