The flanged waveguide antenna: Discrete reciprocity and conservation

Abstract

The flanged waveguide is a prototypical antenna used in the description of both receiving and transmitting applications. This structure embodies much of the physics of more complicated structures. In particular, the fields radiated in the transmitting mode, and the modes created and fields scattered in the receiving mode satisfy basic reciprocity and conservation laws. In this paper it is demonstrated that the discrete formulation of these problems, obtained by a truncated normal mode analysis, satisfies the basic reciprocity and conservation laws. These discrete relationships hold regardless of the size of the truncated system N, as long as N is greater than the number of propagating modes in the waveguide. Thus, the adherence of this approximate numerical method to the reciprocity and conservation laws does not necessarily imply its accuracy. Several numerical examples are given to illustrate this point.