Patent Publication Number: US-2011070831-A1

Title: Coupler and communication system

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority from Japanese Patent Application No. 2009-216629, filed on Sep. 18, 2009, the entire subject matter of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     Aspects of the present invention relate to a coupler that couples a plurality of secondary antennas to a communication device having a primary antenna, and a communication system thereof. 
     BACKGROUND 
     A related-art communication device transmits power or a signal in a non-contact manner by electromagnetic induction or radio waves. As such a communication device, for example, there is known a radio frequency identification (hereinafter referred to as an “RFID”) system which includes a wireless tag communication device that performs transmission/reception of information with respect to a wireless tag circuit element that can store information. 
     In some type of business such as sales, logistics or the like, this RFID system is used in clearance work on goods in stock, which is periodically performed to confirm the goods in stock, in searches for specified goods, and the like. In such goods management, in order to facilitate transmission/reception of information between a non-contact type data carrier terminal and a wireless tag provided on a goods item and to improve work efficiency, a plurality of external antennas are provided separately from an internal antenna provided in the non-contact type data carrier terminal. 
     Specifically, for example, two external antennas for the non-contact type data carrier terminal are provided on the left and right working gloves, respectively. When a goods item is grasped with both hands, a distance between the wireless tag provided on the goods and the external antennas becomes smaller, and thus, the transmission/reception of a signal such as identification information or the like can be easily performed. 
     However, when performing transmission/reception of information with a wireless tag using the working gloves provided with the external antennas as described above, if signals transmitted from the respective external antennas do not have the same signal level, a difference occurs in the communication range for each external antenna. As a result, when performing a read operation to a wireless tag using the working gloves, there may occur the case where the external antenna provided on the right-handed glove can read a wireless tag, whereas the external antenna provided on the left-handed glove cannot read a wireless tag. In this case, since a worker typically does not care such difference in communication range, reception omission may occur. 
     SUMMARY 
     Accordingly, it is an aspect of the present invention to provide a coupler and a communication system, which can make a communication range of a plurality of secondary antennas substantially equal to each other, which are coupled to a primary antenna provided on the communication device by the coupler. 
     According to an illustrative embodiment of the present invention, there is provided a coupler to be provided between a primary antenna provided in a communication device and a plurality of secondary antennas. The coupler includes: a substrate which configures a coupler main body; a first coil antenna which is connected to a first secondary antenna and provided on a first surface side of the substrate; and a second coil antenna which is connected to a second secondary antenna and provided on a second surface side of the substrate, wherein the first coil antenna and the second coil antenna are configured so as to have a same degree of electromagnetic coupling with respect to the primary antenna. 
     According to another illustrative embodiment of the present invention, there is provided a coupler to be provided between a primary antenna provided in a communication device and a plurality of secondary antennas. The coupler includes: a substrate which configures a coupler main body and includes a first surface and a second surface; a first coil antenna which is connected to a first secondary antenna and includes a first portion provided on the first surface side and a second portion provided on the second surface side; and a second coil antenna which is connected to a second secondary antenna and includes a first portion provided on the first surface side and a second portion provided on the second surface side, wherein the first coil antenna and the second coil antenna are configured so as to have a same degree of electromagnetic coupling with respect to the primary antenna. 
     According to a further illustrative embodiment of the present invention, there is provided a communication system including: a communication device including a primary antenna configured to transmit and receive information; and a coupler provided between the primary antenna and a plurality of secondary antennas. The coupler includes: a substrate which configures a coupler main body; a first coil antenna which is connected to a first secondary antenna and provided on a first surface side of the substrate; and a second coil antenna which is connected to a second secondary antenna and provided on a second surface side of the substrate, wherein the first coil antenna and the second coil antenna are configured so as to have a same degree of electromagnetic coupling with respect to the primary antenna. 
     According to a further illustrative embodiment of the present invention, there is provided a secondary antenna unit including: a coupler to be mounted on a communication device including a primary antenna; and first and second secondary antennas connected to the coupler. The coupler includes: a substrate which configures a coupler main body; a first coil antenna which is connected to the first secondary antenna and provided on a first surface side of the substrate; and a second coil antenna which is connected to a second secondary antenna and provided on a second surface side of the substrate. The first coil antenna and the second coil antenna are configured so as to have a same degree of electromagnetic coupling with respect to the primary antenna when the coupler is mounted on the communication device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects of the present invention will become more apparent and more readily appreciated from the following description of exemplary embodiments of the present invention taken in conjunction with the attached drawings, in which: 
         FIG. 1  is a system configuration diagram illustrating an example of the entire configuration of a communication system according to an illustrative embodiment of the present invention; 
         FIG. 2  is a functional block diagram of the communication system; 
         FIGS. 3A and 3B  are plan views illustrating an example of a coupler according to an illustrative embodiment of the present invention; 
         FIG. 4  is a schematic sectional view illustrating a case where the coupler shown in  FIGS. 3A and 3B  is provided on a communication device; 
         FIG. 5  is a schematic view illustrating an example of magnetic field generated by the coupler; 
         FIGS. 6A and 6B  are plan views illustrating another example of a coupler according to an illustrative embodiment of the present invention; 
         FIG. 7  is a schematic sectional view illustrating a case where the coupler of  FIGS. 6A and 6B  is provided on a communication device; 
         FIGS. 8A and 8B  are plan views illustrating a further example of a coupler according to an illustrative embodiment of the present invention; 
         FIG. 9  is a schematic sectional view illustrating the coupler taken along line IX-IX shown in  FIG. 8B ; 
         FIGS. 10A and 10B  are plan views illustrating a case where the coupler according to an illustrative embodiment of the present invention is provided on a communication device; and 
         FIG. 11  is a schematic sectional view illustrating a case where a coupler according to a modified example is provided on a communication device. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, illustrative embodiments of the present invention will be described with reference to the accompanying drawings. In a wireless communication system  400  of  FIGS. 1 and 2 , a wireless tag communication device  100  on which a coupler  200  according to an illustrative embodiment is provided. The wireless tag communication device  100  includes a primary antenna  152  that is a device antenna, and the primary antenna  152  is coupled to two secondary antennas  300  in an electromagnetic coupling method via the coupler  200 , so that the transmission/reception of information with a wireless tag T is performed. 
     The wireless communication system  400  of  FIG. 1  includes the coupler  200  provided between the primary antenna  152  and the two secondary antennas  300 . The wireless communication system  400  is used for goods management such as sales, logistics, distribution, factories, and the like (see  FIG. 2 ). For example, a worker M has the wireless tag communication device  100  in a chest pocket, and the secondary antennas  300  are provided on both hands of the worker. The secondary antennas  300  are connected to the coupler  200  which is provided on the wireless tag communication device  10 , via lead wires  500 . The secondary antennas  300  are provided on wrist hands or working gloves. 
     Specifically, plural storage boxes B are put on a goods storing shelf S, and a wireless tag T having a different ID is provided on each storage box B. Also, various kinds of goods (not illustrated) are contained in the storage boxes B. The ID of the wireless tag T is associated with information (manufacturing date, lot number, and the like) of the goods contained in the storage box B, and is read through the secondary antennas  300  provided on both hands of the worker M when the worker M takes a desired goods item out of the storage box B. Accordingly, the information of the goods taken out of the storage box B can be specified, and the information is displayed on a display unit  160  or notified by a notification unit (not illustrated). 
     Since the two secondary antennas  300  have the same communication range, the worker M can perform the work by equally operating both arms without caring the communication range of the secondary antennas. Also, reading omissions caused by the different communication ranges of the secondary antennas can be reduced, which causes increase in the work efficiency. Hereinafter respective components in the wireless communication system will he described. 
     With reference to  FIG. 2 , the configuration of the wireless tag communication system  400  will be described. The wireless tag communication device  100  includes a high-frequency circuit  112  that processes signals read from the wireless tag T through the secondary antennas  300  and the primary antenna  152 . The wireless tag communication device  100  further includes a Central Processing Unit (CPU)  154 , a Random Access Memory (RAM)  156  and a Read Only Memory (ROM)  155  as storage unit, which are electrically connected via a bus. 
     The high-frequency circuit  112  generates a carrier signal for the wireless tag T operating. In order to perform communication with the wireless tag T, the high-frequency circuit  112  generates a transmission command to the wireless tag T based on an instruction from the CPU  154 , modulates the carrier signal to transmit the carrier signal as a high-frequency signal, and receives and demodulates the high-frequency signal modulated in the wireless tag T to transmit the demodulated signal to the CPU  154 . 
     The CPU  154 , while using a temporary storage function of the RAM  156 , controls the entire wireless tag communication device  100  by performing a signal process according to a program pre-stored in the ROM  155 . Also, the wireless tag communication device  100  includes an input unit  170  such as ten keys (numeral keys) through which operator&#39;s instructions and information are input, and a display unit  160  which displays information or a message. 
     The primary antenna  152  is provided near the surface of a device main body portion of the wireless tag communication device  100 . In the case where the secondary antennas  300  are not mounted on the wireless tag communication device  100  by the coupler  200 , the wireless tag communication device  100  communicates with the wireless tag T through the primary antenna  152 . 
     In the case where the secondary antennas  300  are mounted on the wireless tag communication device  100  via the coupler  200 , the secondary antennas  300  performs transmission/reception of signals with the wireless tag T in the wireless tag communication system  400 . In this illustrative embodiment of the present invention, two secondary antennas  300  are provided. 
     The coupler  200  corresponding to the two secondary antennas  300  has a first coil antenna  210  and a second coil antenna  220  for performing transmission/reception of a high-frequency signal with respect to the secondary antennas. In the case where the coupler  200  is mounted on the wireless tag communication device  100 , the wireless tag communication device  100  operates as follows. That is, the primary antenna  152  generates a magnetic field in a communicable area by electric energy of the received radio wave, and is electromagnetically coupled to the coupler  200  by the mutual induction based on the magnetic field. 
     The first coil antenna  210  and the second coil antenna  220  of the coupler  200  generate induced current by the mutual induction. As the induced current flows to the secondary antennas  300  connected through coaxial cables or the like, the high-frequency signal from the high-frequency circuit  112  is supplied thereto. The secondary antennas  300  resonate with the frequency of the high-frequency signal supplied from the coupler  200 , and transmit the high-frequency signal to the wireless tag T. 
     On the other hand, when receiving a response signal from the wireless tag T, the induced current that flows through the secondary antennas  300  is changed by a modulated signal of the wireless tag T, and due to this change, the magnetic field generated from the first coil antenna  210  or the second coil antenna  220  of the coupler  200  also changes. Accordingly, the current that flows through the primary antenna  152  of the wireless tag communication device  100  that is electromagnetically coupled by the mutual induction also changes. This current change is demodulated by the high-frequency circuit  112 , and is transmitted to the CPU  154  as the received signal. 
     Herein, the communication range of the secondary antennas  300  is an area which is determined by the distance that the high-frequency signal output from the secondary antennas  300  can reach. If the degrees of electromagnetic coupling of the first coil antenna  210  and the second coil antenna  220  with respect to the primary antenna  152  are different from each other, the amounts of induced current flowing through the respective coil antennas are also different from each other, resulting in a different in the communication range among the secondary antennas  300 . 
     Accordingly, in order to make the communication ranges of the respective secondary antennas  300  equal to each other, it is necessary to make the degrees of electromagnetic coupling of the respective coil antennas  210  and  220  with respect to the primary antenna  152  equal to each other. The configuration of coupler  200  will be described hereinafter. 
     &lt;Differentiate the Opening Area of the Coil Antenna&gt; 
     Referring to  FIGS. 3A ,  3 B and  FIG. 4 , the configuration of the coupler  200  according to this illustrative embodiment of the present invention will be described. The coupler  200  includes a substrate  201  configuring the coupler  200 , a first coil antenna  210  (see  FIG. 3A ) formed by printing on a first surface side  10  of the substrate  201 , and a second coil antenna  220  (see  FIG. 3B ) formed by printing on a second surface side  20  of the substrate  201 . The first coil antenna  210  and the second coil antenna  220  are connected to the corresponding secondary antennas  300 , respectively, via lead wires (not illustrated) connected to terminals  206 . 
     In the case where the coupler  200  is mounted on the wireless tag communication device  100  as shown in  FIG. 4 , it is assumed that the surface of the substrate  201  of the coupler  200  that is closer to the primary antenna  152  provided on the wireless tag communication device  100  is a first surface  10 , and the surface of the substrate  201  that is farther from the primary antenna  152  than the first surface  10  is a second surface  20 . The thicknesses of conductor wires constituting the respective antenna coils are the same. 
     Here, as shown in  FIG. 5 , the first coil antenna  210  formed on the first surface side  10  of the substrate  201  and the second coil antenna  220  formed on the second surface side  20  have different distances from the primary antenna  152  by a thickness t of the substrate  201 . Accordingly, as shown in  FIG. 5 , the amount of linkage magnetic flux of the radio wave signal output from the primary antenna  152  is different between the first surface  10  and the second surface  20 . As a result, even though the first coil antenna and the second coil antenna have the same configuration, if these are provided on the first surface and the second surface, respectively, the coupling degrees of the first coil antenna and the second coil antenna with respect to the primary antenna  152  are different from each other. 
     In this illustrative embodiment, as shown in  FIGS. 3A and 3B , an opening  225  of the first coil antenna  210  that is provided on the first surface side  10  closer to the primary antenna  152  and an opening  226  of the second coil antenna  220  that is provided on the second surface side  20  are formed so that the opening area (see  FIG. 3A ) of the opening  225  of the first coil antenna  210  is smaller than the opening area (see  FIG. 3B ) of the opening  226  of the second coil antenna  220 . 
     The induced current I(A) of the coil antenna is in proportion to the multiplication of the magnetic field, strength H(A/m) flux-linking the coil antenna, the number N of windings of the coil antenna, and the opening area A(m 2 ) of the coil antenna. Accordingly, if it is intended to make the induced currents of the antenna coils having different magnetic field strengths equal to each other, for example, it is necessary to adjust the numbers of windings of the respective coil antennas in the case where the opening areas of the coil antennas are equal to each other, while it is necessary to adjust the opening areas or the respective coil antennas in the case where the numbers of windings of the coil antennas are equal to each other. 
     As shown in  FIG. 5 , the magnetic field E generated from the primary antenna of the wireless tag communication device  100  is relatively stronger on the side of the first coil antenna  210  provided on the first surface side  10  in comparison to the side of the second coil antenna  220  provided on the second surface side  20 . Accordingly, by making the opening area of the opening  225  of the first coil antenna  210 , at which the magnetic field is stronger, smaller than the opening area of the opening  226  of the second coil antenna  220 , the induced currents induced in the first coil antenna  210  and the second coil antenna  220  can be equal to each other, and the coupling degrees of the first coil antenna  210  and the second coil antenna  220  with respect to the primary antenna  152  can become equal to each other (see  FIG. 4 ). Therefore, the high-frequency signal output from the primary antenna  152  can be transmitted to the plurality of secondary antennas  300  to provide same information communication range. Accordingly, for example, in the case where a worker performs reading of the wireless tag using this communication system  400 , reading omissions caused by the different communication ranges of the secondary antennas  300  can be reduced. 
     In this case, it is assumed that the numbers of windings of the first coil antenna  210  and the second coil antenna  220  and the thicknesses of the conductor wires constituting the coil antennas are equal to each other, respectively. Also, the sizes of the opening areas of the first coil antenna  210  and the second coil antenna  220  are appropriately adjusted in accordance with the thickness of the substrate or the position relation between the primary antenna and the first and second coil antennas  210  and  220 . 
     &lt;Differentiate the Numbers of Windings of the Coil Antennas&gt; 
     Referring to  FIGS. 6A and 6B , and  FIG. 7 , the configuration of a coupler  200 A according to another illustrative embodiment of the present invention will be described. The same reference numerals as in  FIGS. 3A and 3B , and  FIG. 4  are used for the same elements, and the detailed explanation thereof will be omitted. In this illustrative embodiment, comparing the number of windings of the first coil antenna  210 A (see  FIG. 6A ) which is provided on the first surface side  10  that is closer to the primary antenna  152  with the number of windings of the second coil antenna  220 A (see  FIG. 6B ) which is provided on the second surface side  20 , the number of windings of the first coil antenna  210 A is smaller than that of the second coil antenna  220 A. In this case, it is assumed that the opening areas of the openings  225 A and  226 A of the coil antennas are equal to each other. 
     As described above with reference to  FIG. 5 , the magnetic field E generated by the radio wave signal from the primary antenna  152  of the wireless tag communication device  100  is relatively stronger on the first surface side  10  in comparison to the second surface side  20 . Accordingly, by making the number of windings of the first coil antenna  210 A, on which the magnetic field is relatively stronger, smaller than the number of windings of the second coil antenna  220 A, the induced currents induced in the first coil antenna  210 A and the second coil antenna  220 A can he equal to each other. Accordingly, the coupling degrees of the first coil antenna  210 A and the second coil antenna  220 A to the primary antenna  152  can become equal to each other (see  FIG. 7 ). Therefore, the high-frequency signal output from the primary antenna  152  can be transmitted to the plurality of secondary antennas  300  to provide same information communication range. Accordingly, for example, in the case where a worker performs reading of the wireless tag using this communication system  400 , reading omissions caused by the different communication ranges of the secondary antennas  300  can be reduced. 
     In this case, it is assumed that the opening areas of the openings  225 A and  226 A of the first and second coil antennas  210 A and  220 A and the thicknesses of the conductor wires constituting the coil antennas are equal to each other, respectively. Also, the number of windings of the first coil antenna  210 A and the number of windings of the second coil antenna  220 A are appropriately adjusted in accordance with the thickness of the substrate or the position relation between the primary antenna and the first and second coil antennas  210 A and  220 A. 
     &lt;Providing the First Coil Antenna and the Second Coil Antenna on Both Sides of the First Surface and the Second Surface&gt; 
     Referring to  FIGS. 8A and 8B , and  FIG. 9 , the configuration of a coupler  200 B according to a further illustrative embodiment of the present invention will be described. The same reference numerals as in  FIGS. 3A and 3B , and  FIG. 4  are used for the same elements, and the detailed explanation thereof will be omitted. In this illustrative embodiment, as shown in  FIG. 9 , in the case where the coupler  200 B is mounted, the first coil antenna  210 B includes a first-surface-side first coil antenna portion  211  (see  FIG. 8A ), which is provided on the first surface side  10  that is a surface closer to the primary antenna  152 , and a second-surface-side first coil antenna portion  212  (see  FIG. 8B ), which is drawn from a through-hole  30  and is provided on the second surface side. 
     Also, in  FIG. 9 , the second coil antenna  220 B includes a first-surface-side second coil antenna portion  221  (see  FIG. 8A ), which is provided on the first surface side  10 , and a second-surface-side second coil antenna portion  222  (see  FIG. 8B ), which is drawn from a through-hole  31  and is provided on the second surface side. It is noted that the first-surface-side first coil antenna portion  211  and the first-surface-side second coil antenna portion  221  have substantially same number of windings and same opening area  225 B, and the second-surface-side first coil antenna portion  212  and the second-surface-side second antenna coil portion  222  have substantially same number of windings and same opening area  226 B. 
     As described above, although the strength of the magnetic field generated from the primary antenna  152  of the wireless tag communication device  100  on the first surface side  10  is different from that on the second surface side  20 , the first coil antenna  210 B has the first-surface-side first coil antenna portion  211  and the second-surface-side first coil antenna portion  212 , and the second coil antenna  220 B has the first-surface-side second coil antenna portion  221  and the second-surface-side second coil antenna portion  222 . 
     Since the first-surface-side first coil antenna portion  211  and the first-surface-side second coil antenna portion  221  provided on the first surface side  10  have substantially same opening area, the same number of windings, and the same distance from the primary antenna  152 , the amounts of induced current are substantially equal to each other. Additionally, the second-surface-side first coil antenna portion  212  and the second-surface-side second coil antenna portion  222  provided on the second surface side  20  have substantially same amount of induced current. Accordingly, the induced currents induced in the first coil antenna  210 B and the second coil antenna  220 B can be equal to each other. 
     Accordingly, the induced currents induced in the first coil antenna  210 B and the second coil antenna  220 B can be made equal to each other more accurately, and therefore, the high-frequency signal output from the primary antenna  152  can be transmitted to the plurality of secondary antennas  300  to provide same information communication range. Therefore, for example, in the case where a worker performs reading of the wireless tag using this communication system  400 , reading omissions caused by the different communication ranges of the secondary antennas  300  can be reduced. 
     Referring to  FIG. 10A , the configuration of a case where the coupler  200  is mounted on the wireless tag communication device  100 . The wireless tag communication device  100  of this illustrative embodiment is provided with a display unit  160  on the surface of a device main body portion  180 , and in the case where the coupler  200  is mounted on the wireless tag communication device  100 , the entire of the display unit  160  is exposed through a window portion  260  formed in the coupler  200 . It is assumed that the primary antenna  152  is provided closer to the display unit  160 . 
     The window portion  260  is formed inside an opening of the first coil antenna (not illustrated) provided in the coupler  200  and an opening  226  of the second coil antenna  220 . As an example, the position relations among the wireless tag communication device  100 , the display unit  160 , and the window portion  260  of the coupler  200  in left and right directions in  FIGS. 10A and 10B  are as follows. In  FIGS. 10A and 10B , the window portion  260  is indicated by a thick line. 
     It is assumed that the distance from a left end  182  of the device main body portion  180  of the wireless tag communication device  100  to a left end  162  of the display unit  160  is L 3 , and the distance from a right end  181  of the device main body portions  180  to a right end  161  of the display unit  160  is also L 3 . Additionally, if it is assumed that the distance from a left end  262  of the window portion  260  to a left end  232  of the coupler  200  is L 1 , and the distance from a right end  261  of the window portion  260  to a right end  231  of the coupler  200  is L 2 , the relation of L 3 &gt;L 1 &gt;L 2  are satisfied. 
     Accordingly, if the first surface  10  of the substrate  201  of the coupler  200  is mounted to face the side where the display unit  160  of the wireless tag communication device  100  is provided, the display unit  160  is entirely exposed through the window portion  260 . In contrast, if the second surface  20  of the substrate  201  of the coupler  200  is mounted to face the side where the display unit  160  of the wireless tag communication device  100  is provided, due to position relation between the display unit  160  and the window portion  260  of the coupler  200 , a part of the display unit  160  is not exposed through the window portion  260  (see  FIG. 10B ). Therefore, the erroneous mounting state can be easily recognized. 
     In this illustrative embodiment, as shown in  FIGS. 10A and 10B , the distances from the ends in left and right directions of the window portion  260  of the coupler  200  to the display unit  160  are set to be different from each other. However, the distances from the ends in the upper and lower direction of the window portion  260  of the coupler  200  to the display unit  160  may be set to be different from each other. Also, in the case where the display unit  160  and the window portion  260  are in the shape of a circle or an ellipse, the center position of the window portion  260  is set to be different from the center position of the display unit  160 . In this case, if the coupler  200  is arranged opposite to a specified side of the device main body portion  160 , the entire display unit  160  is exposed through the window portion  260 . 
     Additionally, even in the case where the display unit  160  and the window portion  260  have another different shape, if the coupler  200  is arranged opposite to a specified side of the device main body portion  160 , the entire display unit  160  can be exposed through the window portion  260 . 
     &lt;Three or More Secondary Antennas&gt; 
     In the above-described illustrative embodiment, it is exemplified that two secondary antennas  300  are provided, and the coupler  200  is provided with the first coil antenna  210  and the second coil antenna  220  corresponding to such secondary antennas. However, three or more secondary antennas  300  may be provided, 
     For example, in the case where three secondary antennas  300  are provided, as shown in  FIG. 11 , a coupler  200 C includes a multilayer substrate  201 A. A first coil antenna  210 C is provided on a surface that is closest to the primary antenna  152  of the wireless tag communication device  100 , a second coil antenna  220 C is provided on the middle layer, and a third coil antenna  230 C is provided on a surface that is opposite to the surface where the first coil antenna  210 C is provided. 
     In this case, as described above, the first coil antenna  210 C that is closest to the primary antenna has the largest magnetic field strength, and the third coil antenna  230 C that is farthest from the primary antenna has the smallest magnetic field strength. The relation between the first coil antenna  210 C and the second coil antenna  220 C, the relation between the second coil antenna  220 C and the third coil antenna  230 C, or the relation between the first coil antenna  210 C and the third coil antenna  230 C are equal to the relation between the fast coil antenna and the second coil antenna in this illustrative embodiment. 
     Accordingly, in order to make the induced currents induced to the first coil antenna  210 C, the second coil antenna  220 C, and the third coil antenna  230 C equal to one another, the first coil antenna  210 C, the second coil antenna  220 C, and the third coil antenna  230 C are formed so as to provide the above-described relation between the configuration of the first coil antenna  210  and the configuration of the second coil antenna  220  in the coupler  200  or the above-described relation between the configuration of the first coil antenna  210 A and the cont of the second coil antenna  220 A in the coupler  200 A. 
     In this case, in accordance with the thickness of the substrate and the distances between the respective surfaces, the numbers of windings or the opening areas of the first coil antenna  210 C, the second coil antenna  220 C, and the third coil antenna  230 C are determined. 
     Further, even in the case where more than three secondary antennas are provided, the relation between one coil antenna and another arbitrary coil antenna provided in the coupler is same as that in the above, and one coil antenna and another coil antenna are so formed as to have the configurations of the above-described illustrative embodiments. 
     In the above-described illustrative embodiments, it is sufficient if the first coil antenna  210  and the second coil antenna  220  are substantially provided on the first surface  10  and the second surface  20  to have the configurations of the illustrative embodiments, and for some reasons such as drawing of the connection terminal  260  and so on, a part of the antennas may be provided on a different surface. 
     Further, in the above-described illustrative embodiments, it is exemplified that in order to cause the same amount of current to be induced in the respective antenna coils provided on the first surface and the second surface, the numbers of windings of the coil antennas are changed if the respective coil antennas have the same opening area, while the opening areas of the coil antennas are changed if the respective coil antennas have the same number of windings. However, both the number of windings and the opening area of the coil antennas may be changed so that the multiplication of the number of windings and the opening area of the coil antenna that is provided in a position having a smaller magnetic field strength becomes larger than the multiplication of the number of windings and the opening area of the coil antenna that is provided in a position having a larger magnetic field strength. 
     While the wireless tag communication device  100  has been described as an example of the communication device, the communication device may be any other communication device that performs wireless communication. 
     Additionally, while the present invention has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.