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Ferrite electromagnetic wave absorbers are widely used for electromagnetic half reflectionless rooms for EMC measurement and anechoic chambers. If gaps exist between the ferrite tiles, the return loss characteristics are substantially degraded in the low-frequency region between 30 and 200 MHz. In this article, the effects of the gap in ferrite tiles on the return loss characteristics are studied for grid-type ferrite absorbers and planar ferrite absorbers. From the numerical simulations, it is found that the degradation of the characteristics due to the gaps is smaller in the grid-type ferrite absorbers than in the planar ferrite absorbers at low frequencies. This finding is also confirmed by model experiments. Further, filling of the gaps with ferrite powder is studied as a means of reducing the degradation of the characteristics by the gaps. © 2000 Scripta Technica, Electron Comm Jpn Pt 2, 83(2): 52–60, 2000

A novel ferrite grid electromagnetic wave absorber composed of sintered ferrite is proposed. Based on the condition that the return loss should be above 20 dB at 30 MHz, its wideband characteristics for suppressing reflections compared to a single-layer absorber are demonstrated by computer simulation. Calculating the return loss by varying the geometrical parameters of the ferrite grid, an optimum structure is determined which gives the maximum frequency band. In addition, it is found that the return loss of the grid absorber is impaired by an air gap between the ferrite and conductor. Moreover, the operating characteristics of the grid absorber are demonstrated by experimental models.

Fin electromagnetic wave absorbers are proposed in which the sintered ferrite plates are placed in the direction perpendicular to the electric field of the incident electromagnetic field. By numerical calculations, it is shown that this structure has a broadband reflection suppressing characteristic. The characteristics of the absorbers in terms of the structural parameters of the absorber and ferrite permeability are shown, and it is found that the optimum structure of the absorber for a broadband operation depends on the permeability of the ferrite. Further, by means of the model experiment, the broadband characteristics of the proposed absorber are demonstrated.

The frequency characteristics for the power dividers with ferrite toroids, which are extensively used in CATV and/or MATV systems, are analyzed. The analytical optimum design method for the weakly-coupled power divider by the simplified model and the numerical optimum design method for the tightly-coupled power divider by the exact model are proposed, and the designed power dividers with ferrite toroids by the proposed methods have much improved frequency characteristics compared with the original power dividers. Thus, the useful bandwiths of all the power dividers have been extended from 5 to 500 MHz. Practical measurements show very good agreements with theoretical results, and, hence, the validity of the analyses and design methods for the power dividers with ferrite toroids are confirmed. Furthermore, the relations between the optimum circuit and ferrite constants have been clarified in reference to L0(i)Kfm.