Hideto Mikami

Performance of Z-type hexagonal ferrite core under demagnetizing and external static fields

The effects of a demagnetizing field and an external static magnetic field on the effective Snoek’s product of textured Z-type hexagonal ferrite, which is the product of effective susceptibility and resonance frequency, were examined in order to apply the Z-type hexagonal ferrite to high-frequency devices. As a result, the demagnetizing field due to the thin plate geometry increased the resonance frequency and the effective Snoek’s product when a high-frequency magnetic field was applied parallel to the c-plane of the Z-type hexagonal ferrite. Moreover, the resonance frequency, effective susceptibility, and effective Snoek’s product of 7.7 GHz, 10.7, and 82.2 GHz, respectively, were obtained when an external magnetic field that was sufficient to saturate the Z-type hexagonal ferrite slab was applied parallel to the c-plane and perpendicular to the high-frequency magnetic field. Furthermore, the Landau–Lifshitz equation suggested that a large Snoek’s product of over 50 GHz could be obtained with an externa...

Improved lumped-element two-port isolator

In a lumped-element two-port isolator, the relationship between the angle across two central conductors and electric characteristics is revealed using circuit analysis. At /spl phi/=90 degree, high isolation loss is achieved. At /spl phi/=60 degree, the bandwidth of insertion loss becomes maximum. This theoretical prediction at /spl phi/=60 degree was confirmed qualitatively by 360 MHz band experiments. Furthermore, we obtained the interesting result that the perfect isolation conditions at /spl phi/=60 degree is quite similar to three-port circulator conditions.

Novel Method for Evaluating Frequency Response of Permeabilities in the c-Plane and Along the c-Axis of Z-Type Hexagonal Ferrite

In this study, a novel method was developed to evaluate the permeability along a certain direction (directional permeability) in the high-frequency range. Two kinds of polycrystalline textured Z-type hexagonal ferrites whose easy planes of magnetization lie in a certain plane and in a certain direction were prepared by molding under a magnetic field; these ferrites were used in this method. The permeabilities that were measured from three toroids cut from these textured ferrites were converted to directional permeabilities by examining the relationship between the permeability measured from the toroid and directional permeability. It was noted that the highest directional permeability of over 50 was obtained along the c-plane below 300 MHz, whereas negative permeability values were observed from 1.2 to 10 GHz. On the other hand, the lowest directional permeability of 4 was obtained along the direction that is normal to the c-plane. These results can be made use of designing various inductive devices.

Multi-domain resonance in textured Z-type hexagonal ferrite

The resonance frequency of a non-saturated Z-type hexagonal ferrite under a demagnetizing field effect was formulated. The permeabilities along the c-axis and the c-plane were measured by a specimen cut from the c-plane-textured Z-type ferrite, and the resonance frequency was measured as a μ″ peak. The resonance frequency measured from the permeability in the c-plane increases dramatically as the specimen’s thickness increases. On the other hand, the resonance frequency measured from the permeability along the c-axis remains fairly constant. We tried to analyze the reason for the large difference in the resonance frequency depending on the crystal orientation using multi-domain resonance theory. As a result, the resonance frequency of a textured Z-type ferrite has been expressed when the high frequency magnetic field is parallel and normal to the c-plane. Therefore, it is confirmed that a demagnetizing field increases the resonance frequency, especially when the high frequency magnetic field is parallel t...

Directly coupled lumped element isolator with three windings

A new directly coupled lumped element isolator with three windings is proposed. A dummy load and a capacitor are connected to the additional third winding in parallel. As a result of circuit analysis, the configuration of the third winding must be parallel or anti parallel to the first winding, which has a role of direct coupling between the input and the output. When the cross angle between the first and the second windings is nearly 115 degrees, the band width of insertion loss becomes widest. Using HFSS, we confirmed the fundamental behavior of the new isolator.

Lumped-element isolator with lower symmetrical configuration of three windings

Ideal isolator conditions are derived using circuit analysis in a lumped-element isolator with three windings at angles of /spl theta/ and /spl phi/. The angle /spl theta/ can be arbitrary; however, /spl phi/ is restricted to lie on the bisector of cross-angle /spl theta/ or the supplementary angle of /spl theta/. We found that the isolator with /spl theta/=/spl phi/=60 [deg] behaves the same as the one with conventional structure with /spl theta/=/spl phi/=120 [deg]. However, the former has a 0/spl deg/ phase shift and the latter a 180/spl deg/ phase shift between the input and output. The theoretical prediction was experimentally confirmed with an 800-MHz-band isolator.