Patent Publication Number: US-9905926-B2

Title: Antenna device and wireless communication apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to antenna devices, such as antenna devices preferably for use in a non-contact communication system, for example, a near-field communication (NFC) system, and relates to wireless communication apparatuses including the antenna devices. 
     2. Description of the Related Art 
     In recent years, cellular phones and the like each include therein an antenna device used in a non-contact communication system in the 13.56 MHz band, for example. Such an antenna device requires a large coil antenna to obtain a favorable communication range, and the coil antenna is attached to the inner surface of a terminal casing where a relatively large space is available. A feeding circuit (RFIC chip) for processing RF signals is DC-connected to the coil antenna through a connector or pins. 
     However, in the case of DC connection described above, there is a problem in that contact resistance varies with the roughness of the contact surface, oxidization, and contact pressure, and there is also a reliability problem in that contact failure occurs due to a mechanical shock caused by vibration or dropping. 
     Hence, it is proposed in Japanese Unexamined Patent Application Publication No. 2008-306689 and Japanese Patent No. 4325621 that a transmission/reception antenna connected to an RFIC chip mounted on a substrate through wiring provided on the substrate and a resonant antenna provided, for example, on the inner surface of a terminal casing are operated in such a manner as to be electromagnetically coupled to each other. According to this proposition, the problems described above are solved and, in addition, the size of the transmission/reception antenna can be reduced since the transmission/reception antenna need only be coupled to the resonant antenna. 
     However, if the distance between a booster coil antenna and a feeding coil antenna fluctuates, the magnitude of the electromagnetic coupling between the two varies, resulting in a problem in that communication characteristics are degraded since a resonant frequency deviates from a desired value. Further, not all the magnetic fluxes generated by the feeding coil form closed loops. Hence, an increase in the degree of coupling between the two antennas is limited and it is difficult to adjust the degree of coupling to obtain a desired operation frequency. 
     SUMMARY OF THE INVENTION 
     Preferred embodiments of the present invention provide an antenna device and a wireless communication apparatus that allow the degree of coupling between a feeding coil antenna and a booster coil antenna to be easily adjusted and, in particular, allow the degree of coupling to be increased. 
     An antenna device according to a first preferred embodiment of the present invention includes a feeding coil antenna, and a booster coil antenna arranged in such a manner as to be electromagnetically coupled to the feeding coil antenna, wherein the feeding coil antenna includes a plurality of coil portions including at least one magnetic body and each including a coil conductor wound around the at least one magnetic body, the plurality of coil portions are connected to one another in an in-phase mode, and are arranged near one another such that winding axes of the coil conductors are oriented approximately in the same direction and at least portions of respective openings of the coil conductors face one another. 
     A wireless communication apparatus according to a second preferred embodiment of the present invention includes a feeding circuit, a feeding coil antenna connected to the feeding circuit, and a booster coil antenna electromagnetically coupled to the feeding coil antenna, wherein the feeding coil antenna includes a plurality of coil portions including at least one magnetic body and each including a coil conductor wound around the at least one magnetic body, and the plurality of coil portions are connected to one another in an in-phase mode, and are located near one another such that winding axes of the coil conductors are oriented approximately in the same direction and at least portions of respective openings of the coil conductors face one another. 
     In the antenna device, a feeding coil antenna preferably includes a plurality of coil portions, and the resonant frequency of the feeding coil antenna is configured to adjusted in accordance with the positional relationship among the plurality of coil portions. In particular, magnetic flux enters portions between the plurality of coil portions, and magnetic flux radiated from the feeding coil antenna to an inner side portion defines a closed loop. As a result, the degree of coupling between the feeding coil antenna and the booster coil antenna is increased such that communication characteristics are enhanced. 
     According to various preferred embodiments of the present invention, the degree of coupling between a feeding coil antenna and a booster coil antenna is easily adjusted and, in particular, the degree of coupling is increased such that communication characteristics are enhanced. 
     The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded perspective view of major portions of an antenna device according to a preferred embodiment of the present invention. 
         FIGS. 2A and 2B  are equivalent circuits of the antenna device. 
         FIG. 3  is a perspective view of a first example of a feeding coil antenna. 
         FIG. 4  is an explanation diagram illustrating electromagnetic coupling between the feeding coil antenna and a booster coil antenna in the antenna device. 
         FIGS. 5A to 5F  are explanation diagrams illustrating various arrangement patterns of the feeding coil antenna. 
         FIG. 6A  is a plan view illustrating an advantage of the first example of the feeding coil antenna, and  FIG. 6B  is a plan view of a comparative example of the feeding coil antenna. 
         FIG. 7  is a perspective view of a second example of the feeding coil antenna. 
         FIGS. 8A and 8B  illustrate a third example of the feeding coil antenna, wherein  FIG. 8A  is an explanation diagram illustrating an arrangement pattern, and  FIG. 8B  is an explanation diagram illustrating electromagnetic coupling between the feeding coil antenna and the booster coil antenna. 
         FIGS. 9A and 9B  illustrate a fourth example of the feeding coil antenna,  FIG. 9A  is an explanation diagram illustrating an arrangement pattern, and  FIG. 9B  is an explanation diagram illustrating electromagnetic coupling between the feeding coil antenna and the booster coil antenna. 
         FIG. 10  is an explanation diagram illustrating a fifth example of the feeding coil antenna. 
         FIG. 11  is an explanation diagram illustrating a sixth example of the feeding coil antenna and electromagnetic coupling between the feeding coil antenna and the booster coil antenna. 
         FIG. 12  is an explanation diagram illustrating a seventh example of the feeding coil antenna and electromagnetic coupling between the feeding coil antenna and the booster coil antenna. 
         FIG. 13A  is an explanation diagram illustrating the operation of a magnetic layer and  FIG. 13B  is an explanation diagram illustrating a comparative example. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, preferred embodiments of an antenna device and a wireless communication apparatus according to the present invention will be described with reference to the accompanying drawings. Note that components and portions common in the figures are denoted by the same reference symbols and duplicate description thereof is omitted. 
     Referring to  FIG. 1 , an antenna device according to a preferred embodiment has a configuration in which a feeding coil antenna  15  (including coil portions  15 A and  15 B) is arranged on a circuit substrate (printed wire substrate  10 ), a booster coil antenna  20  including coil conductors  22  and  23  respectively provided on the lower surface and upper surface of an insulating layer  21  is provided, and the feeding coil antenna  15  is arranged near a portion of one of the sides of the booster coil antenna  20 . A magnetic layer  25  is provided between the booster coil antenna  20  and the printed wire substrate  10 . The booster coil antenna  20  defines and functions as a radiation element that is capable of transmitting/receiving an HF-band high-frequency signal. 
     This antenna device has an equivalent circuit illustrated in  FIG. 2A . The feeding coil antenna  15  (coil portions  15 A and  15 B) is connected to a feeding circuit (RFIC chip  30 ), and includes an inductor component L 1  (composite inductor component of the coil portions  15 A and  15 B) and a capacitor component C 1  defining a parallel resonant circuit. The resonant frequency is mainly adjusted by changing the capacitance of the capacitor component C 1 . The booster coil antenna  20  defines a series resonant circuit including inductor components L 2  and L 3  respectively corresponding to the coil conductors  22  and  23  and interline capacitor components C 2  and C 3 . The feeding coil antenna  15  (inductor component L 1 ) is electromagnetically coupled (denoted by the symbol M) to the booster coil antenna  20  (inductor components L 2  and L 3 ). 
     A feeding circuit includes the RFIC chip  30 , a memory circuit and a logic circuit. The feeding circuit may be provided as a bare IC chip or a package IC. 
     Referring to  FIG. 3 , the feeding coil antenna  15  includes the first coil portion  15 A and the second coil portion  15 B including magnetic cores  16 A and  16 B and coil conductors  17 A and  17 B respectively wound around the magnetic cores  16 A and  16 B. The feeding coil antenna  15  is mounted on the printed wire substrate  10 , and the coil conductors  17 A and  17 B are connected in series or in parallel with each other via a conductor provided on the printed wire substrate  10  (refer to  FIGS. 2A and 2B ). The first and second coil portions  15 A and  15 B are connected to each other in an in-phase mode and are arranged in such a manner that winding axes  18 A and  18 B of the coil conductors  17 A and  17 B are oriented in about the same direction, and the openings of the coil conductors  17 A and  17 B face each other with a gap G therebetween in such a manner as to be close to each other. 
     The magnetic cores  16 A and  16 B are preferably made of ferrite. The coil conductors  17 A and  17 B may be made of a conductive material using, for example, thin-film photolithography, or may be made of thick layers using conductive paste. Further, the coil conductors  17 A and  17 B may be configured by winding conductors, or may be configured such that by stacking a plurality of magnetic sheets having coil conductors located thereon, the coil conductors provided on the magnetic sheets are connected to one another through via hole conductors thus configuring a spiral shape. The coil conductors  22  and  23  of the booster coil antenna  20  are made of a conductive material on the insulating layer  21 , using, for example, photolithography, although not limited to this. 
     In the antenna device, the feeding coil antenna  15  is provided of the first and second coil portions  15 A and  15 B, and as illustrated in  FIG. 4 , a magnetic flux φ 1  radiated from the feeding coil antenna  15  defines a closed loop going around the coil conductors  22  and  23 , such that the feeding coil antenna  15  and the booster coil antenna  20  are electromagnetically coupled to each other. Further, a magnetic flux φ 2  passing parallel to  15  and on the inner side of the magnetic flux φ 1  penetrates into the gap G between the first and second coil portions  15 A and  15 B thus defining a closed loop. In the case where the feeding coil antenna  15  is a single component, the magnetic flux φ 2  becomes a leakage magnetic flux, but in the present wireless communication apparatus, the magnetic flux φ 2  also defines a closed loop. As a result, the degree of coupling between the feeding coil antenna  15  and the booster coil antenna  20  is increased and, hence, the communication characteristics are enhanced. 
     By dividing the feeding coil antenna  15  into a plurality of components, DC current superposition characteristics are enhanced and variations in inductance due to variations in the magnitude of a current flowing through the feeding coil antenna  15  are reduced. The feeding coil antenna  15  needs to have a larger size to obtain better communication characteristics. However, since the magnetic cores are formed of comparatively fragile sintered bodies, there is a limit to how much the size can be increased. In the present preferred embodiment, by dividing the feeding coil antenna  15  into the first and second coil portions  15 A and  15 B, the sizes of the magnetic cores  16 A and  16 B are made small so as to prevent generation of defects, such as cracks, and realize favorable communication characteristics. 
     The feeding coil antenna  15  is arranged near the booster coil antenna  20  in such a manner that the coil portions  15 A and  15 B are at least partly superposed with a portion of one of the sides of the booster coil antenna  20  (i.e., one side of the coil conductor  22  or  23 ) when viewed in plan in the winding axis direction of the coil conductors  22  and  23  of the booster coil antenna  20 . As a result, a favorable degree of coupling between the antennas  15  and  20  is achieved. 
     Further, the resonant frequency of the feeding coil antenna  15  is adjustable in accordance with the positional relationship between the first and second coil portions  15 A and  15 B. In other words, the total inductance is changeable in accordance with the positional relationship between the first and second coil portions  15 A and  15 B. Hereinafter, referring to  FIGS. 5A to 5F , various patterns of arranging the feeding coil antenna  15  will be illustrated. 
       FIG. 5A  is the first arrangement pattern illustrated in  FIG. 3 . Here, the magnetic cores  16 A and  16 B preferably have the same size, and the coil conductors  17 A and  17 B preferably have the same number of turns. The winding axes  18 A and  18 B coincide with each other. In a second arrangement pattern illustrated in  FIG. 5B , the magnetic cores  16 A and  16 B preferably have the same size and the coil conductors  17 A and  17 B preferably have the same number of turns. The winding axes  18 A and  18 B are oriented in the same direction but are offset from each other. In a third arrangement pattern illustrated in  FIG. 5C , the magnetic cores  16 A and  16 B preferably have the same size and the coil conductors  17 A and  17 B preferably have the same number of turns. The winding axis  18 B is oriented in a direction inclined with respect to the winding axis  18 A. 
     In a fourth arrangement pattern illustrated in  FIG. 5D , the magnetic cores  16 A and  16 B preferably have the same external diameter and the coil conductors  17 A and  17 B preferably have the same number of turns. However, the end portion of the magnetic core  16 B preferably has a tapered shape. The winding axes  18 A and  18 B coincide with each other. In the fourth arrangement pattern, since the end portion of the magnetic core  16 B is tapered, interference with the round corner of the casing of a wireless communication apparatus is avoided. 
     In a fifth arrangement pattern illustrated in  FIG. 5E , the magnetic core  16 B has a smaller external diameter than the magnetic core  16 A. The coil conductors  17 A and  17 B have the same number of turns and the winding axes  18 A and  18 B coincide with each other. In a sixth arrangement pattern illustrated in  FIG. 5F , the magnetic cores  16 A and  16 B have the same size, but the coil conductor  17 B has a smaller number of turns than the coil conductor  17 A, and the winding axes  18 A and  18 B coincide with each other. 
     In recent years, it is difficult to secure a space for mounting an antenna device due to a reduction in device size and increased component mounting density. However, by dividing the antenna device into the first and second coil portions  15 A and  15 B as in the present preferred embodiment, a mounting space is efficiently utilized. For example, as illustrated in  FIG. 6A , when protruding portions  11  and a depressed portion  12  are provided at the edge portion of the printed wire substrate  10 , the first and second coil portions  15 A and  15 B are provided in the protruding portions  11 , avoiding the depressed portion  12 , in the present preferred embodiment. If a feeding coil antenna  15  including a single coil portion is to be used, the feeding coil antenna  15  will be provided in one of the protruding portions  11 , as illustrated in  FIG. 6B . Hence, it is required that a core conductor  17  having a reduced width be wound around a magnetic core  16  with a fine pitch. However, with this configuration, the inductance of the feeding coil antenna  15  is reduced or the radiation characteristics are degraded, resulting in degradation of the communication characteristics. 
     Next, a second example of the feeding coil antenna  15  will be described with reference to  FIG. 7 . This feeding coil antenna  15  has a configuration in which a magnetic core  16  is a single body, two portions of the magnetic core  16  where coil conductors  17 A and  17 B are respectively wound have the same external diameter, and a cut-out portion (gap G) is provided between the two portions. Note that the cut-out portion (gap G) may be filled with a dielectric material. As illustrated in  FIG. 4 , an inner magnetic flux φ 2  defines a closed loop due to the gap G similarly to the first example described above. 
     A third example of the feeding coil antenna  15  will be described with reference to  FIGS. 8A and 8B . This feeding coil antenna  15  has a configuration in which a third coil portion  15 C is provided between first and second coil portions  15 A and  15 B, as illustrated in  FIG. 8A . Also in this third example, coil conductors  17 A,  17 B, and  17 C are connected in series or in parallel with one another in an in-phase mode, and winding axes  18 A,  18 B, and  18 C are oriented in substantially the same direction. Openings of the coil conductors  17 A,  17 B, and  17 C face one another with gaps G therebetween so as to be close to one another. 
     This feeding coil antenna  15  has a configuration in which an end portion of the first coil portion  15 A is arranged near the inner side portions of the coil conductors  22  and  23  and an end portion of the second coil portion  15 B is arranged near the outer side portions of the coil conductors  22  and  23 , in plan view. As a result, as illustrated in  FIG. 8B , a magnetic flux φ 1  radiated from the end portion of the second coil portion  15 B flows to the end portion of the first coil portion  15 A passing through a portion directly above the coil conductors  22  and  23 , thus defining a closed loop. Further, a leakage magnetic flux φ 2  radiated from an end portion of the third coil portion  15 C flows through a portion directly above the coil conductors  22  and  23  and returns to the third coil portion  15 C, thus defining a closed loop. As a result, the degree of coupling between the feeding coil antenna  15  and the booster coil antenna  20  is increased and the communication characteristics are enhanced. 
     A fourth example of the feeding coil antenna  15  will be described with reference to  FIGS. 9A and 9B . Referring to  FIG. 9A , this feeding coil antenna  15  includes first and second coil portions  15 A and  15 B similarly to the feeding coil antenna  15  illustrated in  FIG. 3 , but a little wider gap G is provided. Also in this feeding coil antenna  15 , an end portion of the first coil portion  15 A is arranged near the inner side portions of the coil conductors  22  and  23  and an end portion of the second coil portion  15 B is arranged near the outer side portions of the coil conductors  22  and  23 , in plan view. As a result, as illustrated in  FIG. 9B , a magnetic flux φ 1  radiated from the end portion of the second coil portion  15 B flows to the end portion of the first coil portion  15 A passing through a portion directly above the coil conductors  22  and  23 , thus defining a closed loop. Further, a leakage magnetic flux φ 2  radiated from the end portion of the second coil portion  15 B flows through a portion directly above the coil conductors  22  and  23  and returns to the second coil portion  15 B, thus defining a closed loop. As a result, the degree of coupling between the feeding coil antenna  15  and the booster coil antenna  20  is increased and the communication characteristics are enhanced. 
     A fifth example of the feeding coil antenna  15  will be described with reference to  FIG. 10 . This feeding coil antenna  15  has a configuration in which an inductor  19  is arranged between coil conductors  17 A and  17 B of first and second coil portions  15 A and  15 B. As a result, the inductance of the feeding coil antenna  15  is increased. The inductor  19  may be, for example, a chip inductor or may be a meandering or coil-shaped conductor pattern provided on the substrate. 
     A sixth example of the feeding coil antenna  15  will be described with reference to  FIG. 11 . This feeding coil antenna  15  has a configuration in which a first coil portion  15 A has a relatively small diameter and a second coil portion  15 B has a relatively large diameter. As a result, a magnetic flux φ 1  radiated from an end portion of the second coil portion  15 B flows to an end portion of the first coil portion  15 A passing through a portion directly above the coil conductors  22  and  23 , thereby defining a closed loop. Further, a leakage magnetic flux φ 2  radiated from the end portion of the second coil portion  15 B flows through a portion directly above the coil conductors  22  and  23  and returns to the second coil portion  15 B, thus defining a closed loop. As a result, the degree of coupling between the feeding coil antenna  15  and the booster coil antenna  20  is increased and the communication characteristics are enhanced. Further, a flux flowing through the coil portions  15 A and  15 B can be given a high directivity in a direction inclined with respect to the printed wire substrate  10  (refer to an arrow Y). 
     A seventh example of the feeding coil antenna  15  will be described with reference to  FIG. 12 . This feeding coil antenna  15  has a configuration in which a third coil portion  15 C having a relatively small diameter is provided between first and second coil portions  15 A and  15 B. A magnetic flux φ 1  radiated from an end portion of the second coil portion  15 B flows to the end portion of the first coil portion  15 A passing through a portion directly above the coil conductors  22  and  23 , thus defining a closed loop. Further, a leakage magnetic flux φ 2  radiated from the end portion of the second coil portion  15 B flows through a portion directly above the coil conductors  22  and  23  and returns to the second coil portion  15 B, thus defining a closed loop. As a result, the degree of coupling between the feeding coil antenna  15  and the booster coil antenna  20  is increased and the communication characteristics are enhanced. The magnetic flux passing through the coil portions  15 A,  15 B, and  15 C is given a high directivity along a curved path (refer to an arrow Y). 
     In the present antenna device, the magnetic layer  25  is arranged between the feeding coil antenna  15  and the booster coil antenna  20 . Here, the operation of the magnetic layer  25  will be described with reference to  FIG. 13 . The magnetic layer  25  is preferably made of ferrite. 
       FIG. 13  illustrates a schematic internal configuration of a wireless communication apparatus (specifically, a cellular phone), and various electronic components  31  and an IC  32  other than the feeding coil antenna  15  are mounted on the printed wire substrate  10 . If the magnetic layer  25  is not arranged, a magnetic flux φ 3  passing through the booster coil antenna  20  collides with the electronic components  31  and the IC  32 , as illustrated in  FIG. 13B . On the other hand, the magnetic flux φ 3  is drawn into the magnetic layer  25  as illustrated in  FIG. 13A  by arranging the magnetic layer  25 . As a result, interference with the electronic components  31  and the IC  32  is considerably avoided and the communication characteristics are enhanced. 
     OTHER PREFERRED EMBODIMENTS 
     Note that the antenna device and the wireless communication apparatus according to the present invention are not limited to the preferred embodiments described above, and various modifications are possible within the scope of the present invention. 
     In particular, for example, details of the configurations and shapes of the feeding coil antenna and booster coil antenna are not particularly limited. Further, the present invention is not limited to a wireless communication apparatus for NFC in an HF band, and may be used in other frequency bands, such as a UHF band, and other communication systems. 
     As described above, preferred embodiments of the present invention are useful for antenna devices and communication apparatuses and, in particular, provide an advantage in that the degree of coupling between a feeding coil antenna and a booster coil antenna is easily adjusted and the degree of coupling is increased. 
     While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.