Antenna equipment

Abstract

This system provides a configuration that can suppress deterioration of reading accuracy even when reading wireless tags attached to metal objects. [Solution] Multiple openings 31 are formed in a metal radome 30 that is positioned opposite the radio wave radiating surface 21a of the antenna 21, and these openings function as slot antennas that re-radiate radio waves emitted from the antenna 21.

Description

Technical Field

[0001] The present invention relates to an antenna device having a radome.

Background Art

[0002] Conventionally, when storing an item in a storage shelf or taking an item out of a storage shelf, an operator sequentially reads information codes such as barcodes displayed on the item, the storage shelf, a work instruction sheet, etc. using a portable reader device, and a system for managing the inventory status of items in the storage shelf to be managed is operated. In such a system premised on the operation of an operator reading information codes for each item, there are problems such as a decrease in inventory management accuracy due to human error, etc., and high management costs due to complicated reading operations.

[0003]

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] ​ By the way, when metal objects with wireless tags to be read are placed in a storage rack, if the metal object is placed near an antenna installed on the rack, electromagnetic coupling may occur between the placed metal object and the antenna. When this interference occurs between the metal object and the antenna, there is a problem in that the reading accuracy of the wireless tags attached to the metal object deteriorates.

[0006] The present invention was made to solve the above-mentioned problems, and its objective is to provide a configuration that can suppress deterioration of reading accuracy even when reading wireless tags attached to metal articles. [Means for solving the problem]

[0007] To achieve the above objective, the present invention Antenna (21) and, A metal radome (30, 30a, 30b) is positioned opposite the radiating surface (21a) of the aforementioned antenna, An antenna device (20, 20a, 20b) comprising, The radome is characterized by having openings (31, 32, 33) that function as slot antennas for re-radiating radio waves emitted from the antenna. The symbols within the parentheses above indicate the correspondence with the specific means described in the embodiments described later. [Effects of the Invention]

[0008] In this invention, a metal radome positioned opposite the radiating surface of the antenna has an opening formed in it that functions as a slot antenna for re-radiating radio waves emitted from the antenna.

[0009] As a result, even when a metal object with a wireless tag attached is placed near the antenna, the radome interposed between the metal object and the antenna reduces the electromagnetic coupling between the metal object and the antenna. Furthermore, since radio waves are re-radiated through the radome's opening, the degradation of radiation characteristics caused by the presence of a metal radome can be suppressed. Therefore, an antenna device can be realized that can suppress the deterioration of reading accuracy even when reading wireless tags attached to metal objects.

[0010] The aperture may be formed in a position that does not expose the antenna elements of the antenna when viewed from the direction opposite the radiating surface. This allows for more reliable suppression of electromagnetic coupling between the metal object and the antenna, although this may slightly degrade the radiation characteristics.

[0011] The aperture may be formed such that its circumference is equal to n times the wavelength of the radio wave (where n is an odd number). This makes the slot antenna more resonant, thereby improving the radiation characteristics for radio waves re-radiated through the radome aperture.

[0012] The aperture may be formed such that its short axis aligns with the principal polarization direction of the antenna's radiated electric field. This allows for better opposition of the electric field in the slot compared to when the aperture is formed with its long axis aligned with the principal polarization direction of the antenna's radiated electric field, thereby improving the radiation characteristics for radio waves re-radiated through the radome aperture.

[0013] The aperture may be formed such that its circumference is equal to n times the wavelength of the radio wave (where n is an odd number), and its minor axis aligns with the principal polarization direction of the antenna's radiated electric field. This not only makes the slot antenna more resonant, but also allows for better opposition of the slot's electric field, thereby further improving the radiation characteristics for radio waves re-radiated through the radome aperture.

[0014] The opening may be formed in a meandering shape at a position where the antenna element of the antenna is not exposed when viewed from the direction opposite to the radiation surface. As a result, since the area occupied by the opening can be reduced while ensuring the necessary perimeter, it becomes easier to form the meandering opening at a position where the antenna element of the antenna is not exposed when viewed from the direction opposite to the radiation surface, so that electromagnetic coupling between the metal article and the antenna can be more reliably suppressed.

Brief Description of the Drawings

[0015] [Figure 1] It is an explanatory diagram for explaining an article management system in which the antenna device according to the first embodiment is adopted. [Figure 2] It is a perspective view of the management shelf in FIG. 1 as viewed from the entrance / exit side. [Figure 3] FIG. 3(A) is a schematic plan view of the antenna device in the first embodiment, and FIG. 3(B) is a schematic plan view in a state where the radome is removed from FIG. 3(A). [Figure 4] It is an explanatory diagram for explaining the positional relationship between the antenna and the radome in the facing direction. [Figure 5] It is a block diagram showing the schematic configuration of the wireless tag reader in FIG. 1. [Figure 6] FIG. 6(A) is an explanatory diagram for explaining the storage state in which an article is stored in the management shelf, and FIG. 6(B) is an explanatory diagram for explaining the storage state in which an article is further stored from the state of FIG. 6(A). [Figure 7] It is a graph for explaining the relationship between the presence or absence of the radome and the frequency deviation in the first embodiment. [Figure 8] It is a schematic plan view of the antenna device in the second embodiment. [Figure 9] It is a graph for explaining the relationship between the presence or absence of the radome and the frequency deviation in the second embodiment. [Figure 10] It is a schematic plan view of the antenna device in the third embodiment. [Figure 11] It is a graph for explaining the relationship between the presence or absence of the radome and the frequency deviation in the third embodiment.

Best Mode for Carrying Out the Invention

[0016] [First Embodiment] Hereinafter, a first embodiment in which an antenna device according to the present invention is embodied will be described with reference to the drawings. The antenna device 20 according to the present embodiment is used when reading and writing information recorded on a wireless tag T such as an RF tag attached to an article G, and is installed and used on a management shelf 10 in an article management system 1 that manages articles G that are received and shipped to and from the management shelf 10. As shown in FIGS. 1 and 2, the article management system 1 is configured to include an antenna device 20 installed on the management shelf 10 and a management device 40 that manages the receipt and shipment of the article G through the entrance / exit 11 of the management shelf 10.

[0017] The article G to be managed is, for example, a packing box in which predetermined parts are stored and packed, and a wireless tag T such as an RF tag in which a unique tag ID is recorded so as to be readable by non-contact communication is attached to the side surface or the like. In the present embodiment, the tag ID functions as information that can identify the article G, and is registered in a server or the like so as to be associated with the article G itself to which the wireless tag T recording the tag ID is attached and the type and number of the parts accommodated in the article G. Therefore, by inquiring a server or the like about the tag ID or the like read from the wireless tag T, the article G to which the wireless tag T recording the tag ID is attached can be identified. Note that the article G is not limited to being configured as a packing box or the like as described above, and may be configured as the product itself, and the wireless tag T may be attached to the product itself.

[0018] As shown in Figures 1 and 2, the storage shelf 10 in this embodiment has a roughly rectangular box shape, with a rectangular opening at the front entrance 11, and the space enclosed by the upper wall 12, bottom wall 13, side walls 14, 15, and back wall 16 is configured to be the storage space for the stored items G. In this embodiment, each wall of the storage shelf 10 is made of resin material, but it is not limited to this, and at least a part of it may be made of glass material, wooden material, etc. Note that in Figure 1 and Figure 6 described later, the side wall 15 is omitted from the illustration for convenience.

[0019] As shown in Figures 3 and 4, the antenna device 20 in this embodiment is configured to include an antenna 21 and a metal radome 30 positioned opposite the radio wave radiating surface 21a of the antenna 21.

[0020] In this embodiment, the antenna 21 is a so-called planar antenna and is configured to include a microstrip line 23 formed by arranging a plurality of antenna elements 24 of the same dimensions on a dielectric substrate 22, as shown in Figure 3(B). The antenna elements 24 have a strip conductor 25 extending along the arrangement direction (y direction in Figure 3) and a stub conductor 26 branching off from the strip conductor 25 and extending in the x direction, and are arranged such that a predetermined gap 27 which is a non-conductive portion is interposed between the strip conductors 25.

[0021] With this arrangement, the antenna 21 is configured such that the direction of the arrangement (y-direction in Figure 3) is the main polarization direction of the radiated electric field, and it comprises a series branch circuit that equivalently includes a capacitive component due to the gap 27 and a parallel branch circuit that equivalently includes an inductive component due to the stub conductor 26. In particular, in this embodiment, the antenna 21 operates in the leakage wave region by setting parameters such as the dimensions of the antenna elements 24 and the gap 27 so that the absolute value of the effective refractive index of the transmission line of the antenna 21 is less than 1. This makes it possible to bring the radiation direction of the radio waves radiated from the antenna 21 closer to the direction perpendicular to the radio wave radiation surface 21a (z-direction in Figure 4).

[0022] The radome 30 functions as a metallic shield and is formed in a substantially thin plate shape from, for example, aluminum, copper foil, or silver nanoparticles. The radome 30 has multiple rectangular openings 31 that function as slot antennas to re-radiate radio waves emitted from the antenna 21.

[0023] Each aperture 31 is formed such that its circumference Ls (see Figure 3(A)) is equal to one times the wavelength λ of the radio wave, specifically, for example, between 0.7λ and 1.3λ, in order to facilitate resonance as a slot antenna. In this embodiment, assuming an operating frequency of approximately 920 MHz and a wavelength λ = approximately 32 cm, the aperture is formed such that the circumference Ls is 250 mm and 0.78 λ.

[0024] Furthermore, each aperture 31 is formed such that its short axis (a line segment running along the short sides 31a and 31b, passing through the center of the aperture and connecting the center of one long side to the center of the other long side) aligns with the main polarization direction of the radiated electric field of the antenna 21 (y-direction in Figure 3) in order to counteract the electric field generated when it functions as a slot antenna. In this embodiment, each aperture 31 is formed such that its short axis aligns with the main polarization direction of the radiated electric field of the antenna 21, as shown in Figure 3(A). However, it is not limited to this, and the short axis may be formed to be slightly tilted with respect to the main polarization direction of the radiated electric field of the antenna 21. In addition, each aperture 31 is formed in a position that exposes a portion of the microstrip line 23 in line with the position of the gap 27 when viewed from the opposite direction of the radio wave radiating surface 21a (z-direction in Figure 4).

[0025] As shown in Figure 4, the radome 30 is positioned such that the distance zr from the radio wave radiating surface 21a of the antenna 21 is a sufficiently small value with respect to the wavelength λ of the radio wave, for example, about 10 mm.

[0026] The antenna device 20 is connected to the wireless tag reader 50 of the management device 40 via a coaxial cable or the like, and is installed with its radome 30 facing upwards on the inner surface of the bottom wall 13 of the management shelf 10 that forms the lower part of the entrance / exit 11. With this installation, the antenna device 20 operates using predetermined power supplied from the wireless tag reader 50 to make the entrance / exit 11 of the management shelf 10 within its reading range. Note that the antenna device 20 is not limited to being installed on the inner surface of the bottom wall 13; it may also be installed on the inner surface of the top wall 12 to keep it away from the goods G being stored, or on the inner surfaces of the side walls 14, 15 or the back wall 16.

[0027] The management device 40 is configured to include a wireless tag reader 50 and a management terminal 41. The wireless tag reader 50 is a so-called RFID reader and is configured to output the tag ID etc. read from the wireless tag T via the antenna device 20 to the management terminal 41. As shown in Figure 5, the wireless tag reader 50 includes a control unit 51, a storage unit 52, a communication processing unit 53, an antenna 54, and an external interface 55, etc. The control unit 51 is mainly composed of a microcontroller and has a CPU, system bus, input / output interface, etc., and together with the storage unit 52 which consists of semiconductor memory etc., it constitutes an information processing device.

[0028] As shown in Figure 5, the communication processing unit 53 includes a transmitting circuit 53a, a receiving circuit 53b, and the like. The transmitting circuit 53a is composed of, for example, a carrier oscillator, an encoding unit, a modulation unit, and an amplifier. The carrier oscillator outputs a carrier wave of a predetermined frequency, and the encoding unit is connected to the control unit 51. The encoding unit encodes the transmission data output from the control unit 51 and outputs it to the modulation unit. The modulation unit receives the carrier wave from the carrier oscillator and the transmission data from the encoding unit. It generates a modulated signal that is ASK (Amplitude Shift Keying) modulated by the encoded transmission code (modulation signal) output from the encoding unit when a command is transmitted to the communication target, and outputs this to the amplifier. The amplifier amplifies the input signal (the modulated signal modulated by the modulation unit) at a set amplification factor, and this amplified signal is output to the antenna 54 as a transmission signal.

[0029] The input terminal of the receiving circuit 53b is connected to the antenna 54, and the radio signal (received signal) corresponding to the response wave from the wireless tag T received by the antenna 54 is input to the receiving circuit 53b. The receiving circuit 53b is composed of, for example, an amplifier and a demodulator, and the received signal received by the antenna 54 is amplified by the amplifier, and the amplified signal is demodulated by the demodulator. Furthermore, the signal corresponding to the demodulated signal waveform is output to the control unit 51 as received data.

[0030] The external interface 55 is configured as an interface for data communication with external devices such as the management terminal 41, and is configured to perform communication processing in cooperation with the control unit 51.

[0031] The management terminal 41 is a personal computer or the like, and is configured to perform inventory management processing, such as managing the entry and exit of items G through the entrance and exit 11 of the management shelf 10, using the tag ID read via the antenna device 20 from the wireless tag T passing through the entrance and exit 11 by the wireless tag reader 50.

[0032] In the item management system 1 configured in this way, as illustrated in Figure 6(A), when an item G1 is placed in the storage shelf 10 via the entrance / exit 11, the wireless tag T1 attached to the item G1 passes through the reading range of the antenna device 20. Therefore, the item G1 placed in the storage shelf 10 can be identified by using the tag ID read from the wireless tag T1 via the antenna device 20 by the wireless tag reader 50 during the inventory management process performed at the management terminal 41. Furthermore, as illustrated in Figure 6(B), even when another item G2 is placed in the storage shelf 10, the item G2 with the wireless tag T2 attached can be identified by reading the tag ID from the wireless tag T2 that has passed through the reading range.

[0033] In the inventory management process, when a tag ID without an inventory flag set to indicate its inventory status is read, the inventory flag is set for that tag ID and it is registered as an inventory item in a predetermined database built in the storage unit of the management terminal 41, along with the inventory time, etc. Also, in the inventory management process, when a tag ID with an inventory flag set is read, the inventory flag is removed for that tag ID and an inventory flag is set, and it is registered as an inventory item in the predetermined database, along with the inventory time, etc. Therefore, in the inventory management process, it is possible to determine whether an item G is being received or shipped based on whether or not an inventory flag is set for the read tag ID.

[0034] Next, the effect of a configuration in which a metal radome 30, each with an opening 31 formed therein, is positioned opposite the radio wave radiating surface 21a of the antenna 21 will be explained with reference to Figure 7. Figure 7 is a graph illustrating the relationship between the frequency shift ΔF of the antenna 21, which is affected by the distance zm when a metal plate is brought close to the antenna 21, and the presence or absence of the radome 30. The simulation result of the frequency shift without the radome is shown by the dashed line ΔF0, and the simulation result of the frequency shift with the radome 30 is shown by the solid line ΔF1.

[0035] As can be seen from Figure 7, in an antenna device without a radome (see ΔF0), as the distance zm decreases, the electromagnetic coupling between the antenna 21 and the metal plate increases, resulting in a larger frequency shift ΔF of the antenna 21. In other words, when a metal object G with a wireless tag T attached is placed near the antenna 21, the frequency shift ΔF increases as described above, making it impossible to maintain the required operating bandwidth, which leads to a deterioration in reading accuracy, such as missed readings of the wireless tag T.

[0036] On the other hand, in the antenna device 20 with a metal radome 30 (see ΔF1), even when the distance zm becomes small, the electromagnetic coupling is reduced by the radome 30 interposed between the antenna 21 and the metal plate, and radio waves are re-radiated through the aperture 31, thereby suppressing the frequency shift ΔF of the antenna 21. In other words, even if a metal object G with a wireless tag T attached is placed near the antenna 21, the frequency shift ΔF is suppressed as described above, so the necessary operating bandwidth is maintained, and thus deterioration of reading accuracy can be suppressed.

[0037] As described above, in the antenna device 20 according to this embodiment, a plurality of apertures 31 that function as slot antennas for re-radiating radio waves emitted from the antenna 21 are formed in a metal radome 30 that is positioned opposite the radio wave radiating surface 21a of the antenna 21.

[0038] As a result, even when a metal object G with a wireless tag T attached is placed near the antenna 21, the radome 30 interposed between the metal object G and the antenna 21 reduces the electromagnetic coupling between the metal object G and the antenna 21. Furthermore, since radio waves are re-radiated through each aperture 31 of the radome 30, the deterioration of radiation characteristics due to the presence of the metal radome 30 can be suppressed. Therefore, an antenna device 20 can be realized that can suppress deterioration of reading accuracy even when the wireless tag T attached to the metal object G is the target of reading.

[0039] In particular, in this embodiment, each aperture 31 is formed in a range of, for example, 0.7λ to 1.3λ such that its circumference Ls is equal to one times the wavelength λ of the radio wave. This makes it easier for each aperture 31 to resonate as a slot antenna, thereby improving the radiation characteristics of the radio waves re-radiated through each aperture 31 of the radome 30. Note that the above effect is also achieved even if each aperture 31 is formed so that its circumference Ls is equal to n times the wavelength of the radio wave (where n is an odd number) (i.e., formed in a range of 0.7nλ to 1.3nλ).

[0040] Furthermore, in this embodiment, each aperture 31 is formed such that its short axis aligns with the main polarization direction of the radiated electric field of the antenna 21. This allows the electric field of the slot to be more opposed compared to the case where the long axis is aligned with the main polarization direction of the radiated electric field of the antenna 21, thereby improving the radiation characteristics of the radio waves re-radiated through each aperture 31 of the radome 30. In other words, in this embodiment, the circumference Ls is equal to n times the wavelength of the radio wave (where n is an odd number), and the short axis is formed to align with the main polarization direction of the radiated electric field of the antenna 21. This not only makes the slot antenna more resonant, but also allows the electric field of the slot to be more opposed, further improving the radiation characteristics of the radio waves re-radiated through each aperture 31 of the radome 30.

[0041] Each aperture 31 is not limited to being formed in a rectangular shape; it may also have a long axis and a short axis, with the short axis aligned with or slightly tilted to coincide with the main polarization direction of the radiated electric field of the antenna 21.

[0042] [Second Embodiment] Next, the antenna device according to this second embodiment will be described with reference to the drawings. In this second embodiment, the main difference from the first embodiment and the like is that the radome opening is formed in such a way that the antenna is not exposed. Therefore, components that are substantially the same as those in the first embodiment are denoted by the same reference numerals, and their descriptions are omitted.

[0043] The antenna device 20a according to this embodiment is configured to have a radome 30a in place of the radome 30 compared to the antenna device 20 described above. As shown in Figure 8, the radome 30a has apertures 32, which are used in place of apertures 31 in the radome 30, and are formed so as to be at equal intervals when viewed from the direction opposite to the radio wave radiating surface 21a (the z direction in Figure 8), in a position that does not expose each antenna element 24 (microstrip line 23). In this embodiment, each aperture 32 is formed such that its circumference Ls is equal to the wavelength λ of the radio wave.

[0044] The effects of this configuration, in which a metal radome 30a with each aperture 32 is positioned opposite the radio wave radiating surface 21a of the antenna 21, will be explained with reference to Figure 9. Figure 9 is a graph illustrating the relationship between the frequency shift ΔF of the antenna 21, which is affected by the distance zm when a metal plate is brought close to the antenna 21, and the presence or absence of the radome 30a. The simulation result of the frequency shift when the radome 30a is present is shown by the solid line ΔF2. The simulation result of the frequency shift when the radome is absent is the same as in Figure 7, and is shown by the dashed line ΔF0.

[0045] As can be seen from Figure 9, in the case of an antenna device with a metal radome 30a (see ΔF2), even when the distance zm becomes small, the electromagnetic coupling is reduced by the radome 30a interposed between the antenna 21 and the metal plate, and radio waves are re-radiated through each aperture 32, thereby suppressing the frequency shift ΔF of the antenna 21.

[0046] In particular, in this embodiment, each aperture 32 is formed in a position that does not expose each antenna element 24 (microstrip line 23) of the antenna 21 when viewed from the opposite direction of the radio wave radiating surface 21a (z direction in Figure 8). As a result, although the radiation characteristics deteriorate somewhat, electromagnetic coupling between the metal object G and the antenna 21 can be suppressed more reliably. Therefore, as can be seen from the comparison results in Figures 7 and 9, the frequency shift ΔF of the antenna 21 can be suppressed more reliably than with the radome 30, and the deterioration of reading accuracy caused by frequency shift can be suppressed more reliably.

[0047] Furthermore, each aperture 32 can be formed such that, when viewed from the opposite direction of the radio wave radiating surface 21a, the antenna elements 24 are not exposed, and the circumference Ls is equal to n times the wavelength of the radio wave (where n is an odd number) (formed in the range of 0.7nλ to 1.3nλ). This further improves the radiation characteristics of the radio waves re-radiated through each aperture 32.

[0048] [Third Embodiment] Next, the antenna device according to this third embodiment will be described with reference to the drawings. In this third embodiment, the main difference from the second embodiment and others is that the opening of the radome is formed in a meander shape. Therefore, components that are substantially the same as those in the second embodiment are denoted by the same reference numerals, and their descriptions are omitted.

[0049] The antenna device 20b according to this embodiment is configured to have a radome 30b instead of a radome 30a compared to the antenna device 20a described above. As shown in Figure 10, the radome 30b has apertures 33 that are used in place of apertures 32 in the radome 30a, and these apertures 33 are arranged at equal intervals and meander-shaped positions when viewed from the direction opposite to the radio wave radiating surface 21a (z direction in Figure 10) so as not to expose each antenna element 24 (microstrip line 23).

[0050] By forming them in this meander shape, the circumference of each aperture 33 can be increased without increasing the aperture area occupied by each aperture 33. In this embodiment, each aperture 33 is formed such that its self-resonant frequency is equal to 920 MHz, based on the following known formula (1) which gives structural conditions for a meander line antenna, with a circumference Ls of 604 mm (302 mm × 2) obtained by 10 steps of meander horizontal lines W = 22.6 mm, meander vertical lines L = 75 mm, and width b = 1 mm × 2. TIFF2026094913000002.tif16169

[0051] The effects of the configuration in which a metal radome 30b, in which each of the openings 33 is formed, is positioned opposite the radio wave radiating surface 21a of the antenna 21 will be explained with reference to Figure 11. Figure 11 is a graph that explains the relationship between the frequency shift ΔF of the antenna 21, which is affected by the distance zm when a metal plate is brought close to the antenna 21, and the presence or absence of the radome 30b. The simulation result of the frequency shift when the radome 30b is present is shown by the solid line ΔF3. The simulation result of the frequency shift when the radome is absent is the same as in Figures 7 and 9, and is shown by the dashed line ΔF0.

[0052] As can be seen from Figure 11, in the case of an antenna device with a metal radome 30b (see ΔF3), even when the distance zm becomes small, the electromagnetic coupling is reduced by the radome 30b interposed between the antenna 21 and the metal plate, and radio waves are re-radiated through each aperture 33, thereby suppressing the frequency shift ΔF of the antenna 21.

[0053] In this embodiment, each aperture 33 is formed in a meander shape at a position where each antenna element 24 (microstrip line 23) of the antenna 21 is not exposed when viewed from the opposite direction of the radio wave radiating surface 21a (z direction in Figure 8). Even in this case, although the radiation characteristics deteriorate somewhat, similar to the case in which a radome 30a is used, electromagnetic coupling between the metal object G and the antenna 21 can be suppressed more reliably. As can be seen from the comparison results in Figures 7 and 11, the frequency shift ΔF of the antenna 21 can be suppressed more effectively than with the radome 30, thus more reliably suppressing the deterioration of reading accuracy caused by frequency shift.

[0054] In particular, in this embodiment, since each aperture 33 is formed in a meander shape, the area occupied by the aperture 33 can be reduced while securing the required circumference Ls. This makes it easier to form the meander-shaped aperture in a position where each antenna element 24 is not exposed when viewed from the opposite direction of the radio wave radiating surface 21a, thus achieving both suppression of electromagnetic coupling between the metal article G and the antenna 21 and improvement of radiation characteristics.

[0055] The present invention is not limited to the embodiments described above, and may be further embodied as follows, for example. (1) The radome 30 is not limited to being configured such that each of the openings 31 is arranged at equal intervals in line with the position of the gap 27, but may also be configured such that only one opening is formed and exposes at least a part of the antenna element 24, or two or more openings may be formed and arranged at equal or unequal intervals so that each exposes at least a part of the antenna element 24.

[0056] (2) The radome 30a is not limited to being configured such that each of the openings 32 is arranged at equal intervals, but may also be configured such that only one opening is formed and does not expose the antenna element 24, or two or more openings may be formed and arranged at equal or unequal intervals so that each does not expose the antenna element 24.

[0057] (3) The radome 30b is not limited to being configured such that each of the openings 33 is arranged at equal intervals. Alternatively, one or more meander-shaped openings may be formed so as not to expose the antenna element 24, or two or more meander-shaped openings may be formed so as to be arranged at equal or unequal intervals so as not to expose the antenna element 24.

[0058] (4) The antenna 21 is not limited to being configured to include a microstrip line 23 in which multiple antenna elements 24 of the same shape are arranged in one direction, but may also be configured as a planar antenna that extends long in the direction of the main polarization of the radiated electric field.

[0059] (5) The antenna devices 20, 20a, and 20b according to the present invention are not limited to being installed and used on the management shelf 10 in an item management system 1 that manages items G that are moved in and out of the management shelf 10, but may also be used as antenna devices for a reading device in which a metal item with a wireless tag to be read is placed nearby. [Explanation of symbols]

[0060] 20, 20a, 20b Antenna equipment 21 Antennas 21a Radio wave emission surface 30, 30a, 30b radomes 31,32,33 aperture G Goods Ls Perimeter T Wireless Tag ΔF frequency shift

Claims

1. Antenna and, A metal radome is positioned opposite the radiating surface of the aforementioned antenna, An antenna device comprising, The antenna device is characterized in that the radome has an opening that functions as a slot antenna for re-radiating radio waves emitted from the antenna.

2. The antenna device according to claim 1, characterized in that the opening is formed in a position that does not expose the antenna elements of the antenna when viewed from the direction opposite to the radiating surface.

3. The antenna device according to claim 1, characterized in that the aperture is formed such that its circumference is equal to n times (where n is an odd number) the wavelength of the radio wave.

4. The antenna device according to claim 1, characterized in that the aperture is formed such that its short axis aligns with the main polarization direction of the radiated electric field of the antenna.

5. The antenna device according to claim 1, characterized in that the aperture has a circumference equal to n times the wavelength of the radio wave (where n is an odd number), and the minor axis is formed to align with the main polarization direction of the radiated electric field of the antenna.

6. The antenna device according to claim 1, characterized in that the opening is formed in a meander shape at a position that does not expose the antenna elements of the antenna when viewed from the direction opposite to the radiating surface.

Images