JP2017184150A - Antenna device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inhibit antenna characteristics from changing when covered with a protective cover made of a synthetic resin in an antenna device constituted by a dielectric substrate.SOLUTION: Disclosed is an antenna device which includes: an antenna device body 4 having a dielectric substrate 10, a conductor pattern which is provided on one surface of the dielectric substrate and constitutes a radiating element 12, and a ground conductor plate provided on the side opposite to the radiating element across the dielectric substrate; and a protective cover made of a synthetic resin covering the antenna device body. The dielectric substrate has a frame part 40 which is provided so that the frame part surrounds the conductor pattern constituting the radiating element 12 and that the height from the dielectric substrate becomes higher than that of the conductor pattern, and by this frame part, a space is formed between the protective cover and the conductor pattern.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an antenna device including a dielectric substrate provided with a radiating element on one side.

  As an antenna device used for reading identification information from an RFID tag, a planar antenna made of a dielectric substrate having a ground conductor on the back surface and a conductor pattern serving as a radiating element on the surface is known ( For example, see Patent Document 1).

  In this planar antenna, the ground conductor functions as a ground conductor plate for the radiating element (in other words, a reflective element), and the radiation direction of the radio wave is outward from the substrate surface of the dielectric substrate provided with the radiating element. The emission of radio waves from the substrate surface provided with is limited.

  Therefore, when this type of antenna device is installed, for example, on a cash register in a store so that the radiating element faces upward, the store clerk simply places a product with an RFID tag on the cash register, and the reader (generally a reader / writer). ) Can be read the product identification information.

JP 2011-217205 A

  By the way, when the antenna device is installed on a register stand or the like, if the conductor pattern and the ground conductor constituting the radiating element are exposed, these conductors are corroded or the connection portion of the signal line to the radiating element is The period in which the antenna device can be used is shortened due to disconnection.

  For this reason, the antenna device is usually used in a state where it is covered with a protective cover made of synthetic resin. In this case, since the conductor pattern constituting the radiating element is provided on the substrate surface of the dielectric substrate, the protective cover is in contact with the conductor pattern.

  As a result, the antenna characteristics change between when the antenna device is covered with a protective cover and when the antenna device is not covered. For example, when a protective cover is placed on the radiating element, the resonance frequency of the antenna device is lowered, and the antenna gain in the desired communication frequency band may be reduced.

  Therefore, when the antenna device is covered with a protective cover, the antenna device must be designed so that the antenna characteristics obtained when the protective cover is provided are the desired characteristics, and the design is troublesome. It was.

  In addition, when the antenna device is covered with a protective cover, the antenna characteristics change depending on the material of the protective cover. Therefore, when changing the protective cover to be used due to a design change, the antenna device is either redesigned or the antenna characteristics are changed. It is necessary to separately provide a member for correcting the above.

  In one aspect of the present invention, in an antenna device configured with a dielectric substrate, the antenna characteristics are prevented from changing when covered with a protective cover made of synthetic resin, and the antenna device can be easily designed or changed. The aim is to be able to do it.

The antenna device of the present invention made to achieve the above object includes an antenna device body, a protective cover that covers the antenna device body, and a gap member.
The antenna device main body includes a dielectric substrate, a conductor pattern that is provided on one side of the dielectric substrate and forms a radiating element, and a ground conductor plate that is provided on the opposite side of the radiating element across the dielectric substrate. Have.

  The gap member supports the protective cover at an interval on one side of the dielectric substrate on which the conductor pattern constituting the radiating element is provided in the antenna device body, so that the dielectric between the protective cover and the radiating element is supported. The rate is lower than the dielectric constant of the protective cover.

  For this reason, according to the antenna device of the present invention, it is possible to suppress changes in antenna characteristics caused by covering the antenna device body with a protective cover. As a result, workability at the time of designing or changing the antenna device is improved. Can be improved.

Here, the gap member may be configured to protrude to one side of the dielectric substrate to support the protective cover, and to form a space between the protective cover and the conductor pattern.
In this way, air having a low dielectric constant (approximately 1) is interposed between the conductor pattern constituting the radiating element and the protective cover, so that the substance in contact with the conductor pattern of the radiating element depending on the presence or absence of the protective cover. It is possible to prevent the dielectric constant from changing.

  By the way, in this case, stable antenna characteristics can be obtained unless the protective cover is crushed when the antenna device is used. For example, the protective cover is made of a soft synthetic resin, and the protective cover is used when the antenna device is used. It is conceivable that the antenna characteristics deteriorate when the is deformed and comes into contact with the conductor pattern constituting the radiating element.

Therefore, in order to prevent this problem, the protective cover may be made of a hard synthetic resin so that the protective cover is not deformed when the antenna device is used.
Further, by providing a filler having a dielectric constant lower than that of the protective cover (for example, foamed plastics such as foamed polystyrene described in the embodiments described later) in the space formed by the gap member, the antenna device is protected during use. The cover may be deformed so as not to contact the conductor pattern constituting the radiating element.

  In addition, in this way, when a filler having a lower dielectric constant than the protective cover is provided between the conductor pattern constituting the radiating element in the antenna device body and the protective cover, the filler can support the protective cover. You may comprise by a plate-shaped member (for example, the board of a polystyrene foam).

  In this case, since the plate-like member functions as a gap member that supports the protective cover, it is not necessary to separately provide a member for supporting the protective cover, and the configuration can be simplified.

  Next, the antenna device main body is provided with a conductor pattern constituting a radiating element on one side of a dielectric substrate, and a ground conductor plate on the opposite side of the radiating element, similar to that described in Patent Document 1, The radiation direction of the radio wave may be set only on one side of the dielectric substrate.

  On the other hand, the antenna device body includes a pair of dielectric substrates each having a conductor pattern constituting a radiating element provided on one side, and the back surface of the pair of dielectric substrates opposite to the conductor pattern is connected to the ground conductor. You may comprise as a composite antenna which can radiate | transmit an electromagnetic wave from both surfaces by arrange | positioning opposingly on both sides of a board.

  If the antenna device body is configured with such a composite antenna, the antenna device body has radiation characteristics in both directions of the plate surface of the antenna device body. By adjusting the radiation characteristics, desired radiation can be achieved in all directions centering on the antenna device. An omnidirectional antenna having characteristics can be realized.

It is explanatory drawing showing the state which looked at the antenna apparatus of 1st Embodiment from the outer peripheral edge side of the dielectric substrate. It is explanatory drawing showing the conductor pattern of the radiation element provided in the single side | surface of the dielectric substrate. It is a diagram showing the voltage standing wave ratio (VSWR) of the antenna apparatus of embodiment and the comparative examples 1 and 2. FIG. It is a diagram showing the antenna gain (GAIN) of the antenna apparatus of embodiment and the comparative examples 1 and 2. FIG. It is explanatory drawing showing the state which looked at the antenna apparatus of 2nd Embodiment from the outer peripheral edge side of the dielectric substrate. It is explanatory drawing showing the structure of the antenna apparatus of FIG. 5, and the synthetic | combination circuit connected to this. FIG. 6 is a diagram showing directivity characteristics of a single antenna device body in the upper part of FIG. 5. FIG. 6 is a diagram showing directivity characteristics of a single antenna device body below FIG. 5. FIG. 6 is a diagram showing directivity when the output of the antenna device body of FIG. 5 is combined with a phase difference of zero. FIG. 6 is a diagram showing directivity when the output of the antenna apparatus body of FIG. 5 is synthesized with a phase difference of 90 degrees. FIG. 6 is a diagram showing directivity when the output of the antenna apparatus body of FIG. 5 is synthesized with a phase difference of 180 degrees. FIG. 6 is a diagram showing directivity when the output of the antenna apparatus body of FIG. 5 is combined with a phase difference of 270 degrees. It is explanatory drawing showing the modification of an antenna device.

Embodiments of the present invention will be described below with reference to the drawings.
[First Embodiment]
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. A dielectric substrate 10 constituting the antenna device body 4 is provided.

  The dielectric substrate 10 is an insulator substrate used to constitute a general printed circuit board such as a glass epoxy substrate or a composite substrate, and is a so-called double-sided substrate by laminating a conductor layer on both surfaces of the substrate. It is configured.

  On one substrate surface (the upper surface in FIG. 1, hereinafter referred to as the surface), a conductor pattern (see FIG. 2) constituting the radiating element (patch) 12 of the patch antenna is formed by etching or the like. .

Moreover, the other board | substrate surface (the lower surface in FIG. 1, a back surface is hereafter called the back surface) becomes the ground conductor board 6 comprised in a conductor layer substantially the whole region.
For this reason, the dielectric substrate 10 functions as a planar antenna capable of radiating radio waves from the substrate surface (front surface) on which the radiating element 12 is provided.

As shown in FIG. 2, the substrate surface of the dielectric substrate 10 is substantially square, and one of the four corners on the surface of the dielectric substrate 10 becomes a connection portion 22 for connecting the coaxial cable 30. ing.
The connecting portion 22 includes a ground pattern 24 for connecting the outer conductor 34 of the coaxial cable 30 by soldering or the like, and a terminal portion 26 for connecting the center conductor 36 of the coaxial cable 30 by soldering or the like. ing.

  The terminal portion 26 is the final end portion of the microstrip line 28 that constitutes the transmission path led out from the radiating element 12, and is arranged with a space from the ground pattern 24. The ground pattern 24 is connected to the ground conductor plate 6 on the back surface through a through hole or the like.

In the dielectric substrate 10, a frame portion 40 made of a synthetic resin is laminated so as to surround the radiating element 12 on the outer peripheral portion of the surface where the radiating element 12 is formed.
The frame portion 40 is laminated on the surface of the dielectric substrate 10 on the substrate surface outside the region indicated by the dotted line in FIG. 2, and radiates in substantially the entire area excluding the connection portion 22 for connecting the coaxial cable 30. It is comprised so that the element 12 may be enclosed.

  For this reason, the antenna device body 4 has a plate thickness (eg, 1.3 mm) obtained by adding the plate thickness (eg, 0.8 mm) of the dielectric substrate 10 and the plate thickness (eg, 0.5 mm) of the frame portion 40. Thus, a depression is formed in the central portion of the surface of the dielectric substrate 10.

The frame portion 40 may be made of the same dielectric material as the dielectric substrate 10 or may be made of a synthetic resin different from the dielectric substrate 10.
The antenna device body 4 is housed in a protective cover 50 made of synthetic resin. The protective cover 50 has a shape that covers the entire outer periphery of the antenna device body 4 with, for example, hard vinyl chloride resin.

  For this reason, the protective cover 50 contacts the back surface of the dielectric substrate 10, the surface of the frame portion 40, and the outer peripheral side surfaces of the dielectric substrate 10 and the frame portion 40 to protect the antenna device 2. Then, the surface side of the radiating element 12 surrounded by the frame part 40 is covered with the protective cover 50 with an interval corresponding to the plate thickness of the frame part 40. Therefore, the space is filled with air having a dielectric constant of approximately 1 and smaller than the dielectric constant of the protective cover 50. That is, in this embodiment, the frame part 40 functions as a gap member.

Next, the conductor pattern provided on the surface of the dielectric substrate 10 will be described.
As shown in FIG. 2, a substantially square conductor pattern constituting a radiating element (patch) 12 of the patch antenna is formed on the surface of the dielectric substrate 10 at substantially the center.

  This conductor pattern constitutes a radiating element (patch) 12 of the patch antenna, and this conductor pattern has cross-shaped cross portions connecting the central portions of two sides parallel to each other on the outer periphery thereof. A plurality of slits 14 parallel to each side are provided.

  The plurality of slits 14 are for making the width L of the radiating element 12 delimited by the slits 14 shorter than the shortest width of the outer shape of the opening surface of the communication target antenna provided in the RFID tag. .

  In other words, the patch antenna is a far-field antenna. If the entire area of the radiating element 12 constituting the patch is formed of a conductor pattern, the patch antenna is provided when the RFID tag is arranged near the patch. The resonance frequency of the communication target antenna is shifted. As a result, the identification information cannot be read from the RFID tag on the side of the reading device (generally a reader / writer) connected via the coaxial cable 30.

  Therefore, in the present embodiment, by providing a plurality of slits 14 with a predetermined interval in the conductor pattern constituting the radiating element (patch) 12 of the patch antenna, the conductor pattern divided by each slit 14 is provided. The width is shortened.

As a result, the radiating element 12 functions as both an antenna element for far field communication and an antenna element for near field communication.
In the antenna device 2 of the present embodiment, the communication target antenna is an antenna provided in the RFID tag. However, there are many types of RFID tags having different sizes, and the RFID tags are provided in the RFID tags. The size of the antenna is also different.

  For this reason, the width of the conductor pattern delimited by the slit 14 is small in the antenna size (opening surface) in various communication target antennas, and particularly narrower than the width of the antenna having the smallest outer length of the opening surface. Is set to be

  As a result, the radiating element 12 is an antenna element that can perform far-field communication and near-field communication with all communication target antennas provided in the RFID tag from which identification information is read.

  The plurality of slits 14 are formed in an L shape along two sides of the outer periphery of the conductor pattern constituting the radiating element 12, but cross the conductor pattern in the vertical and horizontal directions. It is not formed on the cross-shaped cross portion.

  This is because if the slit 14 is formed also in this cross portion, the conductor pattern 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.

  Further, in the radiating element 12 shown in FIG. 2, the central portion has no conductor pattern and is an opening. This is because, in the patch antenna, even if the central portion of the patch serving as the radiating element 12 is opened, there is little influence on the antenna characteristics, and a cross-shaped conductor pattern may be provided in the central portion. Needless to say.

  Next, the antenna device 2 of the present embodiment is for performing communication with a linearly polarized antenna provided on the RFID tag, and the direction of the antenna varies depending on the arrangement state of the RFID tag. .

  Therefore, in this embodiment, the patch antenna realized by the radiating element 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 radiating element 12 has two central portions adjacent to each other on its outer periphery as feed points P, and each feed point P is connected to the signal synthesis circuit 18 via the impedance converter 16. It is designed to function as a circularly polarized antenna.

Here, the impedance converter 16 includes three types of microstrip lines 16 a, 16 b, and 16 c formed on the same substrate surface as the radiating element 12.
Among these, the microstrip line 16a has high impedance, and one end is connected to each of the feeding points P.

  Further, one end of the microstrip line 16c is connected to the signal synthesis circuit 18, and is set to a specific impedance (for example, 50Ω) corresponding to the signal synthesis circuit 18.

The microstrip line 16b connects the microstrip lines 16a and 16c, and has an intermediate impedance between them.
The length of each of the microstrip lines 16a to 16c 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.

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

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

  One output end To of the hybrid ring is connected (grounded) to the ground conductor plate 6 on the back surface of the dielectric substrate 10 via the termination resistor 20 in the vicinity of the connection portion 22 of the coaxial cable 30. The termination resistor 20 and the ground conductor plate 6 are connected through lands and through holes provided on the substrate surface on which the termination resistor 20 is installed.

  The other output end To of the hybrid ring extends to the connection portion 22 of the coaxial cable 30 via a microstrip line 28 formed on the same substrate surface as the radiating element 12 so as to surround the periphery of the radiating element 12. It is installed.

The final end portion of the microstrip line 28 serves as a terminal portion 26 for connecting the central conductor 36 of the coaxial cable 30 by soldering or the like.
The microstrip line 28 is for enabling near-field communication with the antenna to be communicated even on the substrate surface around the radiating element 12.

  Therefore, in the present embodiment, the space between the microstrip lines 28 is bent in a U shape so as to be shorter than the shortest width of the outer shape of the opening surface of the antenna to be communicated so as to surround the periphery of the radiating element 12. Is formed.

  As a result, according to the antenna device 2 of the present embodiment, near-field communication can be performed not only on the radiating element 12 constituting the patch of the patch antenna but also on the substrate surface around the radiating element 12.

The frame portion 40 described above is provided on the substrate surface of the dielectric substrate 10 so as to surround the microstrip line 28 along the outer periphery of the dielectric substrate 10.
As described above, in the antenna device 2 according to the present embodiment, the radiating element 12 constituting the patch capable of far-field communication and near-field communication is formed on one surface of the dielectric substrate 10, and the periphery is surrounded by the near-field communication. A microstrip line 28 is provided.

  In addition, a frame portion 40 as a gap member is laminated on the substrate surface of the dielectric substrate 10 provided with these portions so as to surround the radiating element 12 and the microstrip line 28, thereby protecting the entire antenna device 2. The cover 50 is provided on the frame portion 40.

  Therefore, the radiating element 12 and the microstrip line 28 are covered with the protective cover 50 with an interval corresponding to the height of the frame 40 from the dielectric substrate 10, and the space is filled with air. Will be.

  Therefore, a change in antenna characteristics caused by the protective cover 50 compared to the case where the frame portion 40 is not provided on the substrate surface of the dielectric substrate 10 and the radiating element 12 and the microstrip line 28 are directly covered by the protective cover 50. Can be suppressed.

  3 and 4 show the voltage standing wave ratio (VSWR) and the antenna gain, respectively, measured for the antenna device 2 of the present embodiment, Comparative Example 1 and Comparative Example 2 through the coaxial cable connected to the connection unit 22. The measurement result of (GAIN) is represented.

  In addition, the comparative example 1 is a single antenna device body 4 that is not provided with the frame portion 40 and the protective cover 50, and the comparative example 2 is obtained by directly covering the antenna device main body 4 with the protective cover 50.

  As is clear from FIGS. 3 and 4, in the comparative example 2 in which the protective cover 50 is provided directly on the radiator (the radiating element 12 and the microstrip line 28), communication is performed as compared with the comparative example 1 without the protective cover. On the high frequency side of the band, VSWR increases and GAIN decreases.

  This is considered to be because when the protective cover 50 is in direct contact with the radiator, the resonance point of the radiating element 12 is shifted to the low frequency side as compared with the case where the protective cover 50 is not provided. .

  On the other hand, when the space is formed between the protective cover 50 and the radiator by providing the frame portion 40 on the substrate surface of the dielectric substrate 10 as in this embodiment, the antenna characteristics are both VSWR and GAIN. The change from that of Comparative Example 1 is reduced.

  In this embodiment, the dielectric constant of air in contact with the radiating element 12 is approximately 1, whereas in Comparative Example 2, the dielectric constant of the protective cover 50 in contact with the radiating element 12 is several times that of air (about 3 .5).

And, according to the antenna device 2 of the present embodiment, the change in antenna characteristics caused by providing the protective cover 50 can be suppressed as compared with the comparative example 2. Therefore, workability at the time of designing or changing the design of the antenna device. Can be improved.
[Modification 1]
Here, in the first embodiment, the protective cover 50 has been described as being made of hard vinyl chloride resin. However, if the protective cover 50 is not deformed during use and does not contact the radiating element 12, soft vinyl chloride is used. You may comprise with resin.

  In addition, the protective cover 50 may be configured using a synthetic resin different from the vinyl chloride resin, such as silicone resin or synthetic rubber, or may be configured using natural rubber, paper, wood, or the like. However, even in this case, since these have a dielectric constant several times that of air, when the protective cover 50 is in contact with the radiator, the antenna characteristics are greatly changed.

  Therefore, a gap member such as the frame portion 40 may be provided on the substrate surface of the dielectric substrate 10 so that the protective cover 50 does not contact the radiating element 12 even if the material of the protective cover 50 is changed. .

  Further, as shown in FIG. 13A, the space formed between the protective cover 50 and the radiating element 12 by the frame portion 40 is sandwiched between the protective cover 50 and the radiating element 12, A filler 42 that supports the protective cover 50 may be provided. FIG. 13A is a cross-sectional view taken along line XX shown in FIG.

  If the filler 42 has a lower dielectric constant than that of the protective cover 50, the change in antenna characteristics can be suppressed as compared with the case where the protective cover 50 is directly provided on the radiating element 12. The dielectric constant should be close to the dielectric constant of air.

  For this reason, when a filler is provided in the space between the protective cover 50 and the radiating element 12, the member may be made of foamed plastics in which bubbles are finely dispersed in a synthetic resin. In this case, for example, it is desirable to use a foamed polystyrene composed mostly of air, such as a foamed polystyrene.

  Next, in the first embodiment, it has been described that the gap member is configured by the frame portion 40 provided so as to surround the radiating element 12 and the surrounding microstrip line 28. However, the gap member is a protective cover. It is only necessary to support 50 and prevent the protective cover 50 from contacting the radiating element 12.

  For this reason, the gap member may be constituted by, for example, protrusions provided along two pieces facing each other at the outer peripheral edge of the dielectric substrate 10, or dispersed on the substrate surface of the dielectric substrate 10. It may be composed of protrusions arranged in a row.

  The microstrip line 28 constitutes a transmission path capable of near-field communication, and the antenna characteristics do not change greatly even when a dielectric made of synthetic resin or the like is laminated. The protrusions or the frame portion 40 of the above embodiment may be stacked on the microstrip line 28.

  Further, when the filler 42 is provided between the protective cover 50 and the radiating element 12 as described above, if the charging material 42 is constituted by a plate-like member 44 obtained by cutting a foamed polystyrene or the like into a plate shape, FIG. ), The plate-like member 44 can function as a gap member that supports the protective cover 50 at a distance from the radiating element 12. Note that FIG. 13B is a cross-sectional view corresponding to FIG.

  In the first embodiment, the frame portion 40 is described as being laminated on the substrate surface of the dielectric substrate 10 on which various conductor patterns including the radiating elements 12 are formed. However, the frame portion 40 is a raw material such as paper or synthetic resin. In manufacturing the dielectric substrate 10, the frame portion 40 may be integrally formed.

  In this case, the conductor pattern on the radiation surface side of the radio wave such as the radiating element 12 is formed inside the frame portion 40 by printing or the like, or a metal plate constituting the conductor pattern is attached. do it.

  Moreover, in the said embodiment, the dielectric substrate 10 is a double-sided board comprised by laminating | stacking a conductor layer on both surfaces of a board | substrate, and the ground conductor board 6 is comprised by the conductor layer of the back surface of a double-sided board. Explained as being.

  However, the dielectric substrate 10 may be a single-sided substrate in which a conductive layer is laminated on one side of the substrate, and a conductive pattern such as the radiating element 12 may be formed on the conductive layer. In this case, the ground conductor plate 6 may be disposed on the back side of the dielectric substrate 10.

  In the first embodiment, the dielectric substrate 10 includes the radiating element 12 as a rectangular patch provided with a slit 14 so that far-field communication and near-field communication can be realized. In the above description, the microstrip line 28 capable of near-field communication is disposed.

However, the antenna device of the present invention may be a patch antenna having a rectangular patch as a radiating element, or a planar antenna in which a radiating element such as a dipole is configured by a conductor pattern on a dielectric substrate. There may be.
[Second Embodiment]
Next, a second embodiment of the present invention will be described.

As shown in FIG. 5, the antenna device 8 of the present embodiment includes a pair of antenna units 4A and 4B as the antenna device body.
As in the antenna device body 4 of the first embodiment, the antenna portions 4A and 4B are provided with conductor layers constituting the ground conductor plates 6A and 6B on the back surface, and conductors constituting the radiation element 12 and the like on the front surface. Dielectric substrates 10A and 10B provided with patterns and frame portions 40A and 40B are provided.

  The conductive patterns on the front surfaces of the dielectric substrates 10A and 10B have the same shape as the dielectric substrate 10 of the first embodiment, and the dielectric substrates 10A and 10B have the same potential as the ground conductor plates 6A and 6B on the back surface. Thus, the radiating surfaces are stacked so as to face in opposite directions.

  That is, in the present embodiment, the antenna device main body is configured as a so-called composite antenna by stacking the pair of antenna portions 4A and 4B as described above. The antenna device body is covered with a protective cover 50, and coaxial cables 30A and 30B are drawn out from the connection portions 22A and 22B of the antenna portions 4A and 4B.

  Since the antenna units 4A and 4B are configured in the same manner as the antenna device body 4 of the first embodiment, the connection units 22A and 22B include ground patterns 24A and 24B and terminal units 26A and 26B, respectively. Composed.

  In the coaxial cables 30A and 30B, the outer conductors 34A and 34B are connected to the ground patterns 24A and 24B, and the center conductors 36A and 36B are connected to the terminal portions 26A and 26B. Further, termination resistors 20A and 20B are disposed in the vicinity of the connection portions 22A and 22B.

The antenna device 8 of the present embodiment configured as described above is connected to the mixing unit 60 via coaxial cables 30A and 30B as shown in FIG.
The mixing unit 60 includes a variable phase shifter 66 and a mixing circuit 68. One of the outputs from the antenna units 4A and 4B obtained via the coaxial cables 30A and 30B (in the figure, from the antenna unit 4B). Output) is delayed by the variable phase shifter 66 and mixed by the mixing circuit 68.

  Therefore, in the mixing unit 60, the outputs from the antenna units 4A and 4B are combined with a predetermined phase difference, and the phase difference can be arbitrarily set by the phase shift amount of the variable phase shifter 66. become able to.

  Therefore, the user manually adjusts the amount of phase shift of the variable phase shifter 66 or changes it automatically using the controller 70 shown in FIG. Thus, the antenna device 8 can function as an omnidirectional antenna.

Hereinafter, the measurement result of the directivity of the antenna device 8 of the present embodiment will be described.
In measuring the directional characteristics, the antenna device 8 has the connection portions 22A and 22B of the antenna portions 4A and 4B below and the dielectric substrates 10A and 10B of the antenna portions 4A and 4B as shown in FIG. The plate surface was placed so as to be perpendicular to the ground.

  And when the radiation center axis of the radio wave of each antenna unit 4A, 4B is the Y axis, the horizontal axis perpendicular to the Y axis and parallel to the ground is the X axis, and the vertical axis perpendicular to the Y axis and perpendicular to the ground is the Z axis The horizontal plane directivity that becomes the XY plane and the vertical plane directivity that becomes the ZY plane were measured.

  The horizontal plane directivity is a directivity characteristic on the XY plane around the Z axis where the radiation center axis direction (Y-axis direction) of the antenna unit 4A is 0 degree, and the vertical plane directivity is the radiation center of the antenna unit 4A. This is a directivity characteristic on the Z-Y plane around the X-axis with the axial direction (Y-axis direction) being 0 degrees.

  As shown in FIGS. 7 and 8, the horizontal plane directivity and the vertical plane directivity of each antenna unit 4A, 4B are respectively the radiation center axes (0 degrees, 180 degrees) of each antenna unit 4A, 4B. The reception gain becomes maximum, and the reception gain decreases as the distance from the central axis of the radiation increases. This is a radiation characteristic peculiar to a planar antenna and cannot be received in the reverse direction.

  On the other hand, when the outputs of the antenna units 4A and 4B are phase-combined with a phase difference of 0 degree via the mixing unit 60, the horizontal plane directivity approaches a circle as shown in FIG. Is a figure of 8 divided by a horizontal plane.

  Further, when the outputs of the antenna units 4A and 4B are phase-combined with a phase difference of 180 degrees via the mixing unit 60, the vertical plane directivity approaches a circle as shown in FIG. 11, and the horizontal plane directivity is The figure is a figure of 8 divided by a vertical plane.

  On the other hand, when the outputs of the antenna units 4A and 4B are phase-combined with a phase difference of 90 degrees and 270 degrees via the mixing unit 60, as shown in FIGS. 10 and 12, the vertical plane directivity and horizontal plane directivity are shown. Is 0 degree and 180 degrees, and the reception gain becomes maximum.

  Further, in both the vertical plane directivity and the horizontal plane directivity, the reception gain is not greatly reduced even at 90 degrees and −90 degrees (in other words, 270 degrees) compared to the directivity characteristics shown in FIGS. Thus, the antenna device 8 becomes omnidirectional.

Therefore, according to the antenna device 8 of the present embodiment, an omnidirectional antenna having a desired directivity can be realized by adjusting the amount of phase shift of the variable phase shifter 66.
For example, if the control unit 70 is used to automatically and continuously change the phase shift amount of the variable phase shifter 66 from 0 degrees to 360 degrees, the communication sensitivity for the RFID tag to be communicated is maximized. Thus, the identification information can be more reliably acquired from the RFID tag.

  Further, the antenna device 8 of the present embodiment can be used alone, but as illustrated in FIG. 13C, the antenna device 2 of the first embodiment is arranged at intervals on both sides in the radial direction. Thus, the antenna device 2 may be used in combination.

In this case, by directing the radiation directions of the antenna devices 2 on both sides toward the antenna device 8, the identification information can be satisfactorily read from the RFID tags that move between the antenna device 8 and the two antenna devices 2. As a result, RFID tags can be managed in a wide range.
[Modification 2]
Here, in the antenna device 8 of the second embodiment, the antenna device body is configured by stacking a pair of antenna parts 4A and 4B configured in the same manner as the antenna device body 4 of the first embodiment. explained.

  On the other hand, using a multilayer substrate in which one conductor layer serving as the ground conductor plates 6A and 6B is sandwiched between the dielectric substrates 10A and 10B, a conductor pattern constituting the radiating element 12 and the like on both surfaces of the multilayer substrate. Even if the antenna device 8 is provided, the antenna device 8 of the second embodiment can be realized.

  In the antenna device of the second embodiment, the antenna units 4A and 4B have been described as being configured in the same manner as the antenna device body 4 of the first embodiment, but the antenna units 4A and 4B and the protective cover 50 are The configuration may be as described in the first modification.

  Then, as described in the first modification, when the dielectric substrate 10 is formed of a single-sided substrate and a conductor pattern such as the radiating element 12 is formed on the conductor layer, FIG. As shown in D), the back surfaces of the two dielectric substrates 10 formed of single-sided substrates are opposed to each other, and a metal plate to be the ground conductor plate 6 is sandwiched between them.

  Further, as in the above-described embodiment, the back surface of the dielectric substrate configured by the double-sided substrate (that is, the ground conductor plate 6) is opposed to the back surface of the dielectric substrate configured by the single-sided substrate described in Modification 1. Thus, a composite antenna can be configured simply by bonding.

  Further, as in the antenna device 8 of the second embodiment, the conductor patterns constituting the radiation elements 12 and the like are provided on the surfaces of the dielectric substrates 10A and 10B sandwiching the ground conductor plate, respectively, so that omnidirectionality is achieved. When configuring the antenna, it is not necessary to provide the protective cover 50 depending on the application.

  In this case, it is not necessary to provide the frame portions 40A and 40B on the surfaces of the dielectric substrates 10A and 10B to form a space above the radiating element, and an antenna as an omnidirectional antenna can be formed by using only the multilayer substrate. The device 8 can also be realized.

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 above embodiment, the antenna devices 2 and 8 have been described as being planar antennas for far-field and near-field communication used for acquiring identification information from an RFID tag. However, the present invention can be applied in the same manner as in the above-described embodiment to obtain the same effect as long as it is a planar antenna in which a radiating element and a ground conductor plate are provided on the front and back surfaces of a dielectric substrate. Therefore, the present invention can be applied even to a planar antenna that performs only far-field communication.

  DESCRIPTION OF SYMBOLS 2,8 ... Antenna apparatus, 4 ... Antenna apparatus main body, 4A, 4B ... Antenna part, 6, 6A, 6B ... Ground conductor plate, 10, 10A, 10B ... Dielectric substrate, 12 ... Radiation element, 14 ... Slit, 16 ... impedance converter, 16a, 16b, 16c, 28 ... microstrip line, 18 ... signal synthesis circuit, 20, 20A, 20B ... termination resistor, 22, 22A, 22B ... connection, 24, 24A, 24B ... ground pattern, 26, 26A, 26B ... terminal portion, 30, 30A, 30B ... coaxial cable, 34, 34A, 34B ... outer conductor, 36, 36A, 36B ... center conductor, 40, 40A, 40B ... frame portion, 42 ... filler, 44 ... plate-like member, 50 ... protective cover, 60 ... mixing unit, 66 ... variable phase shifter, 68 ... mixing circuit, 70 ... control unit.

Claims (5)

An antenna having a dielectric substrate, a conductor pattern that is provided on one side of the dielectric substrate to form a radiating element, and a ground conductor plate that is provided on the opposite side of the radiating element across the dielectric substrate The device body;
A protective cover for covering the antenna device body;
By supporting the protective cover at an interval on one side of the dielectric substrate on which the conductor pattern constituting the radiating element is provided in the antenna device body, a dielectric between the protective cover and the radiating element is supported. A gap member whose rate is lower than the dielectric constant of the protective cover;
An antenna device comprising:   The gap member is configured to protrude to one side of the dielectric substrate to support the protective cover, and to form a space between the protective cover and the conductor pattern. Antenna device.   The antenna device according to claim 2, wherein a filler having a lower dielectric constant than that of the protective cover is provided in the space formed by the gap member.   The antenna device according to claim 1, wherein the gap member is configured by a plate-like member having a lower dielectric constant than the protective cover, and supports the protective cover by the plate-like member.   The antenna device body includes a pair of dielectric substrates provided with a conductor pattern constituting the radiating element on one side, and the back surfaces of the pair of dielectric substrates opposite to the conductor pattern are disposed on the ground surface. The antenna device according to any one of claims 1 to 4, wherein the antenna device is configured as a composite antenna capable of radiating radio waves from both sides by being disposed opposite to each other with a conductor plate interposed therebetween.