Patent Publication Number: US-2002013159-A1

Title: Portable radio device having a structure for improving antenna characteristic

Description:
BACKGROUND OF THE INVENTION  
       [0001] The present invention relates to technology on a portable radio device having an antenna.  
       [0002] A portable radio device having an antenna performs radio communication (reception and transmission) by radiating an electromagnetic wave from the antenna, and antenna gain changes according to the radiation characteristic of antenna.  
       [0003] The radiation characteristic of antenna changes according to characteristics of antenna itself such as antenna shape, antenna length and impedance, and a set position of antenna in the portable radio device.  
       [0004] Regarding the set position of antenna, the antenna is frequently set at a position where obstacles to radio communication are as few as possible at its surroundings, for example, an upper end portion of a portable radio device. Thus setting the antenna at the upper end portion makes the radiation characteristic of antenna good.  
       [0005] Since the above antenna usually uses a λ/4 antenna, case current flows mach.  
       [0006] When a portable telephone is used in a state where a case is held by a hand of a user, the current distribution of the case is disturbed by influence of his hand, so that the antenna gain decreases.  
       SUMMARY OF THE INVENTION  
       [0007] In view of this circumstance, an object of the invention is to improve antenna characteristic when a portable radio device having an antenna is really used.  
       [0008] In order to achieve the above object, a portable radio device having an antenna is characterized in that there are provided a first case connected to the antenna and a second case which is located on the side surface of the antenna when the portable radio device is used, and which is made of metal or a material including metal, and in that the first and second cases are connected to each other.  
       [0009] According to this portable radio device, when the portable radio device is used, the second case made of the metal material is positioned on the side surface of the antenna. Therefore, the current that has flown conventionally in the first case comes to flow also in the second case by electromagnetic connection,  
       [0010] Under the above state, the current that has flown conventionally in whole of the case is dispersed. In case of the above two cases, the current flows also in the second case, so that the current that has flown in the first case decreases. Accordingly, the disturbance of the current distribution in case that the first case is held by a hand of the user decreases, so that it is possible to reduce the deterioration of the antenna gain.  
       [0011] According to the second aspect of the invention, a portable radio device having an antenna is characterized in that there are provided a first case connected to the antenna and a second case which is located between the antenna and a user when the portable radio device is used, and which is made of metal or a material including metal, and in that the first and second cases are connected to each other.  
       [0012] According to this portable radio device, there is provided the second case which is located between the antenna and the user when the portable radio device is used, and which is made of metal or a material including metal, whereby the current that has flown conventionally in the first case flows also in the second case made of the metal material by the electromagnetic connection.  
       [0013] Accordingly, since the current that has flown in the first case decreases, the disturbance of the current distribution in case that the first case is held by a hand of the user decreases, so that it is possible to reduce the deterioration of the antenna gain.  
       [0014] According to the third aspect of the invention, a portable radio device is characterized in that there is provided a hinge portion for rotatably connecting the first and second cases to each other, and in that when the portable radio device is used, the first and second cases rotate about the hinge portion and stop at a predetermined angle that is smaller than 180 degrees.  
       [0015] According to this portable radio device, even in the foldable portable radio device having the hinge portion, when it is used, the second case is positioned near the antenna. Therefore, the current that has flown only in the first case flows also in the second case, and the disturbance of the current distribution in case that the first case is held by the user&#39;s hand decreases, so that it is possible to reduce the deterioration of the antenna gain.  
       [0016] According to the fourth aspect of the invention, a portable radio device is characterized in that the first case is a main body case in which a main substrate of the portable radio device is housed, and the second case is a cover case of the main body case.  
       [0017] According to this portable radio device, even if it is used in a state where the first case that is a main body case is held by the user&#39;s hand, since the current that has flown only in the first case flows also in the second case, the disturbance of the current distribution of the first case decreases, so that it is possible to reduce the deterioration of the antenna gain.  
       [0018] According to the fifth aspect of the invention, a portable radio device is characterized in that the second case is provided with a receiver portion that outputs sound.  
       [0019] According to this portable radio device, even if the receiver portion is put on the user&#39;s ear and the first case is held by his hand, since the current that has flown only in the first case flows also in the second case, the disturbance of the current distribution in the first case decreases, so that it is possible to reduce the deterioration of the antenna gain.  
       [0020] According to the sixth aspect of the invention, a portable radio device of according to any one of the first to fifth aspects is characterized in that the antenna includes a whip antenna that can be pulled out.  
       [0021] According to this portable radio device, even if it is used in a state where the whip antenna is pulled out and the first case is held by the user&#39;s hand, since the current that has flown only in the first case flows also in the second case, the disturbance of the current distribution in the first case decreases, so that it is possible to reduce the deterioration of the antenna gain. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0022]FIG. 1 is a perspective view of the whole of a portable telephone.  
     [0023]FIG. 2 is a sectional view showing schematically the constitution of the portable telephone.  
     [0024]FIG. 3 is a current distribution diagram showing the current distribution of a case in a conventional portable telephone, in which FIG. 3A shows the current distribution of the case in case that an antenna is housed, and FIG. 3B shows the current distribution of the case in case that the antenna is extended.  
     [0025]FIG. 4 is a current distribution diagram of cases in a portable telephone according to this embodiment, in which FIG. 4A shows the current distribution of the cases in case that an antenna is housed, FIG. 4B shows the current distribution of the cases in case that the antenna is extended, FIG. 4C shows the current distribution of cases in case that an antenna having an angle is housed, and FIG. 4D shows the current distribution of the cases in case that the antenna having an angle is extended.  
     [0026]FIG. 5 is a diagram showing the improvement rate of antenna gain in the portable telephone. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
     [0027]FIG. 1 is a perspective view of the whole of a portable telephone, FIG. 2 is a sectional view showing schematically the constitution of the portable telephone, FIG. 3 is a current distribution diagram of a case in a conventional portable telephone, FIG. 4 is a current distribution diagram of a case in a portable telephone according to this embodiment, and FIG. 5 is a diagram showing the improvement rate of antenna gain in the portable telephone.  
     [0028] Referring to FIGS. 1 and 2, the constitution of a portable radio device will be described.  
     [0029] Taking a portable radio device in this embodiment as a portable telephone  10  having a receiver of a receiving unit and a microphone of a transmission unit, the constitution will be described.  
     [0030] The portable telephone  10  comprises a main body case  20  (a first case), a cover case  30  (a second case) and a hinge portion  40  for rotatably connecting these cases to each other.  
     [0031] In the main body case  20 , there are a microphone  22  that is a transmission unit for inputting voice made by a user of the portable telephone  10 , and an operation key  24  including a power ON/OFF switch of the portable telephone  10 , a ten key for inputting English characters and numerals, and a function key for selecting and executing various functions.  
     [0032] And, as a part of the main body case  20 , there is provided an antenna-housing portion  21  in which an antenna  50  is housed.  
     [0033] Further, inside the main body case  20 , there is a main substrate  26  on which electronic parts  28  such as a CPU for performing processing of various signals, a memory for recording various data and the like are mounted.  
     [0034] Further, a feeder  52  of the antenna  50  is connected to the main substrate  26 .  
     [0035] Further, in the main body case  20 , a comparatively heavy unit such as, for example, a power battery (not shown) is housed. Therefore, the center of gravity of the portable telephone  10  is located on the main body case  20  side. Accordingly, when the portable telephone  10  is used, the user holds the main body case  20  in his hand from a viewpoint of stability, so that the forceful power is not applied onto the hinge portion  40 .  
     [0036] The cover case  30  is formed of metal or a material including metal, for example, magnesium. In the cover case  30 , a receiver  32  that is a receiver unit through which the user of the portable telephone  10 , hears the voice, a display portion  34  of the portable telephone  10 , and a sub-substrate  36  through which these receiver  32  and display portion  34  are connected.  
     [0037] Further, the sub-substrate  36  is connected to the main substrate  26  by a flexible substrate (not shown), and the various electrical signals are transmitted and received between the substrates  36  and  26 . Further, the flexible substrate is connected through the inside of the hinge portion  40  to the respective substrates.  
     [0038] The hinge portion  40  connects the main body case  20  and the cover case  30  to each other rotatably. When the portable telephone  10  is used, these cases can be kept opening at a predetermined angle, for example, as shown in FIG. 2, a predetermined angle that is smaller a little than 180 degrees.  
     [0039]FIG. 2 is a sectional view showing schematically the constitution of the portable telephone  10  in the using state.  
     [0040] The antenna  50 , in this embodiment, is a whip antenna that can be extended and housed. When the antenna  50  is housed, it is housed in the antenna-housing portion  21  with its leading end portion remained.  
     [0041] Further, in the embodiment, when the antenna  50  is extended, as shown in FIG. 2, a predetermined angle θ 1  is formed by the antenna  50  and a reverse surface  31  of the cover case  30 .  
     [0042] The foregoing is the whole constitution of the portable telephone  10 .  
     [0043] Next, referring to FIGS. 3 and 4, a test result of current distribution of cases in a portable telephone  100  having an antenna  500  and in a portable telephone  10  having an antenna  50  will be described.  
     [0044]FIGS. 3 and 4 are current distribution diagrams showing the current distribution of the cases in the portable telephones  100  and  10 . In these figures, the portable telephones  100  and  10  under the using state are viewed from the opposite side to the side opposed to the user and from the perpendicular direction of the main body cases  200  and  20 .  
     [0045] Further, a dotted line drawn in each case is a line formed by connecting the same current values of the cases in the portable telephones  100 ,  10  (equivalent current line), and the close to the antennas  500 ,  50  the line is, the higher the current value is. Further, the absolute difference of the current values between the adjacent current lines is constant.  
     [0046]FIG. 3A, in the conventional portable telephone  100 , shows the current distribution of the case in case that the antenna  500  is housed, and FIG. 3B, in the conventional portable telephone  100 , shows the current distribution of the case in case that the antenna  500  is extended.  
     [0047]FIG. 4A, in the portable telephone  10  according to the embodiment, shows the current distribution of the case in case that the antenna  50  is housed in the antenna-housing portion  21 , and FIG. 4B shows the current distribution of the case in case that the antenna  50  is extended.  
     [0048]FIG. 4C, in the portable telephone  10  according to the embodiment, shows the current distribution of the case in case that the antenna  50  is housed in the antenna-housing portion  21 , and FIG. 4D shows the current distribution of the case in case that the antenna  50  is extended.  
     [0049] The antenna  50  in FIGS. 4C and 4D, as clear from FIG. 4D, when the portable telephone  10  is used, forms a predetermined angle θ 2  with the portable telephone  10  in the longitudinal direction, that is, with the long sides of the main body case  20  and cover case  30 .  
     [0050] Turning to FIG. 3A, the antenna  500  is housed in an antenna housing portion  210 . In the main body case  200 , current is produced by the antenna  500 , and equivalent current lines  200   a ,  200   b ,  200   c ,  200   d , and  200   e  are produced. When current values of the respective current lines are taken as I( 200   a ), I( 200   b ), I( 200   c ), I( 200   d ) and I( 200   e ), the current values become smaller in this order with the current value I( 200   a ) as a maximum value.  
     [0051] Accordingly, the current flows from the equivalent current line  200   a  to the current line of which the current value is lower. Since the portable telephone  100  is used in a state where the main body case  200  is held by a hand of a user, the current distribution of the main case  200  has been disturbed and the antenna gain has decreased.  
     [0052] Next, referring to FIG. 3B, it is different from FIG. 3A in that the antenna  500  is pulled out. By pulling the antenna  500 , the current distribution in the main body cover case  200  changes slightly. However, similarly to in FIG. 3A, in case that the portable telephone was used in a state where the main body case  200  is held by the user&#39;s hand, the current distribution of the main body case  200  has been disturbed and the antenna gain has decreased.  
     [0053] Next, referring to FIG. 4A, the current distribution of the case in the portable telephone  10  according to this embodiment will be described.  
     [0054] The antenna  50  is housed in the antenna-housing portion  21 . In case that equivalent current lines are taken as  30   a,    30   b,    30   c,    30   d,  and  30   e  in order close to the antenna  50  in the cover case  30 , and current values of the respective current lines are taken as I( 30   a ), I( 30   b ), I( 30   c ), I( 30   d ), and I( 30   e ), the current values become smaller in this order with the current value I( 30   a ) as a maximum value.  
     [0055] Accordingly, the current produced by the antenna  50  flows from the equivalent current line  30   a  toward the equivalent current line  30   e.    
     [0056] Further, in FIG. 4A, the current is produced also in the main body case  20  by the antenna  50 , and equivalent current lines  20   a  and  20   b  are produced. The respective current values are I( 20   a ) and I( 20   b ), and the current values become smaller in this order with the current value I( 20   a ) as a maximum value.  
     [0057] Accordingly, the current flows the equivalent current line  20   a  toward the equivalent current line  20   b.  However, the maximum current value I( 20   a ) in the main body case  20  was lower than the maximum current value I( 200   a ) of the main body case  200  in the conventional portable telephone  100 .  
     [0058] This is because since the cover case  30  is made of a metal material such as magnesium, the current is easier to flow in the metal material than in a resin material.  
     [0059] Next, referring to FIG. 4B, it is different from FIG. 4A in that the antenna  50  is pulled out. By pulling the antenna  50 , the current distribution of the cover case  30  changes slightly. However, similarly to in FIG. 4A, the maximum current value I( 20   a ) of the main body case  20  was lower than the maximum current value I( 200   a ) of the main body case  200  in the conventional portable telephone  100 .  
     [0060] Accordingly, the amount of the current flowing in the main body case  20  becomes smaller than that of the current having flown in the conventional main body case  200 . Therefore, even if the portable telephone  10  is used in a state where the main body case  20  is held by the user&#39;s hand, the disturbance of the current distribution of the main case  20  becomes small and the deterioration of antenna gain can be reduced.  
     [0061] Here, the improvement rate of antenna gain of the portable telephone  10 , which was obtained by a test, is shown in FIG. 5.  
     [0062] The improvement rate of antenna gain in FIG. 5 shows the improvement rates of antenna gain of the portable telephones  10  in the embodiment shown in FIGS. 4A, 4B and FIGS. 4C, 4D on the basis of the antenna gain in the conventional portable telephone  100  shown in FIGS. 3A and 3B.  
     [0063] The comparison at the antenna housed is comparison between FIG. 3A and FIGS. 4A, 4C, and the comparison at the antenna extended is comparison between FIG. 3B and FIGS. 4B, 4D.  
     [0064] As shown in FIG. 5, in case that the antenna  50  in the portable telephone  10  shown in FIGS. 4A, 4B was housed, compared with the antenna in the conventional portable telephone, the antenna gain improved by 5-11(%) resultantly; and in case that the antenna  50  was extended, the antenna gain improved by 1-5(%) resultantly.  
     [0065] Further, as shown in FIG. 5, in case that the antenna  50  in the portable telephone  10  shown in FIGS. 4C, 4D was housed, compared with the antenna in the conventional portable telephone, the antenna gain improved by 6-12(%) resultantly, and in case that the antenna  50  was extended, the antenna gain improved by 1-6(%) resultantly.  
     [0066] In the description of the embodiment, the antenna  50  is a whip antenna that can be extended and housed. However, it may be a reverse F antenna that can be built in the main body case  20  or may be a diversity antenna by combination of the whip antenna and the reverse F antenna.  
     [0067] According to this portable radio device, when it is used, the second case made of the metal material is positioned on the side surface of the antenna. Therefore, the current that has flown conventionally in the first case comes to flow also in the second case by electromagnetic connection.  
     [0068] Under the above state, the current that has flown conventionally in the whole case of the portable radio device is dispersed, and in case of the above two cases, the current flows also in the second case, so that the current that has flown in the first case decreases. Accordingly, the disturbance of the current distribution in case that the first case is held by the user&#39;s hand decreases, so that it is possible to reduce the deterioration of antenna gain.