The theoretical approach proposed here was aimed at accurately describing the electromagnetic response of self-biased Y-junction circulators made of polycrystalline hexaferrites. The accuracy of circulator response was enhanced by considering the real magnetization state of the material through a calculation of the permeability tensor; this tensor remains valid whatever the strength of the local effective dc field in the ferrite is. Moreover, the hysteresis phenomenon was introduced in the calculation of tensor through the use of the Stoner and Wolhfart [IEEE Trans. Magn. 27, 3475 (1948)] law; as a consequence, the tensor took into account the privileged direction of easy-axis distribution due to the manufacturing process, which allowed us to treat the polycrystalline hexaferrites as being magnetically self-biased. However, the results issued from our approach indicate that this higher accuracy is at the expense of Y-junction circulator performances, which are far from those reported in the literature or obtained with electromagnetic commercial simulators and based on the frequent assumption of saturated hexaferrite, even at the remanent state.
We propose a theoretical approach aimed at accurately describing the electromagnetic (EM) response of a microstrip Y-junction circulator. This analysis is predictive since it relies on the insertion of both the nonuniformity of the static field of polarization and the ferrite material magnetization state. We fabricated proof-of-concepts to compare the responses issued from two available EM analyses, namely our approach and the HFSS software one. The key-role of a rigorous modeling of the microstrip Y-junction circulator is highlighted through a comparison of simulation data and experimental results.Index Terms-Ferrite circulators, magnetic field effects.
The electromagnetic analysis of a Y-junction circulator proposed here is more realistic than the conventional one, as it accounts for two aspects that are usually neglected despite their frequent occurrence in practice: 1) the nonuniformity of the dc-bias field met in planar technology and 2) the introduction of a tensor to take into account all the magnetization states of the ferrite material. Slicing the ferrite sample into concentric zones allows us to consider the radial variation of the bias field in the electromagnetic calculation. A magnetostatic calculation of the internal field provides the true internal field within each region of the ferrite disk. We replace the Polder tensor, which describes only one specific magnetization state of the material, with another tensor that allows the true magnetization of the ferrite rings to be taken into account.
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