TABLE OF CONTENTS A transmission-line or waveguide allows the guidance of electromagnetic energy along a certain path. Usually the radiation of energy from the line into the environment and also the excitation of waves on the line by environmental fields should be avoided. The transmission-line concept is based on the description of the guided wave by voltages and currents, whereas the term waveguide is related to the field description of the guided wave. In its narrower sense the term transmission-line applies to structures of two or more unconnected conductors between which voltages can be applied. The introduction of generalized voltages and currents, however, allows the application of the transmission-line concept to other types of waveguides. Particularly with regard to the generality of the field concept, transmission-lines may also be considered as waveguides. Therefore the decision whether the term transmission-line or waveguide is more appropriate is also related to the methodology we apply for the investigation of the respective structure. Waveguides and transmission-lines are treated in detail in [1 5].
We use the expression waveguide to denote various structures that have the purpose to guide electromagnetic energy. We therefore introduce the following definition: A waveguide is a structure consisting of various materials that can guide electromagnetic waves along a given curve in space. A homogeneous cylindrical waveguide has the shape of a generalized homogeneous cylinder. A generalized cylinder is a surface that is generated by moving a closed curve in parallel to a line. A homogeneous cylinder is invariant...
