Patent Publication Number: US-2012038443-A1

Title: Communication terminal

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority to Japanese Patent Application No. 2010-180924 filed Aug. 12, 2010, and Japanese Patent Application No. 2010-265215 filed Nov. 29, 2010, the entire contents of each of these applications being incorporated herein by reference in their entirety. 
     FIELD OF THE INVENTION 
     The present invention relates to communication terminals that can be used in radio frequency identification (RFID) systems that communicate with external devices via electromagnetic signals. 
     BACKGROUND 
     In recent years, RFID systems using a high-frequency (HF) band, such as about a 13.56-MHz band, have been in widespread use. Examples of such RFID systems include FeliCa (registered trademark) and near field communication (NFC) systems. For example, Japanese Patent No. 3975918 discloses an antenna device for an RFID system. 
       FIG. 1  is a cross-sectional view illustrating an antenna device of a communication terminal  90  disclosed in Japanese Patent No. 3975918. The antenna device includes an asymmetric coil  71  having an upper winding portion  71   a  larger in winding pitch and a lower winding portion  71   b  smaller in winding pitch. The upper winding portion  71   a  and the lower winding portion  71   b  face each other with respect to a center of the winding region of the coil  71 . The upper winding portion  71   a  is provided with a magnetic body  72  on a side remote from an input part  94  facing an integrated circuit (IC) card  1 . In other words, the lower winding portion  71   b  is provided with the magnetic body  72  on a side adjacent to the input part  94  facing the IC card  1 . A reader/writer circuit  50  is connected to the coil  71 . The antenna device is placed in a recessed portion  97   a  of a metal housing  97  and protected by a resin member  98 . The magnetic field distribution of the antenna device is an asymmetric distribution where the magnetic field is enhanced in the upper winding portion  71   a  where the winding pitch and the line width of the coil  71  are large. This makes it possible to ensure good communication conditions in a direction perpendicular to a principal plane of the antenna device. 
     When a communication terminal is held over a communication partner, such as a reader/writer, an angle between an antenna of the communication terminal and an antenna of the communication partner is not necessarily constant. This may lead to unstable communication or communication failure, depending on the positional relationship (angular relationship) between the antennas. Such a tendency is particularly pronounced in an RFID system where communication terminals communicate with each other, as compared to an RFID system where a communication terminal (reader/writer) and an IC card (IC tag) communicate with each other. 
     SUMMARY 
     The disclosure provides a communication terminal that can reduce degradation of communication performance and is capable of communicating with a communication partner over a wide angular range, regardless of the positional relationship with the communication partner. 
     In an embodiment of the present disclosure, a communication terminal includes an antenna coil composed of a magnetic core having a first principal surface and a second principal surface, a coil conductor wound around the magnetic core; and housing configured to house or hold the antenna coil. The coil conductor has a first conductor portion located adjacent to the first principal surface of the magnetic core, and a second conductor portion located adjacent to the second principal surface of the magnetic core and at a position different from that of the first conductor portion in plan as viewed from the first principal surface or the second principal surface. The antenna coil is positioned such that the second principal surface of the magnetic core faces toward an outer surface of the housing. 
     In a more specific embodiment of a communication terminal, the magnetic core and the coil conductor may be configured such that a length of a portion of the magnetic core where the second conductor portion of the coil conductor is adjacent to the magnetic core is larger than a length of a portion of the magnetic core where the first conductor portion of the coil conductor is adjacent to the magnetic core. 
     In another more specific embodiment of the communication terminal, the magnetic core and the coil conductor may be configured such that the length of the portion of the magnetic core where the first conductor portion of the coil conductor is adjacent to the magnetic core is smaller than a width of the first conductor portion. 
     In another more specific embodiment of the communication terminal, the antenna coil may be positioned such that the first conductor portion of the coil conductor is located near an end portion of the housing in a longitudinal direction of the housing. 
     In yet another more specific embodiment of the communication terminal, a circuit board having a planar conductor may be provided within the housing, and the antenna coil may be provided opposite the planar conductor. 
     In another more specific embodiment of the communication terminal, the magnetic core may be a mixture of magnetic powder and resin material molded into a substantially sheet-like shape, or may be a sintered magnetic body divided into a plurality of small pieces. 
     In another more specific embodiment of the magnetic core of the communication terminal, a width of a portion of the magnetic core adjacent to the first conductor portion may be larger than a width of a portion of the magnetic core adjacent to the second conductor portion. 
     Other features, elements, characteristics and advantages will become more apparent from the following detailed description with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view illustrating an antenna device of a communication terminal disclosed in Japanese Patent No. 3975918. 
         FIG. 2A  is a plan view of an antenna coil included in a communication terminal according to a first exemplary embodiment, and  FIG. 2B  is a front view of the antenna coil. 
         FIG. 3  is a plan view of a state in which a flexible substrate having a coil conductor and a magnetic core are separated from each other. 
         FIG. 4A  to  FIG. 4C  illustrate a configuration of an antenna device and a communication terminal including the antenna device according to the first exemplary embodiment.  FIG. 4A  is a plan view of the antenna device,  FIG. 4B  is a front view of the antenna device, and  FIG. 4C  is a schematic cross-sectional view of the communication terminal. 
         FIG. 5A  and  FIG. 5B  schematically illustrate how a magnetic flux passes through the antenna coil when an angle θ shown in  FIG. 4C  is varied.  FIG. 5A  illustrates the case where θ is about 90°, and  FIG. 5B  illustrates the case where θ is about 45°. 
         FIG. 6A  and  FIG. 6B  schematically illustrate how a magnetic flux passes through the antenna coil when the angle θ shown in  FIG. 4C  is varied.  FIG. 6A  illustrates the case where θ is about 0°, and  FIG. 6B  is a perspective view schematically illustrating how a magnetic flux behaves when θ is about 0°. 
         FIG. 7A  is a perspective view of a state where communication terminals communicate with each other, and  FIG. 7B  is a cross-sectional view of  FIG. 7A . 
         FIG. 8A  is a perspective view of another state where the communication terminals communicate with each other, and  FIG. 8B  is a cross-sectional view of  FIG. 8A . 
         FIG. 9A  to  FIG. 9D  illustrate a configuration of an antenna coil according to a second exemplary embodiment.  FIG. 9A  is a plan view of a flexible substrate having a coil conductor formed thereon,  FIG. 9B  illustrates a shape of an upper coil conductor portion of the coil conductor,  FIG. 9C  illustrates a shape of a lower coil conductor portion of the coil conductor, and  FIG. 9D  illustrates a state in which the lower coil conductor portion and the upper coil conductor portion overlap with each other. 
         FIG. 10A  is a plan view of the antenna coil according to the second exemplary embodiment, and  FIG. 10B  is a front view of an antenna device including the antenna coil. 
         FIG. 11A  is a cross-sectional view of a main part of a communication terminal according to a third exemplary embodiment, and  FIG. 11B  is a front view of an antenna coil according to the third exemplary embodiment. 
         FIG. 12A  is a plan view of an antenna coil according to a fourth exemplary embodiment, and  FIG. 12B  is a front view of the antenna coil according to the fourth exemplary embodiment. 
         FIG. 13A  is a plan view of a magnetic core included in an antenna coil according to a fifth exemplary embodiment, and  FIG. 13B  is a plan view of the antenna coil according to the fifth exemplary embodiment. 
         FIG. 14A  is a plan view of a magnetic core included in an antenna coil according to a sixth exemplary embodiment, and  FIG. 14B  is a plan view of the antenna coil according to the sixth exemplary embodiment. 
         FIG. 15  is a cross-sectional view of a main part of a communication terminal according to a seventh exemplary embodiment. 
         FIG. 16A  is a perspective view of a communication terminal according to an eighth exemplary embodiment, and  FIG. 16B  is a cross-sectional view of the communication terminal. 
         FIG. 17A  is a perspective view of a communication terminal according to a ninth exemplary embodiment, and  FIG. 17B  is a cross-sectional view of the communication terminal. 
         FIG. 18  is a cross-sectional view of a main part of a communication terminal according to a tenth exemplary embodiment. 
         FIG. 19  illustrates how a coupling coefficient to a reader/writer antenna changes when a positional relationship between the magnetic core and a coil conductor is varied. 
         FIG. 20  is a front view of an antenna coil included in a communication terminal according to an eleventh exemplary embodiment. 
         FIG. 21A  to  FIG. 21C  are front views of antenna coils for comparison. 
     
    
    
     DETAILED DESCRIPTION 
     In the communication terminal  90  disclosed in Japanese Patent No. 3975918, the antenna device is placed in the recessed portion  97   a  of the metal housing  97 , as illustrated in  FIG. 1 . Therefore, when the communication terminal  90  receives a magnetic flux in a direction perpendicular to the principal plane of the antenna device, it is possible to ensure good communication conditions. The inventors realized, however, that as an angle between an antenna of the reader/writer and an antenna of the communication terminal increases and, moreover, as a distance between these antennas increases, it becomes difficult to ensure satisfactory communication characteristics. 
     Embodiments consistent with the present disclosure can address the circumstances described above and provide a communication terminal that can reduce degradation of communication performance and is capable of communicating with a communication partner over a wide angular range, regardless of the positional relationship (particularly the angular relationship) with the communication partner. 
     A communication terminal according to a first exemplary embodiment of the disclosure is used, for example, as a mobile communication terminal, such as a cellular phone terminal.  FIG. 2A  and  FIG. 2B  illustrate an antenna coil  21  included in the communication terminal. The antenna coil  21  is used as an antenna for an RFID system using an HF band, such as about a 13.56-MHz band.  FIG. 2A  is a plan view of the antenna coil  21 , and  FIG. 2B  is a front view of the antenna coil  21 . The antenna coil  21  includes a magnetic core  8  having a first principal surface MS 1  and a second principal surface MS 2 , and a coil conductor  9  wound around the magnetic core  8 . The coil conductor  9  has a first conductor portion  11  located adjacent to the first principal surface MS 1  of the magnetic core  8 , and a second conductor portion  12  located adjacent to the second principal surface MS 2  of the magnetic core  8  and at a position different from that of the first conductor portion  11  (i.e., at a position not overlapping with the first conductor portion  11 ) in plan view from the first principal surface MS 1 . 
     As illustrated in  FIG. 2A , the magnetic core  8  is formed by molding a mixture of ferrite powder and resin material into a substantially rectangular plate-like shape. The coil conductor  9  is formed by patterning a thin film of metal, such as copper, silver, or aluminum, on a surface of the flexible substrate  10  of polyethylene terephthalate (PET) or the like into a substantially rectangular spiral shape. The coil conductor  9  has a terminal electrode  91  at one end, and a terminal electrode  92  at the other end. The terminal electrodes  91  and  92  are connected to a feed circuit (not shown). 
       FIG. 3  is a plan view of a state in which a flexible substrate  10  having the coil conductor  9  and the magnetic core  8  are separated from each other. As illustrated in  FIG. 3 , the flexible substrate  10  has a substantially rectangular aperture AP at a position corresponding to a winding center of the coil conductor  9 . The magnetic core  8  is inserted into the aperture AP. Thus, the coil conductor  9  has the first conductor portion  11  adjacent to the first principal surface MS 1  of the magnetic core  8 , and the second conductor portion  12  adjacent to the second principal surface MS 2  of the magnetic core  8 . The magnetic core  8  and the coil conductor  9  constitute the antenna coil  21 . 
       FIG. 4A  to  FIG. 4C  illustrate a configuration of an antenna device  101  and a communication terminal  201  including the antenna device  101  according to the first exemplary embodiment.  FIG. 4A  is a plan view of the antenna device  101 ,  FIG. 4B  is a front view of the antenna device  101 , and  FIG. 4C  is a schematic cross-sectional view of the communication terminal  201 . 
     A circuit board  20  illustrated in  FIG. 4A  is formed of thermosetting resin, such as epoxy resin. As an inner layer, the circuit board  20  includes a ground conductor GND serving as a planar conductor. Although not shown, the feed circuit connected to the antenna coil  21  and various electronic components constituting the communication terminal  201  are mounted on the front and back surfaces of the circuit board  20 . 
     As illustrated in  FIG. 4B , the antenna coil  21  is mounted on the circuit board  20  with a bonding member interposed therebetween, with the first principal surface MS 1  of the magnetic core  8  facing the circuit board  20 . Therefore, the first principal surface MS 1  of the magnetic core  8  faces the ground conductor GND. That is, the antenna coil  21  is positioned such that it overlaps with the ground conductor GND in plan view from the first principal surface MS 1  or the second principal surface MS 2  of the magnetic core  8 . As illustrated in  FIG. 4B , however, the coil conductor  9  and the ground conductor GND are spaced from each other by a distance G. Since the circuit board  20  having the ground conductor GND as an inner layer is used, the distance G can be created between the coil conductor  9  and the ground conductor GND. Thus, as described below, it is possible to provide enhanced communication characteristics when an azimuth angle θ of a magnetic flux is about 0°. 
     The antenna coil  21  is positioned such that the first conductor portion  11  of the coil conductor  9  is closer to the ground conductor GND than the second conductor portion  12  of the coil conductor  9  is to the ground conductor GND. 
     At the same time, the antenna coil  21  is positioned such that the first conductor portion  11  of the coil conductor  9  is located near an end portion E (see  FIG. 4C ) of a housing  200  in the longitudinal direction of the housing  200 . The end portion E of the housing  200  in the longitudinal direction becomes an upper end portion of the housing  200  when the communication terminal  201  is held upright. 
     As illustrated in  FIG. 4A , the magnetic core  8  of the antenna coil  21  is configured and positioned such that, in plan view, an end portion of the magnetic core  8  protrudes from an end portion of the ground conductor GND by a distance T. For example, the distance T is about 1 mm to 5 mm (e.g., about 3 mm under normal conditions). This structure makes it easier to pick up a magnetic flux. 
     In the communication terminal  201 , a strong magnetic field is generated at the end portion E (upper end portion) of the housing  200  in the longitudinal direction. The communication terminal  201  has good directivity over a wide angular range from a direction A to a direction B in  FIG. 4C . Therefore, in wireless communication where the end portion E (upper end portion) of the housing  200  is directed toward the communication partner, the communication terminal  201  can communicate with the communication partner over a wide angular range. 
       FIGS. 5A and 5B  and  FIGS. 6A and 6B  schematically illustrate how a magnetic flux passes through the antenna coil  21  when the angle θ shown in  FIG. 4C  is varied. A magnetic flux is indicated by a broken line in  FIGS. 5A and 5B  and  FIGS. 6A and 6B . 
     When the angle θ is about 90°, as illustrated in  FIG. 5A , a magnetic flux enters the antenna coil  21  from an outer end portion of the magnetic core  8  (i.e., from a position near an end portion of the ground conductor GND) and exits the antenna coil  21  from an inner end portion of the magnetic core  8 . When the angle θ is about 45°, as illustrated in  FIG. 5B , a magnetic flux enters the antenna coil  21  from the outer end portion and the second principal surface MS 2  of the magnetic core  8 , and exits the antenna coil  21  from the inner end portion of the magnetic core  8 . When the angle θ is either about 90° or about 45°, the magnetic flux passes through the winding center of the coil conductor  9 . 
     When the angle θ is about 0°, as illustrated in  FIG. 6A , a magnetic flux φe enters the antenna coil  21  from the second principal surface MS 2  of the magnetic core  8  and exits the antenna coil  21  toward the outer end portion of the magnetic core  8 . As illustrated in  FIG. 6B , which is a perspective view, magnetic fluxes φs 1  and φs 2  enter the antenna coil  21  from the second principal surface MS 2  of the magnetic core  8  and exit the antenna coil  21  toward sides of the ground conductor GND. Thus, when the angle θ is about 0°, as in the cases where the angle θ is about 90° and 45°, the magnetic fluxes pass through the winding center of the coil conductor  9 . 
       FIG. 7A  is a perspective view of a state where first and second communication terminals  201 A and  201 B communicate with each other, and  FIG. 7B  is a cross-sectional view of  FIG. 7A . The first communication terminal  201 A and the second communication terminal  201 B communicate with each other, with their upper end portions E being close to each other. In this example, if the two communication terminals  201 A and  201 B are mirror symmetrical, the angle of each housing  200  with respect to the mirror plane is about 45°. Each antenna coil  21  is closer to the antenna of the communication partner than the ground conductor GND is to the antenna of the communication partner. 
     As illustrated in  FIG. 5B , the coil conductor  9  of the antenna coil  21  is interlinked with the magnetic flux that passes in the direction of about 45°. Therefore, even when the upper end portions E of the communication terminals  201 A and  201 B obliquely face each other as illustrated in  FIG. 7A  and  FIG. 7B , the communication terminals  201 A and  201 B can wirelessly communicate with each other. 
       FIG. 8A  is a perspective view of another state where the first and second communication terminals  201 A and  201 B communicate with each other, and  FIG. 8B  is a cross-sectional view of  FIG. 8A . The first communication terminal  201 A and the second communication terminal  201 B communicate with each other, with their upper end portions E being close to each other. In this example, if the two communication terminals  201 A and  201 B are mirror symmetrical, the angle of each housing  200  with respect to the mirror plane is about 90°. In  FIG. 8A , the two communication terminals  201 A and  201 B are depicted as if their upper end portions E face each other at an angle. However, this is for illustrative purposes only, and the upper end portions E of the communication terminals  201 A and  201 B actually face in parallel with each other. 
     As illustrated in  FIG. 5A , the coil conductor  9  of the antenna coil  21  is interlinked with the magnetic flux that passes in the direction of about 90°. Therefore, even when the upper end portions E of the communication terminals  201 A and  201 B face each other in a straight line as illustrated in  FIG. 8A  and  FIG. 8B , the communication terminals  201 A and  201 B can wirelessly communicate with each other. 
     As described above, communication can be performed over a wide range of angles at which one communication terminal is held over the antenna device of the communication partner. 
       FIG. 9A  to  FIG. 9D  illustrate a configuration of an antenna coil according to a second exemplary embodiment of the disclosure. 
       FIG. 9A  is a plan view of the flexible substrate  10  having the coil conductor  9  formed thereon. The coil conductor  9  is formed on the upper surface of the flexible substrate  10 . 
       FIG. 9B  illustrates a shape of an upper coil conductor portion  9 S of the coil conductor  9 .  FIG. 9C  illustrates a shape of a lower coil conductor portion  9 U of the coil conductor  9 .  FIG. 9D  illustrates a state in which the lower coil conductor portion  9 U and the upper coil conductor portion  9 S overlap with each other. 
     The lower coil conductor portion  9 U and the upper coil conductor portion  9 S have a substantially rectangular spiral shape. An insulating layer is interposed between the lower coil conductor portion  9 U and the upper coil conductor portion  9 S. However, an inner end portion of the lower coil conductor portion  9 U and an inner end portion of the upper coil conductor portion  9 S are electrically connected in series. Thus, the coil conductor  9  is formed into a substantially spiral shape around a coil conductor aperture CW. 
     The flexible substrate  10  is provided with the terminal electrode  91  extending continuously from an outer end portion of the upper coil conductor portion  9 S, and the terminal electrode  92  electrically connected to an outer end portion of the lower coil conductor portion  9 U. 
     The lower coil conductor portion  9 U and the upper coil conductor portion  9 S may be formed on the respective surfaces of the flexible substrate  10 , instead of being stacked on one surface of the flexible substrate  10 . 
     As illustrated in  FIG. 9A , the flexible substrate  10  has the aperture AP at a position corresponding to the coil conductor aperture CW. 
       FIG. 10A  is a plan view of an antenna coil  22  according to the second exemplary embodiment, and  FIG. 10B  is a front view of an antenna device including the antenna coil  22 . 
     The antenna coil  22  is formed by inserting the magnetic core  8  into the aperture AP of the flexible substrate  10 . The antenna device is formed by mounting the antenna coil  22  adjacent to or directly on the circuit board  20 . The antenna coil  22  is positioned such that a surface where the terminal electrodes  91  and  92  (see  FIG. 9A ) are formed faces the circuit board  20 . The terminal electrodes  91  and  92  are connected to electrodes on the circuit board  20 . 
     The lower coil conductor portion  9 U and the upper coil conductor portion  9 S of the coil conductor  9  illustrated in  FIG. 9A  to  FIG. 9D  are arranged such that their main parts do not overlap with each other in plan view. Thus, it is possible to reduce stray capacitance between the lower coil conductor portion  9 U and the upper coil conductor portion  9 S of the coil conductor  9  and realize an antenna coil having desired characteristics. 
     A third exemplary embodiment of the disclosure describes an example of the positioning and electrical connection of an antenna coil within a housing of a communication terminal. 
       FIG. 11A  is a cross-sectional view of a main part of a communication terminal according to the third exemplary embodiment.  FIG. 11B  is a front view of an antenna coil  23  according to the third exemplary embodiment. A coil conductor  9   a  and a coil conductor  9   b  are formed on an upper surface and a lower surface, respectively, of the flexible substrate  10 . The patterns of the coil conductors  9   a  and  9   b  are the same as those illustrated in  FIG. 9A  to  FIG. 9D  in the second embodiment. In the example illustrated in  FIG. 9A  to  FIG. 9D , two layers of coil conductors are formed on one surface of the flexible substrate  10 . In the example of  FIG. 11A  and  FIG. 11B , the coil conductors  9   a  and  9   b  are formed on the respective surfaces of the flexible substrate  10 . The coil conductors  9   a  and  9   b  are connected to each other through via electrodes at predetermined points. 
     As illustrated in  FIG. 11A , the antenna coil  23  is attached to an inner surface of the housing  200 . The antenna coil  23  is positioned such that the first conductor portion  11  located near the end portion of the housing  200  in the longitudinal direction is adjacent to the circuit board  20 . 
     The housing  200  is composed of upper and lower parts that can be separated by a plane parallel to flat surfaces of the circuit board  20 . A contact pin  31  upright on the circuit board  20  is in contact with the terminal electrode  91  of the coil conductor  9   b , with the upper part of the housing  200  placed over the lower part of the housing  200 . Since the antenna coil  23  is attached to the upper part of the housing  200 , the feed circuit on the circuit board  20  is electrically connected to the antenna coil  23 . This configuration can create a large distance G between the ground conductor GND and the coil conductors  9   a  and  9   b . Thus, it is possible to improve directivity particularly in the direction of an angle θ of about 0° as illustrated in  FIG. 6A  and  FIG. 6B . 
     A fourth exemplary embodiment of the disclosure will now be described and is an example of positions of the terminal electrodes  91  and  92  of the coil conductor  9 . 
       FIG. 12A  is a plan view of an antenna coil  24  according to the fourth exemplary embodiment.  FIG. 12B  is a front view of the antenna coil  24 . The antenna coil  24  is different from the antenna coil  21  illustrated in  FIG. 2A  and  FIG. 2B  in terms of the positions of the terminal electrodes  91  and  92  of the coil conductor  9 . In the example of  FIG. 12A  and  FIG. 12B , the terminal electrodes  91  and  92  serving as connecting terminals for connection to the feed circuit are positioned such that they do not overlap with the magnetic core  8  in plan view. Therefore, the presence of contact pins that are in contact with the terminal electrodes  91  and  92  has little negative impact on the transmission and formation of magnetic fluxes. It is preferable that both the terminal electrodes  91  and  92  be on one side of the magnetic core  8  in plan view (i.e., the terminal electrodes  91  and  92  are not located on opposite sides of the magnetic core  8 ). 
       FIG. 13A  is a plan view of the magnetic core  8  included in an antenna coil  25  according to a fifth exemplary embodiment of the disclosure.  FIG. 13B  is a plan view of the antenna coil  25  according to the fifth exemplary embodiment. 
     The antenna coil  25  is different from the antenna coil  21  illustrated in  FIG. 3  in the first exemplary embodiment in that the magnetic core  8  is wider at one end than the other. 
     Using the magnetic core  8  having such a shape can improve communication performance, as it is possible to strengthen the magnetic flux that passes through the magnetic core  8 , enhance the coupling of magnetic field to the antenna of the communication partner, and increase the maximum communication distance. In the example of  FIG. 13B , the antenna coil  25  is configured such that the wider portion of the magnetic core  8  is adjacent to the first conductor portion  11 . Alternatively, the antenna coil  25  may be configured such that the wider portion of the magnetic core  8  is adjacent to the second conductor portion  12 . That is, the wider portion of the magnetic core  8  may be adjacent to either the first conductor portion  11  or the second conductor portion  12 . Thus, by using the magnetic core  8  having a wider portion at one end, it is possible to more effectively collect magnetic fields and improve communication performance. Also, by using the magnetic core  8  having a wider end portion adjacent to an end portion of the ground conductor GND, it is possible to reduce the magnetic resistance around the end portion of the ground conductor GND and more effectively collect magnetic fields. 
     In the antenna coil  25  illustrated in  FIG. 13B , the wider end portion of the magnetic core  8  is substantially rectangular in shape. Alternatively, this end portion of the magnetic core  8  can have a substantially trapezoidal shape which widens toward the outside, or can have a substantially butterfly shape which widens from the center to both ends of the magnetic core  8 . 
       FIG. 14A  is a plan view of the magnetic core  8  included in an antenna coil  26  according to a sixth exemplary embodiment of the disclosure.  FIG. 14B  is a plan view of the antenna coil  26  according to the sixth exemplary embodiment. The antenna coil  26  includes the flexible substrate  10  having a coil conductor formed thereon, and the magnetic core  8  having a substantially rectangular plate-like shape. The antenna coil  26  is different from the antenna coil  25  illustrated in  FIG. 13B  in configuration of the magnetic core  8 . 
     The magnetic core  8  illustrated in  FIG. 14A  is a flat ferrite plate having a grid of cut lines, laminated with films on both sides, and divided into small pieces by the cut lines. In  FIG. 14B , each of sections into which the magnetic core  8  is divided by broken lines represents a small piece of sintered magnetic material. This configuration provides flexibility to the magnetic core  8 . Therefore, the antenna coil  26  having the magnetic core  8  can be easily placed along a surface of a support base. For example, the antenna coil  26  can be placed along an inner surface of a housing of a mobile terminal. It is thus possible to easily mount the antenna coil  26  within a housing of various shapes. 
     In the example of  FIG. 14B , the antenna coil  26  is configured such that the wider portion of the magnetic core  8  is adjacent to the first conductor portion  11 . However, as described in the fifth exemplary embodiment, the wider portion of the magnetic core  8  may be adjacent to either the first conductor portion  11  or the second conductor portion  12 . Thus, by using the magnetic core  8  having a wider portion at one end, it is possible to more effectively collect magnetic fields and improve communication performance. 
       FIG. 15  is a cross-sectional view of a main part of a communication terminal according to a seventh exemplary embodiment of the disclosure. In this example, an antenna coil  27  is attached to an inner curved surface of the housing  200 . The antenna coil  27  is flexible if it includes the magnetic core  8  having flexibility (as illustrated in  FIG. 14A  and  FIG. 14B ) and a flexible coil conductor formed on the flexible substrate  10 . In this case, the antenna coil  27  can be placed not only on a single flat surface within the housing  200 , but also along a curved surface of the housing  200 . It is thus possible to easily mount the antenna coil  27  within a housing of various shapes. Moreover, when the antenna coil  27  is attached to the inner surface of the housing  200 , the antenna coil  27  can be spaced apart from the ground conductor GND in the circuit board  20 . Since this increases the area through which magnetic fluxes pass, it is possible to ensure good communication conditions. 
     An eighth exemplary embodiment will now be described and is an example applied to a communication terminal of clamshell type. 
       FIG. 16A  is a perspective view of a communication terminal  208 , and  FIG. 16B  is a cross-sectional view of the communication terminal  208 . A housing of the communication terminal  208  is composed of a top housing portion  200 A and a bottom housing portion  200 B. The antenna coil  21  is disposed near an upper end portion E of the top housing portion  200 A. A liquid-crystal display panel  41  is housed in the top housing portion  200 A. A shield plate  41 S is attached to the backside of the liquid-crystal display panel  41 . The shield plate  41 S corresponds to a planar conductor according to the present invention. The bottom housing portion  200 B includes a key input part  42  and the circuit board  20 . 
     When the communication terminal  208  configured as described above is folded, the antenna coil  21  is not sandwiched between the ground conductor GND in the top housing portion  200 A and the shield plate  41 S in the bottom housing portion  200 B. Therefore, even in a folded state, the communication terminal  208  can wirelessly communicate using the antenna coil  21 . 
     A ninth exemplary embodiment describes an example applied to a communication terminal of slide type. 
       FIG. 17A  is a perspective view of a communication terminal  209 , and  FIG. 17B  is a cross-sectional view of the communication terminal  209 . A housing of the communication terminal  209  is composed of the top housing portion  200 A and the bottom housing portion  200 B. The antenna coil  21  is disposed near the upper end portion E of the top housing portion  200 A. The liquid-crystal display panel  41  is housed in the top housing portion  200 A. The shield plate  41 S is attached to the backside of the liquid-crystal display panel  41 . The shield plate  41 S corresponds to a planar conductor according to the present invention. The bottom housing portion  200 B includes the key input part  42  and the circuit board  20 . 
     The ground conductor GND in the circuit board  20  within the bottom housing portion  200 B is patterned such that a region that overlaps with the antenna coil  21  when the top housing portion  200 A is retracted is a non-ground region. With this structure, even when the top housing portion  200 A is retracted, the communication terminal  209  can wirelessly communicate using the antenna coil  21 . 
     A tenth exemplary embodiment describes a relationship between the coupling coefficient and the position of the magnetic core  8  with respect to the coil conductors  9   a  and  9   b  of the antenna coil  23 . 
       FIG. 18  is a cross-sectional view of a main part of a communication terminal according to the tenth exemplary embodiment. The coil conductor  9   a  and the coil conductor  9   b  are formed on the upper surface and the lower surface, respectively, of the flexible substrate  10 . 
     As illustrated in  FIG. 18 , the antenna coil  23  is attached to the inner surface of the housing  200 . The antenna coil  23  is positioned such that the second conductor portion  12  located near the end portion of the housing  200  in the longitudinal direction faces toward the outer surface of the housing  200  (i.e., toward the communication partner, or upward in  FIG. 18 ). 
     The housing  200  is composed of upper and lower parts that can be separated by a plane parallel to flat surfaces of the circuit board  20 . The contact pin  31  upright on the circuit board  20  is in contact with the terminal electrode  91  of the coil conductor  9   b , with the upper part of the housing  200  placed over the lower part of the housing  200 . Thus, the feed circuit on the circuit board  20  is electrically connected to the antenna coil  23 . 
     The antenna coil  23  illustrated in  FIG. 18  is different from that illustrated in  FIG. 11A  and  FIG. 11B  of the third exemplary embodiment, in terms of the position of the magnetic core  8  with respect to the coil conductors  9   a  and  9   b  of the antenna coil  23 . In  FIG. 18 , the length of a portion where the first conductor portion  11  of the coil conductors  9   a  and  9   b  is adjacent to the magnetic core  8  is indicated by A, and the length of a portion where the second conductor portion  12  of the coil conductors  9   a  and  9   b  is adjacent to the magnetic core  8  is indicated by B. The antenna coil  23  illustrated in  FIG. 18  is configured to satisfy the relationship A&lt;B. At the same time, the antenna coil  23  illustrated in  FIG. 18  is configured such that the length A of the portion where the first conductor portion  11  of the coil conductors  9   a  and  9   b  is adjacent to the magnetic core  8  is smaller than a width C of the first conductor portion  11 . 
     With this configuration, an ineffective magnetic flux φi not interlinked with the antenna coil  23  is suppressed and thus, a magnetic flux φa effectively interlinked with the antenna coil  23  is enhanced. Therefore, the coupling coefficient to an antenna of the communication partner, such as a reader/writer antenna, is increased. 
       FIG. 19  illustrates how a coupling coefficient to a reader/writer antenna changes when a positional relationship between the magnetic core  8  and a coil conductor is varied. A result of the corresponding measurement was obtained under the following conditions: 
     Magnetic core  8 :
 
Length Dimension: about 15 mm
 
Width Dimension: about 16 mm
 
Coil conductor:
 
Outer Dimensions: about 15 mm×20 mm
 
Width C of first conductor portion  11 : about 2 mm
 
Width B of second conductor portion  12 : about 2 mm
 
Relationship with ground conductor:
 
Distance between magnetic core  8  and ground conductor GND: about 3 mm
 
Relationship with reader/writer antenna:
 
Distance to reader/writer antenna: about 17 mm
 
     In  FIG. 19 , the “amount of shift X of magnetic core” represented by the horizontal axis is a distance obtained by subtracting the length A of the portion where the first conductor portion  11  of the coil conductor is adjacent to the magnetic core  8  from the length B of the portion where the second conductor portion  12  of the coil conductor is adjacent to the magnetic core  8 . 
     Under the conditions described above, as shown in  FIG. 19 , a high coupling coefficient can be obtained when the amount of shift X of the magnetic core  8  is in the range of about 2 mm to 7.5 mm. When the amount of shift X of the magnetic core  8  is about 7.5 mm, the magnetic core  8  is adjacent only to the second conductor portion  12  of the coil conductor. Therefore, it is generally effective to define the amount of shift X of the magnetic core  8  such that it is within a range from a value above zero to a value which allows the magnetic core  8  to be adjacent only to the second conductor portion  12  of the coil conductor. 
     In other words, it is preferable that the relationship A&lt;B be satisfied, where A is the length of a portion where the first conductor portion  11  of the coil conductor is adjacent to the magnetic core  8 , and B is the length of a portion where the second conductor portion  12  of the coil conductor is adjacent to the magnetic core  8 . 
       FIG. 20  is a front view of an antenna coil included in a communication terminal according to an eleventh exemplary embodiment of the disclosure. The antenna coil includes the magnetic core  8  having the first principal surface MS 1  and the second principal surface MS 2 , and the flexible substrate  10  on which a coil conductor having a substantially spiral pattern is formed. The coil conductor has the first conductor portion  11  located adjacent to the first principal surface MS 1  of the magnetic core  8 , and the second conductor portion  12  located adjacent to the second principal surface MS 2  of the magnetic core  8  and at a position different from that of the first conductor portion  11  (i.e., at a position not overlapping with the first conductor portion  11 ) in plan view from the first principal surface MS 1  or the second principal surface MS 2 . 
       FIG. 21A  to  FIG. 21C  are front views of antenna coils for comparison.  FIG. 21A  illustrates an antenna coil including the magnetic core  8  which is bent in a step-like shape, and the flexible substrate  10  which is flat.  FIG. 21B  illustrates an antenna coil including the magnetic core  8  which is flat, and the flexible substrate  10  which is bent in a step-like shape.  FIG. 21C  illustrates an antenna coil including the magnetic core  8  which is flat, and the flexible substrate  10  which is bent in a slope-like shape. 
     In the structure of  FIG. 21A  where the magnetic core  8  is bent in a step-like shape, there is a large amount of leakage flux as indicated by broken arrows which represent magnetic fluxes. Therefore, the density of magnetic fluxes effectively interlinked with the coil conductor of the antenna coil is low. Moreover, the overall thickness of the antenna coil is large. In the structure of  FIG. 21B , the coupling coefficient to a magnetic flux that passes in the planar direction of the magnetic core  8  is high. However, since the coil conductor is bent to an acute angle, the overall length of the coil conductor is large, the resistance value is high, and the Q value is low. In the structure of  FIG. 21C , the overall length of the coil conductor is smaller than that in the structure of  FIG. 21B . However, in the structure of  FIG. 21C , the resistance value is higher and the Q value is lower than those in the structure of  FIG. 21B . 
     In contrast, in the antenna coil illustrated in  FIG. 20  where the magnetic core  8  is not bent to an acute angle, the amount of leakage flux is small and it is possible to guide an effective magnetic flux. Additionally, the overall length of the coil conductor is small and the resistance value is low. Moreover, since the magnetic core  8  intersects with the aperture area of the coil conductor at an angle close to 90°, a high level of efficiency can be achieved. That is, since the magnetic flux is interlinked with the aperture area of the coil at an angle close to 90°, the effective aperture area can be increased and it is possible to generate a large electromotive force. 
     With the antenna coil illustrated in  FIG. 20 , a high gain can be obtained over a wide range of angles between the antenna coil and the magnetic flux. Particularly high gain characteristics can be achieved in the direction of about 45°. 
     In the exemplary embodiments described above, the antenna coil is positioned to face the planar conductor. However, the planar conductor is optional. The antenna coil can be positioned not to face the planar conductor. 
     In the embodiments described above, the ground electrode of the circuit board or the shield plate attached to the backside of the liquid-crystal display panel has been described as an example of the planar conductor. However, a conductive film or conductive foil formed on the inner surface of the housing, or a battery pack may be treated as a planar conductor to form an antenna device. The planar conductor may not be a conductor of substantially rectangular shape, but may be of various planar shapes. The planar conductor may not be formed in a single layer, but may be formed in multiple layers. The planar conductor may be partially bent, as long as its main part is substantially planar in shape. 
     Embodiments consistent with the disclosure can be similarly applicable to a communication terminal having a swivel housing. 
     Although a circuit board having a ground conductor as an inner layer has been described as an example in the exemplary embodiments above, other embodiments consistent with the disclosure are similarly applicable to a circuit board having a ground conductor on its surface. 
     Although the antenna coil is disposed within the housing in the exemplary embodiments described above, in other embodiments the antenna coil may be disposed on the outer surface of the housing (i.e., the antenna coil may be held by the outer surface of the housing). In this case, an input and output terminal of the antenna coil may be drawn into the housing. 
     In embodiments of a communication terminal according to the disclosure, a coil conductor of an antenna coil has a first conductor portion located adjacent to a first principal surface of a magnetic core, and a second conductor portion located adjacent to a second principal surface of the magnetic core and at a position different from that of the first conductor portion in plan as viewed from one of the principal surfaces. The antenna coil is positioned such that the first principal surface of the magnetic core is adjacent to a planar conductor, and that the first conductor portion of the coil conductor is located near an upper end portion of housing. Therefore, when wirelessly communicating with a communication partner, with an end portion of the housing in the longitudinal direction directed toward the communication partner, the communication terminal can communicate with the communication partner over a wide angular range without heavily depending on the positional relationship (particularly the angular relationship) with the communication partner. 
     While exemplary embodiments 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 disclosure. The scope of the invention, therefore, is to be determined solely by the following claims and their equivalents.