Abstract:
A mobile phone antenna has: a first conductive radiation element that is formed in a sheet metal conductor and resonates at a predetermined resonance frequency; a second conductive radiation element that is formed in the sheet metal conductor and resonates at the predetermined resonance frequency; and a ground that is connected through a conductive ground connector with the second conductive radiation element. The ground is placed such that the ground is not opposed to the first and second conductive radiation elements.

Description:
The present application is based on Japanese patent application No.2002-262928, the entire contents of which are incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to a mobile phone antenna and, particularly, to a mobile phone antenna that the bandwidth can be broadened without raising the position of an antenna element and that can prevent displacement in resonance frequency in a folding type mobile phone where the position of a board ground is shifted when folded. 
   2. Description of the Related Art 
   Mobile phones and PHS (personal handyphone system) phones are provided with a telescoping whip antenna and a built-in planar antenna so as to facilitate the receiving and transmitting with the base station. The planar antenna used is generally inverted F antenna that has a miniaturized size, a simplified structure and broad bandwidth characteristics. 
     FIG. 1  is a perspective view showing a conventional inverted F antenna for mobile phone. The inverted F antenna  100  for mobile phone is provided with a ground plane  101  as a printed circuit board which is installed in the housing of mobile phone, and the ground plane  101  is composed of interconnection pattern and metal conductors. Above the ground plane  101 , there is provided a planar antenna radiation element  102  of metal plate. Further, a ground connector  103  and a feed point  104  are provided to connect the ground plane  101  with the antenna radiation element  102 . 
   However, in the convention inverted F antenna, it is necessary to raise, by a certain height, the antenna element  102  from the ground plane  101  since the bandwidth narrows according as the antenna element  102  comes closer to the ground plane  101 . Furthermore, since the inverted F antenna is apt to be affected by the ground of printed circuit board (board ground), there occurs a displacement in resonance frequency when the position of board ground varies as the upper and lower housings are opened or closed that are equipped with a folding type mobile phone. 
   SUMMARY OF THE INVENTION 
   It is an object of the invention to provide a mobile phone antenna that the bandwidth can be broadened without raising the position of antenna element and that can prevent displacement in resonance frequency in a folding type mobile phone where the position of board ground is sifted when folded. 
   According to one aspect of the invention, a mobile phone antenna, comprises: 
   a first conductive radiation element that is formed in a sheet metal conductor and resonates at a predetermined resonance frequency; 
   a second conductive radiation element that is formed in the sheet metal conductor and resonates at the predetermined resonance frequency; 
   a ground that is connected through a conductive ground connector with the second conductive radiation element; 
   wherein the ground is placed such that the ground is not opposed to the first and second conductive radiation elements. 
   According to another aspect of the invention, a mobile phone antenna for folding type mobile phone with a pair of housings foldable, comprises: 
   a first ground that is installed in one of the pair of housings; 
   a second ground that is installed in the other of the pair of housings, the second ground being connected through a conductive inter-ground connector with the first ground; 
   first and second conductive radiation elements that are disposed at a position where the first and second conductive radiation elements are not opposed to the first and second ground, the first and second conductive radiation element resonating at a predetermined resonance frequency; and 
   a conductive ground connector that electrically connects the first ground with the second conductive radiation element. 
   In the mobile phone antenna according to the invention, the second conductive radiation element functions as a ground and, therefore, it is not necessary for a ground such as printed circuit board and electronic parts to be placed under or near the conductive radiation element (antenna element). Namely, it is not necessary to raise the conductive radiation element from the ground. Hence, the antenna can offer a broadened bandwidth and prevent displacement in resonance frequency. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The preferred embodiments according to the invention will be explained below referring to the drawings, wherein: 
       FIG. 1  is a perspective view showing the conventional inverted F antenna for mobile phone; 
       FIG. 2A  is a perspective view showing a mobile phone antenna in a first preferred embodiment according to the invention; 
       FIG. 2B  is a side view illustrating the opened state of a LCD ground  23  in  FIG. 2A ; 
       FIG. 2C  is a plain view showing the main part of the mobile phone antenna in  FIG. 2A ; 
       FIG. 3  is a side view showing the schematic composition of a folding type mobile phone installing the mobile phone antenna of the first embodiment; 
       FIG. 4A  is a perspective view showing a mobile phone antenna in a second preferred embodiment according to the invention; 
       FIG. 4B  is a plain view showing the main part of the mobile phone antenna in  FIG. 4A ; 
       FIG. 5  is a perspective view showing a mobile phone antenna in a third preferred embodiment according to the invention; 
       FIG. 6  is a graph showing return loss comparison between the mobile phone antenna of the third embodiment and a comparative example (conventional inverted F dual antenna in FIG.  1 ); 
       FIG. 7  is a perspective view showing a radiation element in a fourth preferred embodiment according to the invention; and 
       FIG. 8  is a perspective view showing a mobile phone antenna in a fifth preferred embodiment according to the invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 2A  is a perspective view showing a mobile phone antenna in the first preferred embodiment according to the invention.  FIG. 2B  is a side view illustrating the opened state of a LCD ground  23  in FIG.  2 A.  FIG. 2C  is a plain view showing the main part of the mobile phone antenna in FIG.  2 A. 
   As shown in  FIG. 2A , the mobile phone antenna includes a radiation element  10  that resonates at a predetermined frequency, a board ground  32 , and a LCD ground  23 . The radiation element  10  is connected through a ground connector  42  with the board ground  32 . The board ground  32  is connected through an inter-board ground connector  41  with LCD ground  23  such that the LCD ground  23  can be opened (FIG.  2 B). The radiation element  10  is provided with a strip-shaped feed member  43  that is disposed adjacent to the ground connector  42  and suspends vertically from radiation element  10 . A feed point  44  lies between the lower end of the feed member  43  and the board ground  32 . 
   The radiation element  10  is, as shown in  FIG. 2C , composed of: a first radiation element  11  which is, as a whole, U-shaped and strip part at one end of which forms main part; a coupling adjuster  12  that is placed adjacent to the first radiation element  11  and extends from the opposite direction to the first radiation element  11 ; a strip-shaped second radiation element  13  that is connected with the first radiation element  11  and the coupling adjuster  12 , wherein there is provided a cutting region  10   a  between the first radiation element  11  and the coupling adjuster  12  to form a planar antenna. 
   The inter-board ground connector  41  is of a material that can endure a number of folding cycles since it is subject to a stress in opening and closing of the LCD ground  23  when it is applied to a folding type mobile phone. The inter-board ground connector  41  connects the board ground  32  and the LCD ground  23  on the second radiation element  13  side. This reduces an influence caused by ground in opening and closing. 
   The ground connector  42  is, as shown in  FIG. 2A , L-shaped and connected with one end of the second radiation element  13 , and its one end (lower end) is connected with a corner of the board ground  32 . 
   The radiation element  10  has, by itself, a function needed to operate as antenna by the first and second radiation elements  11 ,  13  and the coupling adjuster  12  as shown in FIG.  2 A. Therefore, it is not necessary to provide the board ground  32  and the LCD ground  23  under the antenna. Thus, the radiation element  10  can be in such a state that it floats, in relation to high frequency, from the board ground  32 , LCD ground  23  and the other ground (external ground etc.). In other words, it can be in a state of being not connected in relation to high frequency. “state of being not connected in relation to high frequency” means that the radiation element  10  does not have a conduction portion to be always at the same potential as ground. Namely, when the mobile phone antenna  1  is installed in a mobile phone, the radiation element  10  is electrically connected with a high-frequency circuit (e.g., receive and transmit circuit) of the mobile phone only through the interconnection through the feed member  43  with feed point  44  and through the ground connector  42  with the board ground  32 . The radiation element  10  does not contact the other ground and is not connected directly with that, so that it lies independently. 
   In the first embodiment, the radiation element  10  is provided with the coupling adjuster  12  and, therefore, the resonance frequency (≈λ/4) and bandwidth of antenna  1  can be adjusted to a desired value by changing a clearance (t) between the first radiation element  11  and the coupling adjuster  12  and a length (L) of the coupling adjuster  12 . Meanwhile, clearance (t) is preferably 2 mm or less. The radiation element  10 , ground connector  42  and feed member  43  may be integrally manufactured by punching or etching. Thereby, the number of parts can be reduced. 
     FIG. 3  is a side view showing the schematic composition of a folding type mobile phone installing the mobile phone antenna of this embodiment. The folding type mobile phone includes a speaker (not shown), an upper housing  20  on which a liquid crystal display (LCD) is mounted, and a lower housing  30  that has an operation part with numeral keys and cursor keys, a microphone, earphone jack, charging terminal etc. The upper housing  20  is engaged rotatably around a hinge  40  with the lower housing  30 . The mobile phone antenna  1  is installed in the upper housing  20  and the lower housing  30 . 
   The upper housing  20  houses the LCD  21 , a printed circuit board  22  mounted on the back side of LCD  21 , and the LCD ground  23  provided on the back side of the printed circuit board  22 . 
   The lower housing  30  houses a printed circuit board  31  with the board ground  32 . The upper housing  20  can have an angle from zero in shut state to about 150 in opened state with reference to the lower housing  30  around the hinge  40 . Although the radiation element  10  is electrically connected with the lower housing  30 , they are not integrated mechanically and therefore they are movable to each other. 
     FIG. 4A  is a perspective view showing a mobile phone antenna in the second preferred embodiment according to the invention.  FIG. 4B  is a plain view showing the main part of the mobile phone antenna in FIG.  4 A. 
   The mobile phone antenna  1  of the second embodiment is applied to a folding type mobile phone as that in the first embodiment. As shown in  FIG. 4B , in the second embodiment, a third radiation element  14  is added as comparing to the mobile phone antenna  1  of the first embodiment. The other components are the same as those of the first embodiment. 
   The L-shaped third radiation element  14  is disposed such that it protrudes inside the first radiation element  11  near the feed point. Thus, the third radiation element  14  is, as shown in  FIG. 4A , on the same plane as the first radiation element  11 , coupling adjuster  12  and second radiation element  13 . 
   In the mobile phone antenna  1  of the second embodiment, a first resonance frequency is determined by the first and second radiation elements  11 ,  13  and a second resonance frequency is determined by the second and third radiation elements  13 ,  14 . Therefore, it is made to be multiband as compared to the mobile phone antenna of the first embodiment. Also, it can offer a broadened band like that of the first embodiment, and it can prevent displacement in resonance frequency due to opening and closing of the housing. 
     FIG. 5  is a perspective view showing a mobile phone antenna in the third preferred embodiment according to the invention. 
   The mobile phone antenna  1  of the third embodiment is applied to a folding type mobile phone as that in the first embodiment. As shown in  FIG. 5 , in the third embodiment, the third radiation element  14  of the second embodiment is folded at right angles to the other parts and the feed member  43  thereof is omitted. The other components are the same as those of the second embodiment. 
   In the mobile phone antenna  1  of the second embodiment, electromagnetic waves can be radiated from the side. Also, it can be multiband and miniaturized while offering a broadened band, and it can prevent displacement in resonance frequency due to opening and closing of the housing. 
     FIG. 6  is a graph showing return loss comparison between the mobile phone antenna of the third embodiment and a comparative example (conventional inverted F dual antenna in FIG.  1 ). In  FIG. 6 , A represents characteristics of the comparative example, B represents characteristics of the mobile phone antenna of the third embodiment in the opened state of folding type mobile phone, and C represents characteristics of the mobile phone antenna of the third embodiment in the closed state of folding type mobile phone. 
   Table 1 shows specific bandwidth comparison in VSWR=3. In Table 1, GSM stands for global system for mobile communication system and 800 MHz band (870 to 960 MHz) is used in GSM band. DCS stands for digital cellular system and 1.7 GHz band (1710 to 1880 MHz) is used in DCS band. 
   
     
       
             
             
             
           
         
             
               TABLE 1 
             
             
                 
             
             
                 
               Specific bandwidth 
               Specific bandwidth 
             
             
               Characteristic 
               (GSM band) in VSWR = 3 
               (DCS band) in VSWR = 3 
             
             
                 
             
           
           
             
               A 
                7.3% 
               10.2% 
             
             
               B 
               10.6% 
               33.2% 
             
             
               C 
               10.2% 
               20.7% 
             
             
                 
             
           
        
       
     
   
   As shown in FIG.  6  and Table 1, the mobile antenna (B, C) of the third embodiment is enhanced by about 3% in specific bandwidth at GSM band and by about 10 to 23% in specific bandwidth at DCS band as compared to that of the conventional inverted F dual antenna (A). Also, there occurs little displacement in resonance frequency due to opening and closing of the hosing of mobile phone. 
   As described above, the mobile phone antenna of the third embodiment can offer a broadened band both at GSM and DCS band and prevent displacement in resonance frequency due to opening and closing of the housing even when it is installed in a mobile phone. 
     FIG. 7  is a perspective view showing a radiation element in the fourth preferred embodiment according to the invention. In the fourth embodiment, it is intended to prevent displacement in resonance frequency both at GSM band and DCS band. Thus, there is provided a strip-shaped coupling adjuster  15 , on the side face of the radiation element  10 , between the third radiation element  14  and coupling adjuster  12  in the third embodiment in FIG.  5  and parallel to them. The other components are the same as those of third embodiment. The mobile phone antenna of the fourth embodiment can be integrally manufactured by punching or etching, like the first embodiment. Also, in this antenna, a first resonance frequency is determined by the first and second radiation elements  11 ,  13  and a second resonance frequency is determined by the second and third radiation elements  13 ,  14 . The first and second resonance frequencies can be adjusted by the length X 1  of the coupling adjuster  12  on the top face, the length X 2  of the coupling adjuster  15  on the side face, the clearance t 1  between the first radiation element  11  and the coupling adjuster  12  on the top face and the clearance t 2  between the third radiation element  14  and the coupling adjuster  15  on the side face. Hence, this can prevent displacement in DCS band and displacement in resonance frequency both in GSM band and DCS band. Also, the bandwidth at each wavelength band can be adjusted. 
     FIG. 8  is a perspective view showing a mobile phone antenna in the fifth preferred embodiment according to the invention. The mobile phone antenna of the fifth embodiment is applied to mobile phones other than folding type mobile phone. It is composed such that the LCD ground  23  and the inter-board ground connector  41  are omitted from the mobile phone antenna of the third embodiment. The other components are the same as those of the third embodiment. 
   In the fifth embodiment, the bandwidth of mobile phones other than folding type mobile phone can be broadened. 
   Also, the mobile phone antenna in the first, second and third embodiment can be applied to mobile phones other than folding type mobile phone while removing the LCD ground  23  and the inter-board ground connector  41 . 
   Although, in the first to fifth embodiments, the radiation element  10  is connected through the ground connector  42  to the board ground  32 , the ground connector  42  may be connected to the LCD ground  23  or ground of the other electronic parts, mechanism parts (shielding cover, frame etc.) 
   Although the mobile phone antennas in the first to fifth embodiments are applied to mobile phone, they may be applied to PHS (personal handyphone system) mobile phone and PDA (personal digital assistant). 
   Although, in the first to fourth embodiments, the ground includes the LCD ground  23  and board ground  32 , it may include one of them or more than two. 
   Although the invention has been described with respect to the specific embodiments for complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art which fairly fall within the basic teaching herein set forth.