Swihart waves and surface plasmons in a parallel-plate superconducting transmission line

The electromagnetic waves propagating inside a parallel-plate transmission line are investigated. In the case of a finite penetration depth of the ele ctromagnetic field into the metal, a longitudinal electric E wave propagate s in the the line instead of a transverse electromagnetic wave. At small th icknesses of the dielectric this wave goes over to a Swihart wave, and at l arge thicknesses of the dielectric it is converted into a surface wave (pla smon). It is shown that there exists an optimum thickness of the supercondu cting film coating the parallel-plate transmission line, for which the elec tromagnetic wave experiences the maximum slowing down. Using waveguides for surface waves, one can construct surface-wave microwave resonators. These resonators have a highly uniform microwave current distribution and, have a high concentration of microwave current in the superconducting film, and t hey are simple to fabricate. (C) 2000 American Institute of Physics. [S1063 - 777X(00)00502-8].