Search

No detailed analysis has been available on the return loss characteristics of a pyramidal electromagnetic wave absorber. Therefore, an approximate analysis method for the pyramidal absorber has not been established in a rigorous sense. In this paper, the return loss characteristics for the normal incident on the pyramidal absorber are derived by the numerical simulation based on the spatial network method. Also, as an approximate method for the wave absorber that can approximate the obtained results well, a method called the synthesized capacitance model is proposed. By comparison of the numerical results by the two methods, it is found that the approximate results by the synthesized capacitance model provide more accurate results than those by the previous approximate models. Further, by means of the synthesized capacitance model for the normal incidence, the oblique incidence characteristics of the TE wave were computed and the results agreed well with the measured data.

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.

Ferrite is a non-reciprocal material which is used in non-reciprocal devices such as isolators or circulators for the microwave and optical bands. Waveguides containing ferrite, are usually analyzed by 2-dimensional approximations but not by 3-dimensional analysis. This paper utilizes a mode-matching method to analyze ferrite image lines, and the analysis is compared with experiment. First, the mode-matching method is applied to the mode analysis of a ferrite slab and we find its dispersion and field distribution. These modes are then used to analyze the image waveguide, especially its field patterns, which are quite different from those for the dielectric case; finally its validity is confirmed by experiment.

Birefringent material in a thin film dielectric waveguide is used to realize phase matching of the waves with different polarizations. However, this method cannot be used exclusively due to lattice mismatch as happens in a mode conversion type isolator. This paper proposes an artificial anisotropic waveguide realizing phase matching with isotropic dielectric materials only. the structure is a slab waveguide loaded with dielectric strips parallel to the wave propagation direction. This structure can equalize the phase velocities of the Ex and Ey modes. A numerical analysis based on the mode matching technique is used to obtain the phase match condition. the effect of an artificial anisotropy is confirmed in a waveguide fabricated in experiments. A waveguide is realized in which difference of the propagation constants of the Ex and Ey modes is extremely small. It is believed possible that a thin film optical isolator can be reproduced with this waveguide.

To obtain a mode converting optical isolator it is necessary to achieve phase matching of the TE and TM modes propagating through the magnetic film, such as a rare-earth garnet, etc. One of the methods of phase matching employs the birefringence induced by a lattice parameter mismatch between film and substrate. This paper presents measurement of the birefringence in YIC and Bi:YIG films grown on a GGG substrate using liquid phase epitaxy. Moreover, birefringence evaluated from the optoelastic effect and the stress calculated using a bimetal model agree well with the measured values. From these results, the birefringence induced in YIG and Bi:YIG films can be obtained theoretically. It is established that a phase-matched magnetic waveguide can be obtained using Bi:YIG thin film. Further, by using such films nonreciprocal mode convertors and isolators can be realized.

Although a number of components for millimeter-wave integrated circuits based on an open dielectric waveguide have been proposed, little has been reported on nonreciprocal devices and no significant results have been obtained. In this paper we discuss experimental verification of nonreciprocal propagation phenomena in an open ferrite waveguide and their application to open nonreciprocal devices. Based on the results, we propose a circulator of directional coupler type which makes use of nonreciprocal propagation phenomena in an open ferrite waveguide. We also propose a pillbox resonator type circulator and a junction type circulator using the nonreciprocal resonance of an open cylindrical ferrite. Circulators of the directional coupler type and the pillbox type do not need any conductor in principle. The radiation loss can be reduced without significant increase of the conductor loss if a conductor shield is used in the E-plane of the junction circulator. A junction circulator with practical characteristics is developed for millimeter-wave integrated circuits.

Previously, one of the authors proposed a ferrite strip as a non reciprocal waveguide for millimeter and optical waves. It has many features, e.g., it does not require metal conductors and optical anisotropic material (NbO3), and it generates large field displacement for small anisotropy. This type of waveguide is analyzed by a generalized transmission equation and variational method. These methods, however, are time-consuming and cumbersome. This paper proposes a simple analysis method using effective permittivity. The field distribution for weakly guiding waves and the radiation characteristics are discussed in detail. It is clear that the occurrence of large field displacement is attributable to weakly guiding waves. The cut-off condition for the fundamental wave, the condition of edge guide wave generation, the radiation loss and the asymptotic value of the field displacement, are clarified.