Antenna and radio terminal having antenna thereof

An antenna includes an antenna element, and a first magnetic body which is arranged at least a part of the antenna element and has positive magnetostrictive characteristics.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an antenna and a radio terminal having the antenna thereof.

2. Description of the Related Art

A radio terminal such as a portable telephone set and a portable information terminal have miniaturized. With the miniaturization of the radio terminal, a radio terminal having a folded-type case or the like has been proposed and put into practice.

To prevent a reduction in sensitivity of the antenna caused by the miniaturization, an approach to arrange a small piece of a magnetic body near by a case-side power-feeding unit of a planar reverse-F antenna and lower a resonant frequency has been proposed (refer to Kawano et al. “A Study on Miniaturization of Planer Inverted F Antenna utilizing Magneto-Dielectric Material (3)”, B-1-25, 2004, Electronic Information Communication Society Communication Society Convention). Thereby, an antenna length can be apparently long, so that the proposed approach contributes to the miniaturization of the antenna. As for other approach using the magnetic material, a configuration in which an unnecessary current is efficiently restricted is proposed (refer to Jpn. Pat. Appln. KOKAI Publication No. 2002-264255).

In the aforementioned configuration, it is presumed that the antenna is only a planar shape (or bar shape). Therefore, when the antenna is mounted at a curved part such as a corner part of the case of the radio terminal, or when it is mounted at a movable part of the folded-type radio terminal, because a property of the antenna changes, there is the fear of property deterioration that the resonant frequency becomes higher than a desired resonant frequency. Especially, in the case of a folded-type, the antenna is bent. Accordingly, there is a problem that the antenna length becomes apparently short, because bent antennas are capacity-coupled with each other. The same problem occurs when the antenna is mounted at the curved part of the case.

As described above, when mounting the antenna at the curved part of the case of the radio terminal, there is a problem that the folding of the antenna results in deterioration of a property, for instance, that the resonant frequency becomes higher than desired one caused by the folding the antenna. The deterioration of the property mainly results from the coupling among antenna elements, and it is expected to reduce change in antenna characteristics caused by such curvature of the antenna.

BRIEF SUMMARY OF THE INVENTION

The present invention provides an antenna having small change in property thereof resulting from curvature of the antenna and a radio terminal having the antenna thereof.

An antenna according to one aspect of the invention includes: an antenna element; and at least one of a first magnetic body having positive magnetostrictive characteristics and a second magnetic body having negative magnetostrictive characteristics which are arranged at least a part of the antenna element. Then, when the antenna is mounted along the curved part or the folded part by bending the antenna, the antenna is mounted such that the compression stress is applied to the first magnetic body and the tensile stress is applied to the second magnetic body.

In terms of the antenna according to the present invention, a magnetic body having positive magnetostrictive characteristics increases magnetic permeability when a positive stress is applied to the magnetic body. A magnetic body having negative magnetostrictive characteristics increases magnetic permeability when a negative stress is applied to the magnetic body. BY utilizing the increase in the magnetic permeability, even if the antenna is bent and the antenna length is appeared to be short in equivalence, the appearance is cancelled and the change in property due to the curvature of the antenna becomes small.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be set forth with reference to the drawings.

FIG. 1AtoFIG. 1Dare views illustrating one example of a radio terminal to which an antenna of the present invention is applied. InFIG. 1AtoFIG. 1D, the radio terminal is configured to be foldable.FIG. 1Ais a view in which the radio terminal is opened.FIG. 1Bis a front view when the radio terminal is folded.FIG. 1Cis a side view when the radio terminal is folded.FIG. 1Dis a perspective view when the radio terminal is opened.

InFIG. 1AtoFIG. 1D, the radio terminal has a first case10, a second case20and a folded part30supporting the first and second cases10and20to be foldable.

A liquid crystal display (LCD)12is provided on the front surface of the first case10. A lens unit16and a flash18for a camera built in the radio terminal are provided on the rear surface of the first case10. The second case20houses a main printed circuit board (not shown), together with a key input device22, etc. The folded part30supports the first and second cases10and20in fordable manners so that the LCD12and key input device22folded on internal sides, for instance, by means of a bellows configuration. A speaker (not shown) is disposed near by a curved part at an upper part of the first case10, a microphone (not shown) is arranged near by a lower part of the second case20, and then, a communication becomes possible.

Reference symbols50-1to50-6designated at parts of broken-out sections show parts at which the antenna according to an embodiment of the present invention is mounted. As shown inFIG. 1AtoFIG. 1D, the antenna according to the present invention is basically mounted along with the case of the radio terminal. The antenna does not need to be mounted only at the parts50-1to50-6designated with dashed lines, the parts50-1to50-6designated with the dashed-lines may be parts of the antenna. In such case, the antenna mounted at the parts50-1to50-6indicated with the dashed lines to be configured may have at least configuration mentioned below.

FIG. 2AandFIG. 2Bare views illustrating a configuration of the antenna according to an embodiment of the present invention. As shown inFIG. 2AandFIG. 2B, an antenna50regarding the present embodiment has a first magnetic body54having positive magnetostrictive characteristics and a second magnetic body56having negative magnetostrictive characteristics, and the first magnetic body54and the second magnetic body56sandwich an antenna element52. Since the first magnetic body54has the positive magnetostrictive characteristics, it has a property that magnetic permeability increases by applying a compression stress, and that magnetic permeability decreases by applying a tensile stress. Since the second magnetic body56has the negative magnetostrictive characteristics, it has a property that magnetic permeability decreases by applying a compression stress, and that magnetic permeability increases by applying a tensile stress, in contrast to the first magnetic body54. Accordingly, by utilizing the change (increase) of the magnetic permeability of the magnetic body in the case of folding the antenna, the property change resulting from the curvature of the antenna element52are reduced.

More specifically, when the antenna50having the configuration shown inFIG. 2Ais bent as shown inFIG. 2B, the compression stress is applied to the first magnetic body54and the tensile stress is applied to the second magnetic body56. Thereby, both magnetic permeability of the first and second magnetic bodies54and56are increased. Therefore, since a leakage of fluxes from the antenna element52is reduced, the capacity coupling, etc., among the antenna elements52are prevented. Therefore, the property change in the case of bending the antenna element52can be reduced. In the embodiment, it is necessary to arrange the magnetic body having the positive magnetostrictive characteristics on a surface to which the compression stress is applied, and the magnetic body having the magnetostrictive characteristics on a surface to which the tensile stress is applied.

Specific configuration examples will be illustrated inFIG. 3andFIG. 4.FIG. 3andFIG. 4are views showing examples in which the antennas regarding the present embodiments inside and outside the curved parts of the cases, respectively.FIG. 3andFIG. 4are, for example, cross-sectional views when each antenna50is mounted at the curved part14or the folded part30inFIG. 1A, respectively. The antenna50is applicable at various positions, such as the curved part24and other corner part of the second case20in addition to the curved part14. More specifically, the antenna having the configuration regardingFIG. 3is applicable to the antenna mounted at the parts indicated with the symbols50-1to50-5inFIG. 1. The antenna having the configuration relating toFIG. 4is applicable to the antenna mounted at the part indicated with the symbol50-6shown inFIG. 1. Like this, the antenna according to the embodiment is configured so as not to be deteriorated in its performance, for instance, even when it is mounted at the fixed curved parts14,24or the folded part30that is the movable part in the radio terminal ofFIG. 1. In the following description, the curved parts14and24are referred to as “curved part”, and the case in which the antenna50is disposed at the curved part14will be described.

FIG. 3shows the case in which the antenna50is disposed inside the curved part14. As shown inFIG. 3, when disposing the antenna50inside the curved part14of the first case10(of course, the second case20is useful and hereinafter, referred to as only “case”), the antenna50is arranged in the order of the second magnetic body56with the negative magnetostrictive characteristics, the antenna element52, and the first magnetic body54with the positive magnetostrictive characteristics from the case10side. Thereby, the magnetic permeability of each magnetic body increasing, the problem in the case of folding of the antenna element52can be solved.

FIG. 4shows the case where the antenna50is arranged inside the folded part30(part indicating with reference symbol50-6). As shown inFIG. 4, when the antenna50is disposed inside the folded part30, the antenna50is arranged in the order of the magnetic body54with the positive magnetostrictive characteristics, the antenna element52, and the second magnetic body56with the negative magnetostrictive characteristics from the part inside the folded part30. Thereby, like the case ofFIG. 3, the magnetic permeability of each magnetic body increasing, the radio terminal can solve the problem when the antenna52is folded. In the foregoing embodiment, having shown the example in which the antenna element is mounted at the curved part or the folded part of the case, even when the antenna according to the present embodiment is folded and mounted, for example, at inner components such as an LCD holder, the same advantage can be obtained.

In the configurations inFIG. 3andFIG. 4, the mounting of the antenna50onto the case10may be performed, for instance, by bonding. Further, with a attaching part such as a pawl for fixing provided for the case10, with the antenna50engaged into the attaching part, and with the antenna50is fixed by other method, the antenna50is mounted on the case10. Other than this, any method may be useful for the mounting as long as it is possible for the antenna50to be mounted on the radio terminal.

In the aforementioned embodiment, the magnetic bodies with the positive and negative magnetostrictive characteristics are arranged on both sides of the antenna element52, respectively. It is unnecessary to cover the whole surface of the antenna element52by the magnetic bodies, and it is enough to cover only a part of a conductor functioning as the antenna. It is also acceptable to cover only the part functioning as the antenna without covering the whole parts thereof.

It is not always necessary for the magnetic bodies to be disposed both sides of the antenna element52, at least the magnetic body having the positive magnetostrictive characteristics may be disposed at the antenna element52.

In the above-mentioned embodiment, though the configuration of the antenna element52is not specifically described, the antenna element52may be any shape as long as it is foldable, for instance, a variety of shapes, such as a rod shape, loop shape, meander shape, helical shape are applicable to the antenna element52.

According to the present embodiment, the property change caused by the curvature of the antenna can be reduced.