JP4688726B2 - Non-contact IC tag reader / writer antenna - Google Patents

Description

  The present invention relates to a reader / writer antenna of a contactless IC tag for communicating with a contactless IC tag by radio waves and writing and reading necessary data. However, in the present invention, the reader / writer includes a reader intended only for reading data.

  Various proposals have been made for a reader / writer antenna for communicating with a non-contact type IC tag in order to increase the gain and increase the communication distance, and to simplify the overall structure and reduce the size and weight. .

For example, a two-stage stack antenna can be configured by forming two sets of dipole antennas on a substrate via a matching circuit (Patent Document 1). In addition, by arranging two sets of antennas having different antenna axes in a three-dimensional manner, it is possible to realize stable communication with a wide range of IC tags (Patent Document 2). Furthermore, for the purpose of simultaneous communication with a large number of IC tags, there is also known a method of disposing a reflector facing an antenna so as to sandwich the IC tag (Patent Documents 3 and 4).
JP 2003-242451 A JP 2005-134942 A JP 2005-94447 A JP 2005-184213 A

  The conventional techniques have the advantages and disadvantages, have a high gain, and cannot be sufficiently miniaturized. That is, the two-stage stack antenna inevitably tends to have an excessive surface area, and the three-dimensional structure antenna can increase the directivity, but the gain is not sufficient, and the reflector is provided so as to sandwich the IC tag. In this case, it is inevitable that the overall size becomes extremely large. It is known that when a reader / writer antenna is miniaturized to a certain limit or more, it is affected by a metal member such as an exterior case or a structural material for attachment, and a so-called body effect is produced.

  Therefore, in view of the problems of the prior art, the object of the present invention is to add a loop to a dipole antenna and further combine a reflector to increase the gain and reduce the size and eliminate harmful body effects. An object of the present invention is to provide a reader / writer antenna for a contactless IC tag that can be used.

  In order to achieve this object, the configuration of the present invention comprises a printed circuit board on which a dipole antenna is formed and a rectangular reflector disposed in parallel with the printed circuit board. In addition to forming a loop connected to the point, a resonance capacitor connected in parallel to the loop is provided, and the reflector is placed on the feeding point of the dipole antenna with the center line in the long side direction parallel to the dipole antenna, The gist is to arrange it at a distance d = (0.04 to 0.23) λ (where λ is the wavelength of the used radio wave) with the printed circuit board.

  The dipole antenna can be set to each element length a = (0.16-0.28) λ, and the loop can be set as a circular loop with a peripheral length b = 0.066πλ. Can be set such that the length c1 = 0.56λ or more and the width c2 = 0.04λ or more.

  In such a configuration, the reflector reflects the radio wave from the dipole antenna on the printed board, and even if a metal member close to the reflector exists in the opposite direction to the printed board side, the effect of this is effective. In addition to minimizing the body effect, the directional characteristics of the dipole antenna can be improved and the gain can be improved. It is best to use a conductive metal plate such as an aluminum plate as the reflecting plate, and set the distance d = 0.131λ to the printed circuit board, but the distance d = (0.04 to 0. 23) It has been confirmed that λ is sufficient.

  On the other hand, the loop added to the dipole antenna realizes a matching inductance for matching the dipole antenna and the feeding coaxial cable, resonates with the radio wave used by a capacitor connected in parallel, and is electromagnetically coupled to the antenna of the IC tag. Also works as a booster antenna. The loop can be formed as a circuit pattern continuous with the dipole antenna on one side of the printed circuit board, and the resonance capacitor may be mounted on the printed circuit board as a chip-type discrete component, for example. You may form on a printed circuit board as a parallel line pattern of a space | interval.

  The dipole antenna is best to have each element length a = 0.204λ, but it has been confirmed that a = (0.16-0.28) λ is also sufficient. That is, the dipole antenna has a broad frequency characteristic and is easy to adjust. On the other hand, the loop may be any of a circular loop, a rectangular loop, a square loop, and the like, but a circular loop is preferable in that the effective area can be maximized by keeping the circumference constant. Note that the circular loop having the circumference b = 0.066πλ can resonate with the used radio wave of 2450 MHz as the resonance capacitor 1 pF, and has a diameter of about 8 mm, and thus is suitable in terms of size.

  The reflector is best to have a length c1 = 0.572λ and a width c2 = 0.369λ, but the center line in the long side direction is parallel to the dipole antenna and the center is placed on the feeding point of the dipole antenna. It has been confirmed that the effect of preventing the body effect is sufficiently exhibited when the length c1 = 0.56λ or more and the width c2 = 0.04λ or more by properly arranging the relative relationship with the dipole antenna. .

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  The reader / writer antenna of the contactless IC tag includes a printed circuit board 11 forming a dipole antenna 12 and a rectangular reflecting plate 21 arranged in parallel with the printed circuit board 11 (FIG. 1).

  The printed board 11 is a single-sided printed board made of glass epoxy resin, for example, and the dipole antenna 12 is formed on the printed board 11 as a predetermined circuit pattern by etching the copper foil on the printed board 11. The dipole antenna 12 has elements 12a and 12a arranged in a straight line, and a one-turn loop 12b is added to a feeding point between the elements 12a and 12a. The loop 12b is a circular loop, and a resonance capacitor C is connected in parallel. Each element length a of the dipole antenna 12 is set to a = (0.16-0.28) λ as the wavelength λ of the used radio wave, and the circumferential length b of the loop 12b is set to b = 0.066πλ. Yes. The dipole antenna 12 may be printed on the printed board 11 using, for example, a conductive paint.

  The reflecting plate 21 is, for example, a rectangular aluminum plate. The reflector 21 is arranged so that the center line L 1 in the long side direction is parallel to the dipole antenna 12 and the center Lo is placed on the feeding point of the dipole antenna 12. However, on the feed point here means that the reflector 21 passing through the center Lo and the common perpendicular L2 of the printed circuit board 11 pass through the feed point. The length c1 and width c2 of the reflecting plate 21 are set to c1 ≧ 0.56λ and c2 ≧ 0.04λ, respectively. Further, the reflection plate 21 is disposed at a distance d = (0.04 to 0.23) λ with respect to the printed circuit board 11.

  The printed circuit board 11 and the reflection plate 21 can be assembled together with the printed circuit board 31 for the processing circuit 32 and can be compactly assembled as an antenna unit for a reader / writer (FIGS. 2 and 3). 2A and 2B are a plan view and a front view of the antenna unit, respectively.

  The printed circuit board 11 and the reflection plate 21 are integrally assembled via upper and lower set screws 14, 14... Of spacers 13, 13. However, in FIG. 2, the printed circuit board 11 is formed in the same shape and size as the reflector 21 for convenience. Further, the printed circuit board 31 for the processing circuit 32 is screwed to the lower surface of the reflection plate 21 together with the mounting legs 23, 23,. In addition, on each long side of the printed circuit board 11 and the reflecting plate 21, in order to fix the whole to the structural material (not shown) by using the mounting holes at the lower ends of the mounting legs 23, 23. Notch 11a, 11a, 21a, 21a of the same size is formed at the same position.

  On the printed circuit board 11, the feeding point of the dipole antenna 12 is drawn out to the coaxial connector 15 via lines 12c and 12c. Further, another coaxial connector 33 connected to the processing circuit 32 is mounted on the printed circuit board 31 for the processing circuit 32, and the coaxial connectors 15 and 33 are connected via the coaxial cable 16. The processing circuit 32 receives the response data from the transmitter that modulates the radio wave used by data from the outside and transmits it from the dipole antenna 12 to the IC card (not shown) and the IC card that arrives at the dipole antenna 12 by impedance modulation. And a receiving unit that multi-tunes it and sends it to the outside.

  An example of directivity characteristics in a plane perpendicular to the printed circuit board 11 including the elements 12a and 12a of the dipole antenna 12 is shown in FIG. However, the angles and scales (dBd) in FIGS. 4A to 4D are as shown in FIG. 4E, and the 0 ° direction in FIGS. Match the direction. In other words, the IC card to be communicated is placed in the 0 ° direction.

  The directivity characteristic of only the dipole antenna 12 without the reflector 21 is a typical 8-character characteristic (FIG. 4C), and no gain difference (FB ratio) between 0 ° direction and 180 ° direction is recognized. At this time, when the ground metal approaches in the 180 ° direction (FIG. 4D), the gain in the 0 ° direction also decreases, and a clear body effect is recognized. On the other hand, when the reflecting plate 21 is provided ((A) in the same figure), the gain in the 0 ° direction is increased and a clear FB ratio is recognized, and even if the ground metal is close in the 180 ° direction (the same figure). (B)), the gain in the 0 ° direction increases on the contrary, and communication performance is not deteriorated by the body effect.

  FIG. 5 shows changes in frequency characteristics depending on the presence / absence of the reflecting plate 21. The frequency characteristic when the reflector 21 is not provided (FIG. 5C) varies greatly as the ground metal approaches in the 180 ° direction (FIG. 5D to FIG. 5F), but the reflector 21 is provided. (FIG. (A)), even if the ground metal is brought close, there is almost no influence (FIG. (B)).

  4 and 5, the frequency of the used radio wave is 2450 MHz (λ = 122 mm), each element length a of the dipole antenna 12 is 27.5 mm = 0.225λ, and the peripheral length b of the loop 12b is 8.05π mm = 0. 0.06πλ, the length c1 of the reflecting plate 21 = 70 mm = 0.574λ, the width c2 = 45 mm = 0.369λ, and the distance d = 16 mm = 0.131λ between the printed board 11 and the reflecting plate 21. 4 and 5, the ground metal close to the dipole antenna 12 is a 150 × 150 mm aluminum plate parallel to the printed circuit board 11. In FIGS. 4B and 5B, the reflector 21 It was arranged at a position of 4 mm below. 4D, a similar aluminum plate is disposed at a position 20 mm below the printed circuit board 11, and in FIGS. 5D to 5F, the similar aluminum plate is disposed at a position 20 mm below the printed circuit board 11, respectively. They were placed at 10 mm and 5 mm positions.

Schematic configuration perspective view Usage diagram Block diagram of Fig. 2 Operating characteristic diagram (1) Operating characteristic diagram (2)

Explanation of symbols

C: Capacitor Lo ... Center L1 ... Center line a ... Element length b ... Circumference c1 ... Length c2 ... Width d ... Spacing 11 ... Printed circuit board 12 ... Dipole antenna 12b ... Loop 21 ... Reflector

Patent Applicant FCE Co., Ltd.
Attorney Tadaaki Matsuda, Attorney

Claims (4)

  A printed circuit board that forms a dipole antenna, and a rectangular reflector disposed in parallel with the printed circuit board, and on the printed circuit board, forming a loop connected to a feeding point of the dipole antenna, A resonance capacitor connected in parallel to the loop is provided, and the reflector is placed at a center on a feeding point of the dipole antenna with a long-side center line parallel to the dipole antenna, and spaced from the printed circuit board. An antenna for a reader / writer of a contactless IC tag, wherein d = (0.04 to 0.23) λ (where λ is a wavelength of a used radio wave).   2. The antenna for a reader / writer of a contactless IC tag according to claim 1, wherein the dipole antenna is set to have an element length a = (0.16-0.28) [lambda].   3. The antenna for a reader / writer of a contactless IC tag according to claim 1, wherein the loop is set as a circular loop with a peripheral length b = 0.066πλ. 4. The non-contact type IC tag reader / writer according to claim 1, wherein the reflector is set to have a length c1 = 0.56λ or more and a width c2 = 0.04λ or more. antenna.

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