JP2013005211A - Rfid tag - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an RFID tag including: an IC which has an input-output port of two single modes and a common mode port, and functions in the individual single modes and a differential mode synthesized from the individual single modes; and an antenna, the RFID tag capable of completely compensating a null point of directional patterns of two radiation elements crossing each other.SOLUTION: An antenna includes: two radiation elements 2 and 3 crossing each other; and a matching loop circuit 1. The matching loop circuit 1 includes two straight line patterns 1a and 1b which are adjacent to a cross point 23 so as to establish electromagnetic coupling, and extend in parallel to the radiation elements, respectively. One ends of the two straight line patterns 1a and 1b are connected to each other to form an apex 1e, and the other ends thereof are respectively connected to an input-output port of single modes on an IC4. The apex 1e is connected to a common mode port on the IC4.

Description

  The present invention relates to an RFID tag.

  The RFID tag is used by transmitting and receiving signals and supplying power to the tag between the reader / writer and the tag using a radio frequency signal in the UHF band (860 to 960 MHz). In this case, it is desired to efficiently use the electromagnetic wave used for transmission / reception between the reader / writer and the tag, but there is a problem that the directivity is deteriorated due to the polarization plane of the electromagnetic wave and the efficiency fluctuates. For example, when the reader / writer transmits electromagnetic waves with linear polarization and the tag antenna is in a direction perpendicular to the plane of polarization, the efficiency is reduced and the communication distance is drastically reduced.

  In order to solve such a problem, a technique has been disclosed in which two antennas having different polarization planes are provided in a tag to improve directivity and can be efficiently received from any direction (Patent Document 1).

  FIG. 5 is a plan view of a typical example of such an antenna. In the example shown in the figure, the cross dipole antenna is applied to an RFID system that communicates information between a reader / writer and a tag using a radio frequency signal, and includes (a) a pair of dipole antennas 1a and 1b, The pair of dipole antennas 1a and 1b includes a line extending from a feeding point 20 that crosses each other in a cross shape, and (b) a line extending in a triangular shape at a point where the line is bent, and (c) the pair of dipoles The total length of each of the antennas 1a and 1b is longer than λ / 2 of the operating wavelength λ. An RFID tag to which such an antenna is applied has a reading performance close to omnidirectional regardless of the direction of the tag, even if the R / W side uses a linearly polarized antenna. (D) And it has conductive bar 10A, 10B, 11A, 11B connected to each of the line extended from the feeding point 20 of the pair of dipole antennas 1A, 1B, from the feeding point 20 of the conductive bar Impedance adjustment is performed by the position connected to the extended line. (E) The triangular portion may be formed by cutting out the central portion with a conductor in the contour portion of the peripheral portion (see Patent Document 1 above).

  The main points of this prior art (Patent Document 1) are (b) “having a line extending in a triangular shape at a point where a line extending from a feeding point is bent” and (d) “feeding a pair of dipole antennas” It has a conductive bar connected to each of the lines extending from the point, and impedance adjustment is performed according to the position of the conductive bar connected to the line extending from the feeding point. However, (b) “From the feeding point...” Has almost no practical effect, and it is not necessary to use this item. In addition, (d) “a pair of...” Is not specific because there is no description on how to adjust the impedance of the antenna.

  (A) “A pair of dipole antennas cross each other in a cross”, (c) “The total length of each of the pair of dipole antennas is longer than λ / 2 of the operating wavelength λ”, ( e) “The triangular portion is formed by cutting the central portion with the conductor of the contour portion of the peripheral portion” is generally used as a cross dipole or a printed antenna.

Japanese Patent No. 3820862

  The elements on one side of the dipole antenna orthogonal to each other are electrically connected to each other by a conductor 12. In this case, the elements on the side electrically connected to each other often function as a single element (one side of the dipole), and the vector direction of the equivalent current density is shifted. As a result, compared to dipole antennas (cross dipoles) orthogonal to crosses that are completely independent from each other, the directivity of individual dipoles is not orthogonal, so the minimum point (null point) of the radiation pattern of dipoles can be reduced with two elements. It becomes difficult to complement each other.

  An object of the present invention is to provide an RFID tag capable of completely complementing the directivity null point of two radiating elements intersecting each other, which has been difficult in the prior art.

The RFID tag of the present invention has been made in view of the above problems, and the present invention according to claim 1 has two single mode input / output ports and a common mode port, and each single mode and each single mode. An RFID tag including an IC that functions in a differential mode that is further synthesized and an antenna,
The antenna is
Two radiating elements intersecting each other;
Provide two linear patterns with one end tied and apex in close proximity so as to be electromagnetically coupled to the intersection, and connect the other end of each linear pattern to the single mode input / output port of the IC, A matching loop circuit having a vertex connected to a common mode port of the IC;
The RFID tag is characterized by being formed of

The invention according to claim 2 of the present invention includes a matching loop circuit,
A single-mode matching circuit connected to each input / output port of the single mode of the IC and connected to the common mode port via the straight line pattern and the apex is connected to each input / output port and the common mode port. Match the impedance of the antenna circuit with the impedance of each input / output port IC,
Differential mode matching circuit connected to a single mode input / output port of an IC, and connected from one input / output port to the other input / output port via one linear pattern and vertex and the other linear pattern The RFID tag according to claim 1, wherein the impedance of the circuit of the antenna connected between the two input / output ports is matched with the impedance of the IC between the two input / output ports. It is a thing.

  According to a third aspect of the present invention, the matching loop circuit is such that an IC is arranged at the center of the other end of each linear pattern and is symmetrical with respect to a line connecting the apex and the IC. The RFID tag according to claim 1 or 2, wherein the RFID tag is characterized.

  The invention according to claim 4 of the present invention is characterized in that the two radiating elements are line symmetric with respect to the intersection and symmetric with respect to a line connecting the apex and the IC. The RFID tag described in 1. is used.

  The invention according to claim 5 of the present invention is characterized in that the matching loop circuit is formed in a region where the intersecting angle is an acute angle among regions formed by intersecting the two radiating elements. The RFID tag according to any one of? 4.

  Since the RFID tag of the present invention is configured as described above, it can be an RFID tag that completely complements the directivity null point of two radiating elements that intersect each other.

It is explanatory drawing which showed the structure of an example of the antenna which concerns on the RFID tag of this invention. It is explanatory drawing which showed the example of the loop circuit for a matching. It is explanatory drawing which showed the flow of the antenna electric current in the case of matching the impedance of the antenna and IC of the RFID tag of FIG. It is explanatory drawing which showed typically the directivity of the electromagnetic wave of the FRID tag of this invention. It is a top view of the typical example of the conventional antenna. It is explanatory drawing. It is explanatory drawing which showed the example of IC utilized for a FRID tag. It is explanatory drawing which showed the example of the circuit of the input part of IC of FIG. It is explanatory drawing which showed the example which connects IC and the antenna of FIG.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

  Fig.1 (a) is explanatory drawing which showed the structure of an example of the antenna which concerns on the RFID tag of this invention. The RFID tag of this example includes two single mode input / output ports and a common mode port, and includes an IC 4 that functions in each single mode and a differential mode synthesized from each single mode, and an antenna. .

The antenna is formed of a radiating element and a matching loop circuit 1.
The radiating element is formed of a first radiating element 2 and a second radiating element 3 that intersect each other. In the figure, the radiating element is a dipole antenna. First, the matching loop circuit 1 is provided with two linear patterns 1a and 1b with one end connected to each other and in parallel with each radiating element so as to be electromagnetically coupled to the intersection 23a and having a vertex 1e. The other end of each linear pattern 1a, 1b is connected to the single mode input / output port of the IC 4 by the linear pattern 1c, 1d, and the vertex 1e is connected to the common mode port of the IC.

  Thus, the RFID tag of this example is configured, and the impedance of the antenna and the IC can be matched as follows.

  That is, the matching loop circuit 1 is connected to the single-mode input / output port S1 (or S2) of the IC 4 and is connected to the common mode port C1 (or via the linear pattern 1a (or 1b) and the vertex 1e. The single-mode matching circuit connected to C2) includes the impedance of the antenna circuit connected to the input / output port S1 (or S2) and the common mode port C1 (or C2), and the input / output port S1. (Or S2) IC impedance can be matched.

Also, it is connected to the single mode input / output port of the IC, and is connected from one input / output port S1 to the other input / output port S2 via one linear pattern 1a and vertex 1e and the other linear pattern 1b. The differential mode matching circuit can match the impedance of the antenna circuit connected between the two input / output ports S1 and S2 and the impedance of the IC 4 between the two input / output ports S1 and S2.

  With this matching loop circuit, the single mode matching circuit and the differential mode matching circuit can be matched separately. FIG. 2 is an explanatory diagram showing matching of the matching loop circuit according to this example.

  FIG. 2A is a circuit in which two single mode input / output ports S1 and S2 and two common mode ports C1 and C2 are connected to each other, and shows a current flow in each mode. The current in each single mode flows from the input / output port S1 (or S2) through the loop to the common mode port C1 (or C2). In the differential mode, a current flows from one input / output port (for example, S1) to the other input / output port (for example, S2) through the loop through the two common mode ports C1 and C2 and the other loop. . In this case, since a circuit through which a current flows is common in the single mode and the differential mode, it is difficult to match both modes. S1 and S2 are electrically connected.

  FIG. 2B is a circuit in which a part flowing to the common mode port of the loop circuit is integrated in the circuit of FIG. In this case, in the single mode, current flows in the same way as in FIG. 2A, but in the differential mode, one input / output port (for example, S1) passes through the loop and the other input / output port (for example, S2). Current flows and does not go through the common mode port.

  FIG. 2C is an explanatory diagram of the matching circuit of this example. The present invention is a matching circuit based on the current flow of the circuit of FIG. In this circuit, the portion from the apex to the common mode port that flows to the common mode port is integrated with the line pattern 10.

  The matching loop circuit 1 is provided with two linear patterns 1a and 1b with one end connected and apex 1e in close proximity to each other so as to be electromagnetically coupled to the intersection 23a. The other end of each linear pattern 1a, 1b is connected to the single mode input / output ports S1, S2 of the IC 4 by the linear patterns 1c, 1d, respectively, and the vertex 1e is connected to the common mode ports C1, C2 of the IC by the line pattern 10. Connected. In this case, the current in each single mode passes through the linear pattern 1c (or 1d), 1a (or 1b), the vertex 1e, and the line pattern 10 that form a loop from the input / output port S1 (or S2). It flows to the common mode port C1 (or C2). In the differential mode, one input / output port, for example, a linear pattern 1c (or 1d), 1a (or 1b), a vertex 1e, a linear pattern 1b (or 1a), or 1d that forms a loop from S1 (or S2). (Or 1c), the flow to the input / output port S2 (or S1), and not via the common mode port.

  As described above, in the matching loop circuit, the current in the single mode is different from the current in the differential mode, and no current flows through the line pattern 10 in the differential mode. From now on, the alignment can be performed in the differential mode, and the alignment in the single mode can be independently performed by the line pattern 10. For example, as shown in FIG. 2D, the pattern can be independently matched as a line pattern 10 'like a meandering line.

FIG. 3 is an explanatory diagram showing the flow of antenna current when matching the impedance between the antenna of the RFID tag of this example and the IC. FIG. 3A shows the current flow in the single mode, and FIG. 3B shows the current flow in the differential mode. As shown in FIG. 3 (a), the single mode port 1 loop circuit (S1, 1c, 1a, 10,
C1) and the radiating element 2, and the single mode port 2 loop circuit (S2, 1d, 1b, 10, C2) and the radiating element 3 are shown. Here, when flowing through the single-mode port 1 loop circuit and the radiating element 2, a part 3a of the radiating element 3, that is, between the intersection 23 and the end of the radiating element 3 on the side where there is no matching loop circuit. , Current will flow. Further, when flowing through the single mode port 2 loop circuit and the radiating element 3, a part 2a of the radiating element 2, that is, between the intersection 23 and the end of the radiating element 2 on the side where there is no matching loop circuit, Current flows. The same applies to the current in the differential mode, and the current flows from the intersection of each radiating element to the end. As a result of such a current flow, the direction of the current is biased, and the directivity in each single mode is not orthogonal. In such a case, the matching loop circuit can be orthogonalized in directivity by forming it in a region where the crossing angle is an acute angle among the regions formed by the two radiating elements intersecting.

  The matching loop circuit preferably has a shape in which an IC is arranged at the center of the other end of each linear pattern and is symmetric with respect to a line connecting the apex and the IC. Directivity can be improved by making line symmetry with respect to the intersection and making symmetry with respect to the line connecting the vertex and the IC.

  FIG. 4 is an explanatory view schematically showing the directivity of radio waves of the FRID tag of the present invention. In the figure, the XY in-plane antenna directivity in the single mode / differential mode is shown. Note that matching loss and conductor loss are excluded. Since the antenna according to the FRID tag of the present invention has the above operations and effects, the directivity in the single mode by the port 1, the single mode by the port 2, and the differential mode is arranged in a balanced manner as shown in FIG. it can. Therefore, the present invention can provide an RFID tag that can completely complement the directivity null point of two radiating elements intersecting each other, which has been difficult in the prior art.

  In addition, as shown in FIG.1 (b), it is not necessary to form a radiating element on the same surface of a base material, You may form one radiating element in the other surface of a base material. When used in an RFID tag, even if it is formed in this way, there is almost no change in the above electromagnetic effects.

  FIG. 6 is an explanatory diagram showing an example of an IC used for the FRID tag. FIG. 6A includes two terminals that are signal input / output terminals, port 1 and port 2, and two terminals that are common terminals, common 1 and common 2. FIG. 6B shows an example in which one common terminal is provided, and FIG. 6C shows an example in which one signal input / output terminal and one common terminal are provided. FIG. 7 is an explanatory diagram showing an example of the circuit of the input portion of such an IC. In particular, the IC of FIG. Port 1 and port 2 are supplied to the inside as single mode 1 and single mode 2 through buffer circuits, respectively. Then, both the single mode 1 and the single mode 2 are input to the buffer, and are supplied as the differential mode through this. The two common terminals, common 1 and common 2, are connected internally and supplied as a common mode, or connected externally (on the antenna or on the chip) and supplied. Common mode is normally biased to ground. Common 1 and common 2 can also be connected to different grounds.

  FIG. 8 is an explanatory diagram showing an example of connecting such an IC and an antenna, where (a) is a single mode and (b) is a differential mode. In the single mode, one antenna circuit has one end connected to the single mode input / output port S1 of the IC 4 and the other end connected to the common mode port C1. The other antenna circuit has one end connected to the single mode input / output port S2 of the IC 4 and the other end connected to the common mode port C1. In the differential mode, the antenna circuit is connected between the input / output ports S1 and S2.

  The input impedances Zs of the input / output ports S1 and S2 are substantially equal. As shown in FIG. 8B, the input impedance between the input / output ports S1 and S2 in the differential mode is almost double the input impedance Zs of the input / output port S1. For this reason, it is necessary to perform matching separately in the single mode and the differential mode, but the matching circuit according to the present invention is a circuit that can facilitate this.

DESCRIPTION OF SYMBOLS 1 ... Matching loop circuit 10 ... Line pattern 2 ... 1st radiation element 3 ... 2nd radiation element 4 ... IC chip

Claims (5)

An RFID tag having two input / output ports of a single mode and a common mode port, an IC functioning in each single mode and a differential mode synthesized from each single mode, and an antenna,
The antenna is
Two radiating elements intersecting each other;
Provide two linear patterns with one end tied and apex in close proximity so as to be electromagnetically coupled to the intersection, and connect the other end of each linear pattern to the single mode input / output port of the IC, A matching loop circuit having a vertex connected to a common mode port of the IC;
An RFID tag characterized by being formed of Of the matching loop circuit
A single-mode matching circuit connected to each input / output port of the single mode of the IC and connected to the common mode port via the straight line pattern and the apex is connected to each input / output port and the common mode port. Match the impedance of the antenna circuit with the impedance of each input / output port IC,
Differential mode matching circuit connected to a single mode input / output port of an IC, and connected from one input / output port to the other input / output port via one linear pattern and vertex and the other linear pattern 2. The RFID tag according to claim 1, wherein impedance of an antenna circuit connected between the two input / output ports is matched with impedance of the IC between the two input / output ports.   3. The RFID according to claim 1, wherein the matching loop circuit has a shape in which an IC is arranged at the center of the other end of each linear pattern and is symmetrical with respect to a line connecting the apex and the IC. tag.   The RFID tag according to claim 3, wherein the two radiating elements are line-symmetric with respect to the intersection and are symmetric with respect to a line connecting the apex and the IC.   The RFID tag according to any one of claims 1 to 4, wherein the matching loop circuit is formed in a region where the crossing angle is an acute angle among the regions formed by the crossing of the two radiating elements. .