The propagation characteristics of conventional and high-Tc thin-film superconducting strip transmission lines are investigated theoretically by using the London equation and modified two-fluid model incorporated with the microscopic coherence effect. The attenuation constant and phase velocity are studied as functions of temperature and frequency. Special attention is paid to the propagation properties due to the coherence effect. The usual dips observed in the temperature-dependent phase velocities predicted by the traditional two-fluid model are smeared out in our case. Also, the influence of the coherence factor on the phase velocities is more pronounced at high frequencies and temperatures near Tc. The dependence of the attenuation constants on frequency, however, is shown to bear a strong resemblance to the common surface resistance in the microwave region.
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