Abstract:
There is provided a less fragile feeding apparatus for an antenna that can be fitted to clothing. The feeding apparatus uses a coaxial cable for feeding. A center conductor of the coaxial cable is connected to a first radiating element in terms of alternating current at least through capacitive coupling, and an outer conductor of the coaxial cable is connected to a second radiating element in terms of alternating current at least through capacitive coupling.

Description:
TECHNICAL FIELD 
     The present invention relates to a feeding apparatus for feeding an antenna. 
     BACKGROUND ART 
     Various wireless service systems have become available outdoors recently, including cellular phones, wireless LAN hot spot services, and WiMAX. In broadcasting field, digital terrestrial television broadcasting and the like have been started. Improved antenna performance is important in making good use of such a variety of wireless services. Meanwhile, terminals that support the foregoing plurality of services naturally need wideband antennas. The terminals for use in the foregoing services have been miniaturized, causing the problem of desensitization of the built-in antennas. One of the techniques effective to solve such a problem concerns a wearable antenna to be put on clothing or a human body. An antenna attached to clothing or the like can solve the problem of sensitivity since a relatively large antenna can be created. 
     CITATION LIST 
     Patent Literature 
     
         
         {PTL 1} JP-A-2001-119232 
         {PTL 2} JP-A-2003-258520 
         {PTL 3} JP-A-2006-309401 
         {PTL 4} JP-A-11-180545 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     PTL 1 discloses an invention that is intended to provide a circularly polarized antenna of extremely small size which can be mounted on a small-sized portable terminal, and wherein an end of a linearly polarized radiating electrode is located close to an exciting electrode so as to form capacitive coupling therebetween. 
     PTL 2 discloses an invention that is intended to provide an electronic apparatus and an antenna mounting method which allow efficient mounting of an antenna in the limited space of a small-sized electronic apparatus even with improved productivity. According to the invention, an antenna is stamped out of a conductive tape, a coaxial cable is connected to the feeding point of the stamped antenna by soldering, and the antenna is mounted in a recess of the case. 
     PTL 3 describes an invention that is intended to provide an IC tag which can achieve, when attached to a cloth-like object such as clothing, towels, and sheets, a water resistance and mechanical strength for satisfying the IC tag&#39;s reliability, as well as flexibility that neither impairs wearing comfort and usability nor damages the object itself. According to the invention, a part of the IC tags is sewn on a small piece of cloth, and the piece of cloth is then sewn on the inner side of a garment under the collar. 
     PTL 4 discloses a data carrier that is intended to provide a clothing identification apparatus which can automatically identify sheets, lab coats, and the like for an efficient sorting operation when handling a large amount of clothes to wash. The data carrier has, on a flexible printed circuit board, an antenna and a semiconductor electrically connected to the antenna. 
     According to the conventional technologies, the clothing-fitted antenna needs to be made of conductive cloth or the like. The antenna with radiating elements made of conductive cloth is difficult to solder directly, however, and has had difficulty in feeding. The antenna made of a flexible material such as a flexible printed circuit board is capable of soldering, but has had the defect of fragility. If the antenna made of conductive cloth is attached to clothing, it has been difficult to remove the feeding circuit for washing. 
     For example, a conventional feeding apparatus has been connected by means of soldering  511  and  512  as illustrated in  FIG. 19 . If the radiating elements  501  and  502  are made of conductive cloth, direct soldering is difficult. If the radiating elements are made of a flexible material such as a flexible printed circuit board, they are capable of soldering; however, there has been the defect of fragility because repetitive bending of the radiating elements near the soldered locations can break the soldering. 
     It is thus an object of the present invention to provide a less fragile feeding apparatus for an antenna that can be fitted to clothing. 
     Solution to Problem 
     According to the present invention, there is provided a feeding apparatus that uses a coaxial cable for feeding, a center conductor of the coaxial cable being connected to a first radiating element in terms of alternating current at least through capacitive coupling, an outer conductor of the coaxial cable being connected to a second radiating element in terms of alternating current at least through capacitive coupling. 
     Advantageous Effects of Invention 
     According to the present invention, the conductors are connected to the radiating elements in terms of alternating current through capacitive coupling. This provides the effects of 1) no need of direct soldering, 2) less fragility, 3) easy detachment, 4) easy impedance matching, and 5) a higher resistance to breakage even under rough pulling or rough handling. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  A configuration diagram of a first embodiment of the feeding apparatus according to the present invention. 
         FIG. 2  A configuration diagram of a second embodiment of the feeding apparatus according to the present invention. 
         FIG. 3  A detailed view of the feeding apparatus according to the second embodiment. 
         FIG. 4  A configuration diagram of a third embodiment of the feeding apparatus according to the present invention. 
         FIG. 5  A detailed view of the feeding apparatus according to the third embodiment. 
         FIG. 6  A configuration diagram of a fourth embodiment of the feeding apparatus according to the present invention. 
         FIG. 7  A detailed view of the feeding apparatus according to the fourth embodiment. 
         FIG. 8  A configuration diagram of a fifth embodiment of the feeding apparatus according to the present invention. 
         FIG. 9  A detailed view of the feeding apparatus according to the fifth embodiment. 
         FIG. 10  A configuration diagram of a sixth embodiment of the feeding apparatus according to the present invention. 
         FIG. 11  A detailed view of the feeding apparatus according to the sixth embodiment. 
         FIG. 12  A configuration diagram of a seventh embodiment of the feeding method apparatus according to the present invention. 
         FIG. 13  A detailed view of the feeding apparatus according to the seventh embodiment. 
         FIG. 14  A configuration diagram of the seventh embodiment in use. 
         FIG. 15  A configuration diagram of an eighth embodiment of the feeding method apparatus according to the present invention. 
         FIG. 16  A configuration diagram of a ninth embodiment of the feeding method apparatus according to the present invention. 
         FIG. 17  A detailed view of the feeding apparatus according to the ninth embodiment. 
         FIG. 18  A diagram illustrating the shapes of feeding units. 
         FIG. 19  A feeding apparatus of conventional technology. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, a best mode for carrying out the present invention will be described in detail with reference to the drawings. 
       FIG. 1  is a configuration diagram of a first embodiment of the feeding apparatus according to the present invention. Radiating elements  1  and  2  of arbitrary shape are made of a flexible printed circuit board, conductive cloth, or the like that is flexible. A feeding part  20  includes a feeding conductor  30  and an insulator  40 . Typically, the feeding part  20  is integrally made of a flexible printed circuit board or thin printed circuit board. A feeding part  21  similarly includes a feeding conductor  31  and an insulator  41 . Like the feeding part  20 , the feeding part  21  is integrally made of a flexible printed circuit board or thin printed circuit board. The feeding parts  20  and  21  are sewn on and fixed to the radiating elements  1  and  2  with a thread  17 , respectively. 
     The thread  17  may be an ordinary non-conductive thread, a conductive thread, or a conductive wire. 
     A coaxial center conductor  12  is soldered to the feeding conductor  30 , and a coaxial outer conductor  11  is soldered to the feeding conductor  31 . There are generated capacitance between the feeding conductor  30  and the radiating elements  1  and capacitance between the feeding conductor  31  and the radiating element  2 . The feeding conductors  30  and  31  provide the same effect as a direct connection does in terms of high frequencies if the insulators  40  and  41  are made of a sufficiently thin material to increase the capacitance between the feeding conductor  30  and the radiating element  1  and the capacitance between the feeding conductor  31  and the radiating element  2  so that the capacitance values make a sufficiently small reactance at the use frequency. The thicknesses of the insulators  40  and  41  and the areas of the feeding conductors  30  and  31  can be adjusted to modify the capacitances, thereby allowing adjustments for impedance matching when feeding the radiating elements  1  and  2 . 
     Since the feeding parts  20  and  21  are made of a flexible printed circuit board and sewn with the thread  17 , the feeding parts  20  and  21  have the advantage of high conformability to cloth, with no uncomfortable feeling or fragility even when mounted on clothing etc. 
       FIG. 2  is a configuration diagram of a second embodiment of the feeding apparatus according to the present invention. A base  50  is made of soft flexible material such as cloth. Radiating elements  51  and  52  of arbitrary shape are made of conductor cloth, a flexible printed circuit board, or the like that is flexible, and are sewn on the base  50  with a thread  53 . A Velcro™  54  is sewn on near the intended feeding positions of the radiating elements  51  and  52  with the thread  53 . Note that the radiating elements  51  and  52 , and the Velcro™  54  may be bonded with an adhesive or with the adhesive of a heat transfer sheet instead of the thread  53 . A feeding unit  60  is configured to be attached to the Velcro™  54  for feeding. 
       FIG. 3  is a detailed view of the feeding unit  60 . The feeding unit  60  includes a Velcro™  61  and a printed circuit board  62 . The Velcro™  61  is intended to join the feeding unit  60  to the Velcro™  54  on the radiating-element side in  FIG. 2 . The printed circuit board  62  is made of a flexible printed circuit board, thin printed circuit board, or the like that is flexible, and has feeding conductors  63  and  64  as a conductor pattern on its surface. A coaxial center conductor  12  of a coaxial cable  10  is soldered to the feeding conductor  63 . A coaxial outer conductor  11  is soldered to the feeding conductor  64 . When the feeding unit  60  is attached, there are generated capacitance between the feeding conductor  63  and the radiating element  51  and capacitance between feeding conductor  64  and the radiating element  52 , so that feeding is performed by the principle described in  FIG. 1 . 
       FIG. 4  is a configuration diagram of a third embodiment of the feeding apparatus according to the present invention. As in  FIG. 2 , a base  50  is made of soft flexible material such as cloth. Radiating elements  51  and  52  of arbitrary shape are sewn on the base  50  with a thread  53 . A hook  70  is sewn on the intended feeding position of the radiating element  51  with a thread. A Velcro™  71  is sewn on near the intended feeding position of the radiating element  52  with the thread  53 . Again, the Velcro™  71  may be fixed with an adhesive or the like instead of the thread  53  as mentioned previously. 
     A feeding unit  80  includes a hook  81  and a Velcro™  82 , which can be attached to the hook  70  and the Velcro™  71 , respectively, so that the feeding unit  80  is in close contact with the base  50  to feed the radiating elements  51  and  52 . 
       FIG. 5  is a detailed view of the feeding unit  80 . The feeding unit  80  has two possible configurations ( 1 ) and ( 2 ). 
     In the configuration ( 1 ), the feeding unit  80  includes a metal fitting  83  which is made of a conductor, a printed circuit board  86 , and a Velcro™  82 . A hook  81  is integrally formed with the metal fitting  83 . The metal fitting  83  is fixed so as to sandwich the top of the printed circuit board  86  which is made of a thin dielectric. Here, the metal fitting  83  may be effectively fixed with an adhesive, screws, grommets, and other means. The Velcro™  82  is attached to the lower part of the printed circuit board. Again, the Velcro™ may be fixed with a thread  85 , an adhesive, and various other means. The use of the thread  85  is effective if the printed circuit board  86  is an extremely thin member like a flexible printed board. A feeding conductor  88  is formed on the back side of the printed circuit board  86  as an etched conductor pattern. As in  FIG. 3 , a coaxial center conductor  12  and a coaxial outer conductor  11  of a coaxial cable  10  are soldered to the backside of the metal fitting  83  and the feeding conductor  88 , respectively, so that the feeding unit  80  can perform feeding. 
     The configuration ( 2 ) differs from the configuration ( 1 ) in that the metal fitting  83  is divided into a metal fitting  89  and a feeding conductor  87 . Here, the hook  81  is integrally formed with the metal fitting  89 . The feeding conductor  87  is fixed to the metal fitting  89  with conductor screws  90  so that the printed circuit board  86  is sandwiched therebetween. Adhesives, grommets, staples, and other fixing means may be used instead of the screws  90 . As in the description of the configuration ( 1 ), a coaxial center conductor  12  and a coaxial outer conductor  11  of a coaxial cable  10  are then soldered to the feeding conductor  87  and the feeding conductor  88 , respectively, so that the feeding unit  80  can perform feeding. 
     According to the configurations of  FIGS. 4 and 5 , the radiating element  52  and the feeding conductor  88  are connected with each other in terms of high frequencies through their capacitance in the area where the Velcro™  71  is joined to the Velcro™  82 . For the radiating element  51 , the hooks  70  and  81  make an electrical contact with each other for feeding. 
       FIG. 6  is a configuration diagram of a fourth embodiment of the feeding apparatus according to the present invention. Differences from the configurations of  FIGS. 4 and 5  lie in a feeding unit  110  and in that the feeding unit  110  is joined with conductor buttons. More specifically, the feeding unit  110  is joined by engaging conductor buttons  111  that are sewn on the feeding unit  110  by a thread  101  with conductor buttons  100  that are sewn on the radiating elements  51  and  52  by a thread  101 . 
     The thread  101  by which the buttons are sewn on the radiating elements may be an ordinary non-conductive thread, a conductive thread, or a conductive wire. 
       FIG. 7  is a detailed view of the feeding unit  110 . FIG.  7 ( 1 ) illustrates the surface, and FIG.  7 ( 2 ) the back side. The feeding unit  110  includes a printed circuit board  114  which is made of a flexible printed circuit board or thin printed circuit board, and conductors  112  and  113  which are sewn on the printed circuit board  114  with the thread  101 . The conductors  112  and  113  are made of conductive cloth, to the back side of which the buttons  111  are sewn with the thread  101 . Feeding conductors  115  and  116  are formed on the surface of the printed circuit board  114  as etched conductor patterns in approximately the same positions and with approximately the same shapes as those of the conductors  112  and  113 . A coaxial cable  10  is soldered to the feeding conductors  115  and  116  as in  FIG. 3 . The feeding conductors  115  and  116  are connected to the conductors  112  and  113  in terms of high frequencies through their capacitances generated between them and the conductors  112  and  113 , respectively, and the conductors  112  and  113  are in electrical contact with the radiating elements  51  and  52  through the conductor buttons  111  and  100 , whereby the feeding unit  110  performs feeding. 
       FIG. 8  is a configuration diagram of a fifth embodiment of the feeding apparatus according to the present invention. Differences from the configuration of  FIGS. 6 and 7  lie in a feeding unit  120  and in that hooks  70  and  81  are used to establish the joint at the side of the radiating element  51 . 
       FIG. 9  is a detailed view of the feeding unit  120 . FIG.  9 ( 1 ) illustrates the surface, and FIG.  9 ( 2 ) the back side. The feeding unit  120  includes a printed circuit board  114  which is made of a flexible printed circuit board or thin printed circuit board, a metal fitting  89  which includes the conductor hook  81 , and a conductor  113  which is made of conductive cloth. The metal fitting  89  can be fixed to the printed circuit board  114  by using an adhesive, screws, grommets, staples, or the like. The conductor  113  is fixed in the same way as in the description of FIG.  7 ( 2 ). The connections of the coaxial cable  10  at the surface of  FIG. 9  are also established in the same way as in FIG.  7 ( 1 ). 
       FIG. 10  is a configuration diagram of a sixth embodiment of the feeding apparatus according to the present invention. In  FIG. 10 , the components on the side of the base  50  are configured in the same way as in the configuration of  FIG. 4 . A feeding unit  130  is also similarly joined by hooks and Velcro™&#39;s. A difference from  FIG. 4  lies in the structure of the feeding unit  130 . 
       FIG. 11  is a detailed view of the feeding unit  130 . FIG.  11 ( 1 ) illustrates the surface, FIG.  11 ( 2 ) the back side, and FIG.  11 ( 3 ) an exploded view. The feeding unit  130  includes a metal fitting  83  which is fixed to the top of an insulator  131 , and conductive cloth  132  which is accompanied with a Velcro™  133 . The conductive cloth  132  is wound about and sewn on the lower part of the insulator  131 . As illustrated in the surface view of FIG.  11 ( 1 ), a thin printed circuit board  134  such as a flexible printed circuit board is also sewn and fixed to the surface. The conductive cloth  132  is sewn to overlap a conductor pattern of the printed circuit board  134  so that the conductor pattern and the conductive cloth  132  are electrically continuous. The insulator  131  has a recessed part  135  so that the conductive cloth  132  wound about the insulator  131  will not come off easily. 
     In  FIGS. 10 and 11 , the radiating element  51  performs feeding through the electrical contact between the hooks  70  and  81 . The radiating element  52  has a capacitance between it and the conductive cloth  132  and is thus connected to the conductive cloth  132  in terms of high frequencies for feeding. 
       FIG. 12  is a configuration diagram of a seventh embodiment of the feeding apparatus according to the present invention. In  FIG. 12 , the components on the side of the base  50  have the same configuration as in  FIG. 6  except that the radiating elements  51  and  52  are provided with a button  100  each. The buttons  100  are sewn on the radiating elements  51  and  52  which are made of a conductor or conductor cloth with a thread  101 . 
     A feeding unit  200  also has a pair of buttons  111  to be engaged with the buttons  100 . A coaxial cable  201  for feeding is connected to the feeding unit  200 . A connector  202  is connected to the top of the coaxial cable  201 . 
       FIG. 13  is a detailed view of the feeding unit  200 . FIG.  13 ( 1 ) illustrates the connection side, FIG.  13 ( 2 ) the back side, and FIG.  13 ( 3 ) a cross section. The connection side view ( 1 ) depicts that the feeding unit  200  includes a base  210  which is made of an insulator such as plastic and a printed circuit board, two metal fittings  211  which are made of a conductor, and two buttons  111 . The metal fittings  211  are connected with the buttons  111 . If the metal fittings  211  are metal plates and the buttons  111  are made of metal, then the metal fittings  211  and the buttons  111  can be connected by such methods as soldering, caulking, crimping, and metal fitting. In such cases, electrical conduction is also secured. If the buttons  111  are made of metal but hard to solder, or if the buttons  111  are not made of metal, the connection can be established by such means as an adhesive, caulking, crimping, and metal fitting. In such cases, electrical conduction is not secured, which does not matter in terms of the principle of operation (description will be given later). The metal fittings  211  are configured so that their ends can be bent, passed through the base  210 , and bent to the back side of the base  210 . 
     In the backside view ( 2 ), the ends of the metal fittings  211  bent to the back side of the base  210  serve as connecting parts  212 . The connecting parts  212  are connected with the coaxial cable  201 . The coaxial center conductor  220  of the coaxial cable  201  is connected to either one of the connecting parts  212  by soldering or crimping. The coaxial outer conductor  221  of the coaxial cable  201  is connected to the other connecting part  212  by soldering or crimping through a conductor lead  222 . Both the connections are established so as to secure electrical conduction. The connector  202  is connected to the other end of the coaxial cable  201 . 
     The cross-sectional view ( 3 ) depicts the cross section of the feeding unit  200  in detail. The metal fittings  211  are U-shaped when seen in the cross section. 
       FIG. 14  is a configuration diagram of the feeding apparatus of the present invention in use. The buttons  111  of the feeding unit  200  are engaged with the buttons  100  on the radiating elements  51  and  52 , whereby the feeding unit and the radiating elements  51  and  52  can be connected with each other in close contact. The principle of the electrical operation here will be described below. The coaxial center conductor  220  and the coaxial outer conductor  221  of the coaxial cable  201  are electrically connected to the two connecting parts  212 , respectively. The two connecting parts  212 , which are a part of the metal fittings  211 , are naturally electrically continuous with the metal fittings  211 . The engagement of the buttons  111  with the buttons  100  brings the metal fitting  211  extremely close to the radiating elements  51  and  52 . In such situations, the surfaces of the metal fittings  211  have a capacitance between it and the radiating elements  51  and  52 , and the capacitive coupling of the metal fittings  211  with the radiating elements  51  and  52  allows transmission of high-frequency power, i.e., electrical connection. For the sake of appropriate capacitive coupling, the use frequency and the areas of the metal fittings  211  need to be designed to provide a sufficiently small capacitive reactance. 
     Since the electrical connection is established by means of capacitance, the buttons  100  and  111  need not necessarily be made of metal or other conductors. If the buttons  100  and  111  both are made of metal, the metal contact can secure conduction, in which case the feeding may be achieved by the metal contact as well. If so, the metal fittings  211  may have a minimum area for fixing the buttons  111 . 
     Note that if the buttons  100  are so small that the conduction of the radiating elements  51  and  52  in close contact with the buttons  100  is unstable, the areas of the metal fittings  211  should be increased to rely on the capacitive coupling for stable feeding, rather than the contact-based conduction. 
       FIG. 15  is a configuration diagram of an eighth embodiment of the feeding method apparatus according to the present invention. A difference from  FIG. 14  lies in the addition of a band  250 . With the configuration of  FIG. 14 , the coaxial cable  201  is not fixed, and the antenna operation becomes unstable when the coaxial cable swings in the vicinity of the radiating elements  51  and  52  depending on the cable layout. The present embodiment is thus intended to fix the coaxial cable  210  for stable antenna characteristics. 
     In  FIG. 15 , the band  250  may be made of a piece of cloth, an insulator, or even a conductor. Buttons  251  are intended to fix the band  250  to the base  50 , and may be something like snaps or clothes buttons. 
       FIG. 16  is a configuration diagram of a ninth embodiment of the feeding apparatus according to the present invention. A difference from the configuration of  FIG. 12  lies in that a feeding unit  300  includes buttons  100  and  111  in two pairs each. 
       FIG. 17  is a detailed view of the feeding unit  300 . FIG.  17 ( 1 ) illustrates the connection side, FIG.  17 ( 2 ) the back side, and FIG.  17 ( 3 ) a cross section. Upper and lower metal fittings  311  have two buttons  111  each. The greater use of the buttons makes it easier to maintain the metal fittings  311  and the radiating elements  51  and  52  at a close distance from each other, which provides the advantage that stable feeding can be performed through capacitive coupling or by contact. The number of buttons  100  and  111  are not limited to two pairs. Three or more pairs can be effectively used depending on circumstances. 
       FIG. 18  illustrates various examples of the shape of the feeding unit. FIG.  18 ( 1 ) illustrates an example where metal fittings  411  are bent into a U shape along the outer side of a base  401 , thereby forming connecting parts  412 . Such metal fittings may be able to be formed easier than the metal fittings  211  of  FIG. 13 . 
     FIG.  18 ( 2 ) illustrates an example where a base  420 , metal fittings  421 , and connecting parts  422  are formed by etching a printed circuit board. The metal fittings  421  are connected to the connecting parts  422  via through holes  423 . 
     FIG.  18 ( 3 ) also illustrates an example where a base  430 , metal fitting  431 , and connecting parts  432  are formed by etching a printed circuit board. The metal fittings  431  are connected to the connecting parts  432  via through holes  433 . The connecting parts  432  have a circular shape. 
     Note that the metal fittings  211 ,  311 ,  411 ,  421 , and  431  are not limited to such shapes as rectangular and circular, and may have any shape. The same applies to the shapes of the connecting parts  212 ,  312 ,  412 ,  422 , and  432 . 
     The feeding apparatus of the present invention, which connects a coaxial cable to a flexible antenna that includes radiating elements made of conductive cloth or a flexible printed circuit board, has the characteristics of: 
     1) no need of direct soldering, 
     2) less fragility, 
     3) easy detachment, 
     4) easy impedance matching, and 
     5) a higher resistance to breakage even under rough pulling or rough handling. 
     The present application is based on Japanese Patent Application No. 2007-118620 (filed on Apr. 27, 2007) and Japanese Patent Application No. 2008-030440 (Feb. 14, 2008), and claims a priority according to the Paris Convention based on the Japanese Patent Application No. 2007-118620 and the Japanese Patent Application No. 2008-030440. Disclosed contents of the Japanese Patent Application No. 2007-118620 and the Japanese Patent Application No. 2008-030440 are incorporated in the specification of the present application by reference to the Japanese Patent Application No. 2007-118620 and the Japanese Patent Application No. 2008-030440. 
     The typical embodiments of the present invention have been described in detail. However, it is to be understood that various changes, substitutions, and alternatives can be made without departure from the spirit and the scope of the invention defined in the claims. Moreover, the inventor contemplates that an equivalent range of the claimed invention is kept even if the claims are amended in proceedings of the application. 
     INDUSTRIAL APPLICABILITY 
     The present invention can be applied to a feeding apparatus of a wearable antenna to be put on clothing. 
     REFERENCE SIGNS LIST 
     
         
           1 ,  2 : radiating element 
           10 : coaxial cable 
           11 : coaxial outer conductor 
           12 : coaxial center conductor 
           13 : soldering 
           17 : thread 
           20 ,  21 : feeding part 
           30 ,  31 : feeding conductor 
           40 ,  41 : insulator