JP6470132B2 - Antenna device - Google Patents

Description

  The present invention relates to an antenna device suitable for reading identification information from an RFID tag.

  Conventionally, an RFID system configured to manage the position and movement of an article by reading identification information wirelessly transmitted from an RFID tag attached to the article via an antenna device is known (for example, Patent Document 1).

  The RFID system includes an antenna device (planar antenna) for performing wireless communication with an RFID tag, and a reading device (generally a reader / writer) that reads identification information from the RFID tag via the antenna device.

  In addition, since the RFID system can identify an article to which an RFID tag is attached, it can not only manage the position and movement of the article, but also sell products at a cash register (hereinafter simply referred to as a cash register) of a store. It may be used as an input device for calculating the amount.

  In this case, the antenna device is preferably formed in a sheet shape so that the store clerk can read the identification information by placing the product on the antenna device. If it does in this way, an antenna device will be installed in a cash register stand of a store, and identification information can be easily read now from an RFID tag.

  On the other hand, as such a sheet-like antenna device, an antenna pattern is provided on a non-conductive substrate, such as a loop-shaped antenna pattern sandwiched between flexible plastic sheets or a linear antenna pattern formed on a substrate. What was formed is known (for example, refer to Patent Documents 2 and 3).

JP 2004-295599 A JP 2006-33372 A JP 2004-214855 A

  By the way, the conventional sheet-like antenna device is a near-field type in which identification information can be read by approaching an RFID tag, as in the antenna device described in Patent Document 2, or in Patent Document 3 As in the described antenna apparatus, the antenna apparatus is a far-field type capable of reading identification information from an RFID tag located at a position away from the antenna apparatus, and capable of reading identification information in a wide range from the near field to the far field. Did not exist.

For this reason, when reading the identification information from the RFID tag attached to the product at the register stand, it is necessary to prepare the two types of antenna devices.
In other words, when reading the identification information from the RFID tag attached to the product at the cash register, the RFID tag may be placed on the cash register, or the product is large and the RFID tag is located away from the cash register. Sometimes placed. Therefore, in order to be able to read the identification information from the RFID tag under any conditions using the conventional antenna device, the above two types of antenna devices are required.

  However, when the identification information is read from the RFID tag using two types of antenna devices in this way, the reading device side must automatically switch the antenna device used for reading the identification information.

For this purpose, a switching circuit and a control circuit for switching the antenna device are required, which complicates the circuit configuration and causes a problem of increasing the cost of the reading device.
The present invention has been made in view of these problems, and an object of the present invention is to enable far-field communication and near-field communication with an RFID tag in an antenna device for reading identification information from the RFID tag. To do.

  The antenna device of the present invention made to achieve such an object includes a first antenna unit for performing far-field communication with the RFID tag and a second for performing near-field communication with the RFID tag. An antenna portion. Each of these antenna portions is formed by a conductor pattern on a common substrate.

  For this reason, the antenna device of the present invention reads the identification information from the RFID tag even if the RFID tag is placed on the radiation surface of the antenna device or the RFID tag is placed at a position away from the antenna device. Thus, the antenna device is suitable for identifying an article to which an RFID tag is attached at a cash register or the like.

  In particular, the antenna device of the present invention is configured as a sheet-like planar antenna by forming a conductor pattern constituting two types of antenna parts on a substrate, so that it is used by being placed on a register stand. And can be easily installed on a cash register stand.

  By the way, in the case where the two types of antenna units are configured by the conductor pattern on the common substrate as described above, the antenna device becomes large if each antenna unit is independently arranged on the substrate.

  For this reason, the antenna device of the present invention has a double-sided substrate in which an antenna pattern constituting a patch as the first antenna portion is formed on one substrate surface, and a conductor layer serving as a ground is formed on the other substrate surface. It is preferable to use a substrate.

  In this case, the antenna pattern constituting the patch is provided with a plurality of slits, and the width of the antenna pattern divided by each slit is the opening of the communication target antenna provided in the RFID tag. It is set to be shorter than the shortest width of the outer shape of the surface.

  As a result, in the antenna pattern constituting the patch, the narrow portion delimited by the slit functions as the second antenna portion, and it is possible to realize an antenna device for both the far field and the near field.

  In other words, the patch antenna itself is a far-field antenna device. When the entire area of the patch is formed of a conductor pattern (antenna pattern), when the antenna to be communicated is arranged near the patch, the RFID tag The resonance frequency of the communication target antenna provided is shifted, and the identification information cannot be read by the reading device.

  However, as in the present invention, by providing a slit in the antenna pattern constituting the patch so that the width of the antenna pattern is shorter than the minimum width of the outer shape of the opening surface of the communication target antenna, the communication target antenna is located near the patch. Even if it arrange | positions, it becomes difficult to shift | deviate the resonant frequency of a communication object antenna.

  As a result, according to the antenna device of the present invention, near-field communication can be performed with the communication target antenna provided in the RFID tag without greatly changing the resonance frequency of the communication target antenna.

  In addition, since the plurality of slits only need to be able to make the width of the conductor pattern constituting the antenna pattern shorter than the shortest width of the outer shape of the communication target antenna, a straight slit, a curved slit including a free curve, Alternatively, slits having an arbitrary shape combining straight lines and curves may be provided with an interval. Moreover, each slit may be arrange | positioned in parallel and you may arrange | position with arbitrary inclination.

  By the way, the RFID tag is usually provided with a linearly polarized antenna device, and the orientation of the antenna device varies depending on the arrangement state of the RFID tag (in other words, the article to which the RFID tag is attached).

  Therefore, when reading the identification information from the RFID tag using the antenna device of the present invention, the antenna device of the present invention is a circularly polarized antenna, and no matter how the RFID tag is arranged, It is good to make wireless communication possible.

For this purpose, the antenna pattern constituting the patch may be configured such that two points of the antenna pattern are used as power feeds, and each feed point is connected to the signal synthesis circuit.
In this way, a two-point feed type circularly polarized antenna can be configured with an antenna pattern on a double-sided board.

  In this case, even if the feed point cannot be set at a position where a desired impedance (generally 50Ω or 75Ω) characteristic is obtained inside the patch, the feed point is connected via an impedance converter composed of a microstrip line. What is necessary is just to connect to a signal synthesis circuit.

And even if it does in this way, since an impedance converter can be comprised by a conductor pattern on a double-sided board | substrate, a thin sheet-like antenna apparatus can be implement | achieved easily.
In this case, the impedance converter is configured by connecting a plurality of microstrip lines having a length of a quarter of the wavelength of the center frequency of the radio wave wirelessly communicated with the communication target antenna in series. Good.

  In other words, in this way, the impedance converter is constituted by a plurality of microstrip lines connected in series, thereby increasing the resonance point and reducing the frequency band of radio waves transmitted and received when functioning as a far-field antenna. The bandwidth can be increased.

  On the other hand, the signal synthesis circuit may be configured by a hybrid ring having two input ends connected to the opposite side of the impedance converter patch and two output ends. Thus, if the signal synthesis circuit is configured with a hybrid ring, the signal synthesis circuit can be configured with a conductor pattern formed on the double-sided board, and a sheet-shaped antenna with a simpler configuration. The device can be realized.

  Note that the signal synthesis circuit can be configured with a conductor pattern even if a Wilkinson power distribution synthesizer is used. However, in this case, since it is necessary to provide a resistor near the patch, the double-sided substrate is swollen at the center of the substrate surface, and it is difficult to make the entire antenna device flat and thin.

  On the other hand, if the signal synthesis circuit is configured by a hybrid ring, a bulge is not formed at the center of the substrate surface of the double-sided substrate, and a sheet-like antenna device can be easily realized.

  Note that the hybrid ring is not necessarily formed on the substrate surface of the double-sided substrate with a conductor pattern, and may be configured using, for example, an electronic component such as a monolithic microwave integrated circuit (MMIC).

When the signal synthesis circuit is configured by a hybrid ring, one of the two output terminals of the hybrid ring may be grounded via a termination resistor.
In this way, it is only necessary to connect a single feeding cable to the antenna device using the other output end as a feeding point. From the feeding point, a right-handed or left-handed circularly polarized received signal can be received. It can be taken out.

  In addition, the electronic component to be mounted on the double-sided board is only a termination resistor arranged near the output end of the hybrid ring, and the termination resistor only needs to be arranged on the outer peripheral portion of the double-sided board. It can prevent the thinning from being hindered.

  In addition, when a termination resistor is provided at one output end of the hybrid ring in this way, a concave portion or a through hole for embedding the termination resistor is formed in the double-sided board, and the termination resistor is formed in the concave portion or the through hole. It is good to store in.

In this way, it is possible to prevent the terminal resistance from being greatly projected from the substrate surface of the double-sided substrate, and the antenna device can be made thinner and better.
In addition, when the termination resistor is provided in this way, the article is brought into contact with the termination resistor from the identification information reading surface (that is, one substrate surface of the double-sided substrate) on which the antenna pattern is formed, and the impact is caused by the impact of the termination resistor. May be damaged. For this reason, you may make it provide the impact-absorbing material for covering and protecting a termination resistance in the one board | substrate surface of a double-sided board | substrate.

In addition, the hybrid ring may be provided around the antenna pattern on one substrate surface and bent in an L shape along one corner of the antenna pattern.
That is, in this way, the hybrid ring can be formed in an empty area around the antenna pattern and facing the ground pattern on the back surface, and it is not necessary to increase the board area of the double-sided board to form the hybrid ring. The antenna device can be downsized.

  In addition, in the double-sided board, a microstrip line for performing near-field communication with the communication target antenna is formed on one board surface around the antenna pattern constituting the patch. The microstrip line may be connected in parallel or in series with the patch via a signal synthesis circuit.

  In this way, near-field communication can be performed with the communication target antenna even in an empty area around the antenna pattern constituting the patch and facing the ground pattern on the back surface.

  For this reason, when reading the identification information from the RFID tag, the identification information can be acquired from the RFID tag by near-field communication regardless of where the RFID tag is placed on one side of the antenna device.

  The near-field communication microstrip line may be connected in parallel or in series with the patch, but if you want to lower the gain without changing the directivity, connect it in series with the patch. If you do not want to lower it, connect it in parallel.

  Further, the microstrip lines for near-field communication are preferably bent so that the distance between the microstrip lines is shorter than the shortest width of the outer shape of the opening surface of the antenna to be communicated.

  In this way, the area in which near-field communication can be performed around the antenna pattern that constitutes the patch can be expanded, and identification information can be acquired from the RFID tag over substantially the entire area of one side of the double-sided board. Become.

  Next, the antenna device of the present invention is configured by forming a first antenna unit for far-field communication and a second antenna unit for near-field communication with a conductor pattern on a substrate. The antenna device main body constituted by the substrate may be covered with a protective sheet made of synthetic resin.

  If the double-sided substrate is covered with a protective sheet, not only can the antenna device be thin (in other words, a sheet shape), but the antenna device may be deteriorated due to secular change or electrical characteristics ( (Radiation characteristics) can be prevented from changing.

  Note that if the double-sided board is covered with a protective sheet, the radiation characteristics of the antenna device may change depending on the material of the protective sheet (dielectric characteristics). Thus, it is desirable to design an antenna device (specifically, a conductor pattern on a double-sided board).

It is explanatory drawing showing the state which looked at the antenna apparatus from the outer peripheral edge side of the double-sided board. It is explanatory drawing showing the conductor pattern formed in the double-sided board | substrate of an antenna apparatus. It is explanatory drawing showing the example of the RFID tag used as the reading target of identification information. It is explanatory drawing showing the structure of the connection part of the coaxial cable to an antenna apparatus. It is a characteristic view showing VSWR measured at the output end of the antenna device. It is a characteristic view showing the gain of an antenna device. It is explanatory drawing showing the relationship between the stage number of the microstrip line which comprises an impedance converter, and VSWR. It is explanatory drawing showing the modification 1 of the conductor pattern formed in a double-sided board | substrate. It is explanatory drawing showing the modification 2 of the conductor pattern formed in a double-sided board | substrate. It is explanatory drawing showing the modification 3 of the conductor pattern formed in a double-sided board | substrate. It is explanatory drawing showing the modification of the patch which provided the slit. It is explanatory drawing showing the other structural example of a signal synthesis circuit.

Embodiments of the present invention will be described below with reference to the drawings.
The antenna device 2 according to the present embodiment is used to read identification information from an RFID tag attached to an article such as a product, which is placed on a cash register such as a store, as shown in FIG. And a double-sided substrate 10 serving as an antenna device body.

  The double-sided substrate 10 has a conductor pattern (FIG. 2) that constitutes a radiator (patch) of a patch antenna on one substrate surface (upper surface in FIG. 1) of a dielectric substrate 10 a (see FIG. 4) serving as a base material. A conductor layer 40 (in other words, a ground pattern, see FIG. 4) serving as a ground is formed over substantially the entire area of the other substrate surface (the lower surface in FIG. 1). For this reason, the double-sided substrate 10 functions as a planar antenna that can radiate radio waves from one substrate surface.

  Further, the substrate surface of the double-sided substrate 10 is substantially square (see FIG. 2), and a connection portion 22 of the coaxial cable 30 is formed at one of the four corner portions. A coaxial cable 30 for inputting / outputting transmission / reception signals is fixed via a terminal 42.

  The central conductor 32 of the coaxial cable 30 is connected (soldered) to the output end of the conductor pattern formed on one substrate surface, and the outer conductor 34 is formed on the outer peripheral portion of the one substrate surface. It is connected (soldered) to the ground pattern 28 (see FIG. 4).

  Further, in the double-sided substrate 10, the connection portion 22 of the coaxial cable 30 is covered with a sheet-like shock absorbing material 52 from one substrate surface side on which a radiator (patch) of the patch antenna is formed. The entire double-sided substrate 10 is covered with a protective sheet 50 made of synthetic resin.

  In the present embodiment, the impact absorbing material 52 is composed of a high-functional urethane foam (microcell polymer sheet), and the protective sheet 50 is composed of a vinyl chloride sheet.

  Then, the protective sheet 50 covers the double-sided substrate 10 with two sheets of material and covers the entire double-sided substrate 10 by crimping the two sheets of material on the outer peripheral portion of the double-sided substrate 10. It comes to protect.

  When the two sheet materials are pressure-bonded, the sheet material disposed on the other surface (lower surface) side of the double-sided substrate 10 is disposed along the substrate surface, and the other sheet material is disposed on the double-sided substrate 10. By covering from one surface (upper surface) side, the pressure-bonded portion is positioned below the center of the double-sided substrate 10 in the thickness direction.

  This is so that when the antenna device 2 is placed on the register table, the pressure-bonding portion of the protective sheet 50 is along the plate surface of the register table, whereby the operator moves the product on the register table. At this time, the crimping portion of the protective sheet 50 is prevented from becoming an obstacle.

Next, the conductor pattern formed on one substrate surface of the double-sided substrate 10 will be described.
As shown in FIG. 2, a substantially square antenna pattern 12 serving as a radiator of a patch antenna is formed on one substrate surface of the double-sided substrate 10 at a substantially central position.

  The antenna pattern 12 constitutes a patch as a first antenna portion, except for the cross-shaped cross portion that connects the central portions of two sides parallel to each other on the outer periphery of the antenna pattern 12. A plurality of slits 14 parallel to each side are provided.

  In the plurality of slits 14, the width L of the antenna pattern 12 delimited by the slits 14 is larger than the shortest width Lmin (see FIG. 3) of the outer shape of the opening surface of the communication target antenna provided in the RFID tag that reads the identification information. This is for shortening and is arranged in the antenna pattern 12 with a predetermined interval.

  That is, the patch antenna configured by the antenna pattern 12 is a far-field antenna, and when the entire area of the patch is formed of a conductor pattern, when the RFID tag is arranged near the patch, the RFID tag The resonant frequency of the antenna to be communicated provided in is shifted. Then, on the reading device (reader / writer) side connected via the coaxial cable 30, the identification information cannot be read from the RFID tag.

  Therefore, in the present embodiment, by providing a plurality of slits 14 in the antenna pattern 12 constituting the patch antenna patch as described above, the width of the antenna pattern 12 delimited by each slit 14 is set to It becomes shorter than the shortest width Lmin of the outer shape of the opening surface and functions as a second antenna unit for near field communication.

  In the antenna device 2 of this embodiment, the communication target antenna is an antenna provided in the RFID tag. However, as illustrated in FIG. 3, the RFID tag includes a large number of RFID tags 64, .., And the sizes of the antennas 62, 66,... Provided in these RFID tags 64, 68,.

  For this reason, the width of the antenna pattern 12 delimited by the slit 14 is such that the antenna size (opening surface) is small among these various communication target antennas 62, 66,. It is set to be narrower than the width Lmin of the small antenna 62.

  As a result, the antenna device 2 becomes an antenna device capable of performing far-field communication and near-field communication with all communication target antennas provided in the RFID tag from which the identification information is read by the antenna pattern 12. .

  The plurality of slits 14 are formed in an L shape along two corners of the outer periphery of the antenna pattern 12, but the cross-shaped cross portion that crosses the antenna pattern 12 in the vertical and horizontal directions The slit 14 is not formed.

  This is because if the slit 14 is formed also in this cross portion, the antenna pattern 12 becomes a loop antenna and does not function as a patch antenna. In other words, in the present embodiment, this configuration ensures the vertical and horizontal radiation performances orthogonal to each other in the patch antenna.

  In addition, in the antenna pattern 12 shown in FIG. 2, there is no conductor pattern in the center part, and it is an opening. This is because, in the patch antenna, even if the central portion of the patch constituting the radiator has an opening, there is little influence on the antenna characteristics, and a conductor pattern that forms a cross may be provided in the central portion. Needless to say.

  Next, the antenna device 2 is for communicating with a linearly polarized antenna provided in the RFID tag, and the direction of the antenna changes depending on the arrangement state of the RFID tag.

  Therefore, in the present embodiment, the patch antenna realized by the antenna pattern 12 functions as a circularly polarized antenna so that far field communication can be performed with the RFID tag antenna regardless of how the RFID tag is arranged. Has been.

  Specifically, the antenna pattern 12 is formed by a microstrip line formed on the same substrate surface as the antenna pattern 12 with the central portions of two sides adjacent to each other at the outer periphery as feed points P. By connecting to the signal synthesis circuit 18 via the impedance converter 16, it functions as a circularly polarized antenna.

  Here, the impedance converter 16 includes a high-impedance microstrip line 16a connected to each of the feed points P, a specific impedance (for example, 50Ω) microstrip line 16c connected to the signal synthesis circuit 18, and a microstrip. The microstrip line 16b connects the lines 16a and 16c and has an intermediate impedance between them.

  The length of each of the microstrip lines 16a to 16b is a quarter length (λ / 4) with respect to the wavelength λ of the center frequency of the communication frequency with the RFID tag (900 MHz band in this embodiment). Is set to The wavelength λ is a value in consideration of the wavelength shortening rate, and the wavelength used for defining the length in the present invention / specification is also the same.

  On the other hand, the signal synthesis circuit 18 is configured by a hybrid ring having the pair of impedance converters 16 (specifically, two input ends Ti to which a microstrip line 16c having a specific impedance is connected and two output ends To). ing.

  The hybrid ring constituting the signal synthesis circuit 18 is formed of a conductor pattern (microstrip line) formed on the same substrate surface as the antenna pattern 12. This type of hybrid ring is normally formed in a rectangular shape, but in this embodiment, the substrate surface around the antenna pattern 12 is effectively used, and the connection portion 22 of the coaxial cable 30 is formed at the corner of the double-sided substrate 10. Is formed into an L shape.

  Since one output end To of the hybrid ring is grounded to a ground pattern 28 formed on the outer peripheral portion of the same substrate surface of the double-sided substrate 10 via a termination resistor 44 (see FIG. 4) described later, the ground pattern 28 is opened toward the recess 20 for accommodating the termination resistor 44 provided between the terminal resistor 44 and the terminal resistor 44. The ground pattern 28 is connected to the conductor layer 40 (that is, the ground pattern) on the other substrate surface.

  The other output end To of the hybrid ring extends to the connection portion 22 of the coaxial cable 30 via a microstrip line 26 formed on the same substrate surface as the antenna pattern 12 so as to surround the periphery of the antenna pattern 12. It is installed. A recess 20 for accommodating the termination resistor 44 is also formed in the vicinity of the connecting portion 22.

  The microstrip line 26 is for enabling near-field communication with the communication target antenna even on the substrate surface around the antenna pattern 12. In this embodiment, the space between the microstrip lines 26 is bent in a U shape so that the interval between the microstrip lines 26 is shorter than the shortest width of the outer shape of the opening surface of the antenna to be communicated. It is formed throughout.

  As a result, according to the antenna device 2 of the present embodiment, near-field communication can be performed not only in the antenna pattern 12 that constitutes the patch that is the radiator of the patch antenna, but also in the surrounding free space.

  Next, the connection part 22 of the coaxial cable 30 formed in the corner | angular part of the double-sided board | substrate 10 is demonstrated based on FIG. 4A is a plan view of a corner portion of the double-sided substrate 10 provided with the connection portion 22 as viewed from the antenna pattern 12 side of the double-sided substrate 10, and FIG. 4C is a plan view of the corner portion on both sides. It is the reverse view seen from the antenna pattern 12 side of the board | substrate 10, (b) is sectional drawing showing the cross section of the recessed part 20 in which the termination resistance 44 was accommodated.

  As shown in FIG. 4, a through hole 24 for fixing the crimp terminal 42 is formed in the ground pattern 28 at the corner of the double-sided substrate 10. The crimp terminal 42 is fixed.

  The connection part 22 is formed by cutting out the corners of the double-sided substrate 10 so that the coaxial cable 30 can be fixed via the crimp terminal 42, and the coaxial cable 30 is fixed by the crimp terminal 42. A notch for passing the outer conductor 34 at the tip is also provided.

  A ground pattern 28 is formed on the double-sided substrate 10 so as to sandwich the notch, and the outer conductor 34 of the coaxial cable 30 is soldered to the ground pattern 28 around the notch.

  Further, the tip end of the microstrip line 26 is arranged at the further tip portion of the coaxial cable 30 fixed to the corner portion of the double-sided substrate 10 in this way. The conductor 32 is soldered.

  Further, the recess 20 for accommodating the termination resistor 44 is formed near the tip of the microstrip line 26, and the termination resistor 44 is accommodated therein. In this embodiment, the termination resistor 44 is constituted by a chip component (chip resistor), and the depth of the recess 20 is deeper than the thickness of the chip component, and the entire termination resistor 44 can be accommodated in the recess 20. It is like that.

  In the recess 20, the side walls on the output end To side and the ground pattern 28 side of the signal synthesis circuit 18 (hybrid ring) are subjected to metal plating, and the termination resistor 44 is soldered to the metal plating. The output terminal To of the signal synthesis circuit 18 and the ground pattern 28 are connected.

This configuration is an example, and a through hole that can accommodate the termination resistor 44 may be provided instead of the recess 20. Further, the termination resistor 44 may be a resistor having a lead wire.
When the characteristics of the antenna device 2 of the present embodiment configured as described above were measured, the voltage standing wave ratio (VSWR) and the gain (antenna gain) measured at the connection portion 22 of the coaxial cable 30 were respectively shown in FIG. 5. The measurement results shown in FIG. 6 were obtained.

  In FIG. 6, the solid line represents the gain when the microstrip line 26 around the antenna pattern 12 is connected in series to the signal synthesis circuit 18 as in this embodiment, and the dotted line represents the microstrip line 26. The gain when connected in parallel to the signal synthesis circuit 18 is represented.

  From this measurement result, it was found that when the microstrip line 26 is connected in series, the gain is about 0.5 dB lower than when the microstrip line 26 is connected in parallel. For this reason, it suffices to select either serial connection or parallel connection according to the required gain.

  In any case, since the near-field communication can be performed not only with the antenna pattern 12 but also with the microstrip line 26, the antenna device 2 that can perform near-field communication over almost the entire radiation surface can be realized.

  When the microstrip line 26 and the antenna pattern 12 are connected in parallel, the output from the antenna device 2 (connection portion to the central conductor 32 of the coaxial cable 30) is connected to the output end To of the signal synthesis circuit 18, The terminal resistor 44 may be taken out from the output terminal To that is not grounded, and the side opposite to the connection portion of the microstrip line 26 to the signal synthesis circuit 18 may be opened.

  As described above, according to the antenna device 2 of the present embodiment, the antenna pattern 12 constituting the radiator (patch) of the patch antenna is provided with a plurality of slits 14 so that the antenna pattern 12 can perform far field communication. In addition, by providing a microstrip line 26 that is bent in a U-shape around the antenna pattern 12, near-field communication can also be performed with this microstrip line 26. I am doing so.

  For this reason, if the antenna device 2 of this embodiment is installed on a cash register stand and used as an antenna device that reads identification information from an RFID tag attached to a product, the antenna device 2 is not affected by the position of the RFID tag. The identification information can be read from the RFID tag by the device 2 alone.

  Moreover, in this embodiment, since the impedance converter 16 is configured by connecting the microstrip lines 16a to 16c having a length of λ / 4 in series, the frequency bandwidth capable of transmission and reception is widened. The identification information can be read even if the resonance point of the antenna on the RFID tag side is slightly shifted.

  That is, FIG. 7 shows the VSWR when the number of connection stages of the microstrip line for impedance conversion connected to the antenna pattern 12 is changed, such as a single patch antenna, two stages of impedance converters, and three stages of impedance converters. Represents the measurement result. From this measurement result, it can be seen that the greater the number of microstrip line connection stages, the wider the communicable bandwidth.

  This is because if the number of stages of the microstrip line is increased, the resonance point is increased by shifting the resonance frequency of the impedance converter 16 little by little. Therefore, the number of connection stages of the microstrip line constituting the impedance converter 16 may be set as appropriate according to the required communication bandwidth.

  On the other hand, in the present embodiment, since the double-sided substrate 10 constituting the antenna device body is covered with the protective sheet 50 made of vinyl chloride, the antenna device is affected by the characteristics (dielectric constant) of the protective sheet 50. 2 frequency characteristics change.

  Specifically, when the protective sheet 50 is made of vinyl chloride, the peak frequency of the VSWR shown in FIG. 7 (the frequency at the best point where VSWR is closest to 1) shown in FIG. Shift to.

  For this reason, when covering an antenna apparatus main body with the protection sheet 50 like this embodiment, it is good to set an antenna apparatus (specifically conductor pattern) in consideration of the characteristic change by the protection sheet 50.

  Further, in the present embodiment, the signal synthesis circuit 18 is configured by a hybrid ring, and one of the two output terminals To is grounded to the ground pattern 28 by the termination resistor 44. 44 must be implemented.

  However, the termination resistor 44 is mounted at the corner of the double-sided board 10 and in the vicinity of the connection part 22 of the coaxial cable 30, and the mounting part is configured by a recess formed in the double-sided board 10. It is possible to prevent the termination resistor 44 from protruding from the substrate surface of the double-sided substrate 10 and hindering the thickness reduction of the antenna device 2.

  Further, since the shock absorbing material 52 is provided at the corner of the double-sided substrate 10 on which the termination resistor 44 is mounted (the connection portion 22 of the coaxial cable 30), the termination resistor 44 and the coaxial cable 30 are used when the antenna device 2 is used. It is possible to prevent the connection portion 22 (particularly the soldered portion) from being deteriorated in the characteristics of the antenna device 2 due to an external impact.

The ground pattern 28 is provided to prevent the substrate from warping, and may or may not be provided as necessary.
As mentioned above, although one Embodiment of this invention was described, this invention is not limited to the said embodiment, A various aspect can be taken in the range which does not deviate from the summary of this invention.

  For example, in the antenna pattern 12 shown in FIG. 2, there are two slits 14 for each side of the antenna pattern (in other words, four in the vertical direction and four in the horizontal direction, and if the central opening is included, the slit 14 in the vertical direction The number of slits 14 may be further increased within a range in which a desired gain of the patch antenna can be secured, as illustrated in FIG.

  In the above embodiment, the feeding point P of the antenna pattern 12 has been described as two points on the outer periphery of the antenna pattern 12. However, as shown in FIG. 9 and FIG. The feeding point P may be one point or three or more points.

  In the antenna device shown in FIG. 9, the shape (patch shape) of the antenna pattern 12 is circular, and the degenerate elements 12 a are provided at two locations on the axis passing through the center of the antenna pattern 12 on the outer periphery of the antenna pattern 12. A conductor pattern is provided. This is because circularly polarized waves can be transmitted and received by one-point power feeding. Note that the degeneration element 12a may be a notch.

  Further, since the feeding point P of the antenna pattern 12 shown in FIG. 9 is set on the outer periphery of the patch that becomes high impedance, as in the above-described embodiment, the double-sided substrate 10 has a conductive material constituting the impedance converter 16. A body pattern is formed.

  The impedance converter 16 is connected to a microstrip line 26 formed around the antenna pattern 12. This is because a signal synthesis circuit is unnecessary in the case of single-point power feeding.

  Further, the microstrip line 26 is not a rectangle (a U-shape) as in the above-described embodiment, but has a corrugated curved shape, and the tip thereof extends to the connection portion 22 of the coaxial cable. And even if the microstrip line 26 has a curved shape, near-field communication is possible as in the above embodiment.

  In addition, by setting the interval between the waves forming this curve to be shorter than the shortest width of the outer shape of the opening surface of the antenna to be communicated, near-field communication can be performed over the entire substrate surface on which the microstrip line 26 is formed. It will be possible to implement well.

  Further, in the case of one-point power feeding, the frequency bandwidth is narrower than in the case of two-point power feeding, but since no signal synthesizing circuit is required, there is no passing loss in the signal synthesizing circuit. For this reason, the antenna gain is high, which is suitable for a system that requires gain.

  On the other hand, the antenna pattern 12 shown in FIG. 10 is circular like the one shown in FIG. 9, but the slit 14 formed inside is a substantially semicircular arc shape parallel to the outer periphery of the antenna pattern 12. The slits 14 having the same diameter are arranged to face each other with an interval so as to form a circle. The conductor patterns between the slits 14 having the same diameter and the pair are all arranged in a straight line passing through the center of the patch.

  For this reason, the antenna pattern 12 shown in FIG. 10 constitutes a linearly polarized patch antenna. In this case as well, by setting the interval between the arcs of the slit 14 in the same manner as in the above embodiment, Near-field communication can be performed with the conductor pattern along the arc of the slit 14.

  Note that an antenna device for linearly polarized waves has a higher gain (about 3 dB higher) and a longer communicable distance with the antenna than those for circularly polarized waves. Therefore, the antenna device having the antenna pattern 12 shown in FIG. 10 is suitable for reading identification information from the RFID tag in a place where the direction of the RFID tag is substantially constant (for example, a book shelf in a library or a bookstore). Yes.

  Further, a spiral microphone strip line 26 is formed around the antenna pattern 12 on the double-sided substrate 10 shown in FIG. And this space | interval is set so that it may become shorter than the shortest width | variety of the external shape of the opening surface of a communication object antenna similarly to the space | interval of the U-shape of the said embodiment.

  Further, in the antenna pattern 12 shown in FIG. 10, the feeding point P is set at a position entering the inside of the antenna pattern 12 from the outer periphery of the antenna pattern 12. This is because the impedance of the feeding point P is set to a predetermined impedance (50Ω or 75Ω), and this configuration can eliminate the need for an impedance converter.

  Therefore, the surrounding microstrip line 26 is directly connected to the antenna pattern 12 shown in FIG. 10, and the other end of the microstrip line 26 extends to the connection portion 22 of the coaxial cable.

Next, the shape of the patch configured by the antenna pattern 12 may not be a square or a circle as described above.
Specifically, the shape of the antenna pattern 12 constituting the patch may be a rectangle as shown in FIG. 11A or may be an ellipse as shown in FIG. It may be a polygon (hexagon in the figure) other than the square as shown in 11 (c).

  However, in order to enable near-field communication using the antenna pattern 12 constituting the far-field communication patch regardless of the shape, as shown in FIG. It is necessary to form the slit 14.

  In this case, the slit 14 does not necessarily have the shape shown in FIG. 11, and may be a straight shape, a curved shape including a free curve, or an arbitrary shape combining straight lines and curves. May be.

  Next, in the above description, in order to make the patch composed of the square (or circular) antenna pattern 12 function as a two-point feeding type circularly polarized antenna, a hybrid ring constituted by a conductor pattern on a substrate is used. However, the hybrid ring may be configured using an electronic component such as a monolithic microwave integrated circuit (MMIC).

  Further, the signal synthesis circuit of the present invention may be configured using, for example, a 90-degree phase shifter 36 and a distributor / mixer 38 as shown in FIG. 12 instead of the hybrid ring. In this case, the 90-degree phase shifter 36 can be configured by a microstrip line formed on the double-sided substrate. As the distributor / mixer 39, for example, a Wilkinson power distributor / combiner can be used.

  In the above embodiment, the antenna device 2 is described as being used on a cash register stand. However, since the antenna device 2 can perform both far-field communication and near-field communication, such communication characteristics are provided. If it is a place where you need it, you can use it anywhere, not just at the cash register.

  DESCRIPTION OF SYMBOLS 2 ... Antenna apparatus, 10 ... Double-sided board, 10a ... Dielectric board | substrate, 12 ... Antenna pattern, 14 ... Slit, 16 ... Impedance converter, 16a, 16b, 16c, 26 ... Microstrip line, 18 ... Signal synthesis circuit, 20 Recessed portion 22 Connection portion 24 Through hole 28 Ground pattern 30 Coaxial cable 32 Central conductor 34 External conductor 36 90-degree phase shifter 38 Distributor / mixer 40 Conductor layer (ground pattern), 42 ... crimp terminal, 44 ... terminal resistance, 46 ... eyelet, 50 ... protective sheet, 52 ... shock absorber, 62,66 ... antenna (antenna for communication), 64,68 ... RFID tag .

Claims (12)

A first antenna unit for performing far-field communication with the RFID tag;
A second antenna unit for performing near-field communication with the RFID tag;
Each antenna part is formed of a conductor pattern on a common substrate ,
The substrate is formed of a double-sided substrate in which an antenna pattern constituting a patch as the first antenna portion is formed on one substrate surface, and a conductor layer serving as a ground is formed on the other substrate surface. And
The antenna pattern constituting the patch is provided with a plurality of slits,
In the plurality of slits, the width of the antenna pattern partitioned by the slits is shorter than the shortest width of the outer shape of the opening surface of the communication target antenna provided in the RFID tag, and the second antenna unit is An antenna device characterized by being arranged to constitute . As for the antenna pattern constituting the patch, two points of the antenna pattern are feeding points,
The antenna apparatus according to claim 1 , wherein each of the feeding points is connected to a signal synthesis circuit. The feeding point is set on the outer periphery of the antenna pattern,
The antenna apparatus according to claim 2 , wherein each of the feeding points is connected to a signal synthesis circuit via an impedance converter composed of a microstrip line. The impedance converter is configured by connecting a plurality of microstrip lines having a length of a quarter of a wavelength of a center frequency of radio waves wirelessly communicated with the communication target antenna in series. The antenna device according to claim 3 , wherein: The signal combining circuit has two input terminals and the patch of the impedance converter connected to the opposite side, according to claim 3, characterized in that it is constituted by a hybrid ring having two output terminals Or the antenna apparatus of Claim 4 . 6. The antenna device according to claim 5 , wherein one of the two output ends of the hybrid ring is grounded to the ground via a terminating resistor. The antenna according to claim 6 , wherein the double-sided substrate has a recess or a through hole for embedding the termination resistor, and the termination resistor is accommodated in the recess or the through hole. apparatus. The antenna device according to claim 6 or 7 , wherein an impact absorbing material for covering and protecting the termination resistor is provided on one substrate surface of the double-sided substrate. It said hybrid ring, around the antenna pattern on the substrate surface of the one, claim 5 claims, characterized in that it is arranged by being bent in an L-shape along one corner of the antenna pattern Item 9. The antenna device according to any one of Items 8 to 9 . In the double-sided substrate, a microstrip line for performing near-field communication with the communication target antenna is formed around the antenna pattern constituting the patch on the one substrate surface,
The microstrip line for near-field communication is connected in parallel or in series with the patch via the signal synthesis circuit, according to any one of claims 2 to 9 . Antenna device. The near-field communication microstrip lines are formed to be bent so that the distance between the microstrip lines is shorter than the shortest width of the outer shape of the opening surface of the antenna to be communicated. The antenna device according to claim 10 . The antenna device according to any one of claims 1 to 11 , wherein the antenna device main body formed of the double-sided substrate is covered with a protective sheet made of synthetic resin.