JP7721174B2 - patch antenna - Google Patents

Description

The present invention relates to a patch antenna.

Patent document 1 (JP Patent Publication No. 6-177637) discloses an antenna device that is small and has a simple structure and can achieve dual resonance characteristics.

The antenna device described in Patent Document 1 comprises a conductive ground plane, a conductive radiation plate arranged substantially parallel to the ground plane via an insulator, and a feeder line with a ground conductor connected to the ground plane and an ungrounded conductor connected to the radiation plate. At another connection point spaced apart from the connection point of the feeder line, a parasitic line is connected with the ground conductor connected to the ground plane and an ungrounded conductor connected to the radiation plate.

Patent Document 2 (JP 2003-46324 A) discloses an antenna in which a base plate is disposed in a flat, container-shaped case, an antenna element is disposed approximately parallel to the front side away from the base plate, the tip of a coaxial cable is disposed between the bottom surface of the container-shaped case and the base plate, the center conductor passes through the base plate in an insulated state to be electrically connected to the antenna element, and the outer conductor is electrically connected to the base plate, and the antenna has a small number of soldering points in the signal path and is electrically connected to the antenna element using a coaxial structure.
The antenna described in Patent Document 2 has a flat, container-shaped case with a conductive ground plate disposed therein, an antenna element disposed on the front side away from the ground plate and approximately parallel thereto, and the tip of a coaxial cable disposed between the container-shaped bottom surface of the case and the ground plate, with the central conductor passing through the ground plate in an insulated state and electrically connected to the antenna element, and the outer conductor electrically connected to the ground plate.The central conductor is stripped of its coating, bent, and inserted into a roughly cylindrical dielectric member, and then passes through the ground plate, and a shield cover covering the central conductor, dielectric member, and outer conductor of the coaxial cable is disposed on the back side of the ground plate, and the shield cover is electrically connected to the ground plate and the outer conductor.

Patent Document 3 (International Publication No. 2011/062272) discloses an antenna device that includes a radiating element arranged in a specific plane and a conductor plate arranged opposite the specific plane, in which the radiating element and the conductor plate are short-circuited, and a pair of conductors that form a feeder line are both connected to the radiating element.
The antenna device described in Patent Document 3 is an antenna device comprising a radiating element arranged in a specific plane and a conductor plate arranged opposite the specific plane, the radiating element and the conductor plate being short-circuited, and both of a pair of conductors constituting a feeder line being connected to the radiating element.

Patent Document 4 (Japanese Patent Laid-Open Publication No. 2007-173928) discloses a thin microstrip antenna with improved horizontal beam characteristics.
The microstrip antenna described in Patent Document 4 comprises an antenna element, a ground plate having a width equal to or smaller than the antenna element, a power supply part electrically connected to the antenna element, and a support for fixing the antenna element and the ground plate, and the width direction of the antenna element is perpendicular to the resonance direction caused by excitation from the power supply part.

Patent Document 5 (Japanese Patent Laid-Open Publication No. 2006-135672) discloses a patch antenna, an array antenna, and a mounting board provided with the same, which can improve antenna characteristics.
The patch antenna described in Patent Document 5 comprises a dielectric substrate, a substantially rectangular radiating element made of a conductor formed on the dielectric substrate, and a feed line connected to a feed point for feeding power to the radiating element, the feed point having an impedance matching the feed line.

Patent Document 6 (JP 2017-5663 A) discloses a planar antenna that forms a unidirectional pattern and can be made small and flat.
The planar antenna described in Patent Document 6 includes a ground plate which is a conductive plate-like plate, a flat plate which is a conductive plate arranged facing the ground plate at a distance, and a plurality of metamaterial elements which have at least one short-circuiting portion which shorts the ground plate and the flat plate and which exhibit zero-order resonance, one of the plurality of metamaterial elements is a feed element which is connected to the flat plate and has a feed portion which feeds power, and the metamaterial elements other than the feed element are configured as parasitic elements which have parasitic portions which short-circuit the flat plate to the ground plate, and the feed element and parasitic elements are arranged along the radiation direction of the beam.

Patent Document 7 (Japanese Patent Laid-Open Publication No. 2004-129234) discloses an antenna device that can be made small and thin and that can realize a multi-resonance antenna with a simple structure.
The antenna device described in Patent Document 7 includes a dielectric substrate, a feed point provided on one side edge of the dielectric substrate, and a substantially U-shaped antenna element having one end connected to the feed point and the other end shorted to the other side edge of the dielectric substrate, having two parallel sides, and an electrical length equal to or greater than ¼ wavelength of the frequency band used.

Japanese Unexamined Patent Publication No. 6-177637 Japanese Patent Application Laid-Open No. 2003-46324 International Publication No. 2011/062272 Japanese Patent Application Laid-Open No. 2007-173928 Japanese Patent Application Laid-Open No. 2006-135672 Japanese Patent Application Laid-Open No. 2017-5663 Japanese Patent Application Laid-Open No. 2004-129234

As described in Patent Documents 1 to 7, various research and development efforts have been conducted on antennas. However, in recent years, there has been a demand for lightweight antennas that can be mounted on flying vehicles such as drones. Furthermore, even when reading RF tags on items displayed on shelves, there is a risk of malfunction due to contact with the items at the top or back of the shelf, and therefore it is considered preferable to install antennas on the ceiling of the shelf. However, heavy antennas have problems such as falling from the ceiling due to deterioration over time. Therefore, weight reduction has been in high demand in recent years.
Furthermore, since shelves are typically long horizontally and the items displayed on the shelves are also arranged horizontally, it is desirable for the antenna that reads the RF tags of the items to have a region with high communication sensitivity in the horizontal direction.

An object of the present invention is to provide a patch antenna that can be made lighter.
A second object of the present invention is to provide a patch antenna having a horizontally long area with high communication sensitivity.

(1)
A patch antenna according to one aspect includes a radiating element member, a ground plate member disposed opposite the radiating element member, an intermediate member that maintains a gap between the radiating element member and the ground plate member, a radiating element connection feeder that connects one electrode of a high-frequency cable, and a ground plate connection feeder that connects another electrode of the high-frequency cable, wherein the intermediate member is made of foam.

In this case, since the intermediate member is formed from a foam, the weight of the patch antenna can be reduced. In particular, it can be mounted on an aircraft. Furthermore, because the weight of the patch antenna can be reduced, it is less likely to deteriorate over time when attached to the ceiling of a shelf. As a result, the risk of it falling can be reduced. It can also be attached to a shelf after the fact. The foam is preferably any foam, such as a resin foam such as polystyrene foam, urethane foam, polyethylene foam, or polypropylene foam.

(2)
A patch antenna according to a second aspect of the present invention may be such that the radiating element member is composed of a plurality of radiating elements, the plurality of radiating elements being arranged in one direction at predetermined intervals, and a radiating element connection feed portion is arranged on each of the plurality of radiating elements and connected to one electrode of the high-frequency cable.

An example of an antenna with a horizontally high communication sensitivity region is a rod-shaped inverted-F antenna, but the length of the inverted-F antenna depends on the wavelength of the communication signal, and for example, in the case of a UHF band RFID, it is usually about 75 mm. Therefore, in order to have a longer horizontally high communication sensitivity region, it is necessary to have multiple antennas.
In contrast, in the patch antenna according to the second invention, a plurality of radiating elements are arranged in one direction at a predetermined interval, and each radiating element is fed in parallel, thereby providing a horizontally long area with high communication sensitivity on the opposite side of the ground plate member from the radiating elements and on the opposite side of the ground plate member between the radiating elements.
Increasing the spacing between the radiating elements reduces the electric field strength and communication sensitivity on the opposite side of the base plate member between the radiating elements, while decreasing the spacing between the radiating elements reduces the horizontal width of the region with high communication sensitivity for the same number of radiating elements.
Therefore, it is desirable to set the predetermined distance as large as possible within a range in which the electric field strength does not decrease on the side opposite the base plate member between the radiating elements.

(3)
A patch antenna according to a third aspect of the present invention is a patch antenna according to the first aspect or the second aspect of the present invention, wherein the radiating element member and the base plate member may be formed from at least one of silver paste, silver paper, and aluminum foil.

In this case, the weight of silver paste, silver paper, aluminum foil, etc. can be further reduced, thereby further reducing the weight of the patch antenna.

(4)
A patch antenna according to a fourth aspect of the present invention is the patch antenna according to any one of the first to third aspects of the present invention, wherein the radiating element member and the radiating element connection feed portion may be attached with an adhesive or double-sided tape.

In this case, capacitive coupling is achieved between the radiating element member and the radiating element connection power supply section. It also helps to reduce weight increases due to soldering or connecting members, etc.

(5)
A patch antenna according to a fifth aspect of the present invention is the patch antenna according to any one of the first to fourth aspects of the present invention, wherein the ground plate member and the ground plate connecting feed portion may be attached with an adhesive or double-sided tape.

In this case, capacitive coupling is established between the upper plate member and the ground plate member connection power supply section. This also helps to reduce weight increases due to soldering or connecting members, etc.

(6)
A patch antenna according to a sixth aspect of the present invention is the patch antenna according to any one of the first to fifth aspects of the present invention, wherein the capacitance between the radiating element member and the radiating element connection feed portion is preferably 10 pF (picofarads) or more.

In this case, the capacitance between the radiating element member and the radiating element connection power supply is 10 pF or more, enabling capacitive coupling. As a result, the frequency band can be widened. A range of 400 pF to 800 pF is particularly desirable.

(7)
A patch antenna according to a seventh aspect of the present invention is the patch antenna according to any one of the first to sixth aspects of the present invention, wherein the capacitance between the ground plane member and the ground plane connecting power supply portion is preferably 10 pF (picofarads) or more.

In this case, the capacitance between the ground plane member and the ground plane connection power supply is 10 pF or more, so capacitive coupling can be achieved. As a result, the frequency band can be widened. A range of 400 pF to 800 pF is particularly desirable.

(8)
The patch antenna of the eighth invention is the patch antenna of the seventh invention, wherein the radiating element member is provided with four rectangular MSA (left-handed circularly polarized) radiating elements, and it is desirable that two of the radiating elements are fed in parallel.

In this case, the frequency band can be widened and the antenna gain can be improved over a wide range in the direction in which the radiating element is installed. As a result, communication can be easily achieved even if RF tags are overlapping or arranged in random directions.

(9)
A patch antenna according to a ninth aspect of the present invention is the patch antenna according to any one of the first to eighth aspects of the present invention, wherein the radiating element member, the intermediate member and the base plate member are preferably covered with a decorative sheet.

In this case, the patch antenna can be integrated into the shelf by covering the radiating element member, intermediate member, and base plate member with decorative sheets.

1 is a schematic structural diagram showing an example of a shelf series antenna switching system and an RF tag reading system according to an embodiment of the present invention; FIG. 2 is a schematic explanatory diagram showing an example of an antenna switching controller. FIG. 2 is a schematic explanatory diagram showing an example of an antenna switch; FIG. 10 is a schematic explanatory diagram showing another example of an antenna switch; FIG. 10 is a schematic explanatory diagram showing an example of an antenna switch of a shelf-mounted serial antenna switching system. FIG. 1 is a schematic diagram showing an example of a store interior in which a shelf series antenna switching system is installed; FIG. 1 is a schematic diagram showing an example of a shelf on which patch antennas of a shelf series antenna switching system are arranged. 10A and 10B are schematic explanatory diagrams for explaining an example of patch antenna operation on a shelf. FIG. 2 is a plan view showing an example of a radiating element member of a patch antenna. FIG. 2 is a plan view showing an example of a base plate member of a patch antenna. FIG. 1 is a schematic perspective view showing an example of a patch antenna. FIG. 1 is a schematic structural explanatory diagram showing an example of a patch antenna. FIG. 2 is a schematic perspective view showing the arrangement of four aluminum foils, a base plate member, an intermediate member, and a power supply point. FIG. 14(A) is a graph showing the electric field distribution above the aluminum foil when there is one aluminum foil, and FIG. 14(B) is a graph showing the electric field distribution above the aluminum foil when four aluminum foils are arranged in one direction at a predetermined interval. FIG. 10 is an explanatory diagram showing an example of a control signal from an antenna switching controller of the shelf series antenna switching system. 10A and 10B are explanatory diagrams showing an example of a received waveform and sampling of an antenna switch of a shelf-mounted serial antenna switching system. FIG. 10 is an explanatory diagram showing an example of a signal received by an antenna switch of the shelf-mounted serial antenna switching system.

Embodiments of the present invention will be described below with reference to the drawings. In the following description, identical parts will be designated by the same reference numerals. Furthermore, when the reference numerals are the same, the names and functions of the parts will also be the same. Therefore, detailed descriptions of these parts will not be repeated.

(Series Antenna Switching System 100 for Shelves)
Fig. 1 is a schematic structural diagram showing an example of a shelf series antenna switching system 100 and an RF tag reading system according to this embodiment, and Fig. 2 is a schematic explanatory diagram showing an example of an antenna switching controller 210. Fig. 3 is a schematic explanatory diagram showing an example of an antenna switch 221, and Fig. 4 is a schematic explanatory diagram showing an example of antenna switchers 221 to 22n of the shelf series antenna switching system 100.

First, as shown in FIG. 1, the shelf serial antenna switching system 100 includes a reader 200, an antenna switching controller 210, antenna switches 221, 222, 223, 224, 225, and 22n (n is a positive integer), a high-frequency cable 300, and patch antennas 501, 502, 503, 504, 505, and 50n (n is a positive integer).
The RF tag reading system comprises a shelf serial antenna switching system 100 and a PC (personal computer) 201 .
Furthermore, patch antennas 501, 502, 503, 504, 505, and 50n are attached to shelves 901, 902, 903, 904, 905, and 90n (n is a positive integer), respectively.

1, the reader 200 is connected to an antenna switching controller 210 by a high-frequency cable 300. The antenna switching controller 210 is connected in series to antenna switches 221, 222, 223, 224, 225, and 22n by the high-frequency cable 300.
Furthermore, patch antennas 501, 502, 503, 504, 505, and 50n arranged on shelves 901, 902, 903, 904, 905, and 90n are connected to antenna switches 221, 222, 223, 224, 225, and 22n, respectively.

(Antenna switching controller 210)
As shown in FIG. 2, the antenna switching controller 210 has a bit encoder sending circuit 211, a DC voltage input terminal 212 for the antenna switching circuit, a LAN input terminal 213, an input terminal 214 from the reader 200, an output terminal 215, a capacitor C, an RFID signal high-pass capacitor C1, and a DC voltage bypass coil L.
The bit signal sent from the LAN input terminal 213 and output from the bit encoder sending circuit 211 of the antenna switching controller 210 is AC-coupled to the DC voltage bypass coil L via a capacitor C from the DC voltage input terminal 212 for the antenna switching circuit, and to the RFID signal high-pass capacitor C1 from the input terminal 214 from the reader 200, and is then superimposed on the DC voltage as a superimposed signal, which is then sent from the output terminal 215 via the high-frequency cable 300 to the antenna switches 221, ..., 22n.

(Antenna switchers 221, ..., 22n)
Next, the antenna switches 221 to 22n will be described, taking the antenna switch 221 as a representative example. The antenna switches 221 to 22n have the same internal structure.
As shown in FIG. 3, the antenna switch 221 has an input terminal 231, a constant voltage circuit 232, a low-frequency amplifier 233, a bit decoder 234, a timer 235, a switch 236, a connection terminal 237 to the next stage, an antenna connection terminal 238, a control signal capacitor C2, a high-pass capacitor C3, and a DC voltage bypass coil L1.
(An LC parallel circuit is configured.)

An input terminal 231 of the antenna switch 221 is connected to a high frequency cable 300 which is connected to the output terminal 215 of the antenna switch controller 210 shown in FIG.
The superimposed signal from input terminal 231 is split into two signals, one to constant voltage circuit 232 of antenna switch 221, one to low frequency amplifier 233 via control signal capacitor C2, and one to switch 236 via high pass capacitor C3.

The constant voltage circuit 232 is a circuit that generates the power required for the antenna switch 221. The low-frequency amplifier 233 is an amplifier circuit that extracts the bit signal. The bit signal is synchronized with the sampling clock signal by the bit decoder 234, and only when it matches the preset ID data unique to the antenna switch is the switch 236 turned on via the timer 235 for the set number of seconds, and the RFID signal is radiated from the patch antenna 501 via the No contact of the switch 236 through the high-pass capacitor C3.

Furthermore, since the normal RFID signal is connected in series to the n number of antenna switches 221 to 22n at the Nc contact of the constant switch 236, the attenuation rate can be minimized compared to the distribution method.
This operation is then repeated for sampling for n antenna switches 221 to 22n. In this embodiment, it is also possible to specify the ID address of antenna switch 221 and operate only one or more of any of antenna switches 221 to 22n. Specific control techniques for antenna switching controller 210 and antenna switches 221 to 22n will be described later.
Finally, the superimposed signal from the input terminal 231 is connected to a connection terminal 237 for the next stage via a DC voltage bypass coil L1.

Fig. 4 is a schematic explanatory diagram showing another example of the antenna switch 221. Fig. 4 differs from Fig. 3 only in the area surrounding the switch 236.
In the antenna switch 221 of Figure 3, when the antenna switch 221 is not selected, the input signal is input to the antenna switch 221 of the next stage via the DC voltage bypass coil L1, the RFID signal high-pass capacitor C1 and the switch 236, but in the antenna switch 221 of Figure 4 , the input signal is input directly to the antenna switch 221 of the next stage.
On the other hand, in the antenna switch 221 of Figure 3, when the antenna switch 221 is selected, the input signal is not input to the antenna switch 221 of the next stage, but in the antenna switch 221 of Figure 4 , the input signal is always input to the antenna switch 221 of the next stage.

As shown in FIG. 5 , antenna switch 221, antenna switch 222, antenna switch 223, antenna switch 224, antenna switch 225, . . . , antenna switch 22n are connected in series by high frequency cable 300.
Then, after patch antenna 501 connected to antenna switch 221 operates in response to the RFID signal, patch antenna 502 connected to antenna switch 222 operates in response to the RFID signal. In this manner, in the order of serial arrangement, patch antenna 503 connected to antenna switch 223 operates in response to the RFID signal, and then patch antenna 504 connected to antenna switch 224 operates in response to the RFID signal.
The superimposed signal is then grounded at the end of the antenna switch 22n via a resistor R and a capacitor C4.

(Example of a store)
FIG. 6 is a schematic diagram showing an example of the interior of a store in which the shelf series antenna switching system 100 is installed, and FIG. 7 is a schematic diagram showing an example of shelves 901 to 90n in which patch antennas 501 to 50n of the shelf series antenna switching system 100 are installed.
In this case, a single shelf 901 is provided with a plurality of shelf levels, each of which is provided with a patch antenna 501 to 50n, and the patch antennas 501 to 50n on each shelf level are connected in series. A plurality of such shelves 901 are lined up on one floor, and the antenna wires of each shelf 901 are further connected in series.
In this case, the RF tag attached to one product can be read not only by the antenna of the shelf 901 on which the product is placed, but also by the antennas of other shelves 901 placed on the floor, making it possible to read the RF tag more reliably.

As shown in Fig. 6 , a number of shelves 901 to 90n are arranged in the store. In Fig. 6 , shelves 901 to 953 (n = 53) are arranged. A number of items with RFID tags attached are displayed on shelves 901 to 953. For example, RFID tags are attached to any of the following items and are displayed: food, clothing, accessories, cosmetics, accessories, tea, processed products, medicines, toys, musical instruments, textiles, bedding, shoes, bags, pharmaceuticals, alcoholic beverages, fresh foods, confectionery, bread, tools, and parts.
Naturally, in the store, customers pick up items from shelves 901 to 953 to check them, and if they do not wish to purchase them, they return the items to shelves 901 to 953, so the orientation of the RFID tags becomes random. Conventional handheld readers have had the problem of being unable to reliably read RFID tags oriented in random directions. In particular, when RFID tags overlap, the frequency characteristics change, making it impossible to read them from one side. This problem occurs particularly with clothing, small items, and the like, because RFID tags overlap or are oriented in random directions.

(Shelves 901, ..., 90n)
Next, as shown in FIG. 7 , patch antennas 501 to 50n are provided on the ceilings of shelves 901 to 90n, respectively.
In this embodiment, patch antennas 501 to 50n are provided on the ceiling, but this is not limitative and they may be provided on a location other than the ceiling. For example, they may be provided on the base of shelves 901 to 90n, or on a back wall if there is one.
The reason for placing them on the ceiling is that even if items are placed on the platform, since they are on the ceiling, they are less likely to be hit by staff or customers' hands and are therefore less likely to break down.

7, by providing antenna switches 221, 222, and 223 on each shelf 901 to 90n and connecting patch antennas 501 to 50n in series, it is possible to install one high-frequency cable 300. Also, while Fig. 6 shows an example in which there are two patch antennas 501 and two patch antennas 502, if the horizontal length of the shelves 901 to 90n is more than twice the size of the patch antenna 501, two patch antennas 501 may be attached to each level of the shelves 901 to 90n and a branching switch may be provided for each of them.

Next, FIG. 8 is a schematic explanatory diagram for explaining an example of the operation of patch antennas 501 to 50n on shelves 901 and 902. In FIG.
8 , patch antennas 501 to 50n are arranged on the ceiling of shelves 901 and 902. Therefore, patch antenna 501 arranged on the upper level of shelf 901 not only reads the RFID tags of items on the corresponding shelf level, but also reads the RFID tags of items below or to the left or right of the shelf level.
As a result, a customer may take an item from shelf 901 to shelf 90n to check it, and if they do not wish to purchase it, they may return the item to shelf 901 to shelf 90n again. Even if the RFID tags are oriented in a random direction, as shown in Figure 8, patch antenna 50n (indicated by the arrow in the figure) other than patch antenna 501 can read in all directions, so the RFID tags of items oriented in a random direction can be read.

(Patch antennas 501, ..., 50n)
FIG. 9 is a plan view showing an example of the radiating element member 560 of the patch antennas 501 to 50n, and FIG. 10 is a plan view showing an example of the base plate member 580 of the patch antennas 501 to 50n.
FIG. 11 is a schematic perspective view showing an example of patch antennas 501 to 50n, and FIG. 12 is a schematic structural explanatory diagram showing an example of patch antennas 501 to 50n.

As shown in Figures 9 , 10 , 11 and 12 , patch antennas 501 to 50n consist of a radiating element member 560, an intermediate member 570, a ground plane member 580, a radiating element connection feed plate 565, and a ground plane connection feed plate 585.

The radiation element member 560 is formed by bonding aluminum foils 561, 562, and 563 to a thin polyethylene terephthalate (hereinafter referred to as PET) 564.
The radiating element member 560 is made up of four rectangular aluminum foils 561, which are rectangular MSA (left-handed polarized waves), connected in parallel in pairs for parallel power feeding. Aluminum foils 562 connect the two together, and aluminum foils 563 connect the aluminum foils 562 in parallel. A connection portion 566 with a radiating element connection power feed plate 565 is provided in the center of the aluminum foil 563.
As a result, the other frequencies among the multiple mode frequencies can be made lower than one frequency, and a resonance characteristic can be obtained. Naturally, it is preferable that the phase difference between one frequency characteristic and the other frequency characteristics be a value of around π/2.

The intermediate member 570 is made of expanded polystyrene, a type of synthetic resin, mainly made of polystyrene containing air bubbles.
Next, the base plate member 580 is formed by bonding a rectangular aluminum foil 581 to a thin polyethylene terephthalate (hereinafter referred to as PET) 584 .
Furthermore, a connection portion 586 to a ground plane connection power supply plate 585 is provided at the central end of the rectangular aluminum foil 581 .

The radiating element member 560, the intermediate member 570 and the base plate member 580 are bonded together with an adhesive. That is, the patch antennas 501 to 50n have a laminated structure.
The radiating element connection feeder plate 565 and the ground plane connection feeder plate 585 are made of aluminum foil and are adhered to the connection portion 566 of the radiating element member 560 and the connection portion 586 of the ground plane member 580 by adhesive, respectively.
The radiating element connection feeder plate 565 is connected to the inner conductor of the coaxial line of the high frequency cable 300, and the ground plane connection feeder plate 585 is connected to the outer conductor of the coaxial line of the high frequency cable 300. This is a so-called direct feed system.
Although not described in this embodiment, an electromagnetic coupling power supply method may also be used.

As a result, a capacitance (capacitor) is formed between the radiating element connection feeder plate 565 and the radiating element member 560, and a capacitance (capacitor) is formed between the ground plane connection feeder plate 585 and the ground plane member 580. As a result, it is possible to widen the frequency band of the patch antennas 501 to 50n.
In this embodiment, an adhesive is used, but the present invention is not limited to this, and any other connection method may be used, such as direct fixing or double-sided tape.
Furthermore, in this embodiment, aluminum foil is used, but this is not limited to this, and any material and processing method may be used, such as silver paste, silver paper, or metal plate.

As described above, the patch antennas 501, . . . 50n according to this embodiment have an ultra-lightweight total weight, making them easy to mount on aircraft and the like. Furthermore, by attaching them to the ceiling of shelves 901, . . . 90n, they can be prevented from falling due to deterioration over time. Specifically, the weight of the patch antennas 501, . . . 50n according to this embodiment was approximately 100 g.

(Electric field distribution of the radiating element member 560)
The near field distribution when the radiation element member 560 is configured by arranging four aluminum foils 561 (corresponding to the radiation element) in one direction at a predetermined interval was verified by antenna simulation.
FIG. 13 is a schematic perspective view showing the arrangement of four aluminum foils 561, a base plate member 580, an intermediate member 570, and a power supply point 569.
The aluminum foil 561 is square, and a feed point 569 is located slightly off-center. In this simulation, power is fed directly to each feed point 569. The ground plane member 580 is a metal with a thickness of 2 mm, and the intermediate member 570 is a dielectric with a thickness of 2.2.

14 (A) is a graph showing the electric field distribution above the aluminum foil 561 (opposite the base plate member 580) when there is one aluminum foil 561. The X axis is the direction of the X axis in FIG. 16, and the Y axis is the electric field strength at a point in the direction of the Z axis of the aluminum foil 561, at a distance of about half the length of one side of the aluminum foil 561.
The electric field strength is high above the radiating element (corresponding to the aluminum foil 561) and decreases as the distance from the radiating element increases. Therefore, in the case of one radiating element, the spread of the electric field strength in the X-axis direction is approximately equal to the length of one side of the radiating element.

14(B) is a graph showing the near field distribution (the field distribution at a point on the opposite side of the ground plate member 580, at a distance of about half the length of one side of the aluminum foil 561) when four radiating elements are arranged in one direction at a predetermined interval to form the radiating element member 560. In this case, the arrangement of the aluminum foil 561 and the like is as shown in FIG. 16, and the distance between the aluminum foils 561 is approximately equal to the length of one side of the aluminum foil 561.
As can be seen from Figure 14 (B), the electric field strength at the top of the radiating element member 560 is approximately constant at the top of the aluminum foil 561 and at the top between the aluminum foils 561, and using four aluminum foils 561, an approximately constant electric field can be formed in the X direction over a length more than seven times the length of one side of the aluminum foil 561.
Therefore, a patch antenna having a radiating element member 560 formed by arranging four aluminum foils 561 (corresponding to radiating elements) in one direction at a predetermined interval can form a long electric field distribution in one direction and have a long horizontal region with high communication sensitivity.
In addition, according to the results of the antenna simulation, when the distance between the aluminum foils 561 is increased to 1.8 times the length of one side of the aluminum foils 561, the electric field strength at the top between the aluminum foils 561 decreases to approximately 0.6 times the electric field strength at the top of the aluminum foils 561.

Figure 15 is an explanatory diagram showing an example of a control signal from the antenna switching controller 210 of the shelf-use serial antenna switching system 100, Figure 16 is an explanatory diagram showing an example of the received waveforms and sampling of the antenna switches 221 to 22n of the shelf-use serial antenna switching system 100, and Figure 17 is an explanatory diagram showing an example of the received signal of the antenna switches 221 to 22n of the shelf-use serial antenna switching system 100.

The control signal sent by the antenna switching controller 210 and the received waveforms of the antenna switches 221 to 22n will be described below with reference to FIGS. 15 , 16 and 17 .
First, as shown in FIG. 15 , in this embodiment, an example will be described in which the antenna switching controller 210 sends a control signal to the antenna switch 225 (ID=5).

15 , the basic format of the control signal in this embodiment is configured so that, for example, one packet has a 400 msec data section and a 400 msec gap section alternating, for a total of 800 msec. The transmission time T1 of one bit (BIT) is fixed at 50 msec (MSB first).
In addition, the parent antenna switching controller 210 continues to transmit the control signal in an infinite loop, and if the ID data to be transmitted (in this case, ID = 5) changes, it transmits new ID data in synchronization with the transmission timing of the next data section.

Next, the data portion of the control signal will be described. In this embodiment, the data portion of Fig. 15 encodes the 3 bits of ID data into 8 bits in the following procedure. Bit 7 (MSB) is always set to 1 (header).

Next, ID data is indicated by three bits: bit 6, bit 5, and bit 4. In the example of Fig. 15 , ID=5, so 5=101.
Next, bit 3 is always set to (0) by inverting bit 7, bit 2 is set to the inverting bit 6, bit 1 is set to the inverting bit 5, and bit 0 (LSB) is set to the inverting bit 4. The reason for these inversions will be described in detail later. In the example of Fig. 15 , 0 is transmitted consecutively n times for the GAP portion.

Next, the operation of the antenna switchers 221 to 22n, which are slave units, will be described. The antenna switchers 221 to 22n generate a sampling clock. As shown in FIG. 16, when the period of one bit is t, the antenna switchers 221 to 22n generate a sampling clock that is delayed by approximately t/2 from the timing at which they receive a 1 in the header . A normal clock data recovery circuit can be used as the sampling clock generation circuit.

The antenna switches 221 to 22n synchronize with the sampling clock and capture the received waveform into an 8-bit receive buffer. The condition for terminating the decoding reception is to stop the receiving circuit and terminate the process when the receive buffer becomes 0x00.
As a decoding condition, decoding is started when the MSB of the receive buffer becomes 1.
If the condition that the upper 4 bits and the lower 4 bits are inverted is met, the antenna switchers 221, ..., 22n determine that reception has been successful and acquire the data. On the other hand, if the upper 4 bits and the lower 4 bits are not equal, the operation stops and ends.

The reason for the inversion will now be described in detail. There are two reasons why the upper 4 bits and the lower 4 bits are inverted relative to each other.
The first reason is that, as described above, whether reception was successful or unsuccessful is determined by checking whether the upper 4 bits and the lower 4 bits are inverted with each other.
The second reason is to keep the average value of the bit signal constant. The bit string sent from the bit encoder sending circuit changes depending on the value of the sent ID, but of the total 16 bits including the data section and gap section, the number of 0 bits is 12 and the number of 1 bits is 4, which is constant regardless of the value of the sent ID. And because the number of 0 and 1 bits is constant, for example, the DC voltage of 0 and 1 bits after passing through the control signal capacitor C2 can be kept constant, and the signal can be more reliably restored to 0 or 1 signals using a comparator or the like.

Furthermore, if the acquired data is equal to the device's own ID, the antenna switch 221, ..., 22n switches the switch 236 to the No contact and sets the timer 235, which will expire after a certain period of time, to an initial value (n seconds (n is a positive integer)). On the other hand, if the acquired data is different from the device's own ID, the switch 236 switches to the Nc contact and resets the timer 235. Furthermore, if the data itself cannot be acquired, the switch is performed according to the passage of a certain period of time on the timer 235.

Finally, as shown in Fig. 8 , RFID tags attached to many items may be read multiple times, so that items that are read multiple times from the data read by the reader 200 are counted as one item in the PC 201 and processed. As a result, all items can be read.
Furthermore, by providing multiple readers 200 and installing patch antennas 501 to 50n on each shelf 901 to 90n on readers 200 to 20n (n is any integer), it is possible to expect the effect of shortening polling time or shortening waiting time by effectively using LBT (listen before talk). LBT (listen before talk) slightly changes the channel (frequency) of each patch antenna 501 to 50n on each shelf 901 to 90n, thereby eliminating radio wave interference during switching each time the antenna switching controller 210 switches, so that RF tags can be received by each patch antenna 501 to 50n on another shelf or on the same shelf, thereby achieving the effect of shortening time.

As described above, in this invention, patch antennas 501, ..., 50n are provided on each level of each shelf 901, ..., 90n, and the patch antennas 501, ..., 50n are arranged in series, with antenna switches 221, ..., 22n used to switch between the patch antennas 501, ..., 50n that communicate. In this case, since the only wiring work required is serial wiring, the installation work can be reduced in terms of man-hours and costs can be reduced.

In the present invention, shelves 901, ..., 90n correspond to "each shelf," patch antennas 501, ..., 50n correspond to "antennas, patch antennas," antenna switches 221, ..., 22n correspond to "antenna switches," antenna switching controller 210 corresponds to "antenna switching controller," reader 200 corresponds to "reader," high-frequency cable 300 corresponds to "communication cable, high-frequency cable," shelf-use serial antenna switching system 100 corresponds to "shelf-use serial antenna switching system," constant voltage circuit 232 corresponds to "constant voltage circuit," low-frequency amplifier 233 corresponds to "low-frequency amplifier," and bit decoder 234 corresponds to "bit decoder." , timer 235 corresponds to the "timer", switch 236 corresponds to the "switch unit", the superimposed signal corresponds to the "signal obtained by superimposing a DC voltage, a bit signal, and an RFID signal from the reader", radiating element member 560 corresponds to the "radiating element member", base plate member 580 corresponds to the "base plate member", intermediate member 570 corresponds to the "intermediate member", radiating element connection feed plate 565 corresponds to the "radiating element connection feed unit", base plate connection feed plate 585 corresponds to the "base plate connection feed unit", shelf series antenna switching system 100 and PC 201 correspond to the "RF tag reading system", and PC 201 corresponds to the "recognition unit".

While the preferred embodiment of the present invention is as described above, the present invention is not limited thereto. It will be understood that various other embodiments can be made without departing from the spirit and scope of the present invention. Furthermore, while the functions and effects of the configuration of the present invention are described in this embodiment, these functions and effects are merely examples and do not limit the present invention.

100: Shelf serial antenna switching system 200: Reader 201: PC
210: Antenna switching controller 211: Bit encoder sending circuit 212: DC voltage input terminal for antenna switching circuit 213: LAN input terminal 214: Input terminal 215: Output terminal 221, ..., 22n: Antenna switch 231: Input terminal 232: Constant voltage circuit 233: Low frequency amplifier 234: Bit decoder 235: Timer 236: Switch 237: Connection terminal 238: Antenna connection terminal 300: High frequency cable 501, ..., 50n: Patch antenna 560: Radiating element member 565: Radiating element connection power supply plate 566: Connection portion 570: Intermediate member 580: Ground plate member 585: Ground plate connection power supply plate 586: Connection portion 901, ..., 90n: Shelf

Claims (9)

A patch antenna is arranged on the ceiling of a horizontally long shelf and is used to read RF tags of items displayed on the shelf,
a radiating element member;
a base plate member provided opposite the radiation element member;
an intermediate member that maintains a gap between the radiation element member and the base plate member;
a radiating element connection feeder that connects one electrode of a high frequency cable to the radiating element member;
a ground plane connection power supply portion that connects another electrode of the high-frequency cable to the ground plane member,
the intermediate member is made of a foam,
the radiating element member is composed of a plurality of substantially rectangular radiating elements arranged at equal intervals in the horizontal direction at predetermined intervals, and wiring connected with the same line length from the radiating element connection feeder to each of the plurality of radiating elements,
A patch antenna in which the predetermined interval is set large enough to ensure that the electric field intensity at a point between adjacent radiating elements that is a distance away from the intermediate member in the opposite direction of the base plate member that is half the length of one side of the lateral direction of the radiating element does not decrease below a predetermined value relative to the maximum electric field intensity at a point on the radiating element that is the distance away from the intermediate member , and the predetermined value is 0.6 times or more and 1.0 times or less . The patch antenna according to claim 1 , wherein the predetermined value is 0.6 times. A patch antenna as described in claim 1 or 2, wherein the radiating element member and the base plate member are formed from at least one of silver paste, silver paper, and aluminum foil. A patch antenna as described in any one of claims 1 to 3, wherein the radiating element member and the radiating element connection power supply portion are attached with adhesive or double-sided tape. A patch antenna as described in any one of claims 1 to 4, wherein the ground plane member and the ground plane connection power supply portion are attached with adhesive or double-sided tape. A patch antenna as described in any one of claims 1 to 5, wherein the capacitance between the radiating element member and the radiating element connection power supply portion is 10 pF (picofarads) or more. A patch antenna as described in any one of claims 1 to 6, wherein the capacitance between the ground plane member and the ground plane connection power supply portion is 10 pF (picofarads) or more. A patch antenna as described in any one of claims 1 to 7, wherein the radiating element is a square microstrip antenna (left-handed polarized) with notches in the upper left and lower right of a substantially rectangular antenna, and the radiating element member has four radiating elements, two of which are fed in parallel. A patch antenna as described in any one of claims 1 to 8, wherein the radiating element member, the intermediate member, and the base plate member are covered with a decorative sheet.