JP6574733B2 - Antenna, RFID reader device, RFID reader / writer device, and antenna device - Google Patents

Description

  The present invention relates to a patch antenna.

  Conventionally, a conductive foil film (for example, copper foil) on one side of a dielectric called a so-called patch antenna is used as a ground electrode, and the conductive foil film on the opposite side is used as a radiation electrode with the dielectric sandwiched between them. A patch antenna (see Non-Patent Documents 1 and 2 below) shown in FIGS. 11A to 11C is known. Also, use multiple printed boards with conductive foil film on one or both sides of the dielectric, with the insulating layer between the printed boards facing each other, one printed board is the ground electrode, and the other printed board is rectangular A patch antenna shown in FIGS. 12A to 12C for use as a circular radiation electrode is known. Such a patch antenna has a simple structure, can be thinned, and has a high gain, so that it is used in various applications.

  In recent years, there is a communication technique for recognizing and identifying an RFID (Radio Frequency Identification) tag with an RFID reader / writer. In the passive RFID technology, the RFID tag is powered by radio waves radiated from an antenna built in or attached to the RFID reader / writer, the RFID reader / writer communicates with the RFID tag, and recognizes the RFID tag responding to the communication. It is a technology to identify.

Naohisa Goto, “Illustration / Antenna”, IEICE, 1995 Naohisa Goto et al., “Antenna / Wireless Handbook”, Ohm, 2006

  In the patch antenna, since radio waves are radiated from the end of the outer edge of the radiation electrode, the electric field strength is strongest in the vicinity of the end of the radiation electrode and significantly decreases toward the center of the radiation electrode. Therefore, depending on the radio frequency used, the antenna size increases in order to resonate as the radiation electrode, and accordingly, the distance from the end of the radiation electrode to the center also increases, and the electric field in the vicinity immediately above the center of the radiation electrode. The strength becomes extremely weak.

  When the patch antenna is used, for example, in the RFID technology, the RFID tag can be well recognized in the far field where the electric field strength is substantially uniform. However, since the electric field strength at the center of the radiation electrode is extremely weak, the RFID tag that has entered the vicinity of the area directly above the center of the radiation electrode of the patch antenna cannot obtain the electric field strength required for communication, ensuring sufficient power supply. There was a risk that communication (recognition) could not be performed. In this case, by slightly separating the RFID tag from the center of the radiation electrode, the electric field strength is improved and the RFID tag can be recognized. However, many users do not understand the characteristics of such patch antennas.

  The recognition rate can be improved by increasing the transmission power from the RFID reader / writer to the patch antenna in order to improve the recognition rate of the RFID tag placed in the vicinity immediately above the center of the radiation electrode. However, increasing the transmission power unnecessarily widens the communication range, and many RFID tags that do not need to be recognized are included in the widened communication range. Further, by increasing the transmission power, interference with other RFID reader / writers, other RFID tags, other wireless devices, etc. also increases.

  In view of the above problems, the present invention is a patch antenna used for an RFID reader / writer device or the like, where the electric field strength is locally insufficient near the surface of the patch antenna without increasing the transmission power. It is an object of the present invention to provide an antenna that improves the electric field strength of the antenna and enables stable communication even in the vicinity of the antenna.

In order to achieve the above object, the present invention includes a ground electrode and a radiation electrode that resonates with a predetermined radio frequency and is opposed to the ground electrode with an insulating layer electrically insulated from the ground electrode interposed therebetween. a position having a predetermined impedance in the radiation electrode, the feed point for feeding current to the radiation electrode is disposed, the electric field intensity is directed toward the center of the strongest and the radiation electrode at the outer end portion vicinity of the radiation electrode in decreasing the antenna according to the radiation electrode consisting of the planar conductive members, cut out the part of the previous SL radiation electrodes is disposed a plurality of slits, the plurality of slits in the center of the radiation electrode In order to increase the electric field strength in the vicinity thereof, it is most dense in the vicinity of the center of the radiation electrode from the vicinity of the center of the radiation electrode toward the outer edge of the radiation electrode. It is arranged, characterized in that. Thereby, it is possible to improve the electric field strength in the vicinity immediately above the radiation electrode surface.

  In the antenna of the present invention, it is a preferable aspect that the slit is arranged so that the long side of the slit is parallel to a straight line passing through the central portion of the radiation electrode or intersects at an acute angle.

Further, in the antenna of the present invention, prior Symbol plurality of slits, said to be arranged symmetrically with respect to the central portion of the radiation electrode, it is a preferred embodiment.

Further, in the antenna of the present invention, prior Symbol plurality of slits, with respect to a straight line with the previous SL feeding electric point connecting the center portion of the radiation electrode, it is disposed in line symmetry, it is a preferred embodiment.

Further, in the antenna of the present invention, prior Symbol plurality of slits, wherein the thing that is arranged radially around the central portion of the radiation electrode, is a preferred embodiment.

  Moreover, in the antenna of the present invention, it is a preferable aspect that the width of the slit on the center side of the radiation electrode is narrower than the width of the slit on the outer edge side of the radiation electrode. .

  In the antenna of the present invention, it is a preferable aspect that the width of the radially arranged slits is gradually increased from the center side of the radiation electrode toward the outer edge side.

  In the antenna of the present invention, it is a preferred aspect that the radially arranged slits are arranged concentrically around the center of the radiation electrode.

  In the antenna of the present invention, it is a preferable aspect that the slit width arranged on the inner side is narrower than the slit width arranged on the outer side with respect to the slits arranged concentrically.

  In the antenna of the present invention, it is a preferable aspect that the number of slits arranged on the outer side is smaller than the number of slits arranged on the inner side with respect to the slits arranged concentrically.

  Further, in the antenna of the present invention, the concentrically arranged slits are composed of concentric separating slits arranged separately in plural and concentric slits arranged adjacent to the separating slits. It is a preferred embodiment.

Further, in the antenna of the present invention, the plurality of slits constitute a plurality of slit groups each composed of two or more slits, and the slits constituting the plurality of slit groups are arbitrary for each slit group . Arranging with an angle and shape is a preferred embodiment.

Further, in the antenna of the present invention, prior Symbol plurality of slits group, said to be arranged symmetrically with respect to the central portion of the radiation electrode, it is a preferred embodiment.

Further, in the antenna of the present invention, prior Symbol plurality of slit groups is, with respect to a straight line with the previous SL feeding electric point connecting the center portion of the radiation electrode, it is disposed in line symmetry, it is a preferred embodiment.

Further, in the antenna of the present invention, prior Symbol plurality of slits group, wherein is it to be arranged radially around the central portion of the radiation electrode, it is a preferred embodiment.

In the antenna of the present invention, it is a preferable aspect that the length of the long side of the slit is λ / 8 to λ / 4 with respect to the wavelength λ of the resonance frequency of the radiation electrode.

  Further, the present invention is an RFID reader device that includes or can be connected to the antenna.

  Further, the present invention is an RFID reader / writer device that includes or can be connected to the antenna.

  In addition, the present invention is an antenna device that includes the antenna and can be connected to an RFID reader device or an RFID reader / writer device.

  According to the present invention, the electric field strength at a location where the electric field strength is locally insufficient in the vicinity of the surface of the patch antenna is improved, and stable communication can be performed even in the vicinity of the antenna.

It is a schematic perspective view of the near antenna which concerns on embodiment. It is a top view of the near antenna which concerns on embodiment. It is a side view of the near antenna which concerns on embodiment. It is a schematic perspective view of a circular patch antenna. It is a top view of a circular patch antenna. It is a side view of a circular patch antenna. It is the figure which compared the electric field strength of the near antenna which concerns on embodiment, and the conventional type circular patch antenna. It is a figure which shows the simulation result of distribution of the electric field strength in the range of 200 mm x 200 mm on XY plane parallel to the radiation electrode surface 5 mm away in the perpendicular direction from the radiation electrode surface of the near antenna which concerns on embodiment. It is a figure which shows the simulation result of distribution of the electric field strength of YZ plane perpendicular | vertical to the radiation electrode of the near antenna which concerns on embodiment. It is a figure which shows the simulation result of distribution of the electric field strength in the range of 200 mm x 200 mm on XY plane parallel to the radiation electrode surface 5 mm away from the radiation electrode surface of the conventional type circular patch antenna perpendicularly. It is a figure which shows the simulation result of distribution of the electric field strength of the YZ plane perpendicular | vertical to the radiation electrode of the conventional circular patch antenna. It is a figure which shows the simple model of the radiation electrode for confirming about the effect of the slit provided radially from the center part of the radiation electrode of the near antenna which concerns on embodiment. It is a figure which shows the simulation result of the electric field strength of the midpoint on the long side of a slit at the time of changing the length of the slit of the near antenna which concerns on embodiment. It is a figure which shows an example of the shape of a radiation electrode at the time of making the width | variety of the slit of the radiation electrode of the near antenna which concerns on embodiment wide. It is a figure which shows the simulation result of the electric field strength of the middle point on the long side of a slit at the time of changing the width | variety of the slit of the near antenna which concerns on embodiment. It is a figure which shows the variation of the slit (1st) of the antenna which concerns on embodiment. It is a figure which shows the variation of the slit (2nd) of the antenna which concerns on embodiment. It is a figure which shows the variation of the slit (3rd) of the antenna which concerns on embodiment. It is a figure which shows the variation of the slit (4th) of the antenna which concerns on embodiment. It is a figure which shows the variation of the slit (5th) of the antenna which concerns on embodiment. It is a figure which shows the variation of the slit (6th) of the antenna which concerns on embodiment. It is a figure which shows the variation of the slit (seventh) of the antenna which concerns on embodiment. It is a figure which shows the variation of the slit (8th) of the antenna which concerns on embodiment. It is a figure which shows the variation of the slit (9th) of the antenna which concerns on embodiment. It is a schematic perspective view of the conventional patch antenna. It is a top view of the conventional patch antenna. It is sectional drawing of the conventional patch antenna. It is a schematic perspective view of the other conventional patch antenna. It is a top view of the other conventional patch antenna. It is sectional drawing of the other conventional patch antenna.

  Hereinafter, embodiments will be described with reference to the drawings. The antenna described below (hereinafter also referred to as a near-field antenna) comprises a ground electrode and a radiation electrode with two printed boards. However, even if one printed circuit board dielectric (for example, glass epoxy resin, phenolic resin, polytetrafluoroethylene, etc.) is sandwiched, one surface is configured as a ground electrode and the other surface is configured as a radiation electrode. Good. Further, the material of the ground electrode and the radiation electrode may be composed of a conductive material instead of the printed board.

  An example of the near antenna according to the embodiment will be specifically described with reference to FIGS. 1A to 1C. FIG. 1A is a schematic perspective view of a proximity antenna according to an embodiment. FIG. 1B is a plan view of the nearby antenna of FIG. 1A viewed in the direction of arrow 140. FIG. 1C is a side view of the nearby antenna when the side surface of the nearby antenna in FIG. 1A is viewed in the direction of arrow 150.

  The printed board 100 is a printed board having metal layers 100a and 100c of a planar conductive member such as a copper foil on both surfaces of a dielectric 100b. The metal layer 100a on the radiation electrode side of the printed board 100 is configured as a ground electrode. The metal layer 100c on the opposite surface across the dielectric 100b may be configured as a radiation electrode or a component mounting layer for mounting an attached circuit. Further, the metal layer 100c may not be provided.

  The printed board 101 is a printed board having a metal layer 101a of a planar conductive member such as a copper foil on one surface of the dielectric 101b. A metal layer 101a is provided on either surface of the dielectric 101b, and the metal layer 101a is predetermined according to individual conditions constituting the antenna, such as a distance between the printed board 100 and the printed board 101, a dielectric constant of the dielectric 101b, and the like. Although it is configured as a circular radiation electrode that resonates at a frequency (here, for example, 920 MHz), it may be configured by a radiation electrode of an arbitrary shape such as a rectangle.

  In the radiation electrode (metal layer) 101a, radial slits 110 that point toward the outer edge portion (outer peripheral portion) of the radiation electrode 101a with respect to the center portion 130 of the radiation electrode 101a are pointed with respect to the center portion 130 of the radiation electrode 101a. It is provided symmetrically. The provided slit 110 is a part of the radiation electrode 101a cut out. The longitudinal side (long side) of the slit 110 may be parallel to a straight line passing through the central portion 130 of the radiation electrode 101a, or may intersect an acute angle with an arbitrary angle.

  The shape, arrangement, and number of slits may be arbitrary depending on the antenna specifications required for operation. In the near antenna according to the embodiment, in order to improve the electric field strength in the vicinity of the central portion 130 of the radiation electrode 101a, the shape and number of slits are densely arranged near the center of the nearby antenna (the central portion 130 of the radiation electrode 101a). Has been adjusted.

  The slit 110 is arranged so as to avoid the feeding points 101c and 101d. However, a slit that contacts the feeding points 101c and 101d may be provided as long as electrical feeding is possible. The slits 110 are not provided at positions that are point-symmetric with respect to the feeding points 101c and 101d with respect to the central portion 130 of the radiation electrode 101a. This is because the slits 110 are symmetrically arranged in consideration of the deterioration of the axial ratio of circular polarization.

  The printed board 100 and the printed board 101 are arranged so that the surface of the ground electrode 100a and the surface of the radiation electrode 101a face each other in parallel (substantially parallel, the same applies hereinafter) with an air layer interposed therebetween. The feeding shaft 120 (120a, 120b) functions as a feeding line for feeding power to the radiation electrode 101a, and is the same as the feeding method to a general two-point feeding patch antenna. The feeding shaft 120a feeds power to the feeding point 101c of the radiation electrode 101a, and the feeding shaft 120b feeds power to the feeding point 101d of the radiation electrode 101a. The feeding points 101c and 101d are arranged on a straight line in which the lines connecting (passing) the feeding points 101c and 101d and the central portion 130 of the radiation electrode 101a are orthogonal to each other. Ohm (Ω)).

  By supplying power with a phase difference of 90 degrees to the power feeding points 101c and 101d, circularly polarized radio waves are radiated from the surface of the radiation electrode 101a. Electrically, the feeding shaft 120 is connected only to the radiation electrode 101a, and is not connected to the ground electrode 100a. The ground electrode 100a is connected to the reference voltage with a low impedance as an antenna device at a position not shown.

  Here, FIG. 2A to FIG. 2C show an example of the conventional circular patch antenna used in the simulation for comparison with the nearby antenna according to the embodiment. FIG. 2A is a schematic perspective view of a circular patch antenna. FIG. 2B is a plan view of the circular patch antenna of FIG. FIG. 2C is a side view of the circular patch antenna when the side surface of the circular patch antenna of FIG. 2A is viewed in the direction of arrow 250.

  The configuration of the circular patch antenna is basically the same as that of the nearby antenna described above, but the radiation electrode 201 has no slit. Further, the diameter of the circular radiation electrode 201a and the position of the feeding point are readjusted to the resonance frequency of 920 MHz without a slit, and thus differ from the dimensions of the nearby antenna described above. Are the same. In the simulation, the electric field strength is obtained using the finite element method.

  FIG. 3 is a diagram comparing the electric field strength of the nearby antenna shown in FIGS. 1A to 1C and the circular patch antenna shown in FIGS. 2A to 2C. This electric field strength is the electric field strength on a straight line AA ′ parallel to the radiation electrode surface, which is 5 mm away from the radiation electrode surface of the antenna in the vertical direction. The X axis of the graph represents the position on the straight line A-A ′, the point A is 0 mm, the point A ′ is 400 mm, and the position of 200 mm is directly above the center of the radiation electrode at the center point of the straight line A-A ′. . The solid line in the graph indicates the simulation result of the nearby antenna according to the embodiment, and the broken line in the graph indicates the simulation result of the comparative circular patch antenna.

  The circular patch antenna has a high electric field strength in the vicinity of 118 mm and 284 mm of the outer edge portion of the radiating electrode 201a, and the electric field strength is remarkably reduced in the vicinity of 200 mm in the central portion of the radiating electrode 201a. The near antenna according to the embodiment maintains the same electric field strength as that of the circular patch antenna in the vicinity of the outer edge portion of the radiation electrode 101a. Further, it is shown that the drop in electric field strength is improved at the central portion 130 of the radiation electrode 101a, and the electric field strength is greatly improved.

  FIG. 4A shows the simulation result of the electric field intensity distribution in the range of 200 mm × 200 mm on the XY plane parallel to the radiating electrode 101a surface, 5 mm away from the radiating electrode 101a surface of the nearby antenna of FIGS. 1A to 1C in the vertical direction. Show. FIG. 4B shows a simulation result of the electric field intensity distribution in the YZ plane perpendicular to the radiation electrode 101a.

  FIG. 5A is a simulation result of electric field intensity distribution in a range of 200 mm × 200 mm on the XY plane parallel to the radiating electrode 201a surface, 5 mm away from the radiating electrode 201a surface of the circular patch antenna of FIGS. 2A to 2C in the vertical direction. Is shown. FIG. 5B shows a simulation result of the electric field intensity distribution in the YZ plane perpendicular to the radiation electrode 201a.

  According to the simulation result, the electric field strength in the central region of the radiation electrode 201a is approximately 6.7464E + 001 or less (see FIGS. 5A and 5B). On the other hand, the electric field intensity in the central region of the radiation electrode 101a is approximately in the range of 1.2282E + 002 to 5.4928E + 002 (see FIGS. 4A and 4B). By providing the slit, the distribution of the weak electric field strength in the central region of the radiation electrode 201a of the circular patch antenna is improved. That is, regarding the electric field strength near the center of the radiating electrode, the nearby antenna according to the embodiment is higher than the circular patch antenna for comparison, and the electric field strength near the center of the radiating electrode is improved compared to the circular patch antenna. I understand.

  FIG. 6 is a simple model for confirming the effect of slits provided radially around the central portion of the radiation electrode 600 of the nearby antenna according to the embodiment, and shows the shape of the radiation electrode 600 used in the simulation. . The configuration of the ground electrode, the feeding shaft, etc., not shown, is basically the same as that of the nearby antenna according to the embodiment shown in FIG.

  The slit 601 of the simple model has a long side length (slit length) of L (mm) and a short side direction (short side) length (slit width) of W (mm). The slit 601 is arranged so as to face the center of the radiation electrode 600 and have the center of the radiation electrode 600 on the extension in the longitudinal direction. Further, the slit 601 is arranged so that the midpoint 602 (L / 2) in the longitudinal direction of the slit 601 is positioned at R / 2 from the center of the radiation electrode 600. Here, R is the radius of the radiation electrode 600. In addition, the slit 601 has a longitudinal extension of the slit 601 perpendicular to the longitudinal extension of the adjacent slit, and a straight line connecting (passing through) the feeding point and the center of the radiation electrode 600 and the longitudinal direction of the slit. The extension line is arranged to have an angle of 45 degrees.

  FIG. 7 shows a simulation result of the electric field intensity at the midpoint 602 on the long side of the slit 601 when the slit length L of the slit 601 in FIG. 6 is changed to 10 mm, 20 mm, 30 mm, 40 mm, and 50 mm. All the slit widths W are 5 mm. In the simulation, the diameter and the feeding point position of the radiation electrode are adjusted for each slit length L so as to resonate at a predetermined frequency (for example, 920 MHz). As shown in FIG. 7, in the slit 601 of the simple model, when the slit length L is 30 mm or less, the influence of the slit length on the electric field strength is small, and the electric field strength is improved according to the slit length from around 30 mm. I understand that.

  On the other hand, FIG. 9 shows the simulation result of the electric field intensity at the midpoint 602 on the long side of the slit 601 when the slit width W of the slit 601 in FIG. 6 is changed to 2 mm, 10 mm, 20 mm, and 30 mm. FIG. 8 shows an example of the shape of the radiation electrode when the slit width W of the slit 601 of the radiation electrode 600 shown in FIG. 6 is increased.

  All slit lengths L are 30 mm. In the simulation, the diameter and the feeding point position of the radiation electrode are adjusted in size and position for each slit width W so as to resonate at a predetermined frequency (for example, 920 MHz). According to the simulation result of FIG. 9, it can be seen that the electric field strength does not greatly depend on the slit width W in the slit 601 of the simple model.

  From the results shown in FIGS. 7 and 9, when the slit is provided radially from the center of the radiation electrode as in the simple model, the slit length L is increased (for example, the slit length L is equal to the wavelength λ of the resonance frequency of the radiation electrode). Therefore, in order to improve the electric field strength in the vicinity of the radiation electrode, the slit width W is narrowed and the number of slits is reduced. Is preferably increased. However, as the slit is added, the current path that flows on the radiation electrode becomes longer, so the size of the radiation electrode is reduced, and the band of the antenna is reduced to narrow the band. It is preferable to arrange various slits.

  Here, some variations (examples) of the slit will be described. 10A to 10I show examples of the arrangement and shape of the slits.

  A variation of the first slit is shown in FIG. 10A. This variation increases the number of slits near the center of the radiation electrode 1000a because the electric field strength in the vicinity immediately above the center of the radiation electrode 1000a is low. That is, among the short sides of the rectangular slit, the short side on the central portion side of the radiation electrode 1000a is shortened (in an acute angle shape) to improve the density of the slit near the center portion of the radiation electrode 1000a. In order to improve the density of slits near the center of the radiation electrode 1000a, a plurality of slits (not shown) may be further provided near the center of the radiation electrode 1000a.

  A variation of the second slit is shown in FIG. 10B. Similar to the first variation, this variation is for increasing the number of slits near the center of the radiation electrode 1000b, and improves the density of slits near the center of the radiation electrode 1000b. In the case of a rectangular slit, the distance between the slits increases as it goes from the center of the radiation electrode 1000b to the outer edge. Therefore, the short sides or arcs of the slits may be increased stepwise from the center toward the outer edge so that the intervals between the slits are uniform. In the above case, since the slit opening of the conductive thin plate such as the copper foil of the radiation electrode 1000b becomes large, the metal ratio of the radiation electrode 1000b decreases. As a result, the influence of the metal from the radiation electrode 1000b on the RFID tag in the proximity to the antenna is reduced, thereby reducing the characteristic displacement of the RFID tag and contributing to stable communication.

  A variation of the third slit is shown in FIG. 10C. This variation is similar to the first and second variations described above, in order to improve the density of the slits near the center of the radiation electrode 1000c and to make the slit spacing at the outer edge of the radiation electrode 1000c uniform, the radiation electrode 1000c. The slit width on the outer edge side is wider than the slit width on the center side.

  A variation of the fourth slit is shown in FIG. 10D. In this variation, the slit is made radial, and the slit is further divided into two stages of a slit group on the center side of the radiation electrode 1000d and a slit group on the outer edge side. That is, the slits are arranged concentrically around the center of the radiation electrode 1000d. Here, although it is divided into two stages, it is not limited to two stages, and may be a plurality of stages. The radial slit group on the center side increases the slit density by narrowing the slit width, and the radial slit group on the outer edge side has a wider slit width than the slit group on the center side. Further, the number of slits in the center side slit group may be smaller than the number of slits in the outer edge side slit group arranged in the outer circle. By dividing the slit radially into a plurality of stages, obstruction of the current path flowing on the radiation electrode 1000d due to the slit is reduced. Therefore, it is possible to avoid a reduction in the diameter of the radiation electrode more than necessary, and it is possible to reduce the band narrowing.

  A variation of the fifth slit is shown in FIG. 10E. In this variation, slits are arranged symmetrically with respect to a straight line connecting the feeding point and the central portion of the radiation electrode 1000e. Slits adjacent to each other at an angle of 90 ° may be connected and arranged as an L-shaped slit.

  A variation of the sixth slit is shown in FIG. 10F. In this variation, rectangular slits are arranged so as to be radial with a constant (one rate) angle with respect to a straight line passing through the central portion of the radiation electrode 1000f. A slit may be further provided near the center of the radiation electrode 1000f. Further, the slit angle and slit width may be adjusted so that the density of the slit near the center of the radiation electrode 1000f is increased.

  A seventh slit variation is shown in FIG. 10G. In this variation, as shown in FIG. 10D, in addition to the slits (separation slits) in which the radial slits are concentrically divided into a plurality of stages, the slits that are not further divided are separated between, for example, the separation slits (separation slits). It may be arranged as appropriate in the vicinity). This variation is characterized in that it is arranged so that the divided portions of the separation slits arranged concentrically are closed by adjacent concentric slits that are not divided.

An eighth slit variation is shown in FIG. 10H. In this variation, a slit group is composed of an arbitrary number (three in FIG. 10H) of slits having an arbitrary angle (120 ° in FIG. 10H) and an arbitrary shape (rectangular in FIG. 10H), and radial as the slit group. You may make it arrange | position to. Slit groups have a shape connected to each other as shown in FIG. 10H, may be a shape which are separated from each other as shown in FIG. 10I.

  A ninth slit variation is shown in FIG. 10I. This variation is a combination of the slit group shown in FIG. 10H and the slit variation as shown in FIGS. 10A to 10I.

  Although an example of the slit variation has been described above, it is preferable to appropriately provide the best slit according to the antenna shape, size, required communication distance, and the like on the RFID tag side for communication.

  The proximity antenna as described above can also be used for devices such as an RFID reader and an RFID reader / writer device, and can be built in a device such as an RFID reader / writer device or connected as an external antenna device. The locally reduced electric field strength on the surface can be improved without increasing the transmission power to the nearby antenna.

  Further, the above-described embodiment is not limited to the above-described embodiment, and various changes can be made without departing from the gist of the embodiment.

100, 101 Printed board 100a, 100c, 101a Metal layer 100b, 101b Dielectric material 101c, 101d Feed point 110, 601 Slit 120 (120a, 120b) Feed shaft 130 Center part of radiation electrode 140, 150, 240, 250 Arrow 201a, 600, 1000a to 1000f Radiation electrode 602 Midpoint

Claims (19)

A ground electrode and a radiation electrode that resonates with respect to a predetermined radio frequency, facing each other with an insulating layer electrically insulated from the ground electrode interposed therebetween, and at a position having a predetermined impedance in the radiation electrode , In the antenna in which a feeding point for feeding power to the radiation electrode is arranged, and the electric field strength is strongest in the vicinity of the outer edge of the radiation electrode and decreases toward the center of the radiation electrode ,
The radiation electrode consisting of the planar conductive members, cut out the part of the previous SL radiation electrodes is disposed a plurality of slits, the plurality of slits, the electric field strength at the center and its vicinity of the radiation electrode The antenna is arranged so as to be most dense in the vicinity of the central portion of the radiation electrode from the vicinity of the central portion of the radiation electrode toward the outer edge of the radiation electrode so as to increase.   2. The antenna according to claim 1, wherein the slit is arranged so that a long side of the slit is parallel to or intersects an acute angle with a straight line passing through a central portion of the radiation electrode. Before SL plurality of slits, an antenna according to claim 1 or 2, characterized in that it is arranged symmetrically with respect to the center portion of the radiation electrode. Before SL plurality of slits, according to with respect to a straight line with the previous SL feeding electric point connecting the center portion of the radiation electrode, any one of claims 1 to 3, characterized in that it is arranged in line symmetry Antenna. An antenna according to prior Symbol plurality of slits, one of claims 1 to 3, characterized in that radially arranged around the central portion of the radiation electrode. 6. The antenna according to claim 5, wherein the radially arranged slits have a narrower slit width on the center side of the radiation electrode than a slit width on the outer edge end side of the radiation electrode. The antenna according to claim 6, wherein the width of the radially arranged slits gradually increases from the center side of the radiation electrode toward the outer edge end side.   The antenna according to claim 5, wherein the radially arranged slits are arranged concentrically around a central portion of the radiation electrode.   9. The antenna according to claim 8, wherein the slits arranged concentrically have a narrower inner slit width than an outer slit width. A ground electrode and a radiation electrode that resonates with a predetermined radio frequency and is opposed to each other with an insulating layer electrically insulated from the ground electrode interposed therebetween, and feeds the radiation electrode at a position having a predetermined impedance In the antenna that performs
In the radiation electrode composed of a planar conductive member, a plurality of slits are arranged by cutting out at least a part of the radiation electrode,
The plurality of slits are arranged concentrically around the center of the radiation electrode,
Slits arranged in the concentric shape, towards the number of slits arranged in the outer is less than the number of slits arranged in the inside, characterized in that the to luer antenna.   The concentrically arranged slit is composed of a concentric separating slit arranged in a plurality of separated manners, and a concentric slit arranged adjacent to the separating slit. Item 9. The antenna according to Item 8. The plurality of slits constitute a plurality of slit groups each composed of two or more slits, and the slits constituting the plurality of slit groups are arranged at an arbitrary angle and shape with respect to each slit group. The antenna according to claim 1. Before SL plurality of slits group antenna according to claim 12, characterized in that are arranged symmetrically with respect to the center portion of the radiation electrode. Before SL plurality of slits group antenna according to claim 12 or 13 with respect to a straight line with the previous SL feeding electric point connecting the center portion of the radiation electrode, characterized in that it is arranged in line symmetry. An antenna according to the prior SL plurality of slit groups, any one of claims 12 to 14, characterized in that radially arranged around the central portion of the radiation electrode. 16. The antenna according to claim 1, wherein the length of the long side of the slit is λ / 8 to λ / 4 with respect to the wavelength λ of the resonance frequency of the radiation electrode. .   An RFID reader apparatus comprising the antenna according to any one of claims 1 to 16 or capable of being connected thereto.   An RFID reader / writer device comprising the antenna according to claim 1 or capable of being connected.   An antenna device comprising the antenna according to claim 1 and connected to an RFID reader device or an RFID reader / writer device.