JP2010004257A - Loop antenna, and radio transmitting/receiving device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a loop antenna and a radio transmitting/receiving device, capable of coping with two stacked IC cards. <P>SOLUTION: An antenna portion 1 has a receiving loop antenna 10, a transmitting loop antenna 11, and self-resonant loop antennas 12 and 13, which are arranged on a same plane substrate. For the receiving loop antenna, a capacitor C1 is connected to a coil with wire turns n of 1 which is arranged on an outermost periphery within a substrate of 105 mm×70 mm to form a resonance circuit. For the transmitting loop antenna, a capacitor C2 is connected to a coil with wire turns n of 2 which is arranged inside of the receiving loop antenna 10 to form and connect the resonance circuit to a drive circuit for outputting a carrier magnetic field of 13.56 MHz. For each of two self-resonant loop antennas arranged in parallel with each other inside of the receiving loop antenna and the transmitting loop antenna, a capacitor is connected to loop coils arranged outside and inside of each of the loop antennas arranged in parallel to form the resonance circuits respectively which resonate at about 20 MHz. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a loop antenna and a wireless transmission / reception apparatus that perform non-contact transmission / reception with a non-contact type IC card used as a commuter pass in an automatic ticket gate system or the like.

  2. Description of the Related Art In recent years, a wireless transmission / reception device that performs transmission / reception with a non-contact type IC card (hereinafter referred to as an IC card) used as a commuter pass for an automatic ticket gate device or a clerk processing device in a station service device, and determines whether or not traffic is allowed. In many cases, a non-contact type IC card reader / writer (hereinafter referred to as an R / W device) is provided.

  This R / W device communicates with the IC card in a non-contact manner by generating a magnetic field from a loop antenna disposed inside the device (see, for example, Patent Document 1).

  This loop antenna is configured by arranging a transmission loop antenna and a reception loop antenna on the same plane. Since this type of loop antenna is mounted on and used in an automatic ticket gate device, what is an IC card in which a passing customer is held over the reading / writing unit (the antenna unit of the R / W device) of the automatic ticket gate device? Although stable communication is possible, it is desirable not to communicate with an IC card carried by other users.

For this purpose, it is desirable to extend the communication distance between the IC card and the R / W device and to expand the communicable area. The reason for this is that in recent years, IC card issuers have increased, and IC cards with different characteristics are on the market. In order to support these IC cards, communication distance is increased (communication area is increased) and communication is performed. The problem is to reduce the impossible area and improve the communication characteristics. In particular, there is a problem that the communication performance is lowered when two cards are used in an overlapping manner.
Japanese Patent No. 3579899 (page 10-11, FIG. 6)

  As described above, in recent years, an increasing number of systems use two IC cards. When two IC cards are used in an overlapping manner, the amplitude of the return signal from the IC card received by the R / W device becomes extremely small compared to the case where only one IC card is received, and the received signal cannot be demodulated normally. In this case, there is a problem that communication failure occurs.

  The present invention has been made to solve the above problems, and even when two IC cards are used in an overlapping manner, the amplitude of a return signal from the IC card received by the R / W device can be sufficiently secured, It is an object of the present invention to provide a loop antenna and a wireless transmission / reception device including the loop antenna that can reduce the occurrence of communication failure.

  In order to achieve the above object, a wireless transmission / reception apparatus according to claim 1 of the present invention is a wireless transmission / reception apparatus that performs non-contact communication with an IC card by generating a magnetic field, and is larger than the size of the IC card. A receiving loop antenna disposed on the outermost periphery of a planar substrate smaller than twice the size, a transmitting loop antenna disposed inside the receiving loop antenna, and a juxtaposed arrangement inside the transmitting antenna The two self-resonant loop antenna units are connected to the transmission loop antenna, and a carrier frequency voltage is supplied to the transmission loop antenna, thereby radiating a carrier frequency magnetic field from the transmission loop antenna. A drive circuit; and a processing circuit for processing a signal received by the reception loop antenna, the transmission loop antenna A coil having a first number of turns and a capacitor connected between the start and end of winding of the coil and forming a first resonance circuit, wherein the receiving loop antenna has a second A coil having a number of turns and a capacitor that is connected between the start and end of winding of the coil to form a second resonance circuit, and the self-resonant loop antenna unit is disposed outside. A first self-resonant loop antenna having an endless loop formed by a coil having a number of turns of 3 and a capacitor connected between the start and end of winding of the coil and forming a third resonance circuit; A coil having a fourth number of turns disposed inside the first self-resonant loop antenna and a capacitor connected between the start and end of winding of the coil to form a fourth resonance circuit And a second self-resonant loop antenna in which an endless loop is formed. The resonance frequency of the first self-resonant loop antenna and the second self-resonant loop antenna is set to the resonance frequency of the transmission loop antenna. It is characterized by being set to a frequency several MHz higher.

  A loop antenna according to claim 3 of the present invention is a loop antenna of a wireless transmission / reception apparatus that performs non-contact communication with an IC card by generating a magnetic field, and is a plane smaller than twice the size of the IC card. Receiving loop antenna arranged on the outermost periphery of the substrate, a transmitting loop antenna arranged inside the receiving loop antenna, and two self-resonant loop antennas arranged side by side inside the transmitting antenna The transmission loop antenna includes a coil having a first number of turns, and a capacitor connected between a winding start and a winding end of the coil to form a first resonance circuit, The reception loop antenna includes a coil having a second number of turns, and a capacitor connected between the winding start and the winding end of the coil and forming a second resonance circuit. And the self-resonant loop antenna unit is connected between a coil having a third number of turns arranged outside and a winding start and end of the coil, and forms a third resonance circuit. A first self-resonant loop antenna that forms an endless loop, a coil having a second number of turns arranged inside the first self-resonant loop antenna, and the start and end of winding of the coil And a second self-resonant loop antenna having an endless loop formed by a capacitor that forms a fourth resonant circuit and is connected between the first self-resonant loop antenna and the second self-resonant loop antenna. The resonant frequency of the self-resonant loop antenna is set to a frequency several MHz higher than the resonant frequency of the transmitting loop antenna.

  According to the present invention, even when two IC cards are used in an overlapping manner, the amplitude of the return signal from the IC card received by the R / W device can be sufficiently secured, and the occurrence of communication failure can be reduced. An object of the present invention is to provide a loop antenna and a wireless transmission / reception device.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a wireless transmission / reception apparatus 100 including a loop antenna according to a first embodiment of the present invention. The wireless transmission / reception apparatus 100 includes an antenna unit 1, a transmission unit 2, and a reception unit 3 that constitute a loop antenna.

  FIG. 2 is an explanatory diagram expressing the configuration of the antenna unit 1 in an easily understandable manner. Hereinafter, description will be given with reference to this figure.

  The antenna unit 1 includes a reception loop antenna 10 (loop antenna 10), a transmission loop antenna 11 (loop antenna 11), and a self-resonance loop antenna unit.

  The self-collaborative loop antenna unit has a self-resonant loop antenna 12 (first self-resonant loop antenna) and a self-resonant loop antenna 13 (second self-resonant loop antenna) on the same plane substrate. Arranged and configured. In this embodiment, this is realized by a printed circuit board.

  Note that the size of the printed wiring board is preferably approximately the same as the size of the printed circuit board in order to communicate with the IC card using a magnetic field. The reason is that if the outer circumference of the receiving loop antenna is smaller than the IC card, the change will be larger with respect to the distance from the receiving loop antenna, and the communication stability will be improved when many unspecified customers carry it. May get worse. On the other hand, when it is too large, it becomes difficult to perform uniform reception within the reception loop. For the above reasons, in this embodiment, the size of the printed circuit board wiring is set to be a flat base substrate that is larger than the size of the IC card and smaller than twice that.

The loop antenna 10 is arranged in a 104 mm × 67 mm square on the outermost periphery of the antenna unit 1, and the number of turns n of the coil is set to n = 1 (first number of turns). Between the winding end of the winding start and a coil of a coil constituting the antenna, is arranged a capacitor C _2, the resonance circuit (first resonance circuit) is formed for the received signal.

The loop antenna 11 is arranged inside the antenna 10, and the number of turns n of the coil is set to n = 2 (second number of turns). Between the winding end of the winding start and a coil of a coil constituting the antenna, is connected to the capacitor C _1, the resonance circuit (second resonance circuit) is formed on the transmission signal. The loop antenna 11 configured as described above is connected to the drive circuit 2 and generates a 13.56 MHz carrier output from a carrier generator (not shown) as a magnetic field.

  The loop antennas 12 and 13 are arranged side by side inside the loop antenna 10 and the loop antenna 11. The loop antenna 12 includes a loop antenna 12a arranged on the outside and 12b arranged on the inside. Similarly, the loop antenna 13 includes a loop antenna 13a arranged on the outer side and 13b arranged on the inner side.

The loop antennas 12a and 13a arranged on the outer side are similarly configured, and the number of turns of the coil constituting the loop antenna is set to n = 3 (the third number of turns), and the former includes the winding start of the coil and the winding end of the coil. is the capacitor C ₃ is connected between the third resonant circuit is formed, the latter a fourth resonance circuit is formed by connecting a capacitor C _5. Both of these resonate at about 20 MHz, which is several MHz higher than the resonance frequency of the loop antenna 11 (frequency set in the vicinity of 13.56 MHz).

The loop antennas 12b and 13b arranged on the inner side are configured in the same manner, and the number of turns of the coil constituting the loop antenna is set to n = 4 (fourth number of turns), and the former includes the winding start of the coil and the winding end of the coil. fifth resonant circuit capacitor C ₄ is connected is formed between the latter sixth resonant circuit is formed by connecting the capacitor C ₆ is. Both of these resonate at about 20 MHz, which is several MHz higher than the resonance frequency (13.56 MHz) of the loop antenna 11.

  FIG. 3 is a schematic equivalent circuit at the time of reception of the antenna unit 1 shown in FIG. The magnetic field (number of flux linkages) received by the loop antenna 10 is also received by the loop antenna 11 and the antennas 12 and 13 formed on the same plane.

As a result, assuming that the inductance L ₁ of the coil of the loop antenna 10, the capacitor C ₁ , the current I ₁ , and the induced electromotive force is U 1, the equivalent circuit can be roughly expressed by the following equation (1). Since there is no power source other than the induced electromotive force in the receiving circuit, U1 = 0 expressed by the following equation (2). When the impedance of the receiving unit is Z, the voltage extracted to Z can be expressed by the following equation (3). Here, mutual inductances M ₁₂ , M ₁₃ , M ₁₄ , M ₁₅ , and M ₁₆ are mutual inductances with the coils L ₂ , L ₃ , L ₄ , and L ₅ for the coil L ₁ of the loop antenna 10, respectively.

Here, with respect to the electromotive force L ₁ (dI ₁ / dt) induced by the loop antenna 10, the loop antennas 12 and 13 each constitute a resonance circuit composed of a closed circuit. Further, due to the characteristics of the coil in the magnetic field, an electromotive force is generated in the direction that cancels the magnetic field at that time (back electromotive force). Therefore, the presence of the antennas 12 and 13 apparently weakens the strength of the magnetic field.

  The antennas 12 and 13 constitute a series resonance circuit as described above. Accordingly, the impedance of the circuit at the time of resonance is reduced and the current value is increased, so that there is an effect of weakening the magnetic field at the resonance frequency.

  In this embodiment, the resonance frequency is set to about 20 MHz, and it is confirmed that the resonance frequency is good with respect to the reference carrier wave 13.56 MHz.

  Next, the effect of having a plurality of self-resonant loop antennas will be described. For example, when there is only one receiving antenna, it is known that when the IC card 4 is brought close to the antenna unit 1, the strength of the magnetic field changes in inverse proportion to the square of the distance between the IC card and the loop antenna 10. Yes. Here, when wirelessly communicating with the IC card 4, the strength of the magnetic field varies greatly depending on the distance. Therefore, in order to perform stable communication, the distance between the set communication range and communication distance is Accordingly, it is desirable that the magnetic field does not change rapidly.

  For this purpose, it is desired to increase the sensitivity of the reception loop antenna 10 with respect to the IC card 4 and to perform stable reception while expanding the range in which the loop antenna 10 can communicate. In the present embodiment, for this purpose, the inside of the loop antenna 10 is divided into two parts, and a plurality of resonance points are arranged with respect to the spatial magnetic field (four in the embodiment) so as to reduce the fluctuation of the magnetic field strength over a wide range. I made it.

Moreover, by a plurality of self-resonance antenna 12, it is possible to reduce the value of the inductance _{L 3, L 4, L 5} , L 6 of each loop antenna, a capacitor _{C 3, C} 4, C _This has the effect of making the values of ₅ and C ₆ easy to select in practice.

  FIG. 4 is a schematic equivalent circuit at the time of transmission of the antenna unit 1 shown in FIG. The magnetic field generated by the loop antenna 11 has a magnetic flux linkage number that is partially common to the loop antenna 10 and the loop antennas 12 and 13.

As a result, the inductance L ₂ of the coil of the loop antenna 11, the capacitor C ₂ , the current I ₂ , and the mutual inductance between the coils are M ₂₁ , M ₂₃ , M ₂₄ , M ₂₅ , M _26, and the power supplied from the driver When U = E, it can be expressed by the following equation (4).

  Since the operation in this case is generally known in electromagnetism, the detailed description is omitted, but only the essence will be described as follows.

  The loop antenna 10 and the loop antennas 12 and 13 each constitute a resonance circuit composed of a closed circuit. As described above, these loop antennas are generated in the direction to cancel the magnetic flux by the antenna 11 (counterelectromotive force). However, when the driver's supply capability is sufficient, current is supplied to supplement this magnetic flux. The As a result, the effect of the back electromotive force by the loop antenna 10 and the antennas 12 and 13 need not be considered. That is, the effect when there are a plurality of self-resonant loop antennas is obtained at the time of reception, but does not affect the system of the transmission circuit at the time of transmission.

  FIG. 5 is a substantial wiring diagram of the printed wiring board according to the antenna unit 1 described above. In this embodiment, the printed wiring board size (67 mm × 104 mm) is set to the IC card size (54 mm × 85 mm) and within twice the size of the IC card size, and functions required by a smaller printed wiring board than before. Has achieved.

  As described above, by dividing the self-resonant loop antenna of the present invention, a stable received signal can be secured even when the strength of the magnetic field changes suddenly depending on the reception distance. As a result, even when two IC cards are used in an overlapping manner, a loop antenna capable of sufficiently ensuring the amplitude of a return signal from the IC card received by the R / W device and reducing the occurrence of communication failure, and A wireless transmission / reception apparatus including a loop antenna can be provided.

1 is a wireless transmission / reception apparatus including a loop antenna according to a first embodiment of the present invention. Explanatory drawing explaining the structure of the antenna part shown in FIG. 1 clearly. The schematic equivalent circuit at the time of reception of the antenna part shown in FIG. The schematic equivalent circuit at the time of transmission of the antenna part shown in FIG. FIG. 2 is a substantial wiring diagram of a printed wiring board of the antenna unit shown in FIG. 1.

Explanation of symbols

L1 to L6 Inductances C1 to C6 Capacitances Z1 and Z2 Impedance 1 Antenna unit 10 Reception loop antenna 11 Transmission loop antenna 12 to 15 Self-resonant loop antenna 2 Transmission unit 21 Drive circuit 3 Reception unit 100 Wireless transmission / reception apparatus

Claims (4)

A wireless transmission / reception device that performs non-contact communication with an IC card by generating a magnetic field,
A receiving loop antenna disposed on the outermost periphery of the planar substrate that is larger than the size of the IC card and smaller than twice the size;
A transmission loop antenna disposed inside the reception loop antenna;
Two self-resonant loop antenna portions arranged in parallel inside the transmitting antenna;
A drive circuit connected to the transmission loop antenna and radiating a carrier frequency magnetic field from the transmission loop antenna by supplying a carrier frequency voltage to the transmission loop antenna;
A processing circuit for processing a signal received by the reception loop antenna;
With
The transmission loop antenna is
A coil having a first number of turns and a capacitor connected between the beginning and end of winding of the coil to form a first resonant circuit;
The reception loop antenna is
A coil having a second number of turns and a capacitor connected between the start and end of winding of the coil to form a second resonant circuit;
The self-resonant loop antenna unit is
A first self-resonant that forms an endless loop by a coil having a third number of turns arranged outside and a capacitor that is connected between the start and end of winding of the coil and forms a third resonance circuit Loop antenna for
A coil having a fourth number of turns disposed inside the first self-resonant loop antenna and a capacitor connected between the winding start and the winding end of the coil and forming a fourth resonance circuit; A second self-resonant loop antenna forming an endless loop;
A radio transmitting / receiving apparatus comprising: a resonance frequency of the first self-resonance loop antenna and the second self-resonance loop antenna set to a frequency several MHz higher than a resonance frequency of the transmission loop antenna . The resonance frequency of the first resonance circuit of the transmission loop antenna is set in the vicinity of the transmission carrier frequency of 13.56 MHz,
2. The radio according to claim 1, wherein a resonance frequency of the third resonance circuit related to the first self-resonance loop antenna and the fourth resonance circuit related to the second self-resonance loop antenna is 20 MHz. Transmitter / receiver. A loop antenna of a wireless transmission / reception device that performs non-contact communication with an IC card by generating a magnetic field,
A receiving loop antenna disposed on the outermost periphery of the planar substrate smaller than twice the size of the IC card;
A transmission loop antenna disposed inside the reception loop antenna;
Two self-resonant loop antenna portions arranged in parallel inside the transmitting antenna;
The transmission loop antenna is
A coil having a first number of turns and a capacitor connected between the beginning and end of winding of the coil to form a first resonant circuit;
The reception loop antenna is
A coil having a second number of turns and a capacitor connected between the start and end of winding of the coil to form a second resonant circuit;
The self-resonant loop antenna unit is
A first self-resonant that forms an endless loop by a coil having a third number of turns arranged outside and a capacitor that is connected between the start and end of winding of the coil and forms a third resonance circuit Loop antenna for
A coil having a second number of turns disposed inside the first self-resonant loop antenna and a capacitor connected between the start and end of winding of the coil to form a fourth resonance circuit; A second self-resonant loop antenna forming an endless loop;
And a resonance frequency of the first self-resonance loop antenna and the second self-resonance loop antenna is set to a frequency several MHz higher than the resonance frequency of the transmission loop antenna. The resonance frequency of the first resonance circuit of the transmission loop antenna is set in the vicinity of the transmission carrier frequency of 13.56 MHz,
4. The loop according to claim 3, wherein a resonance frequency of the third resonance circuit according to the first self-resonance loop antenna and the fourth resonance circuit according to the second self-resonance loop antenna is 20 MHz. antenna.

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