1. Propagation on fundamental guiding structures

The guiding mechanism can be seen as the propagation of a set of plane waves that bounce off the metal walls surrounding the structure, or off the dielectric interfaces that make it up. In the first case, we're talking about closed guides for which no field exists outside the metal walls if they are perfect. If the external conductors are not perfect, but have a thickness of a few skin depths, the fields are sufficiently attenuated by the conductive wall to be negligible on the outside. In the second case, if the guiding phenomenon takes place via a structure open (at least partially) to free space, we speak of open guides in the sense that fields exist outside the structure and theoretically extend to infinity. As we shall see, the latter attenuate rapidly in the transverse direction when the mode is propagative (above its cut-off frequency).

The calculation procedure...