Electromagnetic modeling of anisotropic ferrites—Application to microstrip Y-junction circulator design

Abstract

This paper presents a theoretical tool, which combines a generalized permeability tensor model, a homemade 3D magneto-static solver, and a commercial electromagnetic simulation software Ansys HFSS™ for accurate modeling of ferrite-based devices regardless of their state of magnetization. A magneto-static analysis is carried out to find the internal biasing fields in the ferrite sample. Permeability tensor components are computed using a generalized permeability tensor model. Real and imaginary parts of permeability tensor components are then integrated into the commercial 3D electromagnetic simulation software HFSS retaining the spatial variations of internal biasing fields in the ferrite sample. Frequency domain simulations are done using HFSS. This theoretical modeling approach is validated by comparing the theoretical simulation results with experimental ones in the case of a coaxial line loaded by a magnetized ferrite. Proposed approach is then applied to the design of a microstrip Y-junction circulator. Finally, a demonstration prototype is manufactured in the Low Temperature Co-fired Ceramics technology.

Design and Synthesis of Ferrite Strip-Line Circulator Based on Enhanced Closed Form Solution and Power Handling Analysis

“…The inner width of the Y-junction strip-line also plays an important role in the matching circuit in terms of maintaining wideband operation and good isolation at the center frequency. The calculated inner strip-line width is directly proportional to the coupling angle, as shown in (12). Figure 6 shows the scattering parameter of the strip-line circulator with varying coupling angle.…”

“…Using equations ( 9)-( 11), we see that the Y-junction coupling angle is ψ = 0.267, while its width is then calculated as W 1 = 0.565 mm using (12). Then, assumed ground plan thickness is equal to two times ferrite height plus conductor thickness.…”

“…Wave admittance is calculated to Y eff = 0.0178 and coupling angle ψ = 0.52 rad is derived from (10). Finally, the inner strip-line width is then calculated using (12). After the whole analysis and calculation, we selected yttrium iron garnet (YG04) ferrite from Ningbov Chiyue [57] for this design, and its customized parameters are summarized in Table 8.…”

“…An empirical analysis of a symmetrical quarterwave coupled Y-junction strip-line circulator, described in terms of the counter-rotating mode, was presented in [9]. Ferrite circulator that employs the relations proved by both Bosma and Fay and Comstock can be found in [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], and [24]. Circulators can be designed to operate either below resonance (BR) or above resonance (AR), depending primarily on the microwave operating frequency and the amount of biasing field applied.…”