JP5655602B2 - Antenna and RFID device - Google Patents

Description

  The present invention relates to an antenna used in a radio communication system such as an RFID (Radio Frequency Identification) system and an RFID device including the antenna, and more particularly to an antenna and an RFID device applied to an HF band RFID system.

  In recent years, as a wireless communication system for managing article information, a reader / writer that generates an induced magnetic field and an RFID tag attached to an article communicate with each other in a non-contact manner using an electromagnetic field to transmit predetermined information. RFID systems have been put into practical use. Here, the RFID tag includes an RFIC chip that stores predetermined information and processes a predetermined RF signal, and an antenna that transmits and receives the RF signal.

  For example, Patent Document 1 discloses an RFID tag using a booster coil. FIG. 1 is a plan view showing an arrangement of booster coils and IC elements provided in the RFID tag. This RFID tag is composed of an RFIC 2 in which an antenna coil is integrally formed, an insulating member 6 in which a booster coil 3 and electrostatic connection conductor films 4a and 4b are formed, and a base body that integrally casing these. ing. A rectangular spiral antenna coil is integrally formed on the RFIC 2, and the antenna coil is attached toward the booster coil forming surface side of the insulating member 6.

  On the back surface of the insulating member 6, conductor films 5 a and 5 b for capacitance connection are formed on the front surface to face the conductor films 4 a and 4 b. The capacitance connecting conductor films 4 a and 4 b formed on the front surface side of the insulating member 6 are electrically connected via the booster coil 3, and the electrostatic capacitance formed on the back surface side of the insulating member 6. The connecting conductor film is electrically connected via a conductive wire.

  In this RFID tag, the antenna coil of the RFIC 2 and the booster coil 3 are electromagnetically coupled, and a signal is transmitted between the RFIC 2 and the booster coil 3.

JP 2002-042083 A

  However, in the RFID tag as shown in FIG. 1, since the antenna coil is the same size as the RFIC chip and the booster coil is the card size, the sizes of both are greatly different. Therefore, it is difficult to increase the degree of coupling between the antenna coil and the booster coil. Patent Document 1 discloses a structure in which the portion of the booster coil on which the RFIC chip is mounted has a shape that approximates the antenna coil, and the degree of coupling between the antenna coil on the RFIC chip side and the booster coil is increased. However, in this structure, the shape of the booster coil is complicated, and the external dimensions of the booster coil tend to be large.

  Moreover, in an antenna provided with an antenna coil and a booster coil, generally, a situation occurs in which magnetic fluxes passing through a region where the antenna coil and the booster coil overlap or in the vicinity thereof cancel each other. Also in the antenna shown in FIG. 1, for example, both the magnetic fluxes B0 and B1 pass through the antenna coil and the booster coil in the same direction, but the magnetic flux B2 passes through the antenna coil and the booster coil in the reverse direction. Therefore, there may be a null point where the magnetic field formed by the antenna coil and the magnetic field formed by the booster coil cancel each other. At this null point, read / write cannot be performed.

  In view of the above-described circumstances, the present invention provides an antenna that has a high coupling degree between a feeding coil and a booster antenna, is excellent in RF signal transmission efficiency, and further suppresses generation of a null point, and an RFID device including the antenna. The purpose is to do.

(1) The antenna of the present invention is configured as follows.
A booster antenna composed of a first booster coil element and a second booster coil element, and a feeding coil coupled to the booster antenna;
The feeding coil is composed of a loop-shaped or spiral-shaped conductor pattern ,
The first booster coil element and the second booster coil element are each configured by a loop-shaped or spiral-shaped conductor pattern ,
The first booster coil element and the second booster coil element are arranged at adjacent positions on a plane, and the conductor pattern of the first booster coil element and the conductor pattern of the second booster coil element are adjacent to each other. Is connected so that the current flows in the opposite direction,
The first booster coil element is composed of a stacked first coil and second coil that are larger than the feeding coil and are coupled to each other via a capacitance.
The feeding coil is disposed at a position where it is electromagnetically coupled to the first booster coil element.

  With this configuration, an antenna having a high coupling degree between the feeding coil and the booster antenna and excellent RF signal transmission efficiency can be obtained.

(2) It is preferable that the said feeding coil is arrange | positioned in the position couple | bonded with an electromagnetic field with respect to both the said 1st coil and a 2nd coil.
This further increases the degree of coupling between the feeding coil and the booster antenna.

(3) It is preferable that the said feeding coil is arrange | positioned inside the external shape of a said 1st booster coil element. With this structure, generation of a null point can be more reliably suppressed.

(4) It is preferable that the second booster coil element is composed of a stacked third coil and fourth coil that are connected to each other or coupled via a capacitor.
With this structure, a high gain can be obtained with a substantially small booster antenna as compared with the case where the first booster coil element and the second booster coil element are formed of a single layer.

(5) Preferably, the first coil and the third coil are formed in a first layer, and the second coil and the fourth coil are formed in a second layer.
With this structure, the booster antenna can be easily configured with a small number of layers.

(6) Each of the feeding coil and the first booster coil element has a rectangular shape having four sides, and the feeding coil and the first booster coil element are layered along three sides of the four sides in a plan view. It is preferable to overlap in the direction.
With this structure, the degree of coupling between the feeding coil and the booster antenna can be further increased.

(7) It is preferable that the resonant frequency of the said feeding coil or the resonant frequency of the circuit by the said feeding coil and the feeder circuit connected to this feeding coil is higher than the resonant frequency of the said booster antenna.

  With this configuration, the feeding coil and the booster antenna can be magnetically coupled to increase the degree of coupling with each other, and communication between the booster antenna and the reader / writer antenna via the magnetic field is also possible.

(8) RFID device of the present invention and a RFIC connected antenna and to the antenna,
The antenna is
A booster antenna composed of a first booster coil element and a second booster coil element, and a feeding coil coupled to the booster antenna;
The feeding coil is composed of a loop-shaped or spiral-shaped conductor pattern ,
The first booster coil element and the second booster coil element are each configured by a loop-shaped or spiral-shaped conductor pattern ,
The first booster coil element and the second booster coil element are disposed at adjacent positions on a plane, and the conductor pattern of the first booster coil element and the conductor pattern of the second booster coil element are adjacent to each other. Is connected so that the current flows in the opposite direction,
The first booster coil element is composed of a stacked first coil and second coil that are larger than the feeding coil and are coupled to each other via a capacitance.
The feeding coil is disposed at a position where the first booster coil element is electromagnetically coupled,
The RFIC is connected to the feeding coil.

  ADVANTAGE OF THE INVENTION According to this invention, the coupling | bonding degree of a feeding coil and a booster antenna is high, it is excellent in the transmission efficiency of RF signal, Furthermore, generation | occurrence | production of the null point was suppressed, and the RFID device provided with the antenna can be comprised.

FIG. 1 is a plan view showing an arrangement of booster coils and IC elements provided in the RFID tag of Patent Document 1. FIG. FIG. 2 is a perspective view of the RFID device 301 according to the first embodiment. FIG. 3 is an exploded perspective view in a state in which the base material of the power feeding device and the base material of the booster antenna are removed. FIG. 4 is an equivalent circuit diagram of the antenna portion of the RFID device 301. FIG. 5 is a diagram illustrating a state of coupling of the power feeding device, the booster antenna, and the reader / writer antenna. FIG. 6 is a diagram showing the relationship among the resonance frequency of the feeding coil 21, the resonance frequency of the booster antenna, and the frequency at which the reader / writer antenna is coupled and communicated. FIG. 7 is a perspective view of an RFID device 302 according to the second embodiment. FIG. 8 is an exploded perspective view of the RFID device 302. FIG. 9 is an equivalent circuit diagram of the antenna portion of the RFID device 302. FIG. 10 is a diagram showing the return loss characteristic (S11) of the RFID device 302 on the Smith chart. FIG. 11 is a diagram showing pass characteristics (S21) of the RFID device 302. In FIG. FIG. 12 is an exploded perspective view of the RFID device 303 according to the third embodiment. FIG. 13 is an equivalent circuit diagram of the antenna portion of the RFID device 303. FIG. 14 is a diagram showing the return loss characteristic (S11) of the RFID device 303 on a Smith chart. FIG. 15 is a diagram showing pass characteristics (S21) of the RFID device 303. In FIG.

<< First Embodiment >>
FIG. 2 is a perspective view of the RFID device 301 according to the first embodiment. FIG. 3 is an exploded perspective view of a portion excluding the base material 20 of the power feeding device and the base material 10 of the booster antenna. The RFID device 301 is used as an RFID tag used in an HF band RFID system. For example, the RFID device 301 is provided in a portable electronic device.

  As shown in FIG. 2, the RFID device 301 includes an RFIC chip 23, a feeding coil 21 connected to the RFIC chip 23, and a booster antenna 110 coupled to the feeding coil 21.

The RFIC chip 23 includes a memory circuit, a logic circuit, a clock circuit, and the like, and is configured as an integrated circuit chip that processes an RF signal.
The power feeding device 210 includes a power feeding device substrate 20, a power feeding coil 21, and an RFIC chip 23. The feeding coil 21 is formed with a rectangular spiral conductor pattern having a plurality of turns over a plurality of layers. The plurality of layers of rectangular spiral conductor patterns are connected via interlayer connection conductors so that the directions of induced currents generated by passage of magnetic flux in the same direction are the same. Input / output electrodes 22A and 22B are formed at both ends of the feeding coil 21, and an RFIC chip 23 is connected to the input / output electrodes 22A and 22B.

  As shown in FIG. 3, the booster antenna 110 includes a booster antenna substrate 10, a first booster coil element 111, and a second booster coil element 112. The first booster coil element 111 is composed of the first coil 11 and the second coil 12, and the second booster coil element 112 is composed of the third coil 13 and the fourth coil 14. The first coil 11 and the third coil 13 are disposed adjacent to each other and are connected in series. Similarly, the second coil 12 and the fourth coil 14 are arranged adjacent to each other and connected in series.

  The power feeding coil 21 of the power feeding device 210 is disposed at a position where it is electromagnetically coupled to the first coil 11 and the third coil 13 of the first booster coil element 111 (overlaid on the first booster coil element 111). Specifically, the feeding coil 21 is disposed inside the outer shape of the first booster coil element 111. The first coil 11 and the second coil 12 of the power supply coil 21 and the first booster coil element are both rectangular, and the power supply coil and the first booster coil element are along the three sides in plan view. Overlapping in the layer direction.

  The winding direction of the third coil 13 and the fourth coil 14 of the second booster coil element 112 with respect to the first coil 11 and the second coil 12 of the first booster coil element 111 is such that the feeding coil 21 of the feeding device 210 is the first booster. This is a direction in which the coil element 111 and the second booster coil element 112 are coupled in phase through an electromagnetic field.

  FIG. 4 is an equivalent circuit diagram of the antenna portion of the RFID device 301. Here, the inductor L0 corresponds to the inductance of the feeding coil 21, and the capacitor C0 corresponds to the capacitance (distributed capacity) of the feeding coil 21. The power feeding circuit 23F is a power feeding circuit of the RFIC chip 23. The inductors L1, L2, L3, and L4 correspond to the first coil 11, the second coil 12, the third coil 13, and the fourth coil 14, respectively. The capacitor C1 corresponds to the distributed capacitance generated between the first coil 11 and the second coil 12, and the capacitor C2 corresponds to the distributed capacitance generated between the third coil 13 and the fourth coil 14.

  The mutual inductance M3 corresponds to magnetic field coupling between the first coil 11 and the third coil 13, and the mutual inductance M5 corresponds to magnetic field coupling between the second coil 12 and the fourth coil 14. The mutual inductance M4 corresponds to magnetic field coupling between the first coil 11 and the second coil 12, and the mutual inductance M6 corresponds to magnetic field coupling between the third coil 13 and the fourth coil 14.

  The mutual inductance M1 corresponds to magnetic field coupling between the feeding coil 21 of the feeding device 210 and the first coil 11 of the first booster coil element 111. The mutual inductance M2 corresponds to magnetic field coupling between the feeding coil 21 of the feeding device 210 and the second coil 12 of the first booster coil element 111.

  FIG. 5 is a diagram illustrating a state of coupling of the power feeding device, the booster antenna, and the reader / writer antenna. FIG. 5A shows the direction of current flowing through the feeding coil 21, the first coil 11, and the third coil 13 (and the second coil 12 and the fourth coil 14) by arrows. FIG. 5B is a diagram showing the magnetic flux of the reader / writer antenna passing through the power feeding device 210 and the booster antenna.

  As shown in FIG. 5A, the feeding coil 21 is coupled to the first coil 11 and the second coil 12 of the first booster coil element via an electromagnetic field.

  The feeding coil 21 has an inductance component (inductor L0 shown in FIG. 4) of the coil itself and a capacitance component (capacitor C0 shown in FIG. 4) constituted by the line capacitance of the feeding coil 21. An LC resonance circuit is configured and has a resonance frequency. Moreover, it has the resonant frequency of the circuit by the feed coil 21 and the feed circuit 23F in the connection state of the feed circuit 23F.

  The booster antenna 110 has a resonance frequency configured by an LC resonance circuit including the inductors L1 to L4 and the capacitors C1 and C2 illustrated in FIG.

  Therefore, as shown in FIGS. 5A and 5B, when a current flows in the direction of the arrows a and b in the drawing at a certain moment, the first coil 11 to the fourth coil of the booster antenna. 14, current is induced in the directions of arrows c to j in the figure. That is, when currents in the directions of arrows a and b flow through the feeding coil 21, currents in the directions of arrows c, d, e, and f flow through the first coil 11 of the first booster coil element due to the current in the direction of arrow a. . In addition, a current in the same direction as the arrows c, d, e, and f flows through the second coil 12. Since the first coil 11 and the second coil 12 of the first booster coil element are electromagnetically coupled to the third coil 13 and the fourth coil 14 of the second booster coil element 112, the third coil 13 and the fourth coil 14 include Current flows in the directions of arrows g, h, i, and j. That is, current flows in the same direction through the first booster coil element and the second booster coil element.

  Since the direction of the magnetic flux due to the current flowing through the feeding coil 21 and the direction of the magnetic flux due to the current flowing through the first coil 11 and the second coil 12 are opposite, the magnetic flux of the reader / writer antenna hardly passes through the feeding coil 21 directly. In other words, the feeding coil 21 does not appear equivalent from the reader / writer antenna. Therefore, the occurrence of a null point as in the conventional antenna is suppressed.

  A condition for preventing the magnetic flux of the reader / writer antenna from passing directly through the feeding coil 21 is that the feeding coil 21 is disposed inside the outer shape of the first coil 11 and the second coil 12 of the first booster coil element. Furthermore, the widths A1 and B1 of the pattern formation ranges of the first coil 11 and the second coil 12 of the first booster coil element are larger than the widths A2 and B2 of the pattern formation range of the power feeding coil 21. What is necessary is just to define the magnitude | size and positional relationship of the feeding coil 21, the 1st coil 11, the 2nd coil 13, the 2nd coil 12, and the 4th coil 14 so that this condition may be satisfy | filled.

  According to the antenna according to the first embodiment, the degree of coupling between the feeding coil and the booster coil can be increased, and the RF signal transmission efficiency is high. Also, a null point is difficult to occur.

  FIG. 6 is a diagram showing the relationship among the resonance frequency of the feeding coil 21, the resonance frequency of the booster antenna, and the frequency at which the reader / writer antenna is coupled and communicated. In FIG. 6, the horizontal axis represents frequency, and the vertical axis represents antenna return loss. The resonance frequency fa of the feeding coil 21 (or the resonance frequency due to the feeding coil 21 and the feeding circuit 23F) fa is higher than the resonance frequency fb of the booster antenna. For example, fa = 14 MHz, fb = 13.6 MHz, and the communication frequency fo is 13.56 MHz.

  If the resonance frequency of the power feeding coil and the booster antenna are the same, the degeneracy is solved and the power feeding coil and the booster antenna are hardly coupled. If the resonance frequency fa of the feeding coil is lower than the resonance frequency fb of the booster antenna, the coupling between the feeding coil and the booster antenna is capacitively coupled, but the capacitive coupling between the coils is not strong, and as a result. High bond strength cannot be obtained.

  In the first embodiment, as described above, since the resonance frequency fa of the feeding coil 21 is higher than the resonance frequency fb of the booster antenna, the feeding coil and the booster antenna are coupled inductively, and a high coupling strength is obtained. .

  In addition, the resonance frequency of the reader / writer antenna is set near the communication frequency fo or fo, and the resonance frequency fb of the booster antenna is set equal to or substantially equal to the communication frequency fo. Since the resonance frequency fa of the feeding coil 21 is set higher than the resonance frequency fb of the booster antenna and higher than the communication frequency fo, the resonance frequency fb of the booster antenna when the booster antenna is strongly coupled close to the reader / writer antenna. Is suppressed to the high frequency side. Therefore, there is an effect that a null point hardly occurs when strongly coupled to the reader / writer antenna. This utilizes the effect of suppressing the frequency change in the direction approaching each other's resonance frequency because two adjacent resonators (in this case, the booster antenna and the feeding coil) are magnetically coupled.

  Further, as shown in FIG. 4, the inductors L1 to L4 in the booster antenna are coupled to each other by mutual inductances M3 to M6. The inductance value is large. As a result, a small booster antenna having a sufficient inductance value can be realized.

<< Second Embodiment >>
FIG. 7 is a perspective view of an RFID device 302 according to the second embodiment. FIG. 8A is an exploded perspective view of the RFID device 302, and FIG. 8B is a diagram showing a coil pattern formed on the lower surface of the booster antenna 120. FIG. In FIG. 8 (B), it is drawn excluding the coil pattern on the upper surface.

  The RFID device 302 includes a power feeding device 220 and a booster antenna 120 coupled to the power feeding device 220.

  The power supply device 220 includes a power supply device substrate 20, a power supply coil 21, and an RFIC chip 23. The feeding coil 21 is formed with a rectangular spiral conductor pattern having a plurality of turns over a plurality of layers. RFIC chips 23 are connected to both ends of the feeding coil 21.

  The booster antenna 120 includes a first booster coil element 121 and a second booster coil element 122. The first booster coil element 121 includes the first coil 11 and the second coil 12, and the second booster coil element 122 includes the third coil 13, the fourth coil 14, and the pad electrodes 15 and 16. The first coil 11 and the third coil 13 are disposed adjacent to each other and are connected in series. Similarly, the second coil 12 and the fourth coil 14 are arranged adjacent to each other and connected in series.

  The first booster coil element 121 includes a first coil 11 wound for nine turns and a second coil 12 wound for nine turns. The second booster coil element 122 includes a third coil 13 wound for nine turns and a fourth coil 14 wound for nine turns. Both coils are illustrated with a reduced number of turns in FIGS. 7 and 8 to avoid complication of the drawings.

  The power feeding coil 21 of the power feeding device 220 is arranged at a position where the first coil 11 and the second coil 12 of the first booster coil element 121 are electromagnetically coupled (overlaid on the first booster coil element). Specifically, the feeding coil 21 is disposed inside the outer shape of the first booster coil element 121. The first coil 11 and the second coil 12 of the power supply coil 21 and the first booster coil element are both rectangular, and the power supply coil and the first booster coil element are along the three sides in plan view. Overlapping in the layer direction.

  In the winding direction of the third coil 13 and the fourth coil 14 of the second booster coil element 122 with respect to the first coil 11 and the second coil 12 of the first booster coil element 121, the feeding coil 21 is connected to the first booster coil element 121 and This is a direction in which the second booster coil element 122 is coupled in phase with an electromagnetic field.

  A pad electrode 15 is connected to the inner peripheral end of the third coil 13, and a pad electrode 16 is connected to the inner peripheral end of the fourth coil 14. The two pad electrodes 15 and 16 are pouched and are DC-conductive. The configuration of the first booster coil element 121 is basically the same as that of the first booster coil element 111 shown in FIG. 3 in the first embodiment.

  The power feeding device 220 is configured by a two-layer rectangular spiral conductor pattern wound for seven turns. 7 and 8 are drawn with a reduced number of turns in order to avoid complication of the drawings. The power supply device 220 has an outer dimension of 5 mm square. The two layers of rectangular spiral conductor patterns are connected via interlayer connection conductors so that the directions of induced currents generated by passage of magnetic flux in the same direction are the same. The rectangular spiral conductor pattern is obtained by patterning a metal foil such as copper, silver, or aluminum by etching or the like. This rectangular spiral pattern is formed on the power supply device substrate 20 made of a thermoplastic resin sheet such as polyimide or liquid crystal polymer. Is provided.

  The power feeding device 220 includes a capacitor chip 24. The capacitor chip 24 is connected in parallel to the feeding coil 21 and the RFIC chip 23. The capacitor chip 24 is provided to adjust the resonance frequency of the power feeding device 220. The resonance frequency of the power feeding device 220 is set to 14 MHz.

  As is clear from FIGS. 8A and 8B, the feeding coil 21 includes the first coil 11, the second coil 12, and the third coil 13 of the second booster coil element. It couple | bonds with 4 coils 14 via an electromagnetic field.

  FIG. 9 is an equivalent circuit diagram of the antenna portion of the RFID device 302. Here, the inductor L0 corresponds to the feeding coil 21 and the capacitor C0 corresponds to the capacitor chip 24 provided in the feeding device 220. The power feeding circuit 23F is a power feeding circuit of the RFIC chip 23. The inductors L1, L2, L3, and L4 correspond to the coils 11, 12, 13, and 14, respectively. The capacitor C1 corresponds to a capacitance generated between the first coil 11 and the second coil 12.

  Since the pad electrodes 15 and 16 shown in FIG. 8 are pouched, there is no capacitor corresponding to the capacitor C2 shown in FIG. 4 in the first embodiment. Therefore, the capacitance component of the booster antenna 120 can be increased, and the size of the booster antenna required for obtaining a predetermined resonance frequency can be further reduced.

  The rectangular spiral conductor pattern constituting the booster antenna is obtained by patterning a metal foil such as copper, silver, or aluminum by etching or the like, and is provided on the power supply device substrate 20 made of a thermosetting resin sheet such as PET. Yes. The booster antenna 120 has a width W1 in the Y direction of 25 mm and a width W2 in the X direction of 10 mm. The resonance frequency of this booster antenna is set to 13.56 MHz.

  The pad electrode 15 and the pad electrode 16 may be connected using an interlayer connection conductor such as a via hole electrode.

  FIG. 10 is a diagram showing the return loss characteristic (S11) of the RFID device 302 on the Smith chart. In this example, the frequency is swept from 9.0 MHz to 25.0 MHz. The point indicated by m1 in the figure is 13.56 MHz. Thus, since one loop is generated at the position indicated by m1 in the middle of the impedance locus, two resonance points are formed by the coupling between the feeding device 220 and the booster antenna 120, both of which are LC resonance circuits. I understand that. FIG. 11 is a diagram showing the pass characteristic (S21) of the RFID device 302. In this figure, the frequency fr is the resonance frequency, and fa is the anti-resonance frequency. Thus, the resonance frequency fr is set to a frequency around 13.56 MHz, which is the use frequency.

<< Third Embodiment >>
FIG. 12 is an exploded perspective view of the RFID device 303 according to the third embodiment. The difference from the second embodiment is the arrangement position of the power feeding device 220 of the booster antenna 130 and the structure of the third coil 13 of the second booster coil element 122 and the pad electrodes 15 and 16 of the fourth coil 14. In FIG. 12, an area MA is an area where the power feeding device 220 is mounted.

  In the second embodiment, as shown in FIGS. 7 and 8, the three sides of the coil 21 of the power feeding device 220 are connected to the three sides of the coil of the first booster coil element 121 on the side far from the second booster coil element 122. The power feeding device 220 is arranged so as to overlap. In the third embodiment, as indicated by the region MA, the first coil 11 and the second coil 12 of the first booster coil element on the side close to the third coil 13 and the fourth coil 14 of the second booster coil element. The power feeding device 220 is arranged so that three sides of the coil 21 of the power feeding device 220 overlap with the three sides.

  In the second embodiment, the pad electrodes 15 and 16 of the third coil 13 and the fourth coil 14 of the second booster coil element are connected in a direct current manner. In the third embodiment, the pad electrodes 15 and 16 of the third coil 13 and the fourth coil 14 of the second booster coil element are opposed to each other through the dielectric layer.

  The first booster coil 121 includes a coil 11 wound for 9 turns and a second coil 12 wound for 9 turns. The second booster coil 122 includes a third coil 13 wound for nine turns and a fourth coil 14 wound for nine turns. However, in FIG. 12, the number of turns of each coil is reduced in order to avoid complication of the drawing.

  FIG. 13 is an equivalent circuit diagram of the antenna portion of the RFID device 303. Here, the inductor L0 corresponds to the feeding coil 21 and the capacitor C0 corresponds to the capacitor chip 24 provided in the feeding device 220. The power feeding circuit 23F is a power feeding circuit of the RFIC chip 23. Inductors L1, L2, L3, and L4 correspond to coils 11, 12, 13, and 14, respectively. The capacitor C1 corresponds to a capacitance generated between the first coil 11 and the second coil 12. The capacitor C <b> 2 corresponds to a combined capacitance of the distributed capacitance generated between the third coil 13 and the fourth coil 14 and the capacitance generated between the pad electrodes 15 and 16.

  In this way, even if the occupied area of the entire second booster coil element is small, a large capacitance component can be obtained with the pad electrodes 15 and 16.

  FIG. 14 is a diagram showing the return loss characteristic (S11) of the RFID device 303 on a Smith chart. In this example, the frequency is swept from 9.0 MHz to 25.0 MHz. The point indicated by m1 in the figure is 13.56 MHz. Also with this structure, it can be seen that two resonance points are formed because one loop is generated at a position indicated by m1 in the middle of the impedance locus. FIG. 15 is a diagram showing the pass characteristic (S21) of the RFID device 303. In this figure, the frequency fr is the resonance frequency, and fa is the anti-resonance frequency. Thus, the resonance frequency fr is set to a frequency around 13.56 MHz, which is the use frequency.

<< Other embodiments >>
In each of the embodiments described above, both the feeding coil and the booster coil are configured by a rectangular spiral conductor pattern, but may be configured by a looped conductor pattern. Further, the number of turns may be one turn as necessary.

  Moreover, in each embodiment shown above, although the example which a feeding coil couple | bonds with a 1st booster coil element and a 2nd booster coil element mainly via a magnetic field was shown, depending on a frequency band, an electric field is mainly shown. You may make it couple | bond together. Further, coupling may be performed via both an electric field and a magnetic field. This is because, in the case of a high-frequency signal, sufficient energy is transmitted even with the capacitance between the feeding coil and the booster antenna.

  Further, in each of the embodiments described above, an example in which the present invention is applied to an RFID device in the HF band has been shown, but the present invention is not limited to the HF band, and can be similarly applied to, for example, an RFID device in the UHF band.

C0, C1, C2 ... capacitors L0 to L4 ... inductors M1 to M6 ... mutual inductance 10 ... booster antenna substrate 11 ... first coil 12 ... second coil 13 ... third coil 14 ... fourth coils 15, 16 ... pad electrodes DESCRIPTION OF SYMBOLS 20 ... Feed device base material 21 ... Feed coil 22A, 22B ... Input / output electrode 23 ... RFIC chip 23F ... Feed circuit 24 ... Capacitor chip 110, 120, 130 ... Booster antenna 111, 121 ... 1st booster coil element 112, 122 ... Second booster coil elements 210, 220 ... feeding devices 301-303 ... RFID devices

Claims (8)

A booster antenna composed of a first booster coil element and a second booster coil element, and a feeding coil coupled to the booster antenna;
The feeding coil is composed of a loop-shaped or spiral-shaped conductor pattern ,
The first booster coil element and the second booster coil element are each configured by a loop-shaped or spiral-shaped conductor pattern ,
The first booster coil element and the second booster coil element are arranged at adjacent positions on a plane,
The conductor pattern of the first booster coil element and the conductor pattern of the second booster coil element are connected such that current flows in the opposite direction in the adjacent portions of each other,
The first booster coil element is composed of a stacked first coil and second coil that are larger than the feeding coil and are coupled to each other via a capacitance.
The antenna according to claim 1, wherein the feeding coil is disposed at a position where it is electromagnetically coupled to the first booster coil element.   The antenna according to claim 1, wherein the feeding coil is disposed at a position where electromagnetic coupling is performed to both the first coil and the second coil.   The antenna according to claim 1, wherein the feeding coil is disposed on an inner side than an outer shape of the first booster coil element.   The antenna according to any one of claims 1 to 3, wherein the second booster coil element is composed of a stacked third coil and fourth coil that are connected to each other or coupled via a capacitor.   The antenna according to claim 4, wherein the first coil and the third coil are formed in a first layer, and the second coil and the fourth coil are formed in a second layer.   Each of the feeding coil and the first booster coil element has a rectangular shape having four sides, and the feeding coil and the first booster coil element overlap in the layer direction along three sides of the four sides in plan view. The antenna according to claim 1.   The resonant frequency of the said feeding coil, or the resonant frequency of the circuit by the said feeding coil and the feeder circuit connected to this feeding coil is higher than the resonant frequency of the said booster antenna, In any one of Claims 1-6. antenna. An RFID device that includes a RFIC connected antenna and to the antenna,
The antenna is
A booster antenna composed of a first booster coil element and a second booster coil element, and a feeding coil coupled to the booster antenna;
The feeding coil is composed of a loop-shaped or spiral-shaped conductor pattern ,
The first booster coil element and the second booster coil element are each configured by a loop-shaped or spiral-shaped conductor pattern ,
The first booster coil element and the second booster coil element are arranged at adjacent positions on a plane,
The conductor pattern of the first booster coil element and the conductor pattern of the second booster coil element are connected such that current flows in the opposite direction in the adjacent portions of each other,
The first booster coil element is composed of a stacked first coil and second coil that are larger than the feeding coil and are coupled to each other via a capacitance.
The feeding coil is disposed at a position where the first booster coil element is electromagnetically coupled,
The RFID device, wherein the RFIC is connected to the feeding coil.

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