Application of Newmann's principle to electromagnetic N-ports

Application of Newmann's principle, well known in crystallography, to electromagnetic N-ports is demonstrated. Using this approach, it is possible to find those symmetrical structures which can be considered as candidates for implementation of the electromagnetic functions including the nonreciprocal ones. Starting from the ideal scattering matrix, a systematic procedure is suggested to find the symmetry of this matrix and the corresponding symmetry of the geometrical structure and dc magnetic field. Two examples from the field of ferrite devices are given in order to illustrate the method.