Accounting for discontinuities
HF-Guiding structures: Modelling and calculations

A discontinuity in a waveguide is defined as any local change in geometry or electrical parameters (permittivity or permeability) that breaks the translational symmetry of the waveguide structure. This results in a change in the solution to the propagation problem because the fundamental mode of the waveguide structure no longer satisfies the boundary conditions in the vicinity of the discontinuity on its own. Higher-order modes then appear—propagated, evanescent, or radiated (in the case of waveguides open to free space)—which, when superimposed on the waves of the fundamental mode (incident, reflected, and possibly transmitted), satisfy the new boundary conditions introduced by the discontinuity.