Source: https://patents.google.com/patent/JP2007228326A/en
Timestamp: 2020-03-30 17:57:11
Document Index: 654423543

Matched Legal Cases: ['arts 13', 'arts 13', 'art 11', 'arts 13', 'art 12', 'art 20']

JP2007228326A - Loop antenna and rfid tag - Google Patents
JP2007228326A
JP2007228326A JP2006047868A JP2006047868A JP2007228326A JP 2007228326 A JP2007228326 A JP 2007228326A JP 2006047868 A JP2006047868 A JP 2006047868A JP 2006047868 A JP2006047868 A JP 2006047868A JP 2007228326 A JP2007228326 A JP 2007228326A
JP2006047868A
幸介 羽山
啓介 齋藤
2006-02-24 Application filed by Omron Corp, オムロン株式会社 filed Critical Omron Corp
2006-02-24 Priority to JP2006047868A priority Critical patent/JP2007228326A/en
2007-09-06 Publication of JP2007228326A publication Critical patent/JP2007228326A/en
A conventional loop antenna has a problem that a high gain cannot be obtained when the size is reduced.
A loop antenna (1) for an RFID tag (100) includes an annular line (10) having meandering portions (13, 14) disposed on a dielectric substrate (2), and a power supply unit (11) provided on the line (10). In addition, the annular line 10 has meandering portions 13 and 14 in addition to the vicinity of the position that becomes the antinode of the standing wave generated in the loop antenna 1.
The present invention relates to a loop antenna or the like used for RFID (Radio Frequency Identification).
Conventionally, as an antenna for an RFID tag, there has been a so-called loop antenna in which lines are arranged in a loop shape along the side of the RFID tag substrate. (For example, refer to Patent Document 1). In such a loop antenna, a structure similar to a structure in which two half-wave dipole antennas are arranged in parallel by bringing the path length of the entire line close to one wavelength of a radio wave used for reading and writing information of the RFID tag. Will operate as. As a result, it can be used as a directional antenna in the loop axis direction, and a higher gain than a half-wave dipole antenna can be obtained.
JP 2006-031473 A (first page, FIG. 1 etc.)
However, in recent years, with the miniaturization of the RFID tag, the loop antenna is also required to be miniaturized.
For example, in the United States where a system using an RFID tag corresponding to a frequency in the UHF band is widespread, the RFID tag is used as a label of a package in the logistics industry. An example of such a label is a small size of 3 × 3 inches (about 75 mm × 75 mm). The size of the RFID tag substrate that can be used for such a substantially square label is 3 × 3 inches or less, and the path length of the loop antenna disposed on the substrate is about 0. 0 of the wavelength of radio waves in the UHF band. 8 wavelengths. Therefore, when miniaturization is attempted, the path length of the loop antenna line cannot be brought close to one wavelength of the radio wave in the UHF band of the RFID tag, the efficiency of radio wave transmission / reception is reduced, and high gain cannot be obtained. was there.
The loop antenna of the present invention is a loop antenna for an RFID tag, and includes an annular line having one or more meandering portions, and a power feeding unit provided on the line, and the annular line includes the loop The loop antenna has the meandering shape portion other than the vicinity of the position that becomes the antinode of the standing wave generated in the antenna.
With such a configuration, it is possible to obtain a high-gain antenna corresponding to a predetermined wavelength by increasing the path length of the whole antenna without increasing the size of the antenna. As a result, the high-gain loop antenna adapted to a predetermined wavelength can be obtained while suppressing the adverse effect on the gain due to the provision of the meandering portion.
Further, the loop antenna of the present invention is the loop antenna, wherein the annular line has at least one of the meandering shape portions at a position where the standing wave generated in the loop antenna is a node. It is an antenna.
With such a configuration, the meandering shape portion is disposed sufficiently away from the position where the antinode is located, and the adverse effect on the gain due to the provision of the meandering shape portion is further suppressed, and a higher gain adapted to a predetermined wavelength is obtained. A simple loop antenna can be obtained.
Further, the loop antenna of the present invention is a loop antenna for an RFID tag in the loop antenna, comprising an annular line having one or more meandering portions, and a power feeding unit provided on the line, The annular line is in a position excluding the vicinity of the position where the feeding part is provided on the annular line and the vicinity of the position where the path length from the feeding part is half the path length of the entire line. It is a loop antenna which has the meandering shape part.
With such a configuration, it is possible to obtain a high-gain antenna corresponding to a predetermined wavelength by increasing the path length of the whole antenna without increasing the size of the antenna. Therefore, the high-gain loop antenna adapted to a predetermined wavelength can be obtained while suppressing the adverse effect on the gain due to the provision of the meandering portion.
Further, in the loop antenna of the present invention, in the loop antenna, the annular line is located on the annular line at a position where the path length from the power feeding unit is 1/4 of the path length of the line. A loop antenna having at least one of the meandering portions.
In the loop antenna according to the present invention, in the loop antenna, the annular line has a rectangular shape, and the annular line is located on a side other than the side where the feeding portion is disposed and the side facing the side. A loop antenna having one or more meandering portions.
With such a configuration, it is possible to obtain a loop antenna with a high gain by suppressing the influence of the meandering shape portion on the side not having the meandering shape portion that becomes the antinode of the line.
The loop antenna of the present invention is an antenna further comprising a matching circuit connected to the power feeding unit in the loop antenna.
With this configuration, a high gain loop antenna can be obtained.
The loop antenna according to the present invention is an RFID tag including the loop antenna, an integrated circuit connected to the power feeding unit, and a dielectric substrate on which the loop antenna is disposed.
With this configuration, a high gain RFID tag can be obtained.
According to the loop antenna or the like according to the present invention, a loop antenna or the like having a high gain can be provided.
Hereinafter, embodiments of a loop antenna and the like will be described with reference to the drawings. In addition, since the component which attached | subjected the same code | symbol in embodiment performs the same operation | movement, description may be abbreviate | omitted again.
FIG. 1 is a plan view showing the configuration of the RFID tag according to the present embodiment.
The RFID tag 100 includes an antenna 1, a dielectric substrate 2, an integrated circuit 3, and a strap 4. The antenna 1 includes a line 10, a power feeding unit 11, and a matching circuit 12. The line 10 has meandering portions 13 and 14.
The antenna 1 is used for transmission / reception of radio waves. Specifically, the antenna 1 is a so-called loop antenna having an annular shape. The material of the antenna 1 may be any material as long as it is a conductor. Normally, a thin film conductor such as metal is used as the antenna 1, but the thickness is not limited. Here, a case where the antenna 1 is made of aluminum rolled to about 15 μm will be described as an example.
The line 10 is an annular conductor having one or more meandering portions. For example, the line 10 has two meandering portions 13 and 14 on the side extending in the vertical direction, that is, on the left and right sides. Here, as an example, the line 10 has a rectangular planar shape along the side of the dielectric substrate 2 having a rectangular shape as a whole. The planar shape of the line 10 does not matter, but in order to operate as a loop antenna, a shape close to a square is preferable. Here, the size of the line 10 is about 68 mm in width and about 70 mm in length, the line width is about 2 to 4 mm on the side other than the side where the meandering shape parts 13 and 14 are provided, and the meandering shape parts 13 and 14 are The width of the side other than the meandering shape portions 13 and 14 of the provided side is about 1 to 3 mm, and the width of the meandering side of the meandering shape portions 13 and 14 is about 0.5 mm to 2 mm. The size of the line 10 is not limited to this value. Also, the width need not be a uniform thickness. The bent portion of the line 10 may have rounded corners as shown in FIG. 1 or may have corners, and the shape is not limited. In addition, the ring described here does not necessarily indicate a shape without a breakpoint. For example, the line 10 is annular, but a part of the line 10 may be cut away in a power supply unit 11 or the like described later. Here, as an example, the line 10 is made of aluminum rolled to about 15 μm, but the thickness, material, etc. are not limited. The meandering portions 13 and 14 included in the line 10 will be described later.
The power feeding unit 11 is provided on the line 10. The power feeding unit 11 is made of a conductor and is used as a terminal for inputting / outputting current between the antenna 1 and other elements. Here, the power feeding unit 11 is provided on one side of a rectangular line. Here, as an example, the power feeding unit 11 is provided in the center of one side of the rectangular line 10. However, the power feeding unit 11 may be arranged at any position on the line 10. By connecting the power feeding unit 11 to the integrated circuit 3, current input / output is performed between the antenna 1 and the integrated circuit 3. Here, a slit is provided at the center of the power supply unit 11, and the integrated circuit 3 and the like are connected so as to bridge the slit. Here, the integrated circuit 3 is connected to the power feeding unit 11 via the strap 4. The shape of the power feeding unit 11 is not limited. Here, as an example, the power supply unit 11 is made of aluminum rolled to about 15 μm, but the thickness, material, and the like are not limited.
The matching circuit 12 is a circuit that is connected to the power feeding unit 11 and performs impedance matching between the antenna 1 and the integrated circuit 3. Here, a case where a so-called T-shaped matching circuit made of a conductor is provided as an example, and the matching circuit 12 is formed integrally with the other part of the antenna 1. Note that the configuration of a matching circuit such as a T-shaped matching circuit is a known technique, and thus description thereof is omitted here. The matching circuit 12 may be omitted when there is no need for impedance matching. Here, the matching circuit 12 is formed inside the line 10 in order to reduce the size of the antenna 1.
The meandering portions 13 and 14 are portions of the line 10 having a meandering shape. A pair of meandering linear portions that are made of a conductor, are connected to the power supply unit 11, and extend on both sides of the power supply unit 11 with the power supply unit 11 as a center. The meandering portions 13 and 14 are formed in the annular line 10 other than the vicinity of the position where the antinode of the standing wave generated in the loop antenna 1 is formed. The antinode is the portion with the largest amplitude of the standing wave. That is, the meandering portions 13 and 14 are on the annular line 10 in the vicinity of the position where the power supply unit 11 is provided, and in the vicinity of the position where the path length from the power supply unit 11 is half the path length of the entire line 10. It is formed at a position excluding. The vicinity means a position that does not contact at least each of the above positions. It is preferable that at least one, preferably all, of the meandering portions 13 and 14 are formed at positions where the annular line 10 becomes nodes of standing waves generated in the loop antenna 1. The knot is the part with the smallest amplitude of the standing wave. That is, at least one, preferably all, of the meandering portions 13 and 14 are formed on the annular line 10 at a position where the path length from the power feeding part 11 is 1/4 of the path length of the entire line 10. It is preferable. Here, “to be a node” and “to be a quarter of the path length” are respectively “so that a part of the node is positioned on the node position”, “route”. This means that a part of it is positioned on a position that is 1/4 of the length. Further, when the loop antenna 1 has a rectangular shape, the meandering portions 13 and 14 are preferably provided on a side other than the side where the power feeding unit is formed and the side facing the side. Here, in particular, the meandering shape portions 13 and 14 are respectively located on the left and right sides of the line 10 at positions where nodes of the standing wave generated in the loop antenna 1 of the annular line 10 become nodes. It arrange | positions so that the center of the extending direction of 14 may be located. That is, the meandering portions 13 and 14 are on the left and right sides of the line 10, respectively, and the path length from the power feeding unit 11 on the annular line 10 is at a position where the path length of the entire line 10 is 1/4. The meandering shape portions 13 and 14 are arranged so that the center in the extending direction is located. Here, the case where the line 10 has two meandering shape portions 13 and 14 will be described. However, the number of meandering shape portions may be one or more. For example, the longitudinal direction is longer than the meandering shape portions 13 and 14. Three or more meandering parts having a small length in the direction, that is, the length in the extending direction of the meandering part may be received. However, it is preferable that the meandering portions are provided symmetrically on the left and right of the line 10. The meandering shape portions 13 and 14 described here are concepts including a so-called meander line structure. The meandering described here refers to a state of extending while bending alternately on the left and right. The direction in which the meandering shape portions 13 and 14 start to be bent is not limited. The meandering shape portion 13 and the meandering shape portion 14 may be a target shape or may not be a target shape. The bent portions of the meandering portions 13 and 14 may have rounded corners or may have corners, and the shape thereof is not limited. In addition, the meandering portions 13 and 14 include a plurality of sides arranged in the extending direction of the meandering portions 13 and 14, which are configured by meandering linear conductors. Moreover, the thickness of the track | line 10 in the meandering shape parts 13 and 14 is not ask | required, and thickness may not be uniform. Here, as an example, the meandering portions 13 and 14 have a symmetrical shape, and the above-mentioned sides of the meandering portions 13 and 14 are perpendicular to the left and right sides of the line 10. The distance between the sides (hereinafter referred to as a meandering interval) P is about 3 mm, and the meandering portions 13 and 14 each have a plurality of recesses 20 formed by meandering of the line 10. The horizontal length W (hereinafter referred to as the meandering width) W is about 12 to 17 mm. Further, the number of times the meandering portions 13 and 14 are folded, that is, the number of the bent portions formed by the folding is 11 here, but the number of times of folding is not limited. The number of times of folding depends on the meandering interval and meandering width, the thickness of the line 10 in the meandering shape portions 13 and 14, the overall size of the antenna 1, and the like. The wavelength is appropriately set so as to be a wavelength. The meandering shape portions 13 and 14 have a shape protruding only from the portion having no meandering shape portions 13 and 14 on the left and right sides of the line 10 toward the inside of the line 10. Thereby, the size of the antenna 1 can be kept at the same size as the size of the line 10 when the meandering portions 13 and 14 are not provided.
The dielectric substrate 2 is used for arranging and fixing the antenna 1. The dielectric substrate 2 is also used for arranging and fixing the integrated circuit 3, the strap 4 and the like. For example, here, the antenna 1 is bonded to the surface of the dielectric substrate 2 using an adhesive or the like. The strap 4 is pressure-bonded to the dielectric substrate 2 at a position where the power feeding unit 11 is arranged so that the wiring arranged on the surface of the strap 4 is connected to the power feeding unit 11 of the antenna 1. The dielectric substrate 2 is made of a dielectric material such as PET (PolyEthylene Terephthalate) or an epoxy resin. The thickness of the dielectric substrate 2 does not matter. However, considering the use of the RFID tag 100 that is used for an IC card, a label for luggage, and the like, the dielectric substrate 2 is preferably thin and flexible. Here, as an example of such a dielectric substrate 2, a transparent PET film having a thickness of 38 μm is used. Usually, the size of the dielectric substrate 2 is the size of the RFID tag. Here, the dielectric substrate 2 has a rectangular shape, specifically, a substantially square shape, but the planar shape of the dielectric substrate 2 does not matter. Here, as an example, it is assumed that the size of the dielectric substrate 2 is equal to or smaller than the size of a label generally used in the US logistics industry, that is, 3 × 3 inches or smaller. However, the size of the dielectric substrate 2 does not matter.
The integrated circuit 3 is connected to the power supply unit 11. The integrated circuit 3 has a configuration of a transmitter / receiver of information such as identification information, and transmits / receives information such as identification information via the antenna 1. Further, the integrated circuit 3 operates with a current fed from the antenna 1 via the feeding unit 11. Any integrated circuit may be used as the integrated circuit 3 as long as it can be used as an integrated circuit of a normal RFID tag, and detailed description thereof is omitted here. The thickness of the integrated circuit 3 does not matter. In the present embodiment, the integrated circuit 3 is sandwiched between the surface of the strap 4 and the surface of the dielectric substrate 2 in the gap formed in the power supply unit 11, so long as it can be arranged in this space. . Here, since the dielectric substrate 2 and the dielectric substrate 42 of the strap have flexibility, an integrated circuit 3 thicker than the thickness of the antenna 1, for example, an integrated circuit 3 having a thickness of about 150 to 180 μm is disposed. Is also possible.
The strap 4 is a member used to connect the integrated circuit 3 to the power feeding unit 11 of the antenna 1 and to fix the integrated circuit 3 to the dielectric substrate 2. The strap 4 has the same configuration as that of the antenna 1 and the dielectric substrate 2 except that the size and the like are different. A thin film wiring 41 is provided on the surface of the strap dielectric substrate 42. The integrated circuit 3 is bonded on the surface of the strap 4 so as to be connected to the wiring 41. The size of the dielectric substrate 42 is, for example, about 25 μm thick, about 4 mm long, and about 9 mm wide. In this example, the wiring has a thickness of about 35 μm, a length of about 3 mm, and a width of 8 mm, and is created by the same method as the antenna 1. For example, the integrated circuit 3 is bonded to the wiring 41 with solder, a conductive adhesive, or the like. This joining method does not matter. The strap 4 is bonded to the antenna 1 and the dielectric substrate 2 so that the wiring 41 and the power feeding portion 11 on the surface of the dielectric substrate 2 are connected. Here, the surface of the strap 4 is attached to the surface of the dielectric substrate 2 so as to face the surface of the dielectric substrate 2. Thus, the integrated circuit 3 is sandwiched between the strap 4 and the dielectric substrate 2 in the gap formed in the power feeding unit 11. For example, as shown in US Pat. No. 6,664,645, the strap 4 has an electrode (not shown) connected to the wiring 41 on the surface, and the surface side is made of a heat-meltable material. The electrode and the back surface of the dielectric substrate 2 are bonded by applying pressure while applying an ultrasonic wave after being arranged so as to face the surface of the dielectric substrate 2 to which the adhesive is applied, that is, the surface on which the antenna 1 is provided. The antenna 1 and the dielectric substrate 2 are joined so that the power feeding unit 11 is connected. Thereby, the power feeding unit 11 and the integrated circuit 3 are connected. However, the joining method of the strap 4 does not matter. The integrated circuit 3 may be connected to the power supply unit 11 as long as it is electrically connected to the power supply unit 11. For example, the integrated circuit 3 does not need to be connected to the power feeding unit 11 via the strap 4 as shown in FIG. 1, and the strap 4 is omitted and the power feeding unit 11 is directly connected to the integrated circuit 3. May be.
The antenna 1 of the RFID tag 100 includes, for example, an aluminum layer formed on the back surface of the dielectric substrate 2 by sticking rolled aluminum to the back surface of the dielectric substrate 2 and the like. After forming by photolithography printing, it is formed by etching with acid or alkali as an etching mask. However, the formation method of the antenna 1 is not ask | required. For example, the antenna may be formed by printing the shape of the antenna 1 on the dielectric substrate 2 using metal ink or the like. In addition, about the method of forming the antenna 1, since it is a well-known technique, description is abbreviate | omitted here.
Next, the operation of the RFID tag 100 will be briefly described. When a carrier wave radiated from an RFID reader / writer (not shown) reaches the antenna 1, power obtained from the carrier by the antenna is supplied to the integrated circuit 3 via the strap 4. Then, the integrated circuit 3 performs an operation corresponding to the signal included in the carrier wave, for example, reading identification information from the memory, by the supplied power. Then, the information obtained as an operation result is transmitted via the antenna 1 using the carrier wave received from the RFID reader / writer as a wave source.
As described above as the background art, when a line-shaped loop antenna is simply arranged along the side of the dielectric substrate in the RFID tag 100, the path length of the loop antenna that can be arranged is limited by the size of the dielectric substrate. The Rukoto. For this reason, if the size of the dielectric substrate is reduced, the path length corresponding to the radio wave of the desired wavelength band, specifically, the path length corresponding to one wavelength of the radio wave cannot be secured, and the radio wave of the desired wavelength band cannot be secured. The antenna cannot radiate or absorb efficiently. That is, the gain cannot be increased. In particular, when a 3 × 3 inch RFID tag is used for the UHF band, the loop antenna path length can be secured only about 0.8 wavelengths of radio waves in the UHF band, and thus a high gain cannot be obtained.
For this reason, in the present embodiment, meandering portions 13 and 14 are provided on the line 10. In the meandering shape portions 13, 14, the path length through which the current flows can be made longer than the length of the meandering shape portions 13, 14 in the extending direction. For this reason, by providing such meandering portions 13 and 14, the path length of the entire line 10 disposed on the dielectric substrate 2 is simply disposed along the side of the dielectric substrate. It is possible to secure a path length corresponding to radio waves in a desired wavelength band, for example, the UHF band, and to achieve a high gain.
FIG. 2 is a schematic diagram for explaining the relationship between the path length of the antenna 1 and the standing wave. In the figure, the same reference numerals as those in FIG. 1 denote the same or corresponding parts. Here, meandering-shaped portions 13 and 14 are provided in the line 10 and the path length of the antenna 1 is adjusted to be the same as λ, which is one wavelength of the radio wave received by the antenna 1. The position A is a position where the power feeding unit 11 is disposed, the position D is a position that is 1/2 of the path of the entire line 10, and the positions G 2 and H 2 are 1/4 of the path of the entire line 10. The positions, positions B, C, E, and F are the positions of the corners of the rectangular line 10, the positions G 1 and G 3 are the positions of both ends of the meandering section 13, and the positions H 1 and H 3 are The positions of both ends of the meandering shape portion 14 are shown. In FIG. 2, when the path length between FB and CE is x, and the path length between BC and EF is y, the path length of the entire line 10 is 2x + 2y = λ, and x + y = λ / 2. Here, it is assumed that the path lengths of the meandering shape portions 13 and 14 are the same, and G 2 and H 2 are the centers of the respective path lengths of the meandering shape portions 13 and 14. When the position A is located between the position B and the position F, the path length between the CDs is λ−x / 2−y = x / 2, and the position D is the position C and the position E. It will be located in the middle. In addition, between FB here refers to the path | route between the position F and the position B which passes the position A.
FIG. 3 is a schematic diagram showing the relationship between the path length and the standing wave of the antenna 1. In the figure, the vertical axis indicates the amplitude of the standing wave generated in the antenna 1, the horizontal axis indicates each position of the antenna 1 shown in FIG. 2, and the distance between the positions in FIG. It corresponds to the path length between the positions shown in FIG. Here, for the sake of convenience, the ratio of path lengths between positions on the horizontal axis in FIG. 3 does not accurately reflect the ratio of path lengths between positions of the actual antenna 1.
As shown in FIG. 3, when the path length of the antenna 1 is substantially the same as one wavelength λ of the radio wave received by the antenna 1, the path length from the power feeding section 11 and the path length from the power feeding section 11 are the total path length. The portion of λ / 2 that is half of the above becomes the antinode of the standing wave. In the standing wave, since the current in the antinode is the largest, the vicinity of this portion works as the antenna with maximum efficiency.
On the other hand, in the meandering shape portions 13 and 14, the line 10 is meandering, so that a reverse current flows between the sides of the adjacent lines that are bent, thereby causing electrostatic coupling and the like. Loss will occur. If such meandering portions 13 and 14 with a large current loss are brought to a high current portion, the current loss is large and the amplitude of the portion that functions as the maximum efficiency as an antenna is disturbed. As a result, the gain of the antenna 1 decreases.
For this reason, in the antenna 1 of the present embodiment, the meandering portions 13 and 14 are positioned at positions other than the position near the antinode of the standing wave, that is, near the position where the power feeding section 11 is provided on the line 10. In addition, the antenna 1 has the highest current and the maximum efficiency as the antenna because the path length from the power supply unit 11 is excluded from the vicinity of the position where the path length is half the path length of the line 10. As a result, the gain of the antenna 1 can be kept high by suppressing the influence of the meandering portions 13 and 14 given to the portion serving as.
Furthermore, in the present embodiment, the position of the standing wave that is the position of the smallest current in the antenna 1, that is, the path length from the power supply unit 11 on the line 10 is equal to the path length of the line 10. The meandering portions 13 and 14 are provided so as to pass through a position that is 1/4, that is, a position that is 1/4 of the path length of the line 10. As a result, the meandering portions 13 and 14 are provided in the vicinity of the node, which is the smallest portion of the standing wave power. By adopting such a structure, the loss of current due to the meandering shape portions 13 and 14 is reduced, and the meandering shape portion 13 is located away from the portion that works efficiently as an antenna, that is, the portion near the antinode of the standing wave. By arranging 14, the influence of the meandering portions 13, 14 on the antenna 1 can be further reduced, and the gain of the antenna 1 can be increased.
Furthermore, in the present embodiment, the position of the standing wave that is the position of the smallest current in the antenna 1, that is, the path length from the power supply unit 11 on the line 10 is equal to the path length of the line 10. The meandering portions 13 and 14 are provided so that the centers G 2 and H 2 of the respective path lengths of the meandering portions 13 and 14 are located at 1/4 positions. As a result, meandering portions 13 and 14 are provided centering on the node that is the smallest portion of the power of the standing wave, and the current loss due to the meandering portions 13 and 14 is minimized, and the AG in FIG. Since the distance between 1 and DG 3 is equal, and the distance between AH 3 and DH 1 is equal, position A and position D are positions where two antinodes of a standing wave that works efficiently as an antenna are generated. By arranging the meandering portions 13 and 14 at the position farthest from both, the influence of the meandering portions 13 and 14 on the antenna 1 is minimized, and the gain of the antenna 1 is further increased. Can do.
FIG. 4 is a schematic diagram for showing a current distribution of the antenna 1 shown in FIG. In the figure, the hatched portion is the current distribution, the current distribution is shown along the line 10, and the amplitude is expressed as the height in the direction perpendicular to the side of the line 10.
In FIG. 4, if the current is flowing clockwise through the antenna 1, a reverse current flows between CE and FB, but since the sign of the current between FB is negative, the current vector between FB Is equal to the current vector between CEs.
On the other hand, between BC and EF, the sign of the current is reversed at the center positions G 2 and H 2 , and the current flows upward between BC, whereas the current flows between EFs. Since it is downward, the direction of current flow is the reverse direction. For this reason, the current vectors of these sides are upside down and left and right.
Since the electric field radiated from the antenna 1 is mainly determined by a current having a large amplitude, the radiated electric field of the antenna 1 is determined by the radiation from the side between the parallel FBs extending in the lateral direction and the side between the CEs. It shows the same characteristics as two dipole antennas parallel to the lateral direction.
On the other hand, the currents on the two sides between the parallel BCs and the EFs extending in the vertical direction have a small amplitude and are opposite to each other, and have little influence on the radiation electric field.
Therefore, in the present embodiment, the meandering shape portions 13 and 14 are provided at positions where the influence of the radiation electric field is small by providing the meandering shape portion 13 on a side perpendicular to the side where the power feeding portion 11 is provided. Therefore, the influence of the meandering portions 13 and 14 on the radiation electric field of the antenna 1 can be suppressed, and a high gain can be achieved.
FIG. 5 is a diagram showing a simulation result showing the relationship between the meandering width W of the antenna 1 and the gain difference in the present embodiment. The gain difference described here is a relative gain of the antenna 1 having the meandering width W when the absolute gain of the antenna 1 is 0 dB when the highest gain is obtained by adjusting the meandering width W.
As shown in FIG. 5, when the meandering width W of the antenna 1 is changed, the gain difference changes. From this result, it can be seen that when the meandering width W is about 12 to 17 mm, the gain difference of the antenna 1 is small and the radiation efficiency of the antenna 1 is the best.
FIG. 6 is a diagram showing a simulation result showing the relationship between the meandering interval P of the antenna 1 and the gain difference in the present embodiment.
As shown in FIG. 6, when the meandering interval P of the antenna 1 is changed, the gain difference changes. From this result, it can be seen that when the meandering interval P is about 3 mm, the gain difference of the antenna 1 is small and the radiation efficiency of the antenna 1 is the best.
From this result, providing the meandering portions 13 and 14 whose meandering width W is about 12 to 17 mm and meandering interval P is about 3 mm is to obtain a loop antenna with high gain and excellent radiation efficiency. It turns out that it is suitable.
As described above, according to the present embodiment, by providing the meandering portions 13 and 14 on the line 10, the path length of the entire antenna 1 is increased without increasing the size of the antenna 1, and the predetermined wavelength is set. A high gain antenna can be obtained. In addition, since the meandering portions 13 and 14 are provided not only in the vicinity of the position that becomes the antinode of the line 10, but also in the position that becomes the node, the adverse effect on the gain due to the provision of the meandering shape portion is suppressed, and a predetermined value is obtained. It is possible to obtain a high-gain antenna adapted to the wavelength of.
In the present embodiment, the two meandering portions 13 and 14 are located at the nodes, but at least one of the plurality of meandering portions may be located at the nodes. By adopting such a configuration, it is possible to reduce the adverse effect of the meandering shape portion on the antenna and increase the gain of the antenna 1 as compared with the case where all of the plurality of meandering shape portions are not located at the nodes. .
In the first embodiment, the case where the power feeding unit 11 is arranged at the center of one side of the rectangular line 10 has been described. However, in the RFID tag according to the first embodiment, the power feeding unit 11 has You may make it arrange | position in any position of 10.
For example, the power feeding unit 11 may be provided at the corners of the line 10 as in Modification 1 shown in FIG. Even in such a case, as shown in FIG. 7, the meandering portions 13 and 14 are provided not only in the vicinity of the position that becomes the antinode of the track 10, but also in the position that becomes the node, that is, the meandering shape portion 13 and 14 are positions on the line 10 excluding the vicinity of the position where the power supply unit 11 is provided and the vicinity of the position where the path length from the power supply unit 11 is half the path length of the line 10, in particular, the line By providing at a position that is 1/4 of the path length of 10, it is possible to obtain a high-gain antenna adapted to a predetermined wavelength while suppressing the adverse effect on the gain due to the provision of the meandering portion.
Further, in the present embodiment, the case where the two meandering portions 13 and 14 are provided has been described. However, in the present invention, not all of the meandering shape portions are arranged near the antinodes of the standing wave. In this case, the meandering shape portion may be one or more.
For example, as in Modification 2 shown in FIG. 8, instead of providing the meandering portions 13 and 14 on the line 10, four meandering portions 15 to 18 are provided on the side extending in the vertical direction of the antenna 1. Anyway. With such a configuration, the path length can be increased without increasing the size of the antenna 1, and the adverse effect on the gain due to the provision of the meandering shape portion can be suppressed to obtain a high gain antenna adapted to a predetermined wavelength. be able to.
Further, in the present embodiment, the case where each of the two meander-shaped portions 13 and 14 is folded is described as 11 times. However, in the present invention, the number of times the meander-shaped portions are folded, The total number of turns of all meandering portions is not limited.
For example, the antenna 1 shown in FIG. 1 may be provided with meandering shape portions 19 and 20 having a number of turns of 5 as shown in FIG. 9 instead of the meandering shape portions 13 and 14. As shown in FIG. 10, meandering-shaped portions 21 and 22 having a folding number of 1 may be provided. Even in such a case, a high-gain antenna similar to that shown in FIG. 1 can be obtained. However, at this time, according to the wavelength of the radio wave used by the antenna 1, the meandering interval P and meandering width W of the meandering shape portions 19 to 22, the thickness of the line 10 in the meandering shape portion, and the like are appropriately adjusted.
As described above, the loop antenna or the like according to the present invention is suitable as an antenna for a small RFID tag, and is particularly useful as an antenna for an RFID tag in the UHF band.
FIG. 3 is a plan view showing the structure of the RFID tag according to the first embodiment. Schematic diagram Schematic diagram showing the relationship between the loop antenna and standing waves Diagram showing the current distribution Figure showing the simulation results Figure showing the simulation results The figure which shows the modification The figure which shows the modification The figure which shows the modification The figure which shows the modification
DESCRIPTION OF SYMBOLS 1 Antenna 2 Dielectric board 3 Integrated circuit 4 Strap 10 Line 11 Feed part 12 Matching circuit 13-22 Meandering part 20 Recess 41 Wiring 42 Dielectric board 100 Tag
A loop antenna for an RFID tag,
An annular track having one or more meandering portions;
A power supply section provided on the line,
The loop line has the meandering portion in addition to the vicinity of the position that becomes the antinode of the standing wave generated in the loop antenna.
2. The loop antenna according to claim 1, wherein the annular line has at least one of the meandering shape portions at a position that becomes a node of a standing wave generated in the loop antenna.
The annular line is in a position excluding the vicinity of the position where the feeding unit is provided on the annular line and the vicinity of the position where the path length from the feeding part is half the path length of the entire line. A loop antenna having the meandering shape portion.
The annular line has at least one of the meandering portions at a position where a path length from the power feeding unit on the annular line is 1/4 of a path length of the line. Item 4. The loop antenna according to item 3.
The annular track has a rectangular shape,
The loop according to any one of claims 1 to 4, wherein the annular line has the one or more meandering shape portions on a side other than a side where the power feeding unit is arranged and a side facing the side. antenna.
The antenna according to claim 1, further comprising a matching circuit connected to the power feeding unit.
An RFID tag comprising the loop antenna according to any one of claims 1 to 6, an integrated circuit connected to the power feeding unit, and a dielectric substrate on which the loop antenna is disposed.
JP2006047868A 2006-02-24 2006-02-24 Loop antenna and rfid tag Pending JP2007228326A (en)
US11/588,272 US20070200708A1 (en) 2006-02-24 2006-10-27 Loop antenna and RFID tag
JP2007228326A true JP2007228326A (en) 2007-09-06
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2006-02-24 JP JP2006047868A patent/JP2007228326A/en active Pending
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