Multilayer magnetic waveguides: Optimizing nonreciprocal propagation in the 50-70 GHz range

Waves in magnetic systems often show nonreciprocal propagation, where the properties of a wave depends on whether it is travelling in a forward or reversed direction. This fundamental property is used in devices such as isolators, which often use a transverse electric (TE) polarized wave. In this paper, we study propagation of electromagnetic waves in small microstrip waveguides where the wave propagates at an arbitrary angle with respect to the magnetization direction. The angle allows mixtures of TE and transverse magnetic (TM) modes. This has distinct benefits, allowing the nonreciprocity typically found in TE modes, but also allowing propagation of low frequency TM modes, which do not have a cut-off frequency. Our calculations, using Barium hexaferrite as the magnetic material, show significant nonreciprocity and isolation are possible. Differences in attenuation above 75 dB/cm are found for these mixed-polarization waves for propagation angles of about 40 degrees. We study nonreciprocal propagation as a function of propagation angle and other material parameters for both primarily TM and primarily TE modes. (C) 2014 AIP Publishing LLC.