Abstract:
A portable radio device has a first case including at least one of a conductive member and a first substrate. The device has a second case for incorporating a second substrate to mount a radio circuit thereon, and an antenna element. The first case and the second case are movably connected to each other. The second substrate is capacitively coupled to at least one of the conductive member and the first substrate.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a portable radio device, and more particularly to grounding of a portable radio device having two cases.  
         [0003]     2. Description of the Related Art  
         [0004]     Many of recent compact portable radio devices, such as a potable telephone set, incorporate communication antennas in cases thereof. The case, which is provided for the portable radio device, for incorporating the antenna must be made of an insulating material such as a resin. In the case of a portable radio device including two cases, one of the cases for incorporating an antenna is made of a resin or the like, while the other case is normally made of a metallic material having high mechanical strength. In such a portable radio device having two cases, the case incorporating an antenna is grounded to the other case. This grounding is realized by a signal line in a flexible substrate connecting circuit boards of the cases to each other. The flexible substrate connects the circuit boards of the cases to each other, and the circuit board in the metal case is connected to the metal case.  
         [0005]     In the grounding described above, when the portable radio device are opened by unfolding the two cases, a sum of a length of the flexible substrate and lengths of the two cases must be equal to a predetermined length which attains good antenna characteristics. Similarly, when the metal case and the circuit board incorporated therein are connected to each other, a sum of a length of the circuit board in the case incorporating the antenna, the length of the flexible substrate, and the length of the metal case must be equal to a predetermined length which attains good antenna characteristics. Under these conditions, if the flexible substrate is long, the length of the circuit board must be reduced. However, the number of devices or modules that can be mounted on a short, i.e., small-area, circuit board is limited. On the other hand, normally, the flexible substrate has a looped portion in a hinge which foldably connects the two circuit boards. When the flexible substrate is made short, a curvature radius of the looped portion of the flexible substrate is reduced, which generates large bending stress. As a result, the flexible substrate becomes easy to be broken. When the two cases are rotatably connected together, twisting stress is generated in the flexible substrate. When the two cases are slidably connected together, tensile stress is generated in the flexible substrate. When the flexile substrate is made short, those stresses are increased, making the flexible substrate easy to be broken.  
         [0006]     JP 2003-347815A discloses a portable radio device composed of one case which has a metal wire for adjusting an antenna length. JP 2002-330206 A discloses a portable telephone set composed of two cases foldably connected together by a hinge. The hinge has a frame grounding portion. However, these well-known technologies are not suited to frame grounding of the two cases connected together to be movable in various modes.  
       SUMMARY OF THE INVENTION  
       [0007]     It is therefore an object of the present invention to realize secure frame grounding in a portable radio device composed of two cases movably connected together.  
         [0008]     The present invention provides a portable radio device including two cases. A first case has at least one of a conductive member and a first substrate. A second case incorporates a second substrate to mount a radio circuit thereon, and an antenna element. The first case and the second case are movably connected to each other, and the second substrate is capacitively coupled to at least one of the conductive member and the first substrate.  
         [0009]     The portable ratio device enables secure and easy grounding between the two cases. In the portable radio device, there is no need to use a flexible substrate for grounding. Thus, as it is not necessary to shorten the circuit board, no restrictions are imposed on mounting of various devices or modules on the substrate. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     The above and other objects, features and advantages of the present invention will become apparent from the following detailed description when taken with the accompanying drawings in which:  
         [0011]      FIGS. 1A and 1B  are side and plan views showing an example of a portable telephone set having two cases that can be folded together;  
         [0012]      FIGS. 2A and 2B  are side views showing an example of a portable telephone set having two cases that can be rotated;  
         [0013]      FIG. 2C  is a plan view of the portable telephone set shown in  FIGS. 2A and 2B ;  
         [0014]      FIGS. 3A and 3B  are side views showing another example of a portable telephone set having two cases that can be rotated;  
         [0015]      FIGS. 4A and 4B  are side views showing an example of a portable telephone set having two cases that can be slid;  
         [0016]      FIG. 4C  is a plan view of the portable telephone set shown in  FIGS. 4A and 4B ;  
         [0017]      FIGS. 5A and 5B  are side views showing another example of a portable telephone set having two cases that can be slid;  
         [0018]      FIGS. 6A and 6B  are side and plan views showing another example of a portable telephone set having two cases that can be folded together;  
         [0019]      FIGS. 7A and 7B  are side and plan views showing yet another example of a portable telephone set having two cases that can be folded together; and  
         [0020]      FIGS. 8A and 8B  respectively show antenna characteristics of a portable telephone set according to the present invention and of a conventional portable telephone set. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]     The preferred embodiments of the present invention will be described below.  FIGS. 1A and 1B  show a portable telephone set as an example of a portable radio device. In the portable telephone set, an upper case  1  and a lower case  2  are foldably connected together via hinges  4  and  5 .  FIGS. 1A and 1B  are side and front views of the portable telephone set when the two cases  1  and  2  are spread out, i.e., unfolded. In each of  FIGS. 1A  and  1 B, a shaded portion indicates an area made of a conductive material (the same applies to throughout the drawings). The upper case  1  has a conductive material. The lower case  2  receives a substrate  3  for mounting a radio circuit  6 , and an antenna element  10 . The lower case  2  is made of an insulating material. The substrate  3  is connected through a power feeding point  7  to the antenna element  10 . The hinge  4  is made of a conductive material, and installed in the upper case  1 . The hinge  5  is made of an insulating material, and installed in the lower case  2 . Metal terminals  8  and  9  are installed in an end of the substrate  3  near the hinge  4 . The metal terminals  8  and  9  are connected to a ground terminal (GRD) of the substrate  3 .  
         [0022]     During a call of the potable telephone set, i.e., during a receiving or transmitting operation of the radio circuit  6 , an antenna current flows from the antenna element  10  through the power feeding point  7  to the substrate  3 . The antenna current passes through mainly a side end of the substrate  3  to reach the metal terminals  8  and  9  grounded to the substrate  3 . As the metal terminals  8  and  9  are capacitively coupled to the conductive hinge  4 , the antenna current flows through the hinge  4  to the upper case  1 . As a result, during the operation of the portable telephone set, the antenna current generated by the antenna element  10  is grounded to the upper case  1 . Even when the cases  1  and  2  are folded together, the metal terminals  8  and  9  can be capacitively coupled to the hinge  4 .  
         [0023]      FIGS. 2A  to  2 C show another example of a portable telephone set. In this portable telephone set, an upper case  1  and a lower case  2  are rotatably connected together through a pivot  11 . FIG.  2 A is a side view of the portable telephone set when the two cases  1 and  2  are unfolded.  FIG. 2B  is a side view of the portable telephone set when the two cases  1  and  2  face each other to be closed.  FIG. 2C  is a plan view of the portable telephone set when the two cases are unfolded.  
         [0024]     In the portable telephone set, as shown in  FIG. 2B , the upper case  1  and the lower case  2  are arranged to face each other and to be stacked in a standby status. During a call, as shown in  FIGS. 2A and 2C , the upper case  1  and the lower case  2  are rotated about the pivot  11  to be unfolded. The upper case  1  has a conductive material. The lower case  2  receives a substrate  3  for mounting a radio circuit  6  thereon, and an antenna element  10 . The lower case  2  is made of an insulating material. The pivot  11  connects a backside of the upper case  1  to a front side of the lower case  2 . Metal terminals  12  and  13  are disposed near the pivot  11  of the upper case  1 . The metal terminals  12  and  13  are connected to a ground terminal (GND) of the upper case  1  or a substrate (not shown) in the upper case  1 .  
         [0025]     During a call, an antenna current generated by the antenna element  10  flows from the antenna element  10  through a power feeding point  7  to the substrate  3 . The antenna current reaches metal terminals  8  and  9  formed in an end of the substrate  3 . The metal terminals  8  and  9  are connected to a ground terminal (GRD) of the substrate  3 . When the cases  1  and  2  are unfolded, the metal terminals  12  and  13  approach the metal terminals  8  and  9  installed in the substrate  3  to be capacitively coupled to the metal terminals  8  and  9 . As a result, the antenna current flows to the upper case  1  or the substrate in the upper case  1 . Thus, as the antenna current is grounded to the upper case  1  during a call, antenna characteristics are improved in a band including a frequency of the antenna current, to thereby provide better communication quality.  
         [0026]      FIGS. 3A and 3B  show yet another example of a portable telephone set. Also in this portable telephone set, an upper case  1  and a lower case  2  are rotatably connected together through a pivot  11 . In the example of the portable telephone set shown in  FIGS. 2A  to  2 C, the metal terminals  8  and  9  and the metal terminals  12  and  13  are capacitively coupled together only when the two cases  1  and  2  are unfolded. However, in the case of the portable telephone set illustrated in  FIGS. 3A and 3B , metal terminals  8  and  9  and metal terminals  12  and  13  are capacitively coupled together even when the upper case  1  and the lower case  2  face each other to be closed. According to this example, the metal terminals  12  and  13  can be connected to a ground terminal (GND) of the upper case  1  or a substrate (not shown) in the case  1 . The metal terminals  12  and  13  can capacitively couple a substrate  3  to the upper case  1 , or the substrate  3  to the substrate (not shown) in the upper case  1 .  
         [0027]      FIGS. 4A  to  4 C show yet another example of a portable telephone set. In this portable telephone set, an upper case  1  and a lower case  2  are slidably connected together. That is, the cases  1  and  2  are relatively moved in parallel to each other to be unfolded.  FIG. 4A  is a side view of the portable telephone set when the two cases  1  and  2  are moved in parallel to each other to be unfolded.  FIG. 4B  is a side view of the portable telephone set when the two cases  1  and  2  face each other to be closed.  FIG. 4C  is a plan view of the portable telephone set when the two cases  1  and  2  are unfolded.  
         [0028]     The upper case  1  has a conductive material. The lower case  2  receives a substrate  3  equipped with a radio circuit  6 , and an antenna element  10 , and it is made of an insulating material. A backside of the upper case  1  and a front side of the lower case  2  are in contact with each other, and these cases relatively move in parallel to each other to be unfolded.  
         [0029]     Metal terminals  12  and  13  are disposed near an end of the upper case  1 . The metal terminals  12  and  13  are connected to a ground terminal (GND) of the upper case  1  or a substrate (not shown) in the upper case  1 . The radio circuit is mounted on the substrate  3  in the lower case  2 . The substrate  3  is connected through a power feeding point  7  to the antenna element  10 . Metal terminals  8  and  9  are disposed near an end of the substrate  3 . The metal terminals  8  and  9  are connected to a ground terminal (GND) of the substrate  3 . As shown in  FIG. 4A , the metal terminals  8  and  9  are capacitively coupled to the metal terminals  12  and  13  when the cases  1  and  2  are unfolded.  
         [0030]     During a receiving or transmitting operation of the radio circuit  6 , an antenna current generated by the antenna element  10  flows through the power feeding point  7  to the substrate  3 . The antenna current further flows to the end of the substrate  3  to reach the metal terminals  8  and  9  grounded to the substrate  3 . As shown in  FIG. 4A , when the cases  1  and  2  are unfolded, the antenna current flows to the upper case  1  to be grounded to the same. As shown in  FIG. 4B , when the cases  1  and  2  are closed, the metal terminals  8  and  9  are not capacitively coupled to the metal terminals  12  and  13 .  
         [0031]      FIGS. 5A and 5B  are side views showing another example of a portable telephone set in which an upper case  1  and a lower case  2  are slidably connected together. According to this example, the upper case  1  further has metal terminals  22  and  23 . Even when the cases  1  and  2  are closed, metal terminals  8  and  9  are capacitively coupled to the metal terminals  22  and  23 .  
         [0032]      FIGS. 6A and 6B  are respectively side and plan views each showing an example of a portable telephone which has a biaxial hinge. This portable telephone set includes upper and lower cases  1  and  2 , and a middle case  20  disposed therebetween. The middle case  20  is foldably connected to the lower case  2  via hinges  4  and  5 . The middle case  20  is further rotatably connected through a pivot  19  to the upper case  1 . The upper case  1  can rotate about the pivot  19 . The middle case  20  has metal terminals  14  and  15 . The upper case  1  has metal terminals  16  and  17 .  
         [0033]     In the above-described portable telephone set, when the cases are unfolded, the metal terminals  8  and  9  are capacitively coupled to the hinge  4 , and the metal terminals  14  and  15  are capacitively coupled to the metal terminals  16  and  17 . Accordingly, an antenna current is grounded through the substrate  3  and the middle case  20  to the upper case  1 . The substrate  3  and the upper case  1  or a substrate in the upper case  1  can be capacitively coupled together only when the cases are unfolded. In the portable telephone set shown in  FIGS. 6A and 6B , even when the cases  1  and  2  are folded, the substrate  3  and the upper case  1  or the substrate therein can be capacitively coupled together.  
         [0034]      FIGS. 7A and 7B  show yet another example of a portable telephone set. In this portable telephone set, a metal terminal  9  is disposed in a center of an end side of a substrate  3 , while a metal terminal  8  is disposed in an end on the end side of the substrate  3 . A high-frequency current, i.e., an antenna current, greatly flows to a side end of the substrate  3  because of a skin effect. Accordingly, as shown in  FIGS. 1A  to  6 B, metal terminals to be capacitively coupled to one another are preferably disposed in both ends of the substrate. However, as shown in  FIGS. 7A and 7B , one metal terminal can be disposed in one of side ends of the substrate.  
         [0035]      FIG. 8A  shows antenna characteristics of the radio circuit  6  of the portable telephone set of the above embodiments.  FIG. 8B  shows antenna characteristics of a radio circuit  6  of a conventional portable telephone set. In  FIGS. 8A and 8B , markers  1  to  4  respectively indicate 830 MHz, 840 MHz, 875 MHz, and 885 MHz. In  FIG. 8A , a return loss is reduced at each frequency. When both smith charts are compared with each other, a bandwidth indicating desired antenna characteristics is enlarged at a frequency band including a frequency (800 MHz) of an antenna current.  
         [0036]     According to the portable telephone set of the above embodiments, the antenna current flowing through the end of the substrate  3  flows through the metal terminal to the upper case by capacitive coupling. Thus, the cases  1  and  2  are electrically connected together at a frequency band including a frequency of the antenna current, and it is not necessary to form a flexible substrate in the hinge. Therefore, there is no need to shorten the substrate  3  in order to obtain desired antenna characteristics.  
         [0037]     For example, even when a frequency of the antenna current is 1.5 GHz, or 1.8 GHz, effects similar to those in the case of 800 MHz can be obtained. The grounding of the embodiments is frame grounding, and the ground terminal is a frame ground terminal. The portable radio device of the present invention can also be applied to a radio device composed of two cases movably connected together, in addition to the portable telephone set.  
         [0038]     While the present invention has been described in connection with certain preferred embodiments, it is to be understood that the subject matter encompassed by the present invention is not limited to those specific embodiments. On the contrary, it is intended to include all alternatives, modifications, and equivalents as can be included within the spirit and scope of the following claims.  
         [0039]     Further, it is the inventor&#39;s intent to retain all equivalents of the claimed invention even if the claims are amended during prosecution.