JP5218251B2 - RFID tag reader - Google Patents

Description

  The present invention relates to an RFID tag reader that reads information stored in an RFID tag.

  The RFID tag reader includes an antenna for wirelessly communicating with the RFID tag, transmits radio waves from the antenna to the RFID tag, and reads information superimposed on the radio waves returned from the RFID tag. As such an RFID tag reader, for example, a device including a dipole antenna is known (Patent Document 1). Further, a chip antenna having a meandering (meandering) conductor is known (Patent Document 2).

Japanese Patent Laying-Open No. 2006-303907 (paragraphs 35 to 37, FIGS. 1, 3 and 6). JP 2000-278037 A (45th paragraph, FIG. 5).

  In an RFID tag reader having a dipole antenna, the dipole antenna is arranged in the width direction of the device. Therefore, if the device is downsized in the width direction, the dipole antenna protrudes from the device, so that downsizing is difficult. Therefore, as shown in FIG. 25, a structure in which both ends of the dipole antenna 60 are bent inward twice to shorten the width of the dipole antenna is conceivable. However, since self-coupling occurs between the linear portion 61 of the dipole antenna 60 and the linear portion 62 formed by bending, the gain of the antenna is reduced.

In addition, in the RFID tag reader provided with a two-element Yagi antenna, as shown in FIG. 26, when both end portions of the radiating element 71 and the reflecting element 72 are bent, the linear portions 71a and 71b and straight lines are also formed. Since self-coupling occurs between the shaped portions 72a and 72b, the gain of the antenna is reduced.
Therefore, the inventor of the present application considered a structure in which the antenna gain is increased by forming the bent portion 62a of the dipole antenna 60 in a meander shape as shown in FIG. 27 (a), but a desired gain is obtained. I couldn't. In addition, as shown in FIG. 27B, a structure is considered in which the gain of the antenna is increased by forming the linear portions 71b and 72b of the radiating element 71 and the reflecting element 72 in a meander shape. Couldn't get.

  Accordingly, the present invention has been made to solve the above-described problems, and an object of the present invention is to realize an RFID tag reader that can increase the gain of the antenna and can reduce the size of the device. And

In order to achieve the above object, the first feature of the present invention is that the information recorded in the RFID tag is read by communicating with the RFID tag (50) by radio waves via the dipole antenna (30). In the configured RFID tag reader (1), the elements constituting the dipole antenna are bent to the same side from both ends of the linear portion (30a) connected to the feeder and the linear portion, A pair of bent portions (30c) facing each other, each of the pair of bent portions being formed in a meander shape that is folded back multiple times, and at least of the meander-shaped portion (30d) in a predetermined range from both ends of the linear portion, the folded portion becomes formed to be longer as the distance from the straight portion, folded them the Part of the end portion of each of the outer, an RFID tag reader which is located perpendicular line passing through the ends of the perpendicular to the straight portion and the straight portion.

The second feature of the present invention is that radio waves are communicated with the RFID tag (50) via the antenna (20) having the radiating element (21), the waveguide element (23), and the reflecting element (22). In the RFID tag reader (1) configured to read information recorded in the RFID tag, at least one of the radiation element, the waveguide element, and the reflection element is a linear portion (21a, 23a, 22a). And a pair of bent portions (21c, 23c, 22c) that are bent on the same side from both ends of the linear portion toward one of the other elements, and the pair of bent portions Are each formed in a meander shape that is folded back multiple times, and among the meander portions, the folded portion (at least within a predetermined range from both ends of the linear portion) ( 1d, 23d, 22 d) is formed to be longer as the distance from the straight portion, of which the folded portion, the ends of each of the outer, orthogonal and the linear and the linear part The RFID tag reader is located on an orthogonal line passing through the end of the unit .

The third feature of the present invention is recorded in the RFID tag by communicating with the RFID tag (50) by radio waves via the antenna (20) having the radiating element (21) and the waveguide element (23). In the RFID tag reader (1) configured to read the information that is read, at least one of the radiating element and the waveguide element includes a linear part (21a, 23a) and the other part from both ends of the linear part. A pair of bent portions (21c, 23c) that are bent on the same side toward the element and are opposed to each other, and the pair of bent portions are each formed in a meander shape that is folded back multiple times, And among each meander-shaped portion, at least in a predetermined range from both ends of the linear portion, the folded portions (21d, 23d) become longer as they move away from the linear portion. So as to be formed becomes, the thereof the folded portion, the ends of each of the outer, RFID tags are located perpendicular line passing through the ends of the perpendicular to the straight portion and the straight portion It is a reading device.

A fourth feature of the present invention is recorded on the RFID tag by communicating with the RFID tag (50) by radio waves via the antenna (20) having the radiating element (21) and the reflecting element (22). In the RFID tag reader (1) configured to read the information that is present, at least one of the radiating element and the reflecting element is connected to the linear part (21a, 22a) and the other element from both ends of the linear part. A pair of bent portions (21c, 22c) that are bent to the same side toward each other, and the pair of bent portions are each formed in a meander shape that is folded back multiple times, and Of each meander-shaped portion, at least in a predetermined range from both ends of the linear portion, the folded portions (21d, 22d) become longer as they move away from the linear portion. So as to be formed becomes, the thereof the folded portion, the ends of each of the outer, RFID tags are located perpendicular line passing through the ends of the perpendicular to the straight portion and the straight portion It is a reading device.

  Furthermore, a fifth feature of the present invention is that in the RFID tag reader (1) having the third or fourth feature described above, the radiating element (21) and the elements (22, 23) other than the radiating element are: The linear portions (22a, 23a) and a pair of bent portions (22c, 23c) are provided, and each bent portion is formed in a meander shape by being folded back multiple times, and each meander shape. The folded portions (22d, 23d) are formed so as to become longer as they move away from the linear portion, at least in a predetermined range from both ends of the linear portion.

  According to a sixth aspect of the present invention, in the RFID tag reader (1) having any one of the first to fifth features described above, at least one meander-shaped portion of the meander-shaped portions. At least in the predetermined range, the folded portions (21d, 23d, 22d) become longer as they move away from the linear portions (21a, 23a, 22a), and in the middle, as they move away from the linear portions. It is to be formed to be shorter.

  A seventh feature of the present invention is the RFID tag reader (1) having any one of the first to sixth features described above, wherein at least one meander-shaped portion of the meander-shaped portions. Is a tapered shape in which the apex of the portions (21d, 23d, 22d) formed in a mountain shape facing inward at least in the predetermined range has an acute angle formed by the side forming the apex and the linear portion It is to be formed.

  An eighth feature of the present invention is that, in the RFID tag reader (1) having the seventh feature described above, at least the top in the predetermined range is formed in a tapered curved surface swelled inward. is there.

  According to a ninth feature of the present invention, in the RFID tag reader (1) having any one of the first to eighth features described above, at least one meander-shaped portion of the meander-shaped portions. Is that at least the predetermined range is formed non-parallel to the linear portion.

  In addition, the code | symbol in each said parenthesis shows the correspondence with the specific means as described in embodiment mentioned later.

The first feature is that, in the dipole antenna, among the meandering portions formed at the bent portions at both ends of the linear portion, the folded portion moves away from the linear portion at least within a predetermined range from both ends of the linear portion. It is to be formed so as to become longer.
Therefore, according to the RFID tag reader having the first feature described above, since the self-coupling between the folded portions can be reduced, the gain of the dipole antenna can be increased and the device can be downsized. Can be achieved.

A second feature of the antenna having a radiating element, a waveguide element, and a reflecting element is a meander-shaped portion in which at least one of the radiating element, the waveguide element, and the reflecting element is formed at the bent portions at both ends of the linear portion. Among them, at least in a predetermined range from both ends of the linear portion, the folded portion is formed to become longer as the distance from the linear portion increases.
Therefore, according to the RFID tag reader having the second feature described above, since the self-coupling between the folded portions can be reduced, the gain of the antenna having the radiating element, the waveguide element, and the reflecting element is increased. And the size of the apparatus can be reduced.

The third feature is that, in an antenna having a radiating element and a waveguide element, at least one of the radiating element and the waveguide element is at least linear among the meandering portions formed at the bent portions at both ends of the linear portion. In the predetermined range from both ends of the part, the folded part is formed so as to become longer as the distance from the linear part increases.
Therefore, according to the RFID tag reader having the third feature described above, since the self-coupling between the folded portions can be reduced, the gain of the antenna having the radiating element and the waveguide element can be increased. And size reduction of an apparatus can be achieved.

  In particular, according to the fifth feature, of the meandering portions of both the radiating element and the waveguide element, at least in a predetermined range from both ends of the linear portion, the folded portion becomes longer as the distance from the linear portion increases. Thus, the antenna gain can be further increased.

A fourth feature is that, in an antenna having a radiating element and a reflecting element, at least one of the radiating element and the reflecting element is at least of the linear portion among the meandering portions formed at the bent portions at both ends of the linear portion. In the predetermined range from both ends, the folded portion is formed to become longer as the distance from the linear portion increases.
Therefore, according to the RFID tag reader having the fourth feature described above, since the self-coupling between the folded portions can be reduced, the gain of the antenna having the radiating element and the reflecting element can be increased, In addition, the apparatus can be reduced in size.

  In particular, according to the fifth feature, of the meandering portions of both the radiating element and the reflecting element, at least in a predetermined range from both ends of the linear portion, the folded portion becomes longer as the distance from the linear portion increases. Thus, the antenna gain can be further increased.

  A sixth feature is that at least one meander-shaped portion of each meander-shaped portion becomes longer as the folded portion moves away from the straight-line portion at least within the predetermined range, and from the middle of the meander-shaped portion, It is to be formed so as to become shorter as the distance from the portion increases.

  Therefore, according to the RFID tag reader having the sixth feature, the self-coupling between the folded portion and the linear portion can be reduced.

In particular, in an antenna in which elements are arranged to face each other, when a bent portion extends in the opposite direction from both ends of each linear portion, the meander-like portion formed in each bent portion is folded back. If the bent portion is formed so as to become longer as it moves away from the linear portion, the portion farthest from the linear portion among the folded portions becomes the longest.
Accordingly, since the longest folded portions approach each other in the elements facing each other, self-coupling between the folded portions increases.

  Therefore, by forming the meander portion of each element as in the sixth feature, it is possible to prevent the longest folded portions from approaching each other, so that the self-coupling between the folded portions can be reduced. it can.

  According to the seventh feature, among each meander-shaped portion, at least one meander-shaped portion has at least the top portion of the portion formed in a mountain shape facing inward in the predetermined range. Since the angle formed between the side and the linear portion is formed in a tapered shape, the element length can be increased, and thus the antenna gain can be further increased.

  According to the eighth feature, since at least the top portion in the predetermined range is formed in a tapered curved surface swelled inward, the self-coupling between the linear portion and the other folded portion is reduced. Can do.

  According to the ninth feature, at least one meander-shaped portion of each meander-shaped portion is formed such that at least the predetermined range is formed non-parallel to the straight-line portion. The self-coupling with the linear portion can be reduced.

1 is a top view showing an external appearance of an RFID tag reader according to a first embodiment of the present invention. It is a left view of the tag reader shown in FIG. It is a front view of the tag reader shown in FIG. It is explanatory drawing of an antenna, (a) is a top view of an antenna, (b) is the elements on larger scale of the antenna shown to (a). It is explanatory drawing which shows the main electrical structures of a tag reader. It is plane explanatory drawing of the antenna used by the simulation in examination 1 of meander structure. It is plane explanatory drawing of the antenna used by the simulation in examination 2 of meander structure. It is a graph which shows the result of the simulation in examination 2 of meander structure. It is a top view of the conventional antenna used for the simulation 1. FIG. It is a top view of the antenna of the invention 1. It is a graph which shows the VSWR (voltage standing wave ratio) characteristic of the conventional antenna. 6 is a graph showing the VSWR characteristics of the antenna of the first invention. It is a top view of the antenna of the invention 2 used for the simulation 2. FIG. It is a graph which shows the VSWR characteristic of the antenna of the invention 2. It is a chart which shows the measurement result of the conventional antenna collectively. It is a table | surface which shows the measurement result of the antenna of invention 2 collectively. It is explanatory drawing of the antenna with which the tag reader which concerns on the example of a change of 1st Embodiment was equipped. It is explanatory drawing which shows the example of a change of an antenna. It is explanatory drawing which shows the example of a change of an antenna. It is explanatory drawing which shows the example of a change of an antenna. It is explanatory drawing which shows a 3 element Yagi antenna. It is plane explanatory drawing of the dipole antenna with which the tag reader which concerns on 2nd Embodiment was equipped. It is explanatory drawing which shows the example of a change of an antenna. It is explanatory drawing which shows the example of a change of an antenna. It is explanatory drawing of the conventional dipole antenna. It is explanatory drawing of the conventional Yagi antenna. (A) is explanatory drawing of the dipole antenna in which the bending part was formed in the meander shape, (b) is explanatory drawing of the Yagi antenna in which the bending part was formed in the meander shape.

<First Embodiment>
A first embodiment according to the present invention will be described with reference to the drawings. FIG. 1 is a top view showing an external appearance of an RFID tag reader (hereinafter referred to as a tag reader) according to the first embodiment. FIG. 2 is a left side view of the tag reader shown in FIG. FIG. 3 is a front view of the tag reader shown in FIG. 4A and 4B are explanatory views of the antenna. FIG. 4A is a plan view of the antenna, and FIG. 4B is a partially enlarged view of the antenna shown in FIG.

[Main components of tag reader]
As shown in FIG. 1, the tag reader 1 includes a case 13, and a display unit 11 and a key operation unit 12 are provided on the upper surface of the case 13. The antenna 20 for communicating with 50 is incorporated. As shown in FIGS. 2 and 3, the antenna 20 has a configuration in which the waveguide element is omitted from the two elements of the radiating element 21 and the reflecting element 22, that is, the Yagi antenna.

  As shown in FIG. 3, when the tag reader 1 is viewed from the front, the reflective element 22 is disposed above the radiating element 21, and the directivity of the antenna 20 is downward. For this reason, when reading the information of the tag 50, as shown in FIG. 2, it is used in a state where the front end back surface of the tag reader 1 faces the tag 50.

As shown in FIG. 4A, the radiating element 21 and the reflecting element 22 are patterned into a film shape on the substrate surface of the substrate 14 by a conductive material, and the substrate surface is the same substrate as the substrate 14. It is covered with the substrate surface. That is, the antenna 20 is held between the substrates.
Copper or the like can be used as the conductive material, and the substrate can be formed of a resin such as an elastomer or a dielectric material such as ceramic. The radiating element 21 is connected to a feeder line (not shown).

  The radiating element 21 includes a linear portion 21a formed in a linear shape and a pair of opposing bent portions bent at right angles from the bending points (both ends) 21b and 21b of the linear portion 21a toward the reflecting element 22, respectively. 21c, 21c. Each of the bent portions 21c is formed in a meander shape that is folded back a plurality of times. At least in a predetermined range from the bent point 21b, the bent portion becomes longer as the distance from the linear portion 21a increases. It forms so that it may become short as it distances from the shape part 21a. Hereinafter, of the meander-shaped portion, a portion formed in a mountain shape facing inward is referred to as a meander portion.

  Each meander part 21d is arranged at equal intervals in parallel with the linear part. Here, with reference to FIG. 4B, the left meander part 21d will be described as an example. The top part 21e of the central meander part 21d3 is formed flat so that the angle formed by the side forming the top part and the straight part 21a is perpendicular. Each top portion 21e of each meander portion 21d other than the central meander portion 21d3 is tapered so that the angle formed by the side forming the top portion 21e and the linear portion 21a is an acute angle.

  The top portions 21e of the meander portions 21d2 and 21d1 disposed between the central meander portion 21d3 and the linear portion 21a are formed in a tapered shape inclined toward the bending point 21b of the linear portion 21a. The tops 21e of the meander parts 21d4 and 21d5 on the opposite side across the meander part 21d3 and the central meander part 21d3 are formed in a tapered shape inclined toward the top part 21e of the central meander part 21d3. In this embodiment, the meander parts 21d1, 21d2 and the meander parts 21d4, 21d5 are formed line-symmetrically with the central meander part 21d3 as the axis of symmetry.

  The reflective element 22 is formed in a line-symmetric shape with the radiating element 21 when the virtual line 14a is taken as the axis of symmetry. The reflecting element 22 includes a linear portion 22a formed in a linear shape and a pair of opposing bent portions bent at right angles from the bending points (both ends) 22b and 22b of the linear portion 22a toward the radiating element 21. 22c, 22c. Each of the bent portions 22c is formed in a meander shape that is folded back a plurality of times. At least in a predetermined range from the bent point 22b, the bent portion becomes longer as the distance from the straight portion 22a increases. It forms so that it may become short as it distances from the shape part 22a. Further, the shape, size, and arrangement interval of each meander part 22 d are the same as those of the meander part 21 d of the radiating element 21.

[Electric configuration of tag reader]
FIG. 5 is an explanatory diagram showing the main electrical configuration of the tag reader. As shown in the figure, the tag reader 1 includes a main control unit 2, a transmission circuit 3, a reception circuit 4, a memory 5, an amplification circuit 6, a filter circuit 7, a circulator 8, a power supply circuit 9, A battery 10 is provided. An antenna 20 is connected to the circulator 8, and a display unit 11 and a key operation unit 12 are connected to the main control unit 2.

  The key operation unit 12 includes a numeric keypad, a trigger switch (not shown) that is operated when reading data from an RFID tag (hereinafter referred to as a tag) 50 is started. The display unit 11 is configured by a liquid crystal display device or the like, and displays the operation state of the tag reader 1 and data read from the tag 50.

  The main control unit 2 includes a CPU, a ROM, a RAM, and the like, and controls the operation of the tag reader 1 according to an operation signal given from the key operation unit 12. Further, the main control unit 2 executes a process for outputting data to the transmission circuit 3, a process for storing data input from the reception circuit 4 in the memory 5, and the like.

  Although the detailed configuration of the transmission circuit 3 is not shown, a conversion circuit that converts data output from the main control unit 2 into a modulation signal, and an ASK (Amplitude Shift Keying) modulation of the signal from the conversion circuit And a modulation circuit. The amplifier circuit 6 amplifies the signal from the modulation circuit with a predetermined amplification factor. The filter circuit 7 passes only a signal having a necessary frequency among the signals from the amplifier circuit 6.

  The circulator 8 prevents the high-frequency signal output from the filter circuit 7 from flowing in the reverse direction. That is, the high frequency signal input from the filter circuit 7 side is output to the antenna 20, and the high frequency signal input from the antenna 20 is output to the reception circuit 4 side. The antenna 20 transmits a high frequency signal as a radio signal to the tag 50 and receives a radio signal from the tag 50.

  Although the detailed configuration of the receiving circuit 4 is not shown, the demodulating circuit that demodulates the signal received by the antenna 20 and output from the circulator 8, and the binarizing circuit that binarizes the signal from the demodulating circuit And a restoration circuit for restoring the response signal from the tag 50 based on the digital data from the binarization circuit. The power supply circuit 9 supplies operating power to the display unit 11 and each circuit based on the power supplied from the battery 10.

  The memory 5 includes a control command storage area 5a shown in FIG. 3, and the control command storage area 5a stores the control command selected by the main control unit 2 from the control command table 2a in an updatable manner. The memory 5 stores the number of tags input by the operator as the number of tags to be read and the number of tags actually read. In this embodiment, the memory 5 is a memory that can rewrite stored data, and is, for example, a flash memory such as an EEPROM, or a RAM.

  In this embodiment, the tag reader 1 and the tag 50 communicate according to the Gen2 (Global Class 1 Generation 2) communication standard of EPC (Electronic Product Code). The communication frequency is the UHF band (0.95 GHz band).

[Examination of meander structure 1]
The inventor of the present application performed a simulation for examining a change in antenna gain due to a difference in antenna meander structure. FIG. 6 is an explanatory plan view of the antenna used in this simulation. This simulation was performed by sandwiching the upper and lower surfaces of the antenna with a dielectric having a dielectric constant ε = 3 and a dielectric having a dielectric constant ε = 10.

  As shown in FIG. 6A, the antenna 40 includes a radiating element 41 and a reflecting element 42. The radiating element 41 includes a linear portion 41a formed in a linear shape and a pair of opposing bent portions bent at right angles from the bending points (both ends) 41b and 41b of the linear portion 41a toward the reflecting element 42. 41c, 41c.

  The reflective element 42 includes a linear portion 42a formed in a linear shape, and a pair of opposing bent portions bent at right angles from the bending points (both ends) 42b and 42b of the linear portion 42a toward the radiating element 41, respectively. 42c, 42c. A portion consisting of a broken line indicated by reference numeral 42d is a meander portion formed by bending a part of the reflective element 42 into a U-shape.

  Then, the inventor of the present application measured the value of the current flowing through the meander part 42d when the dielectric is disposed on both sides of the antenna and the formation position of the meander part 42d is changed. Then, the position where the current was small was evaluated as the position where the loss was small.

  As a result, when two meander portions 42d were formed on both sides of the center P1 of the linear portion 42a, the current value at P1 was 15 A / m. Further, when one meander part 42d is formed in the vicinity of the bending points 42b of the linear part 42a, the current value at each P2 is 10 A / m. Further, when one meander part 42d was formed at each of the distal ends P3 and P3 of the bent parts 42c and 42c, the current value at each P3 was 2.5 A / m.

When the above current values were converted into antenna gain (antenna alone), P1 of the linear portion 42a was 1.7 dBi, P2 was 2.9 dBi, and P3 of the bent portion 42c was 3.2 dBi.
That is, as shown in FIG. 3B, it was found that the antenna gain was highest when one meander part 42d was formed at each end of the bent parts 42c and 42c.

[Examination of meander structure 2]
Next, the inventor of the present application performed a simulation for examining the relationship between the self-coupling between the meander portion and the linear portion and the coupling between the radiating element and the reflecting element. FIG. 7 is a plan view of the antenna used in this simulation. FIG. 8 is a graph showing the results of this simulation.

  In this simulation, the distance D1 between the tip of the bent portion 41c of the radiating element 41 and the linear portion 42 of the reflecting element 42 was maintained at 20 mm. The antenna gain (transmission direction gain) was measured when the distance D2 between the tip of the bent portion 41c of the radiating element 41 and the meander portion 42d of the reflecting element 42 was changed.

  As a result, as shown in FIG. 8, the antenna gain was about 0.5 dBi when the distance D2 was 3 mm, increased as the distance D2 became longer, and exceeded 3 dBi when the distance D2 was 11 mm. The antenna gain was maintained at 3 dBi even when the distance D2 reached 13 mm, and was less than 3 dBi when it reached 15 mm after exceeding 13 mm.

  That is, it was found that an antenna gain of 3 dBi or more can be obtained if the distance D2 between the tip of the bent portion 41c of the radiating element 41 and the meander portion 42d of the reflecting element 42 is set to 11 to 13 mm. In other words, the antenna gain is more influenced by the inter-element coupling F2 between the tip of the bent portion 41c of the radiating element 41 and the meander part 42d than by the self-coupling F1 between the meander part 42d and the linear part 42a of the reflecting element 42. It turns out that is more dominant.

[Conclusion]
From the results of the examination 1 and the examination 2 described above, each meander part of the radiating element 41 and the reflecting element 42 is formed at the tip of each bent part 42c, and the distance between the radiating element 41 and the reflecting element 42 is 11 to 11. It was found that an antenna gain of 3 dBi or more can be secured by setting to 13 mm.

[Simulation 1]
Next, the present inventor created an antenna (hereinafter referred to as the antenna of the invention 1) based on the above conclusion, and compared the performance with a conventional antenna. FIG. 9 is a plan view of a conventional antenna used in the simulation 1. FIG. FIG. 10 is a plan view of the antenna of the first invention. FIG. 11 is a graph showing the VSWR (voltage standing wave ratio) characteristic of the conventional antenna, and FIG. 12 is a graph showing the VSWR characteristic of the antenna of the first invention.

  In this simulation, the upper and lower surfaces of the antenna were sandwiched with a dielectric. The dielectric has a size of 60 × 90 mm, a thickness of 2.5 mm, a dielectric constant ε = 3, and a dielectric loss tangent (dielectric loss) tan δ=0.004@0.953 GHz. The total length W of the radiating element and the reflecting element was unified to 80 mm, and the arrangement interval L between both elements was unified to 50 mm. The meander interval ML was unified to 2 mm, and the line widths of the radiating element and the reflecting element were unified to 1 mm.

  As shown in FIG. 9, the radiating element 41 of the conventional antenna 40 includes a straight portion 41a and a pair of bent portions 41c that are bent from the bending point 41b of the linear portion 41a toward the reflecting element 42 and face each other. With. Each bent part 41c has a plurality of meander parts 41d parallel to the linear part 41a. The reflecting element 42 has a shape symmetrical with the radiating element 41, and includes a linear portion 42 a and a pair of bent portions that are bent toward the radiating element 41 from a bending point 42 b of the linear portion 42 a and face each other. 42c, and each bent part 42c has a plurality of meander parts 42d parallel to the linear part 42a.

  As shown in FIG. 10, the radiating element 21 of the antenna 20 of the invention 1 includes a straight portion 21a and a pair of bent portions that are bent from the bending point 21b of the linear portion 21a toward the reflecting element 22 and face each other. 21c. Each bent part 21c has meander parts 21d1, 21d2, and 21d6 parallel to the linear part 21a. The reflecting element 22 is formed in a line-symmetric shape with the radiating element 21, and has a linear portion 22 a and a pair of bent portions that are bent toward the radiating element 21 from a bending point 22 b of the linear portion 22 a and are opposed to each other. Part 22c. Each bent portion 22c has meander portions 22d1, 22d2, and 22d6 that are parallel to the linear portion 22a.

  In the radiating element 21 and the reflecting element 22, the length protruding inward of each meander part is the shortest at the meander part closest to the straight part and the meander part farthest from the straight part, and the longest at the central meander part. It has become. In other words, the length protruding inward of each meander portion is formed so as to increase as the distance from the linear portion increases, and from the middle thereof, the length decreases as the distance from the linear portion increases. The distance W1 between the shortest opposing meander parts is 68 mm, and the distance W2 between the longest meander parts is 58 mm. The gain (including loss) and radiation efficiency of the conventional antenna and the antenna of Invention 1 were measured.

[Result 1]
As a result, the gain of the antenna was 2.62 dBi for the conventional antenna, but 2.68 dBi for Invention 1, and if the antenna of Invention 1 is used, the gain will be 0.06 dB higher than the conventional. I found out that I could do it. In addition, the radiation efficiency of the conventional antenna was 0.8541, whereas the invention 1 is 0.8609. If the antenna of the invention 1 is used, the radiation efficiency is increased by 0.0068 compared to the conventional antenna. I found out that

  It was estimated that the reason why the antenna gain could be increased in this manner was that the self-coupling with the linear portion could be reduced by shortening the meander portion close to the linear portion. It was also estimated that the element length (element length) could be increased by lengthening the meander portion as it moved away from the linear portion, which was also a factor in improving the antenna gain.

  Furthermore, since the meander part 21d6 farthest from the linear part 21a of the radiating element 21 and the meander part 22d6 farthest from the linear part 22a of the reflective element 22 are brought close to each other, the meander parts 21d6 and 22d6 provide the element. Interbonding is likely to occur. Therefore, it was estimated that one of the factors was that the coupling between the elements could be reduced by shortening the protruding length of the meander portions 21d6 and 22d6.

  That is, each meander part is formed such that the length protruding inward becomes longer as it goes away from the linear part, and from the middle it becomes shorter as it gets away from the linear part, thereby reducing the antenna gain and radiation efficiency. It turned out that it can raise.

[Simulation 2]
Next, the inventor of the present application created an antenna in which the top of the meander portion was formed in a tapered shape (hereinafter referred to as the antenna of the invention 2), and performed a simulation. FIG. 13 is a plan view of the antenna of the invention 2 used in this simulation 2. FIG. FIG. 14 is a graph showing the VSWR characteristics of the antenna of the second invention. The conditions for simulation are the same as those for simulation 1.

  As shown in FIG. 13, the feature of the antenna 20 of the invention 2 is that the top of each meander part of the antenna of the invention 1 (FIG. 10) is tapered. The radiating element 21 includes a linear portion 21a, and a pair of bent portions 21c that are bent toward the reflecting element 22 from a bending point 21b of the linear portion 21a. Each bent part 21c has meander parts 21d1, 21d2, and 21d6 parallel to the linear part 21a. A meander part 21d6, which is the farthest from the linear part 21a and formed at the tip of the bent part 21c, is formed in a linear shape and protrudes inward. The meander part 21d6 is the shortest of the meander parts.

  The top of the meander part 21d1 closest to the straight part 21a is formed in a taper shape toward the bending point 21b. The length protruding inward of the meander part 21d2 adjacent to the meander part 21d1 is longer than the meander part 21d1, and the top part is formed in a taper shape toward the meander part 21d6. The reflective element 22 is formed in line symmetry with the radiating element 21 and includes a linear portion 22a and a pair of bent portions 22c. Each bent portion 22c has meander portions 22d1, 22d2, and 22d6 that are parallel to the linear portion 22a.

  Further, the interval W1 between the meander portions 22d6 (21d6) facing each other is 74 mm, the interval W2 between the meander portions 22d1 (21d1) facing each other is 64 mm, and the interval between the meander portions 22d2 (21d2) facing each other. W3 is 54 mm.

[Result 2]
As a result of simulation, it has been found that the gain of the antenna is 2.75 dBi, and the gain can be increased by 0.13 dBi compared to the conventional case. Also, the radiation efficiency was 0.8724, and it was found that the radiation efficiency can be increased by 0.0183 compared to the conventional case.

  As described above, the antenna gain of the antenna of the invention 2 can be higher than that of the antenna of the invention 1 because the top of each meander part is formed in a taper shape, thereby increasing the element length (element length). It was estimated that it was possible.

  That is, each meander part is formed such that the length protruding inward becomes longer as it goes away from the linear part, and from the middle it becomes shorter as it goes away from the linear part, and the top part of each meander is tapered. It has been found that the antenna gain and the radiation efficiency can be further increased by forming in the shape.

[Simulation 3]
Next, the inventor of the present application changed the overall length W of the radiating element and the reflecting element, the arrangement interval L of both elements, and the interval ML of the meander part based on the above result 2, and performed simulation again. FIG. 15 is a chart collectively showing the measurement results of the conventional antenna, and FIG. 16 is a chart collectively showing the measurement results of the antenna of the invention 2.

[Result 3]
As shown in FIGS. 15 and 16, even when the total length W of the radiating element and the reflecting element, the arrangement interval L between both elements, and the interval ML between the meander portions are changed, the antenna of the invention 2 has an antenna gain higher than that of the conventional antenna. It was found that the radiation efficiency (VSWR) can be increased.

[Conclusion]
From the above results 1 to 3, each meander part is formed such that the length protruding inward becomes longer as it goes away from the linear part, and from the middle it becomes shorter as it gets away from the linear part, and The antenna gain and radiation efficiency can be increased by forming the top of each meander part into a taper shape in which the angle formed by the side forming the top part and the linear part is an acute angle.

  Thereafter, the inventor of the present application further researched, and by increasing the number of meander portions in the antenna of the invention 2, the element length can be increased, and the antenna gain and radiation efficiency can be further increased (FIG. 4). Developed.

[Example of change]
(1) FIG. 17 is an explanatory diagram of an antenna provided in a tag reader according to a modification of the first embodiment. This antenna is characterized in that the top portions of the meander portion 21d of the radiating element 21 and the meander portion 22d of the reflecting element 22 are formed in a tapered curved surface swelled inward. Except for the top of the meander part, it is the same as the antenna 20 (FIG. 4) of the first embodiment described above.

The left bent portion 21c of the radiating element 21 will be described as an example. As shown in FIG. 17B, each of the top portions 21e of the meander portions 21d1 to 21d5 is formed in a tapered curved surface that swells inward.
As described above, the inventor of the present application estimated that the self-coupling between the linear portion and the meander portion can be reduced by forming the top portion of each meander portion into a tapered curved surface swelled inward.

(2) FIG. 18 is an explanatory diagram showing a modification example of the antenna. Each meander part 21 d of the radiating element 21 is formed non-parallel to the linear part 21 a and extends in a direction approaching the reflecting element 22. Each meander portion 22 d of the reflective element 22 is formed non-parallel to the linear portion 22 a and extends in a direction approaching the radiating element 21. The inventor of the present application can increase the distance between the meander part and the linear part by forming each meander part as described above, thereby reducing the self-coupling between the meander part and the linear part. Estimated to be able to.

(3) FIG. 19 is an explanatory diagram showing a modification example of the antenna. The configuration is the same as that of the antenna 20 of the first embodiment, except that the top portions of the meander portions 21d and 22d are formed flat. Even when the antenna 20 shown in FIG. 19 is used, the antenna gain and the radiation efficiency can be increased as compared with the conventional antenna.

(4) Moreover, as shown in FIG. 20, an antenna having a meander part that becomes longer as it gets away from the linear part can be used. Even when this antenna is used, the antenna gain and the radiation efficiency can be increased as compared with the conventional antenna.

(5) Furthermore, as shown in FIG. 21, a 3-element Yagi antenna can also be used. The antenna 20 includes three elements, that is, a radiating element 21, a waveguide element 23, and a reflecting element 22. The meander portion 21d of the radiating element 21 is formed so as to become longer as the distance from the linear portion 21a increases, and from the middle thereof, the meander portion 21d becomes shorter as the distance from the linear portion 21a increases.

  The meander part 22d of the reflective element 22 is formed so as to become longer as the distance from the linear part 22a increases. The waveguide element 23 is bent in a radial direction (direction indicated by a white arrow in the figure) from a straight portion 23a and bending points 23b at both ends of the straight portion 23a, and a pair of opposite bent portions. 23c. Each bent portion 23c has a plurality of meander portions 23d that become longer as the distance from the linear portion 23a increases. Even when the three-element Yagi antenna is used, the antenna gain and the radiation efficiency can be increased as compared with the conventional antenna.

(6) The antenna 20 may have a two-element configuration of a radiating element and a waveguide element. Also in this configuration, the antenna gain and the radiation efficiency can be increased as compared with the conventional antenna by forming the meander portion of each element as in the first embodiment and the modifications described above. When the reflecting element and the waveguide element are parasitic elements, in the two-element antenna of the parasitic element and the radiating element, the parasitic element is guided up to a predetermined length (for example, about 0.48λ). It operates as a wave element, and when it exceeds a predetermined length, the main radiation direction is reversed and it operates as a reflection element. In addition, the gain and FB ratio can be made higher when the parasitic element is operated as a reflective element than when the parasitic element is operated as a waveguide element.

(7) In the two-element configuration or the three-element configuration described above, the bent portion of each element may be formed from both ends of the linear portion toward the radio wave transmission direction or toward the radio wave reception direction. May be. Even when this configuration is used, the same effects as those of the first embodiment and the modified examples can be obtained.

Second Embodiment
Next explained is the second embodiment of the invention. The tag reader according to this embodiment includes a dipole antenna. FIG. 22 is an explanatory plan view of a dipole antenna.

  The dipole antenna 30 includes a linear portion 30a connected to the feeder line, and a pair of bent portions 30c that are bent from the bending points 30b at both ends of the linear portion 30a and face each other. Each bent portion 30c includes a plurality of meander portions 30d that are formed longer as the distance from the linear portion 30a increases. Moreover, the top part of each meander part 30d is formed in the taper shape inclined toward the bending point 30b.

  Based on the results 1 to 3 of the simulations 1 to 3 of the first embodiment, the inventor can increase the antenna gain and the radiation efficiency in the case of the dipole antenna 30 as compared with the conventional dipole antenna as well. Estimated.

[Example of change]
(1) As shown in FIG. 23, the top part of the meander part 30d can also be formed in the taper curved surface shape swelled inside. If the dipole antenna 30 having this configuration is used, the self-coupling between the linear portion 30a and each meander portion 30d can be reduced, so that the antenna gain can be further increased.

(2) As shown in FIG. 24, the top of each meander part 30d can be formed flat. Even when the dipole antenna 30 having this configuration is used, the antenna gain and the radiation efficiency can be increased as compared with the conventional antenna. Further, each meander part 30d can be formed to become longer as it goes away from the linear part 30a, and from the middle of the meander part 30d to become shorter as it goes away from the linear part 30a. If this configuration is used, the antenna gain and the radiation efficiency can be further increased as compared with the antenna.

1..Tag reader (RFID tag reader), 20..Antenna,
21 .. Radiation element, 22 .. Reflection element, 21a, 22a.
21c, 22c ·· bent portion, 21d, 22d · · meander portion (folded portion),
23 .. Waveguide element, 30... Dipole antenna, 30 a.
30c ·· bent portion, 30d ·· meander portion (folded portion).

Claims (9)

In an RFID tag reader configured to read information recorded on an RFID tag by communicating with the RFID tag by radio waves via a dipole antenna,
The elements constituting the dipole antenna are
A straight section connected to the feeder line;
A pair of bent portions that are bent from the both ends of the linear portion to the same side and are opposed to each other;
The pair of bent portions are each formed in a meander shape that is folded back multiple times, and among the meander portions, at least a predetermined range from both ends of the linear portion, the folded portions are the straight lines. The folded portions are formed so that the outer ends thereof are orthogonal to the linear portion and pass through the end portions of the linear portion. An RFID tag reader characterized by being located . In an RFID tag reader configured to read information recorded on an RFID tag by communicating with the RFID tag by radio waves via an antenna having a radiating element, a waveguide element and a reflecting element,
At least one of the radiating element, the waveguide element, and the reflecting element,
A linear section;
A pair of bent portions that are bent on the same side from both ends of the linear portion toward one of the other elements, and are opposed to each other,
The pair of bent portions are each formed in a meander shape that is folded back multiple times, and among the meander-shaped portions, at least in a predetermined range from both ends of the linear portion, the folded portions are The folded portions are formed so as to become longer as they move away from the linear portion , and the outer ends of the folded portions are on orthogonal lines that are orthogonal to the linear portions and pass through the ends of the linear portions. An RFID tag reader characterized by being located in In an RFID tag reader configured to read information recorded in an RFID tag by communicating with the RFID tag by radio waves via an antenna having a radiating element and a waveguide element,
At least one of the radiating element and the waveguide element is
A linear section;
A pair of bent portions that are bent on the same side from both ends of the linear portion toward the other element, and facing each other ;
The pair of bent portions are each formed in a meander shape that is folded back multiple times, and among the meander-shaped portions, at least in a predetermined range from both ends of the linear portion, the folded portions are The folded portions are formed so as to become longer as they move away from the linear portion , and the outer ends of the folded portions are on orthogonal lines that are orthogonal to the linear portions and pass through the ends of the linear portions. An RFID tag reader characterized by being located in In an RFID tag reader configured to read information recorded in an RFID tag by communicating with the RFID tag by radio waves via an antenna having a radiating element and a reflective element,
At least one of the radiating element and the reflecting element is
A linear section;
A pair of bent portions that are bent on the same side from both ends of the linear portion toward the other element, and facing each other ;
The pair of bent portions are each formed in a meander shape that is folded back multiple times, and among the meander-shaped portions, at least in a predetermined range from both ends of the linear portion, the folded portions are The folded portions are formed so as to become longer as they move away from the linear portion , and the outer ends of the folded portions are on orthogonal lines that are orthogonal to the linear portions and pass through the ends of the linear portions. An RFID tag reader characterized by being located in The radiating element and an element other than the radiating element each include the linear portion and a pair of bent portions,
Each of the bent portions is formed in a meander shape by being folded back multiple times, and among the meander portions, at least in a predetermined range from both ends of the linear portion, the folded portion is the straight line. 5. The RFID tag reader according to claim 3, wherein the RFID tag reader is formed so as to become longer as the distance from the shape portion increases. At least one meander portion of each meander portion is:
2. At least in the predetermined range, the folded portion is formed so as to become longer as the distance from the linear portion increases, and from the middle thereof, the folded portion becomes shorter as the distance from the linear portion increases. The RFID tag reader according to claim 5. At least one meander portion of each meander portion is:
The top of the portion formed in a mountain shape facing inward in at least the predetermined range is formed in a taper shape in which the angle formed between the side forming the top and the linear portion is an acute angle. The RFID tag reader according to any one of claims 1 to 6.   8. The RFID tag reader according to claim 7, wherein at least the top portion in the predetermined range is formed in a tapered curved surface bulging inward. At least one meander portion of each meander portion is:
9. The RFID tag reader according to claim 1, wherein at least the predetermined range is formed non-parallel to the linear portion.

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