Radiation loss in microwave devices based on easy-plane ferrites

It has been proposed that in many cases the insertion loss of ferrite microwave devices at relatively low frequencies is largely caused by radiation loss due to excitation of quasistatic interface waves at the interfaces of the ferrite with other materials, such as metal ground planes and dielectric substrates that are coplanar with the ferrite substrate. Detailed calculations are here reported for devices based on ferrite materials that have “easy-plane” anisotropy, the easy plane coincides with the substrate plane, and the bias field is parallel to the propagation direction. The onset frequency for this type of loss is shown to be given by √((f_H+f _M+f_A)(f_H+f_M)), here f_H , f_M and f_A are, respectively, the frequencies corresponding to the internal bias field, the saturation magnetization and the easy-plane anisotropy field