Patent Publication Number: US-8981906-B2

Title: Printed wiring board and wireless communication system

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a printed wiring board and a wireless communication system, and in particular, relates to a printed wiring board and a wireless communication system, preferably for use in an RFID (Radio Frequency Identification) system. 
     2. Description of the Related Art 
     In recent years, as an information management system for articles, there has been put into practical use an RFID system where communication is established between a reader/writer generating an induction magnetic field and an RFID tag attached to an article on the basis of a non-contact method utilizing an electromagnetic field and predetermined information is transmitted. This RFID tag includes a wireless IC chip storing therein the predetermined information and processing a predetermined wireless signal and an antenna (radiator) performing transmission and reception of a high-frequency signal. 
     In some cases, the RFID system is used for information management for printed wiring boards embedded in various kinds of electronic devices. For example, in International Publication No. WO 2009/011144 or International Publication No. WO 2009/011154, an RFID tag is disclosed that utilizes, as an antenna, the ground electrode of a printed wiring board. In this RFID tag, a loop-shaped electrode for matching impedance is provided between a wireless IC chip and a ground electrode. Therefore, it is possible to realize an RFID tag having a simple configuration and a small signal loss. 
     Incidentally, while the RFID tag described in International Publication No. WO 2009/011144 or International Publication No. WO 2009/011154 has a simple configuration, the ground electrode functioning as an antenna becomes a barrier to signal transmission and reception, and the radiation characteristic of a high-frequency signal is not necessarily good. 
     SUMMARY OF THE INVENTION 
     Therefore, preferred embodiments of the present invention provide a printed wiring board and a wireless communication system, each of which has a simple configuration and a good radiation characteristic and is suitable for an RFID system. 
     A printed wiring board according to a first preferred embodiment of the present invention includes a wireless IC element configured to process a high-frequency signal, a circuit substrate in which the wireless IC element is mounted, a loop-shaped electrode configured to be coupled to the wireless IC element, a radiator configured to be coupled to the loop-shaped electrode, and an auxiliary electrode configured to be coupled to the loop-shaped electrode and/or the radiator. 
     A wireless communication system according to a second preferred embodiment of the present invention includes the above-mentioned printed wiring board. 
     In the above-mentioned printed wiring board, the wireless IC element is coupled to the radiator through the loop-shaped electrode, and the radiator functions as an antenna. Furthermore, the wireless IC element is also coupled to the auxiliary electrode through the loop-shaped electrode and/or the radiator, and the auxiliary electrode also functions as an antenna. In this case, the loop-shaped electrode functions as an impedance-matching circuit with respect to the radiator and the auxiliary electrode. More specifically, a high-frequency signal is received in the auxiliary electrode in addition to the radiator, and the wireless IC element operates through the loop-shaped electrode, such that a response signal from the corresponding wireless IC element is radiated from the radiator and the auxiliary electrode to the outside through the loop-shaped electrode. The auxiliary electrode is provided, and hence, the radiation characteristics (a radiation gain and directivity) of a high-frequency signal are greatly improved. 
     According to various preferred embodiments of the present invention, it is possible to provide a printed wiring board including a simple configuration and an antenna with an excellent radiation characteristic, and the corresponding printed wiring substrate may be suitable for use in an RFID system, for example. 
     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 a perspective view illustrating a printed wiring board according to a first preferred embodiment of the present invention. 
         FIG. 2  is a perspective view illustrating a printed wiring board according to a second preferred embodiment of the present invention. 
         FIG. 3  is a perspective view illustrating a printed wiring board according to a third preferred embodiment of the present invention. 
         FIG. 4  is a perspective view illustrating a printed wiring board according to a fourth preferred embodiment of the present invention. 
         FIG. 5  is a perspective view illustrating a state where a printed wiring board is mounted in a mother substrate. 
         FIG. 6  is a schematic configuration diagram of an RFID system utilizing a printed wiring substrate. 
         FIG. 7  is a perspective view illustrating a wireless IC chip as a wireless IC element. 
         FIG. 8  is a perspective view illustrating a state where a wireless IC chip is mounted, as a wireless IC element, on a feeder circuit substrate. 
         FIG. 9  is an equivalent circuit diagram illustrating an example of a feeder circuit. 
         FIG. 10  is a plan view illustrating a laminated structure of the above-mentioned feeder circuit substrate. 
         FIG. 11  is a pattern diagram illustrating a radiation electric field intensity in the first preferred embodiment of the present invention. 
         FIG. 12  is a pattern diagram illustrating a radiation electric field intensity in the second preferred embodiment of the present invention. 
         FIG. 13  is a pattern diagram illustrating a radiation electric field intensity in the third preferred embodiment of the present invention. 
         FIG. 14  is a pattern diagram illustrating a radiation electric field intensity in the fourth preferred embodiment of the present invention. 
         FIG. 15  is a pattern diagram illustrating a radiation electric field intensity in a comparative example. 
         FIG. 16  is a graph illustrating a communication distance in a predetermined frequency band in each of the first to fourth preferred embodiments of the present invention and the comparative example. 
         FIG. 17A  is a perspective view illustrating a first example of a modification of a preferred embodiment of the present invention,  FIG. 17B  is a perspective view illustrating a second example of a modification of a preferred embodiment of the present invention, and  FIG. 17C  is a perspective view illustrating a third example of a modification of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, preferred embodiments of a printed wiring board and a wireless communication system according to the present invention will be described with reference to accompanying drawings. In addition, in each drawing, a same symbol will be assigned to a common component or a common portion, and the redundant description thereof well be omitted. 
     First Preferred Embodiment 
     As illustrated in  FIG. 1 , a printed wiring board  1 A according to a first preferred embodiment of the present invention includes a circuit substrate  11  in which two insulating sheets  11   a  and  11   b  (and a plurality of sheets not illustrated, if necessary or desired) are laminated. On the sheet  11   a , first planar conductors  21   a  and  21   b  and second planar conductors  22   a  and  22   b  are located, and the terminal electrodes of a wireless IC element  50  are electrically connected to ends of the first planar conductors  21   a  and  21   b , which face each other. A radiator  31  having a wide area is located on the sheet  11   b.    
     The other end portions of the first planar conductors  21   a  and  21   b  and two corner portions of the radiator  31  are electrically connected to each other through via hole conductors  32   a  and  32   b . A loop-shaped electrode  20  is defined by the first planar conductors  21   a  and  21   b , the via hole conductors  32   a  and  32   b , and one side of the radiator  31 . The second planar conductors  22   a  and  22   b  extend from the other end portions of the first planar conductors  21   a  and  21   b  preferably in L-shaped or substantially L-shaped configurations along the side surface of the sheet  11   a , end portions thereof face each other through a slit  27 , and the second planar conductors  22   a  and  22   b  function as auxiliary electrodes. 
     The wireless IC element  50  processes a high-frequency signal, and the detail thereof will be described in detail with reference to  FIG. 7  to  FIG. 10 . 
     In the printed wiring board  1 A having the above-mentioned configuration, as the loop-shaped electrode  20 , the first planar conductors  21   a  and  21   b  are coupled to the radiator  31  and the second planar conductors  22   a  and  22   b . Therefore, a high-frequency signal, radiated from a reader/writer in an RFID system and received in the radiator  31  and the second planar conductors  22   a  and  22   b , is supplied to the wireless IC element through the first planar conductors  21   a  and  21   b , and the wireless IC element  50  operates. On the other hand, a response signal from the wireless IC element  50  is transmitted to the radiator  31  and the second planar conductors  22   a  and  22   b  through the first planar conductors  21   a  and  21   b  and radiated to the reader/writer. 
     The loop-shaped electrode  20  functions as a matching circuit for impedance, by causing the wireless IC element  50  and the radiator  31  to be coupled to each other, and functions as a matching circuit for impedance, by causing the wireless IC element  50  and the second planar conductors  22   a  and  22   b  to be coupled to each other. It is possible for the first planar conductors  21   a  and  21   b  to achieve impedance matching, by adjusting the electrical lengths thereof, the electrode widths thereof, or the like. In addition, so as to obtain a maximum radiation characteristic, it is desirable that the total length of the first planar conductor  21   a  plus the second planar conductor  22   a  and the total length of the first planar conductor  21   b  plus the second planar conductor  22   b  preferably are approximately λ/4 with respect to wavelength λ of a communication frequency, for example. 
     In addition, the second planar conductors  22   a  and  22   b  extend along the edge portion of the radiator  31 , and are capacitively coupled to the radiator  31  in a lamination direction. In this way, the second planar electrodes  22   a  and  22   b  functioning as auxiliary electrodes are capacitively coupled to the edge portion of the radiator  31 , in which a high-frequency signal intensively flows owing to an edge effect, and hence, while it is possible to cause the radiator  31  to have directivity in the normal direction of the main surface of the radiator  31 , it is possible to cause the second planar electrodes  22   a  and  22   b  to function as a matching circuit. In particular, when the length of each of the second planar conductors  22   a  and  22   b  is less than or equal to approximately λ/4, for example, a communication distance also becomes long. In addition, such an advantageous effect is true for a second preferred embodiment, a third preferred embodiment, and a fourth preferred embodiment, described later. 
     In the printed wiring substrate  1 A according to the first preferred embodiment, a radiation electric field intensity schematically illustrated in  FIG. 11  is obtained. In addition, a communication distance in a 750 MHz to 1050 MHz band is as illustrated in  FIG. 16  plotted with black quadrangles. 
     Incidentally, as a comparative example,  FIG. 15  illustrates the radiation electric field intensity of a printed wiring board where only the second planar conductors  22   a  and  22   b  are omitted, and a communication distance in the same frequency band is illustrated in  FIG. 16  plotted with black rhombuses. In the present first preferred embodiment, compared with the comparative example, a radiation gain is enhanced and a directional characteristic is improved. 
     Second Preferred Embodiment 
     As illustrated in  FIG. 2 , a printed wiring board  1 B according to a second preferred embodiment includes a circuit substrate  11  in which two insulating sheets  11   a  and  11   b  (and a plurality of sheets not illustrated, if necessary) are laminated. On the sheet  11   a , first planar conductors  21   a  and  21   b  are located, and the terminal electrodes of the wireless IC element are electrically connected to ends of the first planar conductors  21   a  and  21   b , which face each other. On the sheet  11   b , a radiator  31  having a wide area and third planar conductors  23   a  and  23   b  are located. 
     The other end portions of the first planar conductors  21   a  and  21   b  and two corner portions of the radiator  31  are electrically connected to each other through via hole conductors  32   a  and  32   b . A loop-shaped electrode  20  is defined by the first planar conductors  21   a  and  21   b , the via hole conductors  32   a  and  32   b , and one side of the radiator  31 . The third planar conductors  23   a  and  23   b  extend from both end portions of the radiator  31  in L-shaped or substantially L-shaped configurations along the side surface of the sheet  11   b , end portions thereof face each other through a slit  27 , and the third planar conductors  23   a  and  23   b  function as auxiliary electrodes. 
     In the printed wiring board  1 B having the above-mentioned configuration, as the loop-shaped electrode  20 , the first planar conductors  21   a  and  21   b  are coupled to the radiator and the third planar conductors  23   a  and  23   b . Therefore, a high-frequency signal, radiated from a reader/writer in an RFID system and received in the radiator and the third planar conductors  23   a  and  23   b , is supplied to the wireless IC element through the first planar conductors  21   a  and  21   b , and the wireless IC element  50  operates. On the other hand, a response signal from the wireless IC element  50  is transmitted to the radiator  31  and the third planar conductors  23   a  and  23   b  through the first planar conductors  21   a  and  21   b  and radiated to the reader/writer. 
     The loop-shaped electrode  20  functions as a matching circuit for impedance, by causing the wireless IC element  50  and the radiator  31  to be coupled to each other, and functions as a matching circuit for impedance, by causing the wireless IC element  50  and the third planar conductors  23   a  and  23   b  to be coupled to each other. It is possible for the first planar conductors  21   a  and  21   b  to achieve impedance matching, by adjusting the electrical lengths thereof, the electrode widths thereof, or the like. In addition, so as to obtain a maximum radiation characteristic, it is desirable that the total length of the first planar conductor  21   a , the via hole conductor  32   a , and the third planar conductor  23   a  and the total length of the first planar conductor  21   b , the via hole conductor  32   b , and the third planar conductor  23   b  preferably are approximately λ/4, for example, with respect to the wavelength λ of the communication frequency. 
     In the printed wiring substrate  1 B according to the second preferred embodiment, a radiation electric field intensity schematically illustrated in  FIG. 12  is obtained. In addition, a communication distance in a 750 MHz to 1050 MHz band is as illustrated in  FIG. 16  plotted with black triangles. In the present second preferred embodiment, compared with the above-mentioned comparative example, a radiation gain is enhanced. 
     Third Preferred Embodiment 
     As illustrated in  FIG. 3 , a printed wiring board  1 C according to a third preferred embodiment includes a circuit substrate  11  in which two insulating sheets  11   a  and  11   b  (and a plurality of sheets not illustrated, if necessary) are laminated. On the sheet  11   a , first planar conductors  21   a  and  21   b  and fourth planar conductors  24   a  and  24   b  are located, and the terminal electrodes of the wireless IC element  50  are electrically connected to ends of the first planar conductors  21   a  and  21   b , which face each other. On the sheet  11   b , a radiator  31  having a wide area and fifth planar conductors  25   a  and  25   b  are located. 
     The other end portions of the first planar conductors  21   a  and  21   b  and two corner portions of the radiator  31  are electrically connected to each other through via hole conductors  32   a  and  32   b . A loop-shaped electrode  20  is configured using the first planar conductors  21   a  and  21   b , the via hole conductors  32   a  and  32   b , and one side of the radiator  31 . The fourth planar conductors  24   a  and  24   b  extend from the other end portions of the first planar conductors  21   a  and  21   b  in L-shaped or substantially L-shaped configurations along the side surface of the sheet  11   a , end portions thereof face each other through a slit  27 , and the fourth planar conductors  24   a  and  24   b  function as auxiliary electrodes. The fifth planar conductors  25   a  and  25   b  extend from both end portions of the radiator  31  in L-shaped or substantially L-shaped configurations along the side surface of the sheet  11   b , and end portions thereof face each other through a slit  28 . In addition to this, the fifth planar conductors  25   a  and  25   b  are electrically connected to the fourth planar conductors  24   a  and  24   b  through via hole conductors  33   a  and  33   b  and function as auxiliary electrodes. 
     In the printed wiring board  1 C having the above-mentioned configuration, as the loop-shaped electrode  20 , the first planar conductors  21   a  and  21   b  are coupled to the radiator  31 , the fourth planar conductors  24   a  and  24   b , and the fifth planar conductors  25   a  and  25   b . Therefore, a high-frequency signal, radiated from a reader/writer in an RFID system and received in the radiator  31 , the fourth planar conductors  24   a  and  24   b , and the fifth planar conductors  25   a  and  25   b , is supplied to the wireless IC element  50  through the first planar conductors  21   a  and  21   b , and the wireless IC element  50  operates. On the other hand, a response signal from the wireless IC element  50  is transmitted to the radiator  31 , the fourth planar conductors  24   a  and  24   b , and the fifth planar conductors  25   a  and  25   b  through the first planar conductors  21   a  and  21   b  and radiated to the reader/writer. 
     The loop-shaped electrode  20  functions as a matching circuit for impedance, by causing the wireless IC element  50  and the radiator  31  to be coupled to each other, and functions as a matching circuit for impedance, by causing the wireless IC element  50 , the fourth planar conductors  24   a  and  24   b , and the fifth planar conductors  25   a  and  25   b  to be coupled to one another. It is possible for the first planar conductors  21   a  and  21   b  to achieve impedance matching, by adjusting the electrical lengths thereof, the electrode widths thereof, or the like. In addition, so as to obtain a maximum radiation characteristic, it is desirable that the total length of the first planar conductor  21   a , the fourth planar conductor  24   a , the via hole conductor  33   a , and the fifth planar conductor  25   a  and the total length of the first planar conductor  21   b , the fourth planar conductor  24   b , the via hole conductor  33   b , and the fifth planar conductor  25   b  preferably are approximately λ/4 with respect to the wavelength λ of the communication frequency, for example. 
     In the printed wiring substrate  1 C according to the third preferred embodiment, a radiation electric field intensity schematically illustrated in  FIG. 13  is obtained. In addition, a communication distance in a 750 MHz to 1050 MHz band is as illustrated in  FIG. 16  plotted with black circles. In the present third preferred embodiment, compared with the above-mentioned comparative example, a radiation gain is enhanced and a directional characteristic is improved. 
     Fourth Preferred Embodiment 
     As illustrated in  FIG. 4 , a printed wiring board  1 D according to a fourth preferred embodiment includes a circuit substrate  11  in which two insulating sheets  11   a  and  11   b  (and a plurality of sheets not illustrated, if necessary) are laminated. On the sheet  11   a , first planar conductors  21   a  and  21   b  and a sixth planar conductor  26  are located, and the terminal electrodes of the wireless IC element  50  are electrically connected to ends of the first planar conductors  21   a  and  21   b , which face each other. On the sheet  11   b , a radiator  31  having a wide area is located. 
     The other end portions of the first planar conductors  21   a  and  21   b  and two corner portions of the radiator  31  are electrically connected to each other through via hole conductors  32   a  and  32   b . A loop-shaped electrode  20  is defined by the first planar conductors  21   a  and  21   b , the via hole conductors  32   a  and  32   b , and one side of the radiator  31 . The sixth planar conductor extends from the other end portions of the first planar conductors  21   a  and  21   b  along the side surface of the sheet  11   a , is defined as one electrode having an L-shaped or substantially L-shaped configuration, and functions as an auxiliary electrode. 
     In the printed wiring board  1 D having the above-mentioned configuration, as the loop-shaped electrode  20 , the first planar conductors  21   a  and  21   b  are coupled to the radiator and the sixth planar conductor  26 . Therefore, a high-frequency signal, radiated from a reader/writer in an RFID system and received in the radiator  31  and the sixth planar conductor  26 , is supplied to the wireless IC element  50  through the first planar conductors  21   a  and  21   b , and the wireless IC element  50  operates. On the other hand, a response signal from the wireless IC element  50  is transmitted to the radiator  31  and the sixth planar conductor  26  through the first planar conductors  21   a  and  21   b  and radiated to the reader/writer. 
     The loop-shaped electrode  20  functions as a matching circuit for impedance, by causing the wireless IC element  50  and the radiator  31  to be coupled to each other, and functions as a matching circuit for impedance, by causing the wireless IC element  50  and the sixth planar conductor  26  to be coupled to each other. It is possible for the first planar conductors  21   a  and  21   b  to achieve impedance matching, by adjusting the electrical lengths thereof, the electrode widths thereof, or the like. 
     In the printed wiring substrate  1 D according to the fourth preferred embodiment, a radiation electric field intensity schematically illustrated in  FIG. 14  is obtained. In addition, a communication distance in a 750 MHz to 1050 MHz band is as illustrated in  FIG. 16  plotted with *. In the present fourth preferred embodiment, compared with the above-mentioned comparative example, a directional characteristic is improved. 
     Next, a wireless communication system (RFID system) utilizing the above-mentioned printed wiring board  1 A will be described. In addition, it is clear that it is possible to use the printed wiring boards  1 B to  1 D. 
     As illustrated in  FIG. 5 , in the printed wiring board  1 A, an IC circuit component  41  is mounted in the inner region of the second planar conductors  22   a  and  22   b , and the printed wiring board  1 A is mounted on a mother substrate  45 . The mother substrate  45  is preferably built into an electronic device such as a computer, and a number of an IC circuit component  46 , a chip type electronic component  47 , and the like are mounted in the mother substrate  45 . 
     The printed wiring board  1 A capable of establishing communication with a reader/writer is preferably mounted in the mother substrate  45 , and hence, it is possible to manage the mother substrate  45  on the basis of various types of information stored in the wireless IC element  50 , at the manufacturing stage of the mother substrate  45  or in the storage management thereof. As illustrated in  FIG. 6 , when the mother substrates  45  equipped with the printed wiring boards  1 A are placed on a conveyor  40  and sequentially carried on a production line, the mother substrate  45  passes below an antenna  49  connected to a processing circuit  48  in the reader/writer or the antenna  49  is put close to the intended mother substrate  45 , thereby allowing the processing circuit  48  to acquire necessary information. 
     As illustrated in  FIG. 7 , the wireless IC element  50  may also be a wireless IC chip  51  processing a high-frequency signal, and alternatively, as illustrated in  FIG. 8 , the wireless IC element  50  may also include the wireless IC chip  51  and a feeder circuit substrate  65  including a resonant circuit having a predetermined resonance frequency. 
     The wireless IC chip  51  illustrated in  FIG. 7  includes a clock circuit, a logic circuit, a memory circuit, and the like, and stores therein necessary information. In the back surface of the wireless IC chip  51 , input-output terminal electrodes  52  and  52  and mounting terminal electrodes  53  and  53  are provided. The input-output terminal electrodes  52  and  52  are electrically connected to the above-mentioned first planar conductors  21   a  and  21   b  through metal bumps or other suitable members. In addition, Au, solder, or the like may be used as the material of the metal bump. 
     When, as illustrated in  FIG. 8 , the wireless IC element  50  is configured using the wireless IC chip  51  and the feeder circuit substrate  65 , it is possible to provide various types of feeder circuits (including a resonant circuit/matching circuit) in the feeder circuit substrate  65 . For example, as illustrated as an equivalent circuit in  FIG. 9 , the feeder circuit may be a feeder circuit  66  including inductance elements L 1  and L 2 , which have inductance values different from each other and are magnetically coupled to each other (indicated by mutual inductance M) with an opposite phase. The feeder circuit has a predetermined resonance frequency, and achieves impedance matching between the impedance of the wireless IC chip  51  and a radiator or the like. In addition, the wireless IC chip and the feeder circuit  66  may be electrically connected to each other (e.g., through a DC connection) or coupled to each other through an electromagnetic field. 
     The feeder circuit  66  transmits a high-frequency signal, which is sent out from the wireless IC chip  51  and has a predetermined frequency, to a radiator or the like through the above-mentioned loop-shaped electrode, and supplies a high-frequency signal received in the radiator or the like to the wireless IC chip  51  through the loop-shaped electrode. Since the feeder circuit  66  has the predetermined resonance frequency, it is easy to achieve impedance matching with the radiator or the like and it is possible to shorten the electrical length of the loop-shaped electrode. 
     Next, the configuration of the feeder circuit substrate  65  will be described. As illustrated in  FIG. 7  and  FIG. 8 , the input-output terminal electrodes  52  of the wireless IC chip  51  are connected to feeding terminal electrodes  142   a  and  142   b  located on the feeder circuit substrate  65  and the mounting terminal electrodes  53  thereof are connected to mounting terminal electrodes  143   a  and  143   b , through metal bumps or the like. 
     As illustrated in  FIG. 10 , the feeder circuit substrate  65  is obtained by lamination, pressure-bonding, and firing ceramic sheets  141   a  to  141   h  including dielectric or magnetic bodies. In this regard, however, insulation layers configuring the feeder circuit substrate  65  are not limited to the ceramic sheets, and, for example, may also be thermosetting resin such as liquid crystal polymer or resin sheets such as thermoplastic resins. On the sheet  141   a  at an uppermost layer, the feeding terminal electrodes  142   a  and  142   b , the mounting terminal electrodes  143   a  and  143   b , and via hole conductors  144   a ,  144   b ,  145   a , and  145   b  are located. On each of the sheets  141   b  to  141   h  in the second layer to the eighth layer, wiring electrodes  146   a  and  146   b  are arranged to configure the inductance elements L 1  and L 2  and via hole conductors  147   a ,  147   b ,  148   a , and  148   b  are formed, if necessary or desired. 
     By laminating the above-mentioned sheets  141   a  to  141   h , the inductance element L 1  is provided such that the wiring electrode  146   a  is connected in a spiral shape owing to the via hole conductor  147   a , and the inductance element L 2  is provided such that the wiring electrode  146   b  is connected in a spiral shape owing to the via hole conductor  147   b . In addition, capacitance is generated between the lines of the wiring electrodes  146   a  and  146   b.    
     An end portion  146   a - 1  of the wiring electrode  146   a  on the sheet  141   b  is connected to the feeding terminal electrode  142   a  through the via hole conductor  145   a , and an end portion  146   a - 2  of the wiring electrode  146   a  on the sheet  141   h  is connected to the feeding terminal electrode  142   b  through the via hole conductors  148   a  and  145   b . An end portion  146   b - 1  of the wiring electrode  146   b  on the sheet  141   b  is connected to the feeding terminal electrode  142   b  through the via hole conductor  144   b , and an end portion  146   b - 2  of the wiring electrode  146   b  on the sheet  141   h  is connected to the feeding terminal electrode  142   a  through the via hole conductors  148   b  and  144   a.    
     In the above-mentioned feeder circuit  66 , since the inductance elements L 1  and L 2  are wound in directions opposite to each other, magnetic fields generated in the inductance elements L 1  and L 2  cancel each other out. Since the magnetic fields cancel each other out, it is necessary to lengthen the wiring electrodes  146   a  and  146   b  to some extent, so as to obtain a desired inductance value. Since this results in lowering a Q value, the steepness of a resonance characteristic disappears. Therefore, a wider bandwidth is obtained in the vicinity of a resonance frequency. 
     When the perspective plane of the feeder circuit substrate  65  is seen, the inductance elements L 1  and L 2  are provided at left and right different positions. In addition, the directions of the magnetic fields generated in the inductance elements L 1  and L 2  are opposite to each other. Therefore, when the feeder circuit  66  is coupled to the loop-shaped electrode  20 , a reversed current is excited in the loop-shaped electrode  20 , and it is possible to cause a current to be generated in the radiator  31  and the second planar conductors  22   a  and  22   b . Accordingly, due to a potential difference due to the current, it is possible to cause the radiator  31  and the second planar conductors  22   a  and  22   b  to operate as an antenna. 
     By incorporating a resonance/matching circuit in the feeder circuit substrate  65 , it is possible to significantly reduce and prevent a characteristic fluctuation due to an external article, and it is possible to prevent a communication quality from being deteriorated. In addition, if the wireless IC chip  51  configuring the wireless IC element  50  is disposed so as to face toward a center side in the thickness direction of the feeder circuit substrate  65 , it is possible to prevent the wireless IC chip  51  from being destroyed and it is possible to enhance a mechanical strength as the wireless IC element  50 . 
     Additional Preferred Embodiments 
     In addition, a printed wiring board and a wireless communication system according to the present invention are not limited to the above-mentioned preferred embodiments, and it should be understood that various modifications may occur insofar as they are within the scope thereof. 
       FIG. 17A  illustrates a first example of a modification of a preferred embodiment of the present invention. In this first example of a modification of a preferred embodiment of the present invention, the second planar conductors  22   a  and  22   b  are provided on an intermediate layer located between the first planar conductors  21   a  and  21   b  and the radiator  31 , and ends of the second planar conductors  22   a  and  22   b  are connected to the via hole conductors  32   a  and  32   b.    
       FIG. 17B  illustrates a second example of a modification of a preferred embodiment of the present invention. In this second example of a modification of a preferred embodiment of the present invention, the fifth planar conductors  25   a  and  25   b  are provided on an intermediate layer located between the first planar conductors  21   a  and  21   b  and the radiator  31 , and the other ends of the fourth planar conductors  24   a  and  24   b  connected to the first planar conductors  21   a  and  21   b  are connected to the other ends of the fifth planar conductors  25   a  and  25   b  through the via hole conductors  33   a  and  33   b.    
       FIG. 17C  illustrates a third example of a modification of a preferred embodiment of the present invention. In this third example of a modification of a preferred embodiment of the present invention, the fourth planar conductors  24   a  and  24   b  are provided on the same layer as the radiator  31 , ends thereof are connected to the radiator  31  and the via hole conductors  32   a  and  32   b , the fifth planar conductors  25   a  and  25   b  are provided on an intermediate layer located between the first planar conductors  21   a  and  21   b  and the radiator  31 , and the other ends of the fourth planar conductors  24   a  and  24   b  are connected to the other ends of the fifth planar conductors  25   a  and  25   b  through the via hole conductors  33   a  and  33   b.    
     As described above, preferred embodiments of the present invention are useful for a printed wiring board and a wireless communication system, for example, and in particular, preferred embodiments of the present invention have a simple configuration and are superior in terms of an excellent radiation characteristic. 
     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.