ABSTRACT
The basic concepts describing the coupling between two waveguides were laid out in this chapter, for the case of transmission lines modeled as distributed networks. In this chapter, the authors provide missing piece of the picture, constructing a theory that can be applied to any kind of waveguide, not just to conventional transmission lines. The first four sections of this chapter focus on instances of co-directional coupling, a mode on one waveguide is coupled to a mode on a second waveguide that propagates in the same direction. Generally speaking, substantial coupling between modes propagating in opposite directions requires a nonuniform coupling mechanism, and this is treated in the final section of the chapter. The coupling is assumed to be small enough that the individual, uncoupled waveguides approximately retain their distinct character. In this way, they can gain insight into the behavior of coupled modes in waveguides.
