Abstract:
A portable wireless device is formed of a lower housing and an upper housing coupled together by a hinged section, which makes the device foldable. A lower circuit board is coupled to an upper circuit board by a flexible cable, which is placed away from a power feeder of an antenna element with a given space and near the hinged section along the width direction of this foldable device. An end of conductive element is shorted to the lower circuit board with a shorting conductor near a connector which couples the flexible cable to the lower circuit board. The foregoing structure allows the portable and foldable wireless device to reduce an amount of energy supposed to be absorbed into a temporal region of a human body while the electric power of the transmitted radio wave is maintained during a phone conversation.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a portable wireless device of which upper housing is coupled in a foldable/unfoldable manner to its lower housing by a hinged section. 
       BACKGROUND ART 
       [0002]    Portable phones have been widely accepted in the market, and various types of portable phones have been developed. Among these types, a compact and double-backed type is widely used. When the phone is not used, this double-backed type can be folded (double-backed) to be more compact. 
         [0003]    The law effective since June 2002 regulates the average amount of energy of radio wave transmitted from wireless devices such as a portable phone while a phone call is in progress. The law defines the average amount of energy (Specific Absorption Rate, hereinafter referred to as SAR) absorbed for six minutes into a specific portion (particularly to temporal region) of human body. It is thus required that the SAR be reduced to an amount not higher than a regulated amount. 
         [0004]    Reduction of the SAR needs to reduce the electric power of radio wave radiated from the wireless device; however, the reduction of the power lowers the quality of a phone conversation. 
         [0005]    Methods of reducing the SAR and yet maintaining the electric power radiated from wireless devices is disclosed in, e.g. Unexamined Japanese Patent Publication No. 2001-320459, and No. 2004-328346. The portable phones disclosed in the foregoing publications have the following structure: an upper housing and a lower housing of the portable phone are unfolded for starting conversation. In synchronization with this unfolding, a rod antenna falls down apart from the temporal region of the user, so that a peak of antenna current can be isolated from the temporal region for reducing the SAR.  FIG. 5  shows a perspective view illustrating a conventional portable phone. In  FIG. 5 , the lower housing (not shown) includes antenna element  113 , power feeder  112 , lower circuit board  104  and the like. The upper housing (not shown) includes upper circuit board  105 , flexible cable  106  and the like. 
         [0006]    Running through a hollow section of the hinged section, flexible cable  106  is obliged to become close to the temporal region during a phone conversation. In the 2 GHz bandwidth employed in CDMA method, the peak of the antenna current exists not only in power feeder  112  but also it can exist in flexible cable  106 . The distribution of antenna current changes, in general, in response to SAR, so that it is known that the presence of the peak of the antenna current in the temporal region increases the SAR. In other words, closer placement to the temporal region of flexible cable  106 , in which the peak of antenna current exists, invites the higher SAR. The conventional method has thus encountered a difficult problem of reducing the SAR. 
       DISCLOSURE OF INVENTION 
       [0007]    The present invention addresses the foregoing problem, and a portable wireless device of the present invention comprises the following elements:
       a hinged section for coupling a first housing to a second housing and allowing these housings to be folded and unfolded;   a first circuit board placed at the first housing;   a second circuit board placed at the second housing;   a wiring bundle formed of a plurality of conductive cables connecting the first circuit board to the second circuit board;   a power feeder placed at an end along the width direction on the first circuit board near to the hinged section;   an antenna element placed at the first housing and fed by the power feeder;   a conductive element having a given length; and   a shorting conductor coupled to an end of the conductive element.
 
The joint section between the wiring bundle and the first circuit board is placed away from the power feeder with a given space along the width direction of the portable wireless device. The conductive element is shorted to the first circuit board via the shorting conductor, and placed near the joint section between the wiring bundle and the first circuit board.
       
 
         [0016]    The foregoing structure allows the portable wireless device to obtain high radiation efficiency with the upper housing and the lower housing unfolded for carrying out a phone conversation. The peak of antenna current existing in the wiring bundle (flexible cable) close to the temporal region of a human body can be dispersed. The Specific Absorption Rate (SAR) can be thus lowered, and a bandwidth can be widened by compound resonance. 
         [0017]    The portable wireless device of the present invention thus disperses the peak of antenna current existing in the flexible cable close to the temporal region of a human body during a phone conversation, so that the SAR can be lowered. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0018]      FIG. 1A  shows a rear view of a portable phone in accordance with a first embodiment of the present invention. 
           [0019]      FIG. 1B  shows a lateral view of the portable phone in accordance with the first embodiment of the present invention. 
           [0020]      FIG. 2  shows a perspective view illustrating a main portion of the portable phone in accordance with the first embodiment of the present invention. 
           [0021]      FIG. 3  shows a perspective view illustrating a main portion of another portable phone in accordance with the first embodiment of the present invention. 
           [0022]      FIG. 4  schematically illustrates the portable phone, in accordance with the first embodiment of the present invention, during the progress of a phone conversation. 
           [0023]      FIG. 5  shows a perspective view illustrating a main portion of a conventional portable phone. 
       
    
    
     DESCRIPTION OF REFERENCE MARKS 
       [0000]    
       
           101  lower housing (first housing) 
           102  upper housing (second housing) 
           103  hinged section 
           104  lower circuit board (first circuit board) 
           105  upper circuit board (second circuit board) 
           106  flexible cable (wiring bundle) 
           107 ,  108  coupling connector (joint section) 
           109  mouthpiece 
           110  earpiece 
           111  liquid crystal display (LCD) 
           112  power feeder 
           113  antenna element 
           114  conductive element 
           115  shorting conductor 
       
     
       DESCRIPTION OF PREFERRED EMBODIMENT 
       [0038]    Preferred embodiments of the portable wireless device of the present invention are demonstrated hereinafter with reference to the accompanying drawings. 
       Exemplary Embodiment 1 
       [0039]      FIG. 1A  shows a rear view of a portable wireless device in accordance with the first embodiment of the present invention.  FIG. 1B  shows a lateral view of the portable wireless device in accordance with the first embodiment of the present invention.  FIG. 3  shows a perspective view illustrating a main portion of another portable phone in accordance with the first embodiment of the present invention.  FIG. 4  schematically illustrates the portable phone, in accordance with the first embodiment, during the progress of a phone call. 
         [0040]    In  FIGS. 1 and 2 , the portable phone in accordance with the first embodiment includes a foldable mechanism which couples lower housing  101  to upper housing  102  with hinged section  103 . Lower housing  101  accommodates antenna element  113 , power feeder  112  and lower circuit board  104 . Antenna element  13  has a length of approx. a quarter of wavelength of the frequency presently used. Antenna element  13  is bent and shapes like letter “L”. Power feeder  12  powers antenna element  13 . Lower circuit board  104  includes a ground pattern which covers almost all the inner face of lower housing  101 , and the ground pattern works as a conductive pattern having a grounding potential. 
         [0041]    Lower housing  101  has mouthpiece (microphone)  109  and others on its front face. Upper housing  102  has LCD (liquid crystal display)  111  for displaying letters, and earpiece (speaker)  110  on its front face. 
         [0042]    Flexible cable  106  is a wiring bundle formed of plural signal cables and grounding cables. These signal cables electrically couple the circuit components such as LCD  111  and earpiece  110 , which are connected to or mounted to upper circuit board  105  placed inside of the upper housing  102 , to the circuit components typically represented by a control circuit (not shown) which is connected or mounted to lower circuit board  104  placed inside the lower housing  102 . A first end of flexible cable  106  is connected to lower circuit board  104  with connector  107 , and a second end thereof is connected to upper circuit board  105  with connector  108 . 
         [0043]    Lower and upper circuit boards  104  and  105  generally have a width of approx. 40 mm and a length of approx. 80 mm. Flexible cable  106  has a width of approx. 5 mm and length of approx. 40 mm. Connectors  107  and  108  are placed away from power feeder  112  of antenna element  113  by a certain distance, e.g. 30 mm along the width direction of the portable phone and near to hinged section  103 . 
         [0044]    In addition to the preceding elements, conductive element  114  and shorting conductor  115  are also provided to lower housing  101 . Conductive element  114  is longitudinally in parallel with the width direction of lower circuit board  104 , and has a given length of, e.g. 25 mm, widthwise. Shorting conductor  115  has a length of 5 mm, and shorts conductive element  114  to lower circuit board  104 . The width of conductive element  114  and shorting conductor  115  is, e.g. 2 mm. A first end of conductive element  114  is shorted by using shorting conductor  115  near connector  107  which couples flexible cable  106  to lower circuit board  104 , i.e. on the other side of power feeder  112  of antenna element  113  on lower circuit board  104  along the width direction. To be more specific, the first end of conductive element  114  is shorted by using shorting conductor  115  near to hinged section  103  and away from power feeder  112  of antenna element by, e.g. 30 mm. 
         [0045]    An operation of the antenna of the portable phone discussed above is demonstrated hereinafter. In the following description, 2 GHz band employed in CDMA method is used as an operating frequency of the antenna. 
         [0046]    When lower housing  101  and upper housing  102  are folded, antenna element  113  works as a monopole antenna having a quarter of the wavelength. When housings  101  and  102  are unfolded, antenna element  113  works as a resonating element which resonates a conductive pattern, namely, the ground pattern, having a grounding potential and provided on upper circuit board  105 . Circuit boards  105  and  104  work as a dipole antenna by using the ground pattern on circuit board  105  and the ground pattern on circuit board  104  as radiating elements. This dipole antenna has a width over a quarter of the wavelength and a length over one wavelength. At this time, connectors  107  and  108  between flexible cable  106  and lower circuit board  104 , and between flexible cable  106  and upper circuit board  105  are placed on the other side of power feeder  112  along the width direction of the portable phone. This placement allows increasing a radiation resistance, thereby obtaining high radiant efficiency. 
         [0047]    If there is no conductive element  114  or shorting conductor  115 , there could be some place, of which electrical length becomes equal to a half of the wavelength, on the route running from power feeder  112  to the upper end of lower circuit board  104  near hinged section  103 . Thus the antenna current concentrates on flexible cable  106  close to the temporal region of a human body during a phone conversation as shown in  FIG. 4 , thereby inviting a higher SAR (Specific Absorption Rate). 
         [0048]    Considering the foregoing situation, conductive element  114  and shorting conductor  115 , of which electrical length is approx. a quarter of the wavelength, are prepared, so that the antenna current running through flexible cable  106  can be dispersed to conductive element  114  and shorting conductor  115 . An appropriate length of conductive element  114  will reduce the SAR by approx. 20%. In this case, the total electrical length from power feeder  112  to the ends of shorting conductor  115  and conductive element  114  via the upper end of lower circuit board  104  near hinged section  103  is approx. a half of the wavelength. Adding an electrical length of antenna element  113  to the foregoing total electrical length makes the electrical length approx. three quarters of the wavelength. When the electrical length falls into a range from a half of the wavelength to one wavelength, the SAR can decrease by approx. 5% or more. 
         [0049]    Employment of conductive element  114  and shorting conductor  115  also allows generating compound resonance, so that the bandwidth can be widened both in folded and unfolded conditions of lower housing  101  and upper housing  102 . 
         [0050]    As discussed above, the first embodiment of the present invention proves that the placement of connectors  107  and  108  on the other side of power feeder  112  along the width direction of the portable phone allows increasing radiant resistance, thereby obtaining high radiant efficiency. Connectors  107  and  108  couple flexible cable  106  to lower circuit board  104 , and cable  106  to upper circuit board  105  respectively. 
         [0051]    An end of conductive element  114  is shorted, by using shorting conductor  115  near connector  107  which couples flexible cable  106  to lower circuit board  104 , i.e. on the other side of power feeder  112  of antenna element  113  on lower circuit board  104  along the width direction. This structure allows dispersing the peak of antenna current on flexible cable  106 , thereby reducing the SAR. It can be concluded that the employment of conductive element  114  and shorting conductor  115  generates the compound resonance and widens the bandwidth as well. 
         [0052]    In the first embodiment discussed above, bent antenna element  113  is used; however, any antenna element as far as it makes use of the ground pattern of lower circuit board  104 , such as a helical antenna or a telescopic antenna, can expect a similar advantage to what is discussed previously. 
         [0053]    The first embodiment quotes various numbers such as sizes of lower and upper circuit boards  104  and  105  in the width direction, a distance between flexible cable  106  and power feeder  112 , a length of flexible cable  106 ; however, the present invention is not limited to these numbers. For instance, if the distance between flexible cable  106  and power feeder  112  is 20 mm or more than 20 mm, the SAR can be advantageously reduced. 
         [0054]    Appropriate lengths of conductive element  114  and shorting conductor  115  in response to the electrical length of antenna element  113  and that of the ground pattern extending from power feeder  112  to shorting conductor  115  on lower circuit board  104  will allow reducing the SAR. When a sum of the electrical length of antenna element  113  and an electrical length extending from power feeder  112  to both the ends of shorting conductor  115  and conductive element  114  via the upper end of lower circuit board  104  near hinged section  103  is longer than a half of the wavelength and not longer than one wavelength, the SAR can be reduced. When the foregoing sum of the electrical length is set at approx. three quarters of the wavelength, the SAR can be further reduced. 
         [0055]    Conductive element  114  may be formed of a conductive pattern (not shown) on a sub circuit board (not shown) different from lower circuit board  104 , and shorting conductor  115  can be formed of a connector (not show) between lower circuit board  104  and the sub circuit board. This structure can advantageously reduce SAR as well. 
         [0056]    Conductive element  114  and shorting conductor  115  are not limited to discrete components, and they may be integrated into one unit, with a similar advantage to what is discussed above. 
         [0057]    Lower circuit board  104 , conductive element  114 , and shorting conductor  115  may be integrated into one unit, with a similar advantage to what is discussed above. 
         [0058]    Conductive element  114  and shorting conductor  115  may be formed with a conductive pattern of lower circuit board  104  in one plane, with a similar advantage to what is discussed above. 
         [0059]      FIG. 3  shows another portable phone in accordance with the first embodiment of the present invention, and conductive element  114  is situated approx. in parallel with the longitudinal direction of this portable phone. The longitudinal direction of conductive element  114  is not always in parallel with the width direction of the portable phone, but as shown in  FIG. 3 , it can be in parallel with the longitudinal direction of the portable phone, and this structure can also reduce the SAR. 
       INDUSTRIAL APPLICABILITY 
       [0060]    A portable wireless device of the present invention allows reducing SAR (Specific Absorption Rate) without lowering radiated electric power, so that the device can assure quality phone-conversation in progress. The portable wireless device is thus useful for portable phones or the like.