  Sufficient conditions of the existence of electric or magnetic walls on
dielectric interfaces are given for a multizone uniform dielectric waveguiding
system. If one of two adjacent dielectric zones supports a TEM field
distribution while the other supports a TM (TE) field distribution, then the
common dielectric interface behaves as an electric (magnetic) wall, that is,
the electric (magnetic) field line is perpendicular to the interface while the
magnetic (electric) field line is parallel to the interface.
