Extrinsic Attenuation and Phase Velocity in Superconducting Interconnections.

Most evaluations of the dispersion and loss of superconducting transmission lines emphasize intrinsic parameters, assuming an ideal dielectric, linewidth much larger than dielectric thickness and smooth conductors. From this perspective, superconducting microstrip transmission lines offer very low dispersion and (at temperatures well below the transition temperature and frequencies well below the gap frequency) low attenuation. However, practical effects will degrade the performance of such lines relative to their intrinsic performance. Such effects include a frequency dependent dielectric constant due to fringing fields intersecting the air-dielectric interface of conventional microstrips and dielectric loss tangents. This brief report qualitatively reviews these effects and their impact on the dispersion and attenuation of superconducting microstrip transmission lines.