The spectrum of electromagnetic waves guided by a plasma layer

The modal spectrum of a lossless, homogeneous and isotropic planar plasma layer is shown to contain contributions from surface waves and complex modes in addition to the usual continuous spectrum characteristic of open structures. These discrete contributions are only of the E-mode type and occur whenever the plasma dielectric constant ε
p
is negative. The surface waves may be of the forward or the backward type and they carry power in opposite directions in the plasma and air regions. The complex modes are shown to appear always in degenerate pairs and as a consequence they carry no real power but may account for large reactive fields in the neighborhood of sources. For E modes with positive values of ε
p
, and for all H modes, the spectrum is purely continuous; however, nonspectral leaky ways are then present which are significant in radiation considerations.