The theory of coupling in a tapered waveguide

A theory is given which enables the overall coupling between two modes to be calculatedfor a tapered waveguide, if the coupling factor between the modes, the phase constants of the modes, and the characteristic impedances of the waveguide for the two modes are known at all points along the taper. It is thus restricted to those cases where a characteristic impedance can be defined, i.e. waveguides bounded by a very good conductor and not containing very lossy materials. The theory is found to be valid even if one of the modes is cut off over part of the length of the taper. `Taper¿, in the present context, includes the case of uniform dimensions and gradually varying properties of one or more of the materials contained in the guide. The overallcoupling between the H01and H02modes of a copper-walled circular-waveguide taper of raisedcosine form is calculated as an example.