| at a given point in a transmission line or waveguide, the complex ratio of a specified field vector component in an electromagnetic wave in a given mode to the same field vector component in a reference wave in the same mode
NOTE 1 – For a mode of propagation, the reference wave may be one that carries unit power and in which a specified field component has zero phase at a specified point in the reference transverse cross-section. Usually, the transverse component of the electric field vector at the centre point of the reference cross-section is chosen for that purpose.
NOTE 2 – For an evanescent mode, the power carried by the wave is zero. One can then make the integral of the longitudinal complex Poynting vector, over the reference cross-section, equal to the imaginary unit, or use any other well-defined normalization.
NOTE 3 – It is preferable to consider separately the modes of propagation and the evanescent modes because the normalized complex wave amplitude concept is mostly applied to the former.
NOTE 4 – In rare cases where the scattering matrix has to be extended to evanescent modes, it is better to give the user freedom to choose and define his own reference waves.