ABSTRACT
A rectangular waveguide, an E-plane guide and even Gaussian beams in free space may all be considered as particular types of transmission line. A transmission line will have a uniform or periodic structure which guides electromagnetic waves in a given direction. The details of the structure vary from type to type—metal pipes, dielectric fibres, chains of lenses or mirrors, etc—but they all share a set of basic properties. For example, the field patterns in each case may be treated as modes propagating in a particular direction.
