JP2012249204A - Micro wave planar antenna - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a planar antenna which is less likely to block the eyesight while securing high directivity.SOLUTION: A patch antenna includes: a thin plate like ground pattern 20 and a thin plate like patch pattern 10 supported so as to have a predetermined space from the ground pattern 20. Multiple holes 20b are formed in the ground pattern 20 to form meshes. A plate part 20a is provided at a region of the ground pattern 20, which is located immediately below the patch pattern 10, and the holes 20b are not formed in the region.

Description

The present invention relates to a microwave planar antenna (patch antenna) used for radio communication and RFID (Radio Frequency Identification).

  In recent years, automatic recognition systems using RFID tags are becoming popular in factories and warehouses. For example, a UHF (Ultra High Frequency) band RFID tag is attached to a load, and an RFID antenna is attached to a forklift for carrying the load. When carrying a load with a forklift, the ID of the load is read from the RFID tag by an antenna attached to the forklift, and the load is managed based on the read ID.

  It is preferable that the antenna used for the UHF band RFID has directivity only in one direction as much as possible. If the antenna has directivity other than the target direction, there is a possibility that not only the ID of a package to be transported by a forklift but also the ID of an irrelevant package placed behind or around.

  As an antenna suitable for RFID detection, for example, there is a planar antenna (microstrip antenna) described in Patent Document 1. This antenna generally has a structure in which a dielectric plate is sandwiched between a ground plate and a patch. The ground plate has an area several steps wider than the patch. Such a planar antenna has high directivity and has preferable characteristics for use in the automatic recognition system.

JP-A-9-172321

  In the above environment, in order to properly detect the ID of the baggage viewed by the forklift driver with the antenna, it is necessary to arrange the antenna so that the direction of directivity is the same as the direction of the driver's eyes. There is. In this case, the antenna is disposed in the vicinity of the position that is in the driver's field of view.

  However, in the UHF band antenna, since the ground plate is relatively large, usually about 30 cm square, if the antenna is disposed at the above position, the antenna may block the driver's view. For this reason, it becomes difficult to attach the antenna at an optimal position.

  For this reason, the development of an antenna that is transparent and does not obstruct the field of view is considered in the above system. However, when the antenna is made transparent, there is a problem that an antenna having a sharp directivity gain that can detect only the RFID tag in the aimed direction cannot be obtained.

  This invention is made | formed in view of this subject, and it aims at providing the planar antenna which is hard to disturb a visual field, ensuring high directivity.

The microwave planar antenna according to the first aspect of the present invention includes a thin plate-like ground pattern and a thin plate-like patch pattern supported at a predetermined interval with respect to the ground pattern. In the ground pattern, a plurality of holes are formed in a mesh shape.

  According to the microwave planar antenna according to this aspect, since the plurality of holes are formed in the ground pattern, the other side of the ground pattern can be seen through the holes. Moreover, even if the hole is formed in this way, the directivity characteristic of the antenna is not greatly deteriorated. Therefore, it is possible to provide a planar antenna that does not obstruct the field of view while ensuring high directivity.

  The microwave planar antenna according to this aspect may be configured such that the hole is not formed in at least a region immediately below the patch pattern in the region of the ground pattern. In this way, it is possible to suppress a decrease in the directivity characteristics of the antenna.

  In the microwave planar antenna according to this aspect, a plurality of holes may be formed in the patch pattern in a mesh shape. This makes it possible to see the other side of the antenna from the hole in the patch pattern, so that the field of view is more easily prevented.

  In this case, the hole is not formed in the edge portion of the patch pattern that sandwiches the straight line connecting the center of the patch pattern and the feeding point of the patch pattern, and is directly below the edge portion of the ground pattern. It is desirable not to form the hole in the region. In this way, it is possible to effectively suppress a decrease in the directivity characteristic of the antenna.

  When holes are also formed in the patch pattern, it is desirable not to form the holes in regions of the patch pattern where high frequency currents concentrate during operation. Similarly, it is desirable not to form the hole in the region of the ground pattern where the high-frequency current is concentrated during operation. In this way, it is possible to effectively suppress a decrease in the directivity characteristic of the antenna.

  The microwave planar antenna according to this aspect is configured such that a plurality of holes are formed in a mesh shape in all regions except the power feeding portion of the ground pattern and in all regions except the power feeding portion of the patch pattern. Can be done. This makes it easier to see the other side of the antenna, making it difficult for the antenna to obstruct the field of view. Even when the holes are formed in the patch pattern and the ground pattern in this way, the directivity characteristics of the antenna can be ensured. This will be clarified in Example 3.

  When forming a hole in the patch pattern, the center of the hole formed in the ground pattern and the center of the hole formed in the patch pattern are in the overlapping direction of the ground pattern and the patch pattern. It is desirable to match. In this case, since two holes are arranged in the overlapping direction of the ground pattern and the patch pattern, the other side of the antenna can be seen well through these holes.

  In this case, it is preferable that the hole formed in the ground pattern and the hole formed in the patch pattern have the same shape. In this case, the edge of one hole is not hung inside the other hole, and therefore the field of view can be secured without waste.

  In the microwave planar antenna according to this aspect, the pitch of the holes formed in the ground pattern is preferably 1/10 to 1/30 of the wavelength of the radio wave used. If it carries out like this, the directivity characteristic of an antenna can be maintained in a favorable state, ensuring the field of view by a hole.

  In this case, it is most desirable that the pitch of the holes formed in the ground pattern is about 1/16 of the wavelength of the radio wave used. In this way, the directivity characteristic of the antenna can be made the best.

  A microwave planar antenna according to a second aspect of the present invention includes a thin plate-like ground pattern and a thin plate-like patch pattern supported at a predetermined interval with respect to the ground pattern. The ground pattern is a region other than a region immediately below the feeding point of the patch pattern and a region directly under the edge portion of the patch pattern that sandwiches a straight line connecting the center of the patch pattern and the feeding point of the patch pattern. There is a notch.

  According to the microwave planar antenna according to this aspect, since the notch is provided in the ground pattern, the other side of the ground pattern can be seen through the notch. Further, even if the notch is formed in this way, the directivity characteristic of the antenna is not greatly deteriorated. Therefore, it is possible to provide a planar antenna that does not obstruct the field of view while ensuring high directivity.

  In the microwave planar antenna according to the second aspect, the patch pattern may be provided with a notch in a region other than the edge portion. This makes it possible to see the other side of the antenna from the cutout of the patch pattern.

  As described above, according to the present invention, it is possible to provide a planar antenna that does not obstruct the field of view while ensuring high directivity.

  The effects and significance of the present invention will become more apparent from the following description of embodiments. However, the following embodiment is merely an example when the present invention is implemented, and the present invention is not limited to what is described in the following embodiment.

It is a figure which shows the structure of the patch antenna which concerns on a comparative example. It is a figure which shows the structure and gain characteristic of the patch antenna which concern on a comparative example. It is a figure which shows the distribution state of the surface current of the patch antenna which concerns on a comparative example. 1 is a diagram illustrating a configuration of a patch antenna according to Example 1. FIG. It is a figure which shows the directivity and gain characteristic of the patch antenna which concerns on Example 1. FIG. 6 is a diagram illustrating a configuration of a patch antenna according to Example 2. FIG. It is a figure which shows the structure and gain characteristic of the patch antenna which concern on Example 2. FIG. 6 is a diagram illustrating a configuration of a patch antenna according to Example 3. FIG. It is a figure which shows the structure and gain characteristic of the patch antenna which concern on Example 3. FIG. It is a figure which shows the structure of the patch antenna which concerns on Example 4 and Example 5. FIG. It is a figure which shows the structure of the patch antenna which concerns on the example of a change of Example 5. FIG. It is a figure which shows the structure of the patch antenna which concerns on the example of a change of Example 5. FIG. It is a figure for demonstrating the structure of the patch antenna which concerns on the example of a change.

  Embodiments of the present invention will be described below with reference to the drawings.

<Comparative example>
First, a planar antenna (hereinafter referred to as “patch antenna”) according to a comparative example will be described. This patch antenna is used in UHF band RFID.

  1A and 1B are perspective views of a patch antenna according to a comparative example. FIG.1 (b) is a perspective view when it sees from the position one step lower than Fig.1 (a).

  As shown in the figure, the patch antenna according to the comparative example includes a patch pattern 1 made of a conductive metal thin plate and a ground pattern 2 also made of a conductive metal thin plate. Each of the patch pattern 1 and the ground pattern 2 has a square outline in plan view. The patch pattern 1 and the ground pattern 2 have a uniform thickness.

  The patch pattern 1 is supported by the ground pattern 2 so as to be parallel to the ground pattern 2. Specifically, the center of the patch pattern 1 is coupled to the ground pattern 2 via a cylindrical spacer made of an insulator such as resin or metal. For example, the patch pattern 1 and the ground pattern 2 are bonded or screwed to the upper and lower surfaces of the spacer. For convenience, in FIG. 1, a coupling member (including a spacer) for coupling the patch pattern 1 and the ground pattern 2 is omitted. Note that the center of the patch pattern 1 and the center of the ground pattern 2 have zero potential during antenna operation, so there is no problem even if the spacer is made of metal.

  In this comparative example, a dielectric plate is not interposed between the patch pattern 1 and the ground pattern 2 and is a space. That is, air is interposed between the patch pattern 1 and the ground pattern 2.

  The length of one side of the ground pattern 2 is set in the vicinity of the wavelength of the radio wave used. Here, since the wavelength λ of the radio wave used in the RFID in the UHF band is λ = 315 mm, the length of one side of the ground pattern 2 is set to 300 mm. The patch pattern 1 has a side length of 132 mm. The distance between the ground pattern 2 and the patch pattern 1 is 20 mm. The ground pattern 2 and the patch pattern 1 have the same center in plan view, and the corresponding sides are parallel to each other.

  As shown in FIG. 1, when an XYZ axis with the center of the ground pattern as the origin is set, a hole serving as a feeding point 3 is formed at a point 40 mm from the center of the patch pattern 1 in the Y-axis direction. A hole having the same diameter (3 mmφ to 9 mmφ) as that of the dielectric of the coaxial connector is formed at a point 40 mm in the Y-axis direction from the center of the ground pattern 2. A coaxial connector is attached downward in this hole. The inner conductor (1 mmφ to 3 mmφ) of the coaxial connector extends to the patch pattern 1 and is electrically connected at the feeding point 3.

  FIG. 2A is a side view of the patch antenna according to the comparative example as viewed from the side.

  FIG. 2B is a simulation result of the three-dimensional directivity of the patch antenna according to the comparative example. Such a simulation was performed using a 3D electromagnetic field simulator HFSS manufactured by Ansoft.

  Referring to FIG. 2B, the patch antenna according to the comparative example has a large antenna gain of +9.6 dBi in the upward direction (Z-axis positive direction) perpendicular to the surface of the patch pattern 1, and the opposite direction ( In the negative Z-axis direction, there is only a slight gain of -10.8 dBi. When the upper surface of the patch pattern 1 is the front surface of the patch antenna, the gain in the front direction (Z-axis positive direction) is about 20 dB (100 times) larger than the gain in the rear direction (Z-axis negative direction). Therefore, when this patch antenna is used, only the RFID tag in the front direction can be detected smoothly. In addition, since the antenna gain of this patch antenna is as large as +9.6 dBi, an RFID tag that is about 6 m away can be detected smoothly, and sufficient detection sensitivity can be obtained.

However, in the patch antenna according to the comparative example, the ground pattern 2 is formed of a 300 mm square metal and does not transmit light. Therefore, when the patch antenna is arranged in the direction of the user's line of sight, a wide ground pattern is obtained. 2 may cause a problem that the user's view is obstructed.

  In the following, a description will be given of studies made to solve such a problem.

  FIG. 3A is a diagram illustrating a simulation result of the high-frequency surface current flowing through the patch pattern 1 when the patch antenna according to the comparative example is operated. Such a simulation was performed by an unsoft 3D electromagnetic field simulator HFSS. In the figure, a broken line region labeled “High” indicates a region where the surface current appears most frequently, and a broken line region denoted as “Low” indicates a region where the surface current is smallest. In addition, a scale indicating the amount of current per minute with a color is attached to the left part of FIG.

  As shown in the figure, the surface current is concentrated on the upper and lower edge portions of the patch pattern 1, and the surface current of the other portions is as small as 1/4 or less (1/16 or less in terms of power). . That is, when the patch pattern 1 is square like the patch antenna according to the comparative example, the surface current is concentrated on the two side portions sandwiching the straight line connecting the center of the patch pattern 1 and the feeding point 3.

  FIG. 3B is a diagram showing a high-frequency surface current flowing in the ground pattern 2 when the patch antenna according to the comparative example is operated. In the figure, a broken line region labeled “High” indicates a region where the surface current appears most frequently, and a broken line region denoted as “Low” indicates a region where the surface current is smallest. In addition, a scale indicating the amount of current per minute with a color is attached to the left part of FIG.

  As shown in the figure, the surface current is concentrated in the entire area of the ground pattern 2 in the portion directly below the patch antenna 1. In particular, the surface current is concentrated in the peripheral portion of the feeding point 3 and the two portions sandwiching the center of the ground pattern 2 in the vertical direction, and the surface current in the other portions is ½ or less (when converted to electric power) It can be seen that the number is less than 1/4.

  From the result of FIG. 3B, it can be seen that the surface current flowing in the region of the ground pattern 2 excluding the region immediately below the patch pattern 1 (hereinafter referred to as “small current region”) is relatively small. In particular, it can be seen that the surface current decreases in the small current region as it approaches the outer edge of the ground pattern 2. Therefore, it is considered that the characteristics of the patch antenna do not change greatly even if the ground pattern 2 is processed in this small current region.

  Based on this study, the inventor of the present application has studied to form a plurality of holes in the small current region of the ground pattern 2 so that the other side of the ground pattern 2 can be seen through these holes. Hereinafter, the configuration of the patch antenna based on this study will be described.

<Example 1>
FIG. 4 is a diagram illustrating the configuration of the patch antenna according to the first embodiment. 4A is a perspective view of the patch antenna, and FIG. 4B is a plan view of the patch antenna.

  The configuration of the patch pattern 10 is the same as the patch pattern 1 of the comparative example.

Similarly to the comparative example, the ground pattern 20 is made of a conductive thin metal plate and has a square outline in plan view. The length of one side of the ground pattern 20 is 322 mm, which is slightly longer than the wavelength λ (λ = 315 mm) of the radio wave used in the UHF band RFID. A plate portion 20a is formed at the center of the ground pattern 20, and a plurality of holes 20b are formed in a mesh shape around the plate portion 20a. The plate part 20a has a square shape in plan view and has a side length of 164 mm. Moreover, the hole 20b is square in planar view, and the length of one side is 18 mm. The holes 20b are formed at a pitch of 20 mm in each of the X-axis direction and the Y-axis direction. In the present embodiment, four rows of holes 20b are formed on the top, bottom, left and right of the plate portion 20a. The plate portion 20a is slightly larger than the patch pattern 10.

  The patch pattern 10 is supported by the ground pattern 20 so as to be parallel to the ground pattern 20. Specifically, as in the comparative example, the center of the patch pattern 10 is coupled to the ground pattern 20 via a cylindrical spacer made of an insulator such as resin or metal. For example, the patch pattern 10 and the ground pattern 20 are bonded or screwed to the upper and lower surfaces of the spacer. For convenience, in FIG. 4, a coupling member (including a spacer) for coupling the patch pattern 10 and the ground pattern 20 is omitted.

  In the present embodiment, as in the comparative example, a dielectric plate is not interposed between the patch pattern 10 and the ground pattern 20 and is a space. That is, air is interposed between the patch pattern 10 and the ground pattern 20.

  The distance between the ground pattern 20 and the patch pattern 10 is 20 mm as in the comparative example. The ground pattern 20 and the patch pattern 10 have the same center in plan view, and the corresponding sides are parallel to each other.

  As in the comparative example, a hole serving as a feeding point 30 is formed at a point 40 mm in the Y-axis direction from the center of the patch pattern 10. A hole having the same diameter (3 mmφ to 9 mmφ) as the dielectric of the coaxial connector is formed at a point 40 mm in the Y-axis direction from the center of the ground pattern 20. A coaxial connector is attached downward in this hole. An inner conductor (1 mmφ to 3 mmφ) of the coaxial connector extends to the patch pattern 10 and is electrically connected at the feeding point 30.

  The patch antenna according to the present embodiment is a region corresponding to the small current region of the comparative example in the entire region of the ground pattern 20 (in this embodiment, for convenience, this region is referred to as a “small current region”). A plurality of holes 20b are formed. The small current region is originally a region where the surface current is relatively small. In this embodiment, a plurality of holes 20b are formed in this small current region.

  FIGS. 5A and 5B are simulation results of the directivity of the patch antenna according to the present embodiment. This simulation was performed using a 3D electromagnetic field simulator HFSS manufactured by Ansoft as in the comparative example.

  As shown in the figure, the directivity of the patch antenna according to this example is substantially the same as that of the patch antenna of the comparative example. In addition, the patch antenna of this example has an antenna gain of +9.5 dBi, and this antenna gain is only 0.1 dB (2%) lower than the patch antenna of the comparative example. Thus, with the patch antenna according to the present embodiment, the directivity characteristic equivalent to that of the comparative example can be obtained.

  In addition, in this embodiment, the other side of the patch antenna can be seen through the plurality of holes 20b formed in the ground pattern 20. Therefore, when such a patch antenna is arranged in the direction of the user's line of sight, only the central patch 10 part completely blocks the view. Seventy percent of the ground pattern 20 can be seen through the hole 20b. Therefore, even if this patch antenna is arranged in the direction of the user's line of sight, the user's field of view is not easily blocked by the ground pattern 20, and the user can appropriately detect the target RFID tag.

<Example 2>
FIG. 6 is a diagram illustrating the configuration of the patch antenna according to the second embodiment. FIG. 6A is a plan view of the patch pattern, and FIG. 6B is a plan view of the ground pattern. FIG. 7A is a perspective view illustrating the configuration of the patch antenna according to the second embodiment.

  The patch pattern 11 is made of a conductive thin metal plate and has a square outline in plan view. The patch pattern 11 has a plate portion 11a and a plurality of holes 11b formed in a mesh shape. The shape of the holes 11b is an 18 mm square, and the pitch between the holes 11b is 20 mm.

  In FIG. 6A, the broken line region labeled “High” corresponds to the region labeled “High” in FIG. 3A, and is the region where the surface current appears most frequently. In FIG. 6A, a broken line region labeled “Low” corresponds to a region labeled “Low” in FIG. 3A and indicates a region having the smallest surface current. As shown in the drawing, the holes 11b are formed in a portion of the patch pattern 11 where the surface current is small.

  As in the first embodiment, the ground pattern 21 is made of a conductive thin metal plate and has a square outline in plan view. The length of one side of the ground pattern 21 is 322 mm. A plate portion 21a is formed at the center of the ground pattern 21, and a plurality of holes 21b are formed around the plate portion 21a. The shape of the holes 21b and the pitch between the holes 21b are the same as those of the holes 20 of the first embodiment. Therefore, the shape and pitch of the holes 21b are the same as the shape and pitch of the holes 11b.

  In the first embodiment, the plate portion 20 a of the ground pattern 20 is slightly larger than the patch pattern 10. However, in this embodiment, the plate portion 21 a is limited to the range of the region corresponding to the portion immediately below the patch pattern 21. Is done. In plan view, the shape and size of the plate portion 21a are the same as the shape and size of the plate portion 11a of the patch pattern 11 in FIG.

  In FIG. 6B, the broken line region labeled “High” corresponds to the region labeled “High” in FIG. 3B and is the region where the surface current appears most frequently. In FIG. 6B, a broken line region labeled “Low” corresponds to a region labeled “Low” in FIG. 3B and indicates a region having the smallest surface current. As illustrated, the hole 21b is formed in a portion of the ground pattern 21 where the surface current is small.

  The patch pattern 11 is supported by the ground pattern 21 so as to be parallel to the ground pattern 21. Specifically, the four corners of the patch pattern 11 are coupled to the four corners of the ground pattern 21 via columnar spacers made of an insulator such as resin. For example, the patch pattern 11 and the ground pattern 21 are bonded or screwed to the upper and lower surfaces of the spacer. For convenience, in FIG. 7A, a coupling member (including a spacer) for coupling the patch pattern 11 and the ground pattern 21 is omitted.

  In the present embodiment, similarly to the first embodiment, a dielectric plate is not interposed between the patch pattern 11 and the ground pattern 21 and is a space. That is, air is interposed between the patch pattern 11 and the ground pattern 21.

The distance between the ground pattern 21 and the patch pattern 11 is 20 mm as in the first embodiment. The ground pattern 21 and the patch pattern 11 have the same center in plan view, and the corresponding sides are parallel to each other. When the ground pattern 21 and the patch pattern 11 are arranged in this way, the center of the hole 11b of the patch pattern 11 and the center of the hole 21b of the ground pattern 21 corresponding to these holes 11b coincide in plan view. As a result, the side facing through the two holes 11b and 21b can be seen.

  As in the first embodiment, a hole serving as the feeding point 31 is formed at a point 40 mm in the Y-axis direction from the center of the patch pattern 11. A hole having the same diameter (3 mmφ to 9 mmφ) as that of the dielectric of the coaxial connector is formed at a point 41 mm in the Y-axis direction from the center of the ground pattern 21. A coaxial connector is attached downward in this hole. The inner conductor (1 mmφ to 3 mmφ) of the coaxial connector extends to the patch pattern 11 and is electrically connected at the feeding point 31.

  In the present embodiment, the size of the patch pattern 11 is set to 124 mm square so as to optimize the characteristics of the patch antenna, and is slightly smaller than the patch pattern 10 of the first embodiment.

  FIG. 7B is a simulation result of the directivity of the patch antenna according to the present embodiment. This simulation was performed using a 3D electromagnetic field simulator HFSS manufactured by Ansoft as in Example 1.

  As shown in the figure, also in the patch antenna according to the present embodiment, the gain in the front direction (Z-axis positive direction) is significantly larger than the gain in the back direction (Z-axis negative direction). In the patch antenna of this embodiment, the antenna gain is +9.0 dBi, which is slightly lower (0.6 dB = 13%) than the patch antenna of the above comparative example, but sufficient directivity characteristics can be obtained even with this gain. It is done.

  In addition, in this embodiment, the patch pattern 11 and the ground pattern 21 are slightly smaller than those in the first embodiment, and the holes 11b and 21b are also formed in the central portions of the patch pattern 11 and the ground pattern 21. The other side of the patch antenna can be seen through the hole 21b in an area of about 90% of the entire area within the outline of the ground pattern 21. Therefore, even when such a patch antenna is arranged in the direction of the user's line of sight, the user's field of view is not easily blocked by the patch antenna, and the user can appropriately detect the target RFID tag.

<Example 3>
FIG. 8 is a diagram illustrating the configuration of the patch antenna according to the third embodiment. FIG. 8A is a plan view of the patch pattern, and FIG. 8B is a plan view of the ground pattern. FIG. 9A is a perspective view illustrating the configuration of the patch antenna according to the third embodiment.

  The patch pattern 12 and the ground pattern 22 according to the present embodiment have the same configuration as the patch pattern 11 and the ground pattern 21 of the second embodiment except that the number of holes 12b and 22b is increased.

  In the patch pattern 12, holes 12b are formed in a mesh shape over the entire region. In the ground pattern 22, holes 22 b are formed in a mesh shape in a region excluding the plate portion 22 a formed at a position corresponding to the feeding point 32.

  In FIG. 8A, the broken-line regions labeled “High” and “Low” correspond to the regions labeled “High” and “Low” in FIG. 3A, respectively. In FIG. 8B, the broken-line regions labeled “High” and “Low” correspond to the regions labeled “High” and “Low” in FIG. 3B, respectively. In this embodiment, the edge portion of the patch pattern 12 exists in the region where the surface current of the patch pattern 12 is large. Further, a boundary portion between the plate portion 22a or the hole 22b and the hole 22b exists in the region where the surface current of the ground pattern 22 is large.

  The patch pattern 12 is supported by the ground pattern 22 so as to be parallel to the ground pattern 22. Specifically, a rectangular parallelepiped spacer having an upper surface and a lower surface that are large enough to enclose four holes 12b arranged in a rectangle is arranged at the center of the patch pattern 12 (the portion surrounded by the thick frame in FIG. 8A). And the central portion of the ground pattern 22 (the portion surrounded by a thick frame in FIG. 8A), and in this portion, the patch pattern 12 and the ground pattern 22 are fixed to the upper surface and the lower surface of the spacer, respectively. The spacer is made of an insulator such as resin. For example, the patch pattern 12 and the ground pattern 22 are bonded or screwed to the upper and lower surfaces of the spacer. For convenience, in FIG. 9A, a coupling member (including a spacer) for coupling the patch pattern 12 and the ground pattern 22 is omitted.

  Also in the present embodiment, like the first and second embodiments, the dielectric plate is not interposed between the patch pattern 12 and the ground pattern 22 and is a space. That is, air is interposed between the patch pattern 12 and the ground pattern 22. The distance between the ground pattern 22 and the patch pattern 12 is 20 mm as in the first and second embodiments.

  The ground pattern 22 and the patch pattern 12 have the same center in a plan view, and the corresponding sides are parallel to each other. When the ground pattern 22 and the patch pattern 12 are thus arranged, the center of the hole 12b of the patch pattern 12 and the center of the hole 22b of the ground pattern 22 corresponding to these holes 12b coincide with each other in plan view. Thereby, the side facing through the two holes 12b and 22b can be seen well. The position of the feeding point 32 is also the same as in the first and second embodiments.

  Also in the present embodiment, as in the second embodiment, the size of the patch pattern 21 is set to 124 mm square so that the characteristics of the patch antenna are optimized, and is slightly more than the patch pattern 10 of the first embodiment. It is getting smaller.

  FIG. 9B is a simulation result of the directivity of the patch antenna according to the present embodiment. This simulation was performed using a 3D electromagnetic field simulator HFSS manufactured by Ansoft as in the above example.

  As shown in the figure, also in the patch antenna according to the present embodiment, the gain in the front direction (Z-axis positive direction) is significantly larger than the gain in the back direction (Z-axis negative direction). In the patch antenna of the present embodiment, the antenna gain is +8.3 dBi, which is slightly lower (1.3 dB = 26%) than the patch antenna of the comparative example, but sufficient directivity characteristics can be obtained even with this gain. It is done.

  In addition, in this embodiment, since the holes 12b and 22b are formed in almost the entire region of the patch pattern 11 and the ground pattern 21, the patch is formed in the region of about 98% of the entire region of the ground pattern 21 through the hole 22b. You can see the other side of the antenna. Therefore, even when such a patch antenna is arranged in the direction of the user's line of sight, the user's field of view is not easily blocked by the patch antenna, and the user can appropriately detect the target RFID tag.

<Example 4>
FIG. 10A is a perspective view of the patch antenna according to the fourth embodiment.

In the said Examples 1-3, the pitch of the hole was 20 mm. This pitch is about 1/16 of the wavelength (λ = 315 mm) of the radio wave used in the UHF band RFID. On the other hand, in this embodiment, the pitch of the holes 13b and 23b is set to 30 mm. This pitch is
It is about 1/10 of the wavelength of the radio wave. The holes 13b and 23b are each 28 mm square.

  In addition to the holes 13b and 23b, the patch pattern 13 and the ground pattern 23 are formed with plate portions 13a and 23a having no holes 13b and 23b around the feeding point 33. The patch pattern 13 is supported by the ground pattern 23 by arranging a rectangular parallelepiped spacer at the center as in the third embodiment. The spacer is disposed so as not to be hooked on the feeding point 33. For example, the patch pattern 13 and the ground pattern 23 are bonded or screwed to the upper and lower surfaces of the spacer.

  Except for the above configuration, the configuration of the patch antenna of the present embodiment is the same as that of the third embodiment. In the present embodiment, an edge portion of the patch pattern 13 exists in a region where the surface current of the patch pattern 13 is large. Further, in the region where the surface current of the ground pattern 23 is large, there is a boundary portion between the plate portion 23a or the adjacent hole 23b.

  Similar to the above example, the directivity of the patch antenna according to the present example was simulated using the 3D electromagnetic field simulator HFSS manufactured by Ansoft, and the antenna gain was +7.6 dBi. In the patch antenna of this example, the gain (+7.6 dBi) is slightly reduced (2 dB = 37%) as compared with the patch antenna of the comparative example, but sufficient directivity characteristics can be obtained even with this gain.

  In addition, in this embodiment, since the holes 13b and 23b are formed in the region excluding the vicinity of the feeding point 33 (plate portions 13a and 23a) of the patch pattern 13 and the ground pattern 23, about 96% of the entire region of the ground pattern 23 is formed. In this area, the other side of the patch antenna can be seen through the hole 23b. Therefore, even when such a patch antenna is arranged in the direction of the user's line of sight, the user's field of view is not easily blocked by the patch antenna, and the user can appropriately detect the target RFID tag.

  Note that the gain of the patch antenna is better in the third embodiment than in the present embodiment, and the area that can be seen through the hole is better in the third embodiment than in the present embodiment. . From this, it can be said that the pitch of the holes is advantageously about 1/16 of the wavelength of the radio wave, rather than 1/10 of the wavelength of the radio wave.

<Example 5>
In the first to fourth embodiments, holes are formed in the patch pattern and the ground pattern so that the other side of the patch antenna can be seen. On the other hand, the patch antenna according to the present embodiment is configured so that the other side of the patch antenna can be seen by cutting out the patch pattern and the ground pattern.

  FIG. 10A is a perspective view of the patch antenna according to the fourth embodiment. As shown in the figure, the patch antenna according to this embodiment includes a patch pattern 14 made of a conductive metal thin plate and a ground pattern 24 also made of a conductive metal thin plate. Each of the patch pattern 14 and the ground pattern 24 has a uniform thickness.

In plan view, the patch pattern 14 has a shape in which a rectangle of a predetermined size is in contact with the outer edge, and the ground pattern 24 also has a shape in which the predetermined rectangle is in contact with the outer edge. The center of the rectangle in contact with the outer edge of the patch pattern 14 (hereinafter referred to as “the center of the patch pattern 14”) and the center of the rectangle in contact with the outer edge of the ground pattern 24 (hereinafter referred to as “the center of the ground pattern 24”) in plan view. The patch pattern 14 and the ground pattern 24 are arranged at a predetermined interval so that they match and the corresponding sides of these rectangles are parallel to each other.

  In FIG. 10B, for convenience, an XYZ axis having the center of the ground pattern 24 as the origin and the directions parallel to the two adjacent sides of the rectangle as the X axis direction and the Y axis direction is shown. Is set.

  The patch pattern 14 has a shape in which cutouts D11 and D12 in the X-axis negative direction and the X-axis positive direction are provided on a rectangular thin plate. The patch pattern 14 includes a pair of plate portions 14a arranged in the Y-axis direction, and a connecting portion 14b that connects these two plate portions 14a in the Y-axis direction. The two plate portions 14a have the same dimensions. The length of the plate portion 14a in the X-axis direction is 130 mm, and the width in the Y-axis direction is 20 mm. The length of the connecting portion 14b in the Y-axis direction is 130 mm. The two plate portions 14a are each parallel to the X axis.

  The ground pattern 24 has a shape in which notches D21 and D22 in the X-axis negative direction and the X-axis positive direction are provided on a rectangular thin plate. The ground pattern 24 includes a pair of plate portions 24a arranged in the Y-axis direction, and a connecting portion 24b that connects these two plate portions 24a in the Y-axis direction. The two plate portions 24a have the same dimensions. The plate portion 24a has a length in the X-axis direction of 300 mm and a width in the Y-axis direction of 40 mm. The length of the connecting portion 24b in the Y-axis direction is 110 mm, and the width in the X-axis direction is 40 mm. The two plate portions 24a are each parallel to the X axis.

  The patch pattern 14 is supported by the ground pattern 24 so as to be parallel to the ground pattern 24. Specifically, the four corners of the rectangle in contact with the outer edge of the patch pattern 14 are coupled to the ground pattern 24 via columnar spacers made of an insulator such as resin. For example, the patch pattern 14 and the ground pattern 24 are bonded or screwed to the upper and lower surfaces of the spacer. For convenience, in FIG. 10B, a coupling member (including a spacer) for coupling the patch pattern 14 and the ground pattern 24 is omitted.

  Also in this embodiment, a dielectric plate is not interposed between the patch pattern 14 and the ground pattern 24 and is a space. That is, air is interposed between the patch pattern 14 and the ground pattern 24. Also in this embodiment, the distance between the ground pattern 24 and the patch pattern 14 is 20 mm.

  In this embodiment, a hole serving as a feeding point 34 is formed at a point 55 mm in the Y-axis direction from the center of the patch pattern 14. A hole having the same diameter (3 mmφ to 9 mmφ) as that of the dielectric of the coaxial connector is formed at a point 55 mm in the Y-axis direction from the center of the ground pattern 24. A coaxial connector is attached downward in this hole. The inner conductor (1 mmφ to 3 mmφ) of the coaxial connector extends to the patch pattern 14 and is electrically connected at the feeding point 34.

  The shape and dimensions of each part shown in FIG. 10B are obtained by cutting out the ground pattern 24 and the patch pattern 14 from the configuration of the above comparative example while preventing the antenna gain from being lowered as much as possible. Is adjusted to a preferable value. In FIG. 10B, a region indicated by a broken line in the patch pattern 14 corresponds to a region indicated by “High” in FIG. 3A, and a region indicated by a broken line in the ground pattern 24 is illustrated in FIG. This corresponds to the area labeled “High” in 3 (b). In the present embodiment, the plate portion 14a exists in the region where the surface current of the patch pattern 14 is large, and the plate portion 24a or the connecting portion 24b exists in the region where the surface current of the ground pattern 24 is large.

Similar to the above example, the directivity of the patch antenna according to the present example was simulated using the 3D electromagnetic field simulator HFSS manufactured by Ansoft, and the antenna gain was +7.3 dBi. In the patch antenna of the present embodiment, the gain (+7.3 dBi) is slightly reduced (2.3 dB = 41%) compared to the patch antenna of the comparative example, but sufficient directivity characteristics can be obtained even with this gain. .

  In addition, in this embodiment, since the patch pattern 14 and the ground pattern 24 are cut out, the other side can be seen through the cut out portion, and a clear view can be obtained.

  In the present embodiment, the patch pattern 14 and the ground pattern 24 can be variously changed in shape.

  For example, as shown in FIG. 11A, the connecting portion 14b of the patch pattern 14 is expanded in the X-axis positive direction and the X-axis negative direction, and no cutout is provided on the X-axis positive side of the connecting portion 14b. Also good. Further, as shown in FIG. 11B, the patch pattern 14 may not be provided with a notch. In the case of FIG. 11B, the notch D22 on the negative X-axis side of the ground pattern 24 may be reduced as shown. Further, as shown in FIG. 12A, the patch pattern 14 is not formed with a notch, and a mesh-like hole is formed in the area of the patch pattern 14 corresponding to the notch D22 on the negative X-axis side of the ground pattern 24. 14c may be formed. Further, as shown in FIG. 12B, the hole 24c may be formed without forming the notch on the X axis positive side of the ground pattern 24.

  Also in the configurations of FIGS. 11 and 12, since the patch pattern 14 and the ground pattern exist in the region where the surface current is high, it is assumed that the same antenna characteristics as in FIG. 10B can be obtained.

  As described above, according to the patch antennas according to the first to fifth embodiments, it is possible to see the other side of the patch antenna while ensuring the directivity of the patch antenna. Therefore, for example, even if such a patch antenna is attached to a forklift for carrying a load in order to detect an ID from a bag with an RFID tag in a factory or a warehouse, while ensuring a driver's view well, The patch antenna can be focused on the target package.

  Although various embodiments according to the present invention have been described above, the present invention is not limited to the above-described embodiments, and the embodiments of the present invention can be modified in various ways other than the above. .

  For example, in the first to fourth embodiments, the patch pattern and the ground pattern have a square shape. However, these shapes may be other rectangular shapes such as a rectangle, or may be a circle or an ellipse. Also good.

  FIG. 13 is a plan view of the patch antenna when the patch pattern and the ground pattern are circular. FIG. 4A is a diagram showing the patch pattern 15, and FIG. 4B is a diagram showing the ground pattern 25. In this case, the surface current of the patch pattern 15 is concentrated in a region schematically indicated by a broken line in FIG. 5A, and the surface current of the ground pattern 25 is concentrated in a region schematically indicated by a broken line in FIG. concentrate. Therefore, when holes or notches are formed in the patch pattern 15 or the ground pattern 25, holes or notches may be formed in regions that do not hinder these surface currents. For example, in FIG. 6B, a plurality of holes are formed in a region excluding the region 25a immediately below the patch pattern 15 indicated by the alternate long and short dash line in the region of the ground pattern 25.

  The shape of the hole is not limited to the above, and other shapes such as a rectangle, a circle, and the like may be used in addition to a square.

  Furthermore, the dimensions of the patch pattern and the ground pattern are not limited to the above, and other dimensions can be used as appropriate.

  In the above embodiment, the air layer is formed between the patch pattern and the ground pattern. However, a dielectric plate may be interposed between the patch pattern and the ground pattern. However, in order to increase the antenna gain, it is desirable to use an air layer between the patch pattern and the ground pattern as in the above embodiment.

  Moreover, in the said Examples 1-4, although 20 mm (1/16 of wavelength) and 30 mm (1/10 of wavelength) were shown as a pitch of a hole, it made smaller than 20 mm (1/16 of wavelength). Also good. If the hole pitch is reduced, the patch antenna gain can be expected to improve. However, if the pitch is too small, the hole size will be reduced, making it difficult for the antenna to see beyond the antenna, and dust will easily accumulate in the hole. Become. Therefore, it is desirable to suppress the hole pitch to about 10 mm (1/30 of the wavelength). From the simulation results, it is considered that the hole pitch is optimally about 20 mm (1/16 of the wavelength).

  Further, the wavelength band used in the patch antenna is not limited to the above-described wavelength band, and various other changes can be made. Furthermore, the present invention can be used in various situations in addition to a patch antenna attached to a forklift.

  In addition, the embodiment of the present invention can be variously modified as appropriate within the scope of the technical idea shown in the claims.

10, 11, 12, 13, 14 ... Patch pattern 10a, 11a, 12a, 13a, 14c ... Hole 20, 21, 22, 23, 24 ... Ground pattern 20a, 21a, 22a, 23a, 24c ... Hole 30, 31, 32, 33, 34 ... Feed point D11, D12, D21, D22 ... Notch

Claims (13)

A thin ground pattern,
A thin plate-like patch pattern supported at a predetermined interval with respect to the ground pattern,
In the ground pattern, a plurality of holes are formed in a mesh shape,
A microwave planar antenna characterized by that. The microwave planar antenna according to claim 1, wherein
The hole is not formed in at least a region immediately below the patch pattern in the ground pattern region,
A microwave planar antenna characterized by that. The microwave planar antenna according to claim 1 or 2,
In the patch pattern, a plurality of holes are formed in a mesh shape,
A microwave planar antenna characterized by that. The microwave planar antenna according to claim 3,
The hole is not formed in the edge portion of the patch pattern across the straight line connecting the center of the patch pattern and the feeding point of the patch pattern,
The hole is not formed in a region immediately below the edge portion of the ground pattern,
A microwave planar antenna characterized by that. The microwave planar antenna according to claim 4, wherein
In the region of the patch pattern, the hole is not formed in a region where high-frequency current is concentrated during operation.
A microwave planar antenna characterized by that. The microwave planar antenna according to any one of claims 1 to 5,
In the region of the ground pattern, the hole is not formed in a region where high-frequency current is concentrated during operation.
A microwave planar antenna characterized by that. The microwave planar antenna according to claim 3,
A plurality of holes are formed in a mesh shape in all areas excluding the power supply part of the ground pattern and in all areas excluding the power supply part of the patch pattern.
A microwave planar antenna characterized by that. The microwave planar antenna according to any one of claims 3 to 5, wherein
The center of the hole formed in the ground pattern and the center of the hole formed in the patch pattern coincide with each other in the overlapping direction of the ground pattern and the patch pattern.
A microwave planar antenna characterized by that. The microwave planar antenna according to claim 8,
The hole formed in the ground pattern and the hole formed in the patch pattern have the same shape;
A microwave planar antenna characterized by that. The microwave planar antenna according to any one of claims 1 to 9,
The pitch of the holes formed in the ground pattern is 1/10 to 1/30 of the wavelength of the radio wave used.
A microwave planar antenna characterized by that. The microwave planar antenna according to any one of claims 1 to 9,
The pitch of the holes formed in the ground pattern is 1/16 of the wavelength of the radio wave used.
A microwave planar antenna characterized by that. A thin ground pattern,
A thin plate-like patch pattern supported at a predetermined interval with respect to the ground pattern,
The ground pattern is a region other than a region immediately below the feeding point of the patch pattern and a region directly under the edge portion of the patch pattern that sandwiches a straight line connecting the center of the patch pattern and the feeding point of the patch pattern. Is provided with a notch,
A microwave planar antenna characterized by that. The microwave planar antenna according to claim 12,
The patch pattern is provided with a notch in a region other than the edge portion.
A microwave planar antenna characterized by that.