Patent Publication Number: US-7221325-B2

Title: Antenna system and portable radio device

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a built-in-type antenna system to be mounted on a portable radio device such as a cell phone, and more particularly, to an antenna system having two elements for providing for multi-frequency-bands (hereinafter referred to as multibands). 
   2. Description of the Prior Art 
   When using a built-in-type antenna system for a compact portable radio device such as a cellphone, a mounting method thereof becomes a problem. Particularly, in the case of an antenna system having two elements for providing for multibands, its mounting method becomes a problem because the occupying portion of the system requires a large area. 
   Various methods are considered to mount an antenna system having two elements for providing for a multiband in the housing of a portable radio. 
   For example, as shown in  FIGS. 6 to 8 , methods for proximity-arranging two antenna elements are considered. 
   In  FIG. 6 , two coil elements  111  and  112  having element lengths different from each other are horizontally arranged. In  FIG. 7 , two coil elements  111  and  112  having element lengths different from each other are arranged so that they are vertically superimposed. Moreover, in  FIG. 8 , a coil element  111  and a linear element  132  having element lengths different from each other are horizontally arranged. Arrows in  FIG. 6 to 8  show directions of antenna current. 
   When proximity-arranging two elements, these arrangements as shown in  FIGS. 6 to 8  are advantageous for a circuit because it is possible to join one ends of these two elements and unite feeding points into one. However, in any case of  FIGS. 6 to 8 , because two elements are arranged in the same direction, there is a problem that communication performance is deteriorated due to the mutual interference between the elements. 
   To solve the above problem, a method for arranging two elements at positions as separate from each other as possible in a housing is also considered. However, this method is disadvantageous for a circuit because it is difficult to unite feeding point into one. 
   To solve the above problem, an antenna system is proposed in which two elements are proximity-arranged so that central axes of the elements become orthogonal to each other (refer to Patent Documents 1 and 2). 
   [Patent Document 1] Japanese Patent Laid-Open No. 2000-31721 
   [Patent Document 2] Japanese Patent Laid-Open No. 2002-319816 
   BRIEF SUMMARY OF THE INVENTION 
   As described above, by orthogonally arranging two elements, it is possible to eliminate mutual interference and keep good communication performance. Moreover, because proximity-arranging elements, it is possible to unite feeding points into one. 
   A substrate on which not only an antenna system but also various circuits such as a high-frequency circuit and CPU are mounted, is housed in the housing of a portable radio. Therefore, when arranging two elements of an antenna system in a small space in the housing after mounting the substrate, it is necessary to consider not only the arrangement relation between elements but also the arrangement relation between the elements and the substrate. However, the above prior art does not consider the arrangement relation between the elements and the substrate at all. 
   Therefore, it is an object of the present invention to provide an antenna system and a portable radio device which can be mounted while orthogonally arranging two elements in a small space in a housing after setting a substrate by considering not only the arrangement relation between elements but also the arrangement relation between the elements and the substrate. 
   A first antenna system of the present invention is an antenna system to be mounted on a portable radio device in order to achieve the above object, which has a first antenna element and a second antenna element longer than the first element and in which the first antenna element is set so that the direction of the antenna current of the first element becomes vertical to one side of a substrate of the portable radio, and the second antenna element is set so that the direction of the antenna current of the second antenna element becomes parallel with the one side. 
   A second antenna system of the present invention uses the first antenna system in which the first antenna element and the second antenna element are joined at a joining portion and the joining portion is electrically connected with a feeding point, to provide one feeding point and a simple circuit configuration. 
   A third antenna system of the present invention uses the first or second antenna system in which the first antenna element and the second antenna element are coil elements. 
   A fourth antenna system of the present invention uses the first or second antenna system in which the first antenna element and the second antenna element are meander elements. 
   A fifth antenna system of the present invention uses the first or second antenna system in which either of the first antenna element and second antenna element is a coil element and the other of them is a meander element. 
   A first portable radio of the present invention is a portable radio device in which 
   an antenna system including a first antenna element and a second antenna element longer than the first antenna element is mounted in a housing so that an antenna system constituted by orthogonally arranging two elements can be mounted even if the housing is downsized, 
   the first element is set so that the direction of the antenna current of the first antenna element becomes vertical to one side of a substrate to be mounted in the housing, and 
   the second antenna element is set so that the direction of the antenna current of the second antenna element becomes parallel with one side of the substrate. 
   A second portable radio device of the present invention uses the first portable radio in which the first antenna element and the second antenna element are joined at a joining portion and the joining portion is electrically connected with the feeding point, to provide one feeding point and a simple circuit configuration. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view showing a configuration of first embodiment of an antenna system of the present invention; 
       FIGS. 2A and 2B  are illustrations for explaining advantages of the first embodiment; 
       FIG. 3  is a perspective view showing a configuration of second embodiment of an antenna system of the present invention; 
       FIG. 4  is a perspective view showing a configuration of third embodiment of an antenna system of the present invention; 
       FIG. 5  is a perspective view showing a configuration of fourth embodiment of an antenna system of the present invention; 
       FIG. 6  is a perspective view showing a generally-considered antenna system corresponding to a multiband; 
       FIG. 7  is a perspective view showing generally-considered another antenna system corresponding to a multiband; and 
       FIG. 8  is a perspective view showing still another generally-considered antenna system corresponding to a multiband. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Then, embodiments of the present invention are described below by referring to the accompanying drawings. 
     FIG. 1  is a perspective view showing a configuration of first embodiment of an antenna system of the present invention. 
   When referring to  FIG. 1 , it is found that an antenna system  1  is constituted of a high-frequency-band coil element  2  having an element length of L 2  and a low-frequency-band coil element  3  having an element length of L 3  (L 2 &lt;L 3 ). 
   These two coil elements  2  and  3  are arranged as closely to each other as possible and their one ends are joined at a joining portion  4 . Moreover, the joining portion  4  is electrically connected with one feeding point  6  formed on a rectangular substrate  5 . Though not illustrated in  FIG. 1 , electronic components such as a high-frequency circuit and a CPU and an earth plate are mounted on the substrate  5 . 
   The coil element  2 , which is shorter than the coil element  3 , is fixed in the housing (not illustrated) of a portable radio device so that the direction of the antenna current (direction shown by an arrow in  FIG. 1 ) of the coil element  2  is orthogonal to a side  51  of the substrate  5  and longer coil element  3  is fixed in the housing so that the direction of the antenna current of the coil element  3  is parallel with the side  51 . 
   Therefore, because the coil elements  2  and  3  are arranged in the housing so that directions of the antenna currents are orthogonal to each other, it is possible to eliminate mutual interference and keep good communication performance. It is allowed to use the side  51  for any one of four sides of the substrate  5 . For example, when the substrate  4  is mounted on the housing of the portable radio device, it is possible to use the side  51  as an upper side. Moreover, the coil elements  2  and  3  are arranged at positions which are not overlapped with the substrate  5 . By this, the housing of the portable radio device can be thin. 
     FIG. 2A  is an illustration showing a state when mounting the antenna system  1  shown in  FIG. 1  in the housing  7  of the portable radio device. When referring to  FIG. 2A , it is found that two coil elements  2  and  3  are orthogonally arranged in a small space after setting the substrate  5  in the housing  7 . Thus, according to the antenna system  1  of this embodiment considering the arrangement relation with the substrate  5 , it is possible to orthogonally arrange these two coil elements  2  and  3  in a small space in the housing  7  after setting the substrate  5 . 
   On the other hand, when not setting the arrangement relation between the coil elements  2  and  3  and the substrate  5  like this embodiment, (for example, when arranging the coil element  2  in parallel with the side  51  and the coil element  3  vertically to the side  51 ), the mounted state of the antenna system is shown in  FIG. 2B . As a result of comparing  FIGS. 2A and 2B , it is found that a housing  7   a  which is larger than the housing  7  is necessary in order to orthogonally arrange these two coil elements  2  and  3 . 
     FIG. 3  is a perspective view showing a configuration of second embodiment of an antenna system of the present invention. 
   When referring to  FIG. 3 , it is found that an antenna system  31  is constituted of a high-frequency-band meander element  32  having an element length of L 32  and a low-frequency-band meander element  33  having an element length of L 33  (L 32 &lt;L 33 ). 
   These two meander elements  32  and  33  are joined each other at a joining portion  4  which is an end of the elements  32  and  33  and the joining portion  4  is electrically connected with the feeding point  6  formed on the substrate  5 . 
   Moreover, the shorter meander element  32  is fixed to the housing of a portable radio device so that the direction of the antenna current is orthogonal to the side  51  of the substrate  5 , and the longer meander element  33  is fixed to the housing so that the direction of the antenna current is parallel with the side  51 . Therefore, the second embodiment makes it possible to realize an antenna system constituted by orthogonally arranging two elements in a small space in a housing after setting substrate similarly to the case of the first embodiment. 
     FIG. 4  is a perspective view showing a configuration of third embodiment of an antenna system of the present invention. 
   When referring to  FIG. 4 , it is found that an antenna system  41  is constituted of a coil element  42  having an element length of L 42  and a meander element  43  having an element length of L 43  (L 42 &lt;L 43 ). 
   These two elements  42  and  43  are joined at the joining portion  4  which is an end of them and the joining portion  4  is electrically connected with the feeding point  6  formed on the substrate  5 . 
   Moreover, the shorter coil element  42  is fixed to the housing of a portable radio so that the direction of the antenna current is orthogonal to the side  51  of the substrate  5 , and the longer meander element  43  is fixed to the housing so that the direction of the antenna current is parallel with the side  51 . Therefore, the third embodiment also makes it possible to mount an antenna system constituted by orthogonally arranging two elements in a small space in a housing after setting a substrate similarly to the case of the first embodiment. 
     FIG. 5  is a perspective view showing a configuration of fourth embodiment of an antenna system of the present invention. 
   When referring to  FIG. 5 , it is found that an antenna system  52  is constituted of a meander element  53  having an element length of L 53  and a coil element  54  having an element length of L 54  (L 53 &lt;L 54 ). 
   These two elements  53  and  54  are joined at the joining portion  4  which is an end of them and the joining portion  4  is electrically connected with the feeding point  6  formed on the substrate  5 . 
   Moreover, the shorter meander element  53  is fixed to a housing so that the direction of the antenna current is orthogonal to the side  51  of the substrate  5 , and the longer coil element  54  is fixed to the housing so that the direction of the antenna current is parallel with the side  51 . Therefore, the fourth embodiment also makes it possible to mount an antenna system constituted by orthogonally arranging two elements in a small space in the housing after setting substrate similarly to the case of the first embodiment. 
   According to the present invention, a shorter first antenna element of first and second antenna elements is set so that the direction of the antenna current becomes vertical to one side of a substrate and a longer second antenna element is set so that the direction of the antenna current becomes parallel with the one side. Therefore, it is possible to arrange the first and second antenna elements in a small space in a housing after setting the substrate so that the first and second antenna elements are orthogonal (that is, mutual interference is small). As a result, it is possible to obtain good communication quality even if using a small housing. 
   According to the present invention, because first and second antenna elements are joined at a joining portion and the joining portion is electrically connected with feeding points, it is possible to unite the feeding points into one. As a result, it is possible to simplify a circuit configuration.