ABSTRACT
In this chapter, the authors use the orthogonality property of waveguide modes to determine the amplitudes with which modes are excited by a given set of sources. When an electromagnetic wave is incident at an aperture which is large in extent, it is sometimes possible to utilize the Kirchhoff approximation to simplify the analysis. The discrepancy between the two computed fields is one measure of the error they commit by making the Kirchhoff approximation. They illustrate the use of the Kirchhoff approximation. The authors assume more generally completeness property of the modes to describe the transverse components of the total field in a uniform waveguide with sources of bounded extent. Examination of the formulas for excitation of a waveguide reveals some guidelines for enhancing the excitation of a particular mode relative to that of other possible modes.
