A unified electrodynamic approach to the guided wave excitation by external
sources in the waveguiding structures with bianisotropic media is developed.
Effect of electric, magnetic, and magneto- electric losses in such media
manifests itself in the special form of eigenmode orthogonality referred to as
the quasi-orthogonality relation. It reflects the existence of the cross-power
flow and for any pair of modes which are rigidly linked to each other by this
relation. The quasi-orthogonality relation remains true in the limiting case of
lossless waveguides yielding the customary relations of orthogonality and
normalization for propagating (active) modes and also their generalization for
nonpropagating (reactive) modes. It is shown that the eigenmode set for a
waveguiding structure is complete only outside the region of exciting sources.
Inside this region the modal expansions of fields are incomplete and must be
supplemented with the orthogonal complementary fields which extend the proper
Hilbert space spanned by waveguide eigenfunctions. Among exciting sources there
are the external bulk sources (currents, fields, and medium perturbations) and
the external surface currents. Besides, the orthogonal complementary fields
generate the effective surface currents on boundaries of the bulk exciting
sources. The problem of waveguide excitation by external sources is solved by
means of determining both the mode amplitudes for the modal field expansions
and the orthogonal complementary fields inside the source region. The equations
of mode excitation are derived on the basis of three approaches applying the
direct use of Maxwell's equations, the electrodynamic analogy with the
mathematical method of variation of constants, and the conjugate reciprocity
theorem.