A rectangular, circular, or elliptical metal pipe designed to transport electromagnetic waves through its interior.
a waveguide normally consists of a hollow metallic conductor, usually rectangular, elliptical, or circular in cross section. This type of waveguide may, under certain conditions, contain a solid or gaseous dielectric material.
A waveguide used as a long transmission line consists of a solid dielectric filament (optical fiber), usually circular in cross section.
In integrated optical circuits an optical waveguide may consist of a thin dielectric film.
Ionized layers of the stratosphere and refractive surfaces of the troposphere may also act as a waveguide.