Group theoretical approach to eigenvalue problems of symmetrical multiports with gyrotropic media

Eigenvalue problems of symmetrical multiports with gyrotropic media are considered. It is shown that the perturbation method known in quantum mechanics may be used for symmetrical structures with gyrotropic media in order to determine the influence of dc magnetic field on the eigenvalue degeneracy. In gyrotropic structures, an additional degeneracy may appear which is not predicted by the unitary subgroup. The eigenvalue equation for [S]-matrix in the case of magnetic groups of the third category and the problem of calculation of eigenvectors for transposed matrix are investigated. The theory is illustrated by some examples.