Antenna device

Abstract

Provided is an antenna device comprising a dielectric substrate and a transmission line in which a plurality of unit cells are arranged in a prescribed direction at one surface of the dielectric substrate, wherein: reflectors are provided at both ends of the transmission line; each of the plurality of unit cells has a strip conductor extending in the prescribed direction and a stub conductor branched from the strip conductor; a prescribed gap is interposed between the strip conductor and the strip conductor of an adjacent unit cell; and when the length of the transmission line in the prescribed direction is Lant and the wavelength of a radio wave in vacuum is λ0, each parameter of the plurality of unit cells is set so that the absolute value |neff| of the effective refractive index of the transmission line is less than 1, and the expression |neff|<λ0／(4Lant) is satisfied.

Description

Antenna equipment

[0001] This disclosure relates to an antenna device.

[0002] Traditionally, when placing items into or removing items from a storage shelf, workers sequentially scan barcodes or other information codes attached to the item, the storage shelf, and the work instruction sheet using a portable reader. This enables the operation of a system that manages the inventory status of items in the storage shelf. However, this system, in which workers scan information codes for each item, suffers from problems such as reduced inventory management accuracy due to human error and high management costs due to the cumbersome scanning process.

[0003] For this reason, a system has been proposed to manage the inventory status of goods using the reading results of wireless tags such as RF (Radio Frequency) tags that can be read via contactless communication. As an antenna device suitable for such a system, for example, the leaky wave antenna device disclosed in Patent Document 1 below is known. The leaky wave antenna device comprises a pair of CRLH (Composite Right / Left-Handed) transmission lines formed by cascading multiple unit cells between a pair of power supply ports. The pair of CRLH transmission lines are arranged in close proximity to each other, substantially parallel to each other, and electromagnetically coupled to each other. Each of the multiple unit cells has a series branch circuit, a parallel branch circuit, and a transmission line portion. In the leaky wave antenna device, by making the effective refractive index of the transmission line smaller than the refractive index in free space, 1, a portion of the energy of the electromagnetic waves propagating along the transmission line is radiated to the outside of the transmission line as leaky waves. The direction of this radiation varies depending on the effective refractive index. In a leaky wave antenna device that operates in the leaky wave region in this way, reflectors are provided at both ends of the transmission line. This improves the radiation efficiency of the leaky waves radiated to the outside as described above. As a result, reading errors are prevented.

[0004] Japanese Patent Publication No. 2024-142998

[0005] Consider the case where an antenna device is installed at the entrance and exit of a storage rack through which managed items pass when being moved in and out. In this case, it is necessary to match the reading range of the antenna device to the area through which wireless tags may pass during loading and unloading (hereinafter also referred to as the tag monitoring range). This is to prevent any missed readings of wireless tags attached to items being loaded and unloaded. As described above, when installing an antenna device that operates in the leakage wave region, it is necessary to match the length of the antenna device in the direction along the transmission line (i.e., the direction of the main polarization of the radiated electric field) to the tag monitoring range (for example, the width of the entrance and exit of the storage rack).

[0006] However, depending on the size of the tag monitoring range, the length of the antenna device's transmission line may be such that there are points in the antenna device's transmission line where the forward-propagating radio waves and the backward-propagating radio waves reflected by the reflector cancel each other out. As a result, there is a possibility that areas within the control shelf may become difficult to read (i.e., null points).

[0007] This disclosure was made to solve the above-mentioned problems, and its purpose is to provide an antenna device that operates in the leaky wave region without forward-propagating and backward-propagating radio waves canceling each other out, even when the size of the antenna device is suitable for the tag monitoring range.

[0008] An antenna device according to one aspect of the present disclosure comprises a dielectric substrate and a transmission line in which a plurality of unit cells are arranged in a predetermined direction on one surface of the dielectric substrate, wherein reflectors are provided at both ends of the transmission line, each of the plurality of unit cells has a strip conductor extending in the predetermined direction and a stub conductor branching off from the strip conductor, and is arranged such that a predetermined gap is interposed between the strip conductor and the strip conductor of an adjacent unit cell, thereby comprising a series branch circuit that equivalently includes a capacitive component due to the predetermined gap and a parallel branch circuit that equivalently includes an inductive component due to the stub conductor, and the length of the transmission line in the predetermined direction is L ａｎｔ λ is the wavelength of radio waves in a vacuum. ０ In this case, the absolute value of the effective refractive index of the transmission line is |n ｅｆｆThe parameters of each of the plurality of unit cells are set such that | is less than 1 and satisfies the following formula (1). | n ｅｆｆ | < λ ０ / (4L ａｎｔ ) ··· (1)

[0009] In the present disclosure, reflectors are provided at both ends of a transmission line in which a plurality of unit cells are arranged in a predetermined direction on one surface of a dielectric substrate. Each of the plurality of unit cells has a strip conductor extending in the predetermined direction and a stub conductor branched from the strip conductor, and is arranged such that a predetermined gap is interposed between the strip conductor and the strip conductor of an adjacent unit cell. As a result, each of the plurality of unit cells includes a series-branch circuit equivalently including a capacitance component caused by the predetermined gap and a parallel-branch circuit equivalently including an inductor component caused by the stub conductor. Let the length of the transmission line in the predetermined direction be L ａｎｔ , and the wavelength of the radio wave in vacuum be λ ０ . When the absolute value | n ｅｆｆ | of the effective refractive index of the transmission line is less than 1 and satisfies the above formula (1), the parameters of each of the plurality of unit cells are set.

[0010] For example, under the condition that the length L ａｎｔ of the transmission line matches the wavelength λ ａｎｔ of the radio wave in the transmission line, when the radio wave propagating in the forward direction and the radio wave propagating in the reverse direction reinforce each other at the positions of L ａｎｔ / 4 and 3L ａｎｔ / 4 in the transmission line, a null point where the radio wave propagating in the forward direction and the radio wave propagating in the reverse direction cancel each other out occurs at the position of 2L ａｎｔ / 4 in the transmission line. On the other hand, by making the length L ａｎｔ of the transmission line less than λ ａｎｔ / 4 of the wavelength of the radio wave in the transmission line, the radio wave propagating in the forward direction and the radio wave propagating in the reverse direction do not have opposite phases. Therefore, in the transmission line, the radio wave propagating in the forward direction and the radio wave propagating in the reverse direction do not cancel each other out, and no null point occurs. Here, the wavelength λ ａｎｔ of the radio wave in the transmission line is λ ０ (that is, the wavelength of the radio wave in vacuum) / n ｅｆｆ(i.e., the effective refractive index of the transmission line) is equal to n. ｅｆｆ If the above equation (1) is satisfied, the aforementioned cancellation of radio waves does not occur. That is, the length L of the transmission line ａｎｔ Even if the length is such that it fits within the tag monitoring range (for example, the width of the entrance / exit of the management shelf), the effective refractive index n of the transmission line that satisfies the above equation (1) ｅｆｆ By setting this, the occurrence of null points due to the cancellation of radio waves as described above can be prevented. Furthermore, the absolute value of the effective refractive index of the transmission line |n ｅｆｆ By setting | to a value less than 1, the antenna device can be operated in the leakage wave region as described above. Effective refractive index n of the transmission line ｅｆｆ This can be set by the dimensional parameters of the unit cell, etc. Therefore, the above conditions can be set for the effective refractive index n of the transmission line. ｅｆｆ The unit cell dimensions and other parameters are set to satisfy this condition. This makes it possible to realize an antenna device that operates in the leaky wave region without forward-propagating and backward-propagating radio waves canceling each other out, even when the size of the antenna device is within the tag monitoring range.

[0011] This is a diagram illustrating an item management system employing an antenna device according to the first embodiment. This is a perspective view of the storage shelf in Figure 1, seen from the entrance side. This is a schematic plan view of the antenna device according to the first embodiment. This is a diagram illustrating the schematic configuration of a unit cell according to the first embodiment. This is a circuit diagram showing the equivalent circuit model of a unit cell according to the first embodiment. This is a block diagram illustrating the schematic configuration of the wireless tag reader in Figure 1. This is a diagram illustrating the storage of items into the storage shelf. This is a diagram illustrating the storage of further items after the storage in Figure 7A. This is a diagram illustrating the relationship between the current distribution of a transmission line and the wavelength. This is a diagram showing the relationship between radio wave intensity and position within the transmission line when the length of the transmission line is 90 cm, the operating frequency is 1 GHz, and the effective refractive index of the transmission line is 1. This is a diagram showing the relationship between radio wave intensity and position within the transmission line when the phase of the input power in Figure 9A is changed. This is a diagram showing the relationship between radio wave intensity and position within the transmission line when the length of the transmission line is 90 cm, the operating frequency is 1 GHz, and the effective refractive index of the transmission line is 0.8. This figure shows the relationship between radio wave intensity and position within a transmission line when the transmission line length is 90 cm, the operating frequency is 1 GHz, and the effective refractive index of the transmission line is 0.166. This figure shows the relationship between radio wave intensity and position within a transmission line when the transmission line length is 90 cm, the operating frequency is 1 GHz, and the effective refractive index of the transmission line is 0.0833. This figure shows the relationship between radio wave intensity and position within a transmission line when the transmission line length is 90 cm, the operating frequency is 1 GHz, and the effective refractive index of the transmission line is 0.04. This figure shows the relationship between radio wave intensity and position within a transmission line when the transmission line length is 200 cm, the operating frequency is 1 GHz, and the effective refractive index of the transmission line is 0.04. This figure shows the relationship between radio wave intensity and position within a transmission line when the transmission line length is 200 cm, the operating frequency is 1 GHz, and the effective refractive index of the transmission line is 0.018. This figure is used to explain the relationship between radio wave intensity within a unit cell and the length of a unit cell. This figure illustrates the positional relationship between a linear gap and wireless tags that are less prone to reading errors and wireless tags that are prone to reading errors. This figure illustrates the unit cell used in the antenna device according to the third embodiment. This figure illustrates the unit cell used in the antenna device according to a modified example of the third embodiment.This figure illustrates the positional relationship between the stub conductor and wireless tags that are less prone to reading errors and wireless tags that are more prone to reading errors. This figure illustrates the unit cell used in the antenna device according to the fourth embodiment. This figure illustrates the unit cell used in the antenna device according to the first modification of the fourth embodiment. This figure illustrates the unit cell used in the antenna device according to the second modification of the fourth embodiment. This figure illustrates the unit cell used in the antenna device according to the third modification of the fourth embodiment.

[0012] <First Embodiment> Hereinafter, an antenna device according to the first embodiment of this disclosure will be described with reference to the drawings. The antenna device 40 according to this embodiment is used when reading and writing information recorded on a wireless tag T, such as an RF tag, attached to an item G. The antenna device 40 is installed and used on the management shelf 10 in an item management system 1 in which items G that are moved in and out of the management shelf 10 are managed. As shown in Figures 1 and 2, the item management system 1 includes an antenna device 40 installed on the management shelf 10 and a management device 20. The management device 20 manages the movement of items G in and out of the management shelf 10 via the entrance and exit 11.

[0013] The item G to be managed may be, for example, a packaging box in which a predetermined part is contained and packaged. A wireless tag T, such as an RF tag on which a unique tag ID (Identifier) ​​is recorded, is attached to the side of the box. The tag ID can be read from the wireless tag T by contactless communication. In this embodiment, the tag ID is information that can identify the item G. The tag ID is associated with the item G to which the wireless tag T on which the tag ID is recorded is attached, and with the type and number of parts contained in the item G. This association is registered on a server or the like. Therefore, by querying the server or the like for the item G using the tag ID read from the wireless tag T, the item G to which the wireless tag T on which that tag ID is recorded can be identified. Note that the item G is not limited to the packaging box described above. The item G may be a product, and the wireless tag T may be attached to that product.

[0014] As shown in Figures 1 and 2, the storage shelf 10 in this embodiment has a box-like shape that is roughly rectangular. The front entrance 11 opens in a rectangular shape. The space enclosed by the top wall 12, bottom wall 13, side walls 14, 15, and back wall 16 is the storage space for the stored items G. In this embodiment, each wall of the storage shelf 10 is formed of a resin material. However, the material of each wall of the storage shelf 10 is not limited to this. For example, at least a part of the wall may be formed of a metal material, a glass material, or a wooden material. Note that in Figure 1 and Figure 7, which will be described later, the side wall 15 is omitted from the illustration for convenience.

[0015] As shown in Figures 3 and 4, the antenna device 40 in this embodiment comprises a dielectric substrate 50 and a microstrip line 60. The microstrip line 60 is a transmission line in which a plurality of unit cells 61 are arranged in a predetermined direction (for example, the Y direction in Figure 3) on one surface of the dielectric substrate 50 (i.e., the radio wave radiating surface 51). A reflector 53 connected to a power supply port is provided at the power supply side end of the microstrip line 60. A reflector 54 is provided at the end of the microstrip line 60 opposite to the power supply side.

[0016] In the microstrip line 60 of this embodiment, the above-mentioned arrangement direction (i.e., the Y direction in Figure 3) is the main polarization direction of the radiated electric field. The microstrip line 60 is a right-handed / left-handed composite transmission line (CRLH line) that operates in the leakage wave region.

[0017] Each of the multiple unit cells 61 constituting the microstrip line 60 has a strip conductor 62 extending in the alignment direction (i.e., the Y direction in Figure 3) and a stub conductor 63 branching off from the strip conductor 62. The unit cells 61 are arranged such that a predetermined gap (hereinafter also referred to as a gap 64) which is a non-conductive portion is interposed between its own strip conductor 62 and the strip conductor 62 of an adjacent unit cell 61. That is, in the unit cell 61, as shown in Figure 4, the strip conductor 62 and the stub conductor 63 are sandwiched between one half of the gap 64 (hereinafter also referred to as the one-side gap 64a) and the other half of the gap 64 (hereinafter also referred to as the other-side gap 64b). The stub conductor 63 is connected to the ground conductor 52 of the dielectric substrate 50 via a via conductor 65.

[0018] With this arrangement, each of the multiple unit cells 61 in the antenna device 40 has an inductor component L, as shown in Figure 5. Ｒ In addition, the volume component C caused by the gap 64 Ｌ The series branch circuit 61a also equivalently includes the capacitive component C Ｒ In addition, the inductor component L is due to the stub conductor 63. Ｌ The parallel branch circuit 61b, which also equivalently includes, is functionally provided.

[0019] In this embodiment, in order to operate the antenna device 40 in the leakage wave region, the absolute value of the effective refractive index of the transmission line in the antenna device 40 is |n ｅｆｆ | is less than 1, which is the refractive index in free space. The radiation direction of leakage waves radiated outside the transmission line is the effective refractive index n. ｅｆｆ It varies depending on the effective refractive index n. ｅｆｆ The closer this value approaches 0, the closer the radiation direction of the leakage wave approaches the direction perpendicular to the radio wave emission surface 51 (for example, the z direction in Figure 3: perpendicular to the direction of the main polarization of the radiated electric field).

[0020] Effective refractive index n of the transmission line ｅｆｆ This is the volume component C mentioned above. Ｌ The effective permeability and the inductor component L mentioned above are affected by the above. ＬIt changes depending on the effective dielectric, etc., which is affected by the following. For this reason, in this embodiment, the effective refractive index n of the transmission line changes depending on the setting of various dimensional parameters of the strip conductor 62, stub conductor 63, and gap 64 contained in the unit cell 61. ｅｆｆ This will be configured as described below.

[0021] The aforementioned antenna device 40 is connected to the wireless tag reader 30 of the management device 20 via a coaxial cable or the like, and is installed on the inner side of the bottom wall 13 of the management shelf 10, which corresponds to the area below the entrance / exit 11 that is within the tag monitoring range. In order to adjust the reading range to match the tag monitoring range, the length of the antenna device 40 (specifically, the length L of the transmission line) ａｎｔ (See Figure 3)) is slightly smaller than the width of the entrance 11.

[0022] The antenna device 40, installed in this manner, operates using predetermined power supplied from the wireless tag reader 30, setting the entrance / exit 11 of the storage shelf 10 as a tag monitoring range that matches the reading range. Note that the antenna device 40 is not limited to being installed on the inner side of the bottom wall 13. The antenna device 40 may also be installed on the inner side of the top wall 12 to keep it away from the incoming items G. Alternatively, the antenna device 40 may be installed on the inner side of the side walls 14, 15 or the back wall 16.

[0023] The management device 20 includes a wireless tag reader 30 and a management terminal 21. The wireless tag reader 30 is a so-called RFID reader and outputs the tag ID etc. read from the wireless tag T via the antenna device 40 to the management terminal 21. As shown in Figure 6, the wireless tag reader 30 includes a control unit 31, a storage unit 32, a communication processing unit 33, an antenna 34, and an external interface 35, etc. The control unit 31 is implemented using a microcomputer. The microcomputer has a CPU (Central Processing Unit), a system bus, and an input / output interface, etc. The storage unit 32 is implemented using semiconductor memory, etc. The control unit 31 and the storage unit 32 provide the functions of an information processing device.

[0024] As shown in Figure 6, the communication processing unit 33 includes a transmitting circuit 33a and a receiving circuit 33b. The transmitting circuit 33a includes, for example, a carrier oscillator, an encoding unit, a modulation unit, and an amplifier. The carrier oscillator outputs a carrier (i.e., carrier wave) of a predetermined frequency. The encoding unit is connected to the control unit 31 and encodes the transmission data output from the control unit 31 to output the transmission code to the modulation unit. The modulation unit receives the carrier (i.e., carrier wave) from the carrier oscillator and the transmission data from the encoding unit as input. The modulation unit generates a modulated signal by performing ASK (Amplitude Shift Keying) modulation on the carrier (i.e., carrier wave) output from the carrier oscillator using the transmission code (i.e., modulation signal), and outputs it to the amplifier. The transmission code is output from the encoding unit when sending a command to the communication target. The amplifier amplifies the input signal (i.e., the modulated signal output from the modulation unit) at a set amplification factor. This amplified signal is output to the antenna 34 as the transmission signal.

[0025] The input terminal of the receiving circuit 33b is connected to the antenna 34. The radio signal corresponding to the response wave from the wireless tag T received by the antenna 34 (i.e., the received signal) is input to the receiving circuit 33b. The receiving circuit 33b includes, for example, an amplifier and a demodulator. The received signal received by the antenna 34 is amplified by the amplifier. The amplified signal is demodulated by the demodulator. Furthermore, the signal corresponding to the demodulated signal waveform is output to the control unit 31 as received data.

[0026] The external interface 35 is an interface for data communication with external devices such as the management terminal 21. The external interface 35 performs communication processing in cooperation with the control unit 31.

[0027] The management terminal 21 may be a personal computer or the like. The management terminal 21 uses the tag ID read by the wireless tag reader 30 via the antenna device 40 from the wireless tag T passing through the entrance / exit 11 to perform inventory management processing such as managing the entry and exit of items G through the entrance / exit 11 of the management shelf 10.

[0028] In such an item management system 1, as illustrated in Figure 7A, 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 40. Therefore, in the inventory management process of the management terminal 21, 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 40 by the wireless tag reader 30. Furthermore, as illustrated in Figure 7B, even when another item G2 is placed in the storage shelf 10, the tag ID is read from the wireless tag T2 that has passed through the reading range. This makes it possible to identify the placement of the item G2 with the wireless tag T2 attached.

[0029] In the inventory management process, if a tag ID is read that does not have an inventory flag set, an inventory flag is set for that tag ID. The tag ID, along with the inventory time, is then registered as inventory information in a predetermined database built in the storage unit of the management terminal 21. In the inventory management process, if a tag ID with an inventory flag set is read, the inventory flag is removed and an inventory flag is set for that tag ID. The tag ID, along with the inventory time, is then registered as inventory information in the predetermined database. Therefore, in the inventory management process, it is possible to determine whether an item G is being received or shipped depending on whether an inventory flag is set for the read tag ID.

[0030] Next, according to the settings of various dimensional parameters of the unit cell 61, the effective refractive index n of the transmission line is determined. ｅｆｆ The effects of setting this will be explained below. In order to match the reading range of the antenna device 40 to the entrance / exit 11 which is the tag monitoring range, the length of the transmission line L ａｎｔ Let's assume that it matches the size of the entrance / exit 11. In that case, depending on the size of the tag monitoring range, the length L of the transmission line will be ａｎｔ However, this can result in a length where the forward-propagating radio waves and the backward-propagating radio waves reflected by the reflector cancel each other out. As a result, there is a possibility that areas within the control shelf 10 may become difficult to read (i.e., null points).

[0031] Figure 8 illustrates the relationship between the current distribution and wavelength in a transmission line. As can be seen from Figure 8, the amplitude of the current intensity of radio waves propagating through a transmission line changes depending on the position within the transmission line. For example, the length L of the transmission line... ａｎｔ The wavelength λ of the radio waves in the transmission line ａｎｔ Under conditions that match this, L in the transmission line ａｎｔ / 4 and 3L ａｎｔ When forward-propagating and reverse-propagating radio waves reinforce each other at position / 4, resulting in maximum amplitude, then 2L in the transmission line ａｎｔ At position 4, the forward-propagating and reverse-propagating radio waves cancel each other out. In other words, a null point is created.

[0032] In contrast, the length L of the transmission line ａｎｔ The wavelength λ of the radio wave in the transmission line ａｎｔ By setting the ratio to less than / 4, the forward-propagating and reverse-propagating radio waves do not have opposite phases. Therefore, within the transmission line, the forward-propagating and reverse-propagating radio waves do not cancel each other out, and no null points occur. Transmission line length L ａｎｔ It needs to be adjusted to the size of the entrance / exit 11. Therefore, to avoid creating null points, the wavelength λ of the radio waves in the transmission line ａｎｔ You need to configure this.

[0033] Wavelength λ of radio waves in a transmission line ａｎｔ λ is the wavelength of a radio wave in a vacuum. ０ and the effective refractive index n of the transmission line ｅｆｆ It can be determined based on the following equation (4) using and . The wavelength of radio waves in a vacuum is λ ０ This can be determined based on the following equation (5), which uses the speed of light c and the frequency f of radio waves. λ ａｎｔ = λ ０ | / n ｅｆｆ | ...(4) λ ０ =c / f...(5)

[0034] As can be seen from equation (4) above, the wavelength λ of the radio wave in the transmission line ａｎｔ The effective refractive index n of the transmission line ｅｆｆ This is determined by the length L of the transmission line. ａｎｔ The wavelength λ of the radio wave in the transmission lineａｎｔ To keep it less than / 4, the absolute value of the effective refractive index of the transmission line |n ｅｆｆ | is set to satisfy the following equation (1). When the following equation (1) is satisfied, the aforementioned cancellation of radio waves does not occur. |n ｅｆｆ | <λ ０ / (4L ａｎｔ ) ... (1)

[0035] In other words, the length L of the transmission line ａｎｔ Even if the length of the transmission line is such that it fits within the tag monitoring range, such as the width of the entrance / exit 11 of the management shelf 10, the effective refractive index n of the transmission line satisfies the above formula (1). ｅｆｆ By setting this, the occurrence of null points due to the cancellation of radio waves as described above can be prevented.

[0036] For example, to match the size of the entrance / exit 11, the length L of the transmission line ａｎｔ Let's consider the case where the distance is 90 cm and the frequency f of the radio waves used is 1 GHz. The effective refractive index n of the transmission line. ｅｆｆ When is 1, as can be seen from Figure 9A, a position appears on the transmission line where multiple of the aforementioned radio waves cancel each other out (i.e., a null point occurs). Even if the phase of the input power is changed, as can be seen from Figure 9B, the position where the null point occurs does not change. On the other hand, for example, the length L of the transmission line... ａｎｔ The length is 90 cm, the operating frequency f is 1 GHz, and the effective refractive index of the transmission line is n ｅｆｆ When the value is 0.8, as can be seen from Figure 9C, not only do locations with multiple null points appear on the transmission line, but the maximum amplitude also decreases.

[0037] In contrast, the length L of the transmission line ａｎｔ The length is 90 cm, the operating frequency f is 1 GHz, and the effective refractive index of the transmission line is n ｅｆｆ 0.166 (λ ａｎｔ / 2 = L ａｎｔ In this case, as can be seen from Figure 10A, a null point occurs in the center of the transmission line. Even if the phase of the input power is changed, the position where the null point occurs does not change. Furthermore, the length of the transmission line L ａｎｔ The length is 90 cm, the operating frequency f is 1 GHz, and the effective refractive index of the transmission line is n ｅｆｆ 0.0833 (λ ａｎｔ / 4 = L ａｎｔ When it is the case of (2), as can be seen from FIG. 10B, one null point occurs at the power supply side end on the transmission line. Even if the phase of the input power is changed, the position where the null point occurs does not change.

[0038] Therefore, for the length L of the transmission line ａｎｔ when it is 90 cm and the operating frequency f is 1 GHz, so that the above formula (1) is satisfied, the effective refractive index n of the transmission line ｅｆｆ is set to a value smaller than 0.0833 (λ ａｎｔ / 4 = L ａｎｔ ), for example, 0.04. Thereby, as can be seen from FIG. 10C, generation of the null point due to the cancellation of the above-described radio waves can be prevented. And even when the phase of the input power is changed, no null point occurs, and the amplitude becomes substantially uniform for each phase.

[0039] Also, for example, in order to match the size of the entrance / exit 11, for the length L of the transmission line ａｎｔ when it is 200 cm, the operating frequency f of the radio wave used is 1 GHz, and the effective refractive index n of the transmission line ｅｆｆ is 0.04, since the above formula (1) is not satisfied, as can be seen from FIG. 11A, one null point occurs on the transmission line. In contrast, when the length L of the transmission line ａｎｔ is 200 cm and the operating frequency f is 1 GHz, so that the above formula (1) is satisfied, the effective refractive index n of the transmission line ｅｆｆ is set to 0.018. Thereby, as can be seen from FIG. 11B, generation of the null point due to the cancellation of the above-described radio waves can be prevented.

[0040] Thus, by setting the effective refractive index n of the transmission line that satisfies the above formula (1) ｅｆｆ , generation of the null point due to the cancellation of the above-described radio waves can be prevented. Furthermore, by controlling the effective refractive index |n ｅｆｆ | of the transmission line to be less than 1, the antenna device can be operated in the leaky wave region as described above.

[0041] The effective refractive index n of the transmission line ｅｆｆcan be set according to the setting of various dimensional parameters in the strip conductor 62, stub conductor 63, and gap 64 included in the unit cell 61 as described above. As parameters that can be set, for example, the shape dimensions of the strip conductor 62 including the length in the X direction and the length in the Y direction (i.e., the line width W) or the thickness (i.e., the electrode thickness Th) of the strip conductor 62, the length in the X direction and the length in the Y direction or the thickness (electrode thickness Th) of the stub conductor 63, etc., are included, and the width or length of the gap 64, etc., can be adopted.

[0042] For example, the length L of the transmission line ａｎｔ Consider the case where the length L is 90 cm and the operating frequency f is 1 GHz. When the period P (see FIG. 5) in the periodic structure of the transmission line is 3 cm, the capacitance component C Ｒ is 6.62 pF, the inductor component L Ｒ is 5.62 nH, the capacitance component C Ｌ is 5.21 pF, and the inductor component L Ｌ is 3.87 nH, various dimensional parameters of the unit cell 61 are set. As a result, the effective refractive index n ｅｆｆ of the transmission line is set to 0.075. The absolute value |n ｅｆｆ | of the thus-set effective refractive index is smaller than 1 and satisfies the above formula (1), so that the generation of null points due to the cancellation of radio waves described above can be prevented.

[0043] As described above, the antenna device 40 according to the present embodiment includes a microstrip line 60 in which a plurality of unit cells 61 are arranged in a predetermined direction (the Y direction in FIG. 3) on one surface of the dielectric substrate 50. Reflectors 53 and 54 are provided at both ends of the microstrip line 60, respectively. Each of the plurality of unit cells 61 has a strip conductor 62 extending in the predetermined direction and a stub conductor 63 branched from the strip conductor 62. The unit cell 61 is arranged such that a predetermined gap 64 is interposed between the strip conductor 62 and the strip conductor 62 of the adjacent unit cell 61. As a result, the unit cell 61 includes a circuit 61a of a series branch that equivalently includes a capacitance component C Ｌ caused by the gap 64, and an inductor component L ＬA parallel branch circuit 61b that equivalently includes and functionally comprises. The length of the transmission line in the predetermined direction is L ａｎｔ λ is the wavelength of radio waves in a vacuum. ０ When this is the case, the absolute value of the effective refractive index of the transmission line is |n ｅｆｆ The various parameters of the unit cell 61 are set such that | is less than 1 and satisfies the above formula (1).

[0044] The above conditions apply to the effective refractive index n of the transmission line. ｅｆｆ By setting the dimensional parameters of the unit cell 61 to satisfy this condition, it is possible to realize an antenna device 40 that operates in the leaked wave region without forward-propagating and backward-propagating radio waves canceling each other out, even when the size of the antenna device 40 is sized to fit the tag monitoring range.

[0045] <Second Embodiment> Next, an antenna device according to the second embodiment will be described with reference to the drawings. The second embodiment differs from the first embodiment in that the length of the unit cell is set so as to prevent the occurrence of null points within the unit cell. 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.

[0046] Even within a single unit cell 61, the length L of the unit cell 61 in the predetermined direction (i.e., the Y direction in Figure 3) ｕｎｉｔ Depending on the period P (corresponding to the periodic structure of the transmission line), null points may occur. This is because the out-of-phase components of the radio waves generated within the unit cell 61 cancel each other out. Null points generated within individual unit cells 61 do not affect the reading of wireless tags far from the antenna, but they do affect the reading of wireless tags near the antenna. Therefore, if the reading of wireless tags near the antenna is important, it is necessary to prevent the generation of null points within each unit cell 61.

[0047] Therefore, in this embodiment, the above-mentioned conditions (i.e., the absolute value of the effective refractive index of the transmission line |n) are met. ｅｆｆ In addition to the fact that | is less than 1 and satisfies the above formula (1), the length L of the unit cell 61 satisfies the following formula (2). ｕｎｉｔ This is set. That is, the length L of the unit cell 61.ｕｎｉｔ This is the wavelength λ of the radio wave within the unit cell 61, which is calculated using the following formula (3). ｕｎｉｔ It is less than 1 / 4 of n. ｕｎｉｔ This is the effective refractive index of a unit cell 61, determined according to the operating frequency f, the width (i.e., line width W) and thickness (i.e., electrode thickness Th) of the strip conductor 62, and the dielectric constant and height (i.e., substrate thickness H) of the dielectric substrate 50. As a result, no out-of-phase components of radio waves are generated within a single unit cell 61, thus preventing the occurrence of null points due to the aforementioned cancellation of radio waves within a single unit cell 61. ｕｎｉｔ <λ ｕｎｉｔ / 4...(2) λ ｕｎｉｔ = λ ０ / |n ｕｎｉｔ | ... (3)

[0048] For example, given that the line width W is 10.2 mm, the substrate thickness H is 2.4 mm, the electrode thickness Th is 0.01 mm, the relative permittivity εr is 4.9, and the operating frequency f is 1 GHz, the effective refractive index n within the unit cell 61 is ｕｎｉｔ Let's consider the case where is 2. In this case, from equation (3) above, the wavelength λ of the radio wave within the unit cell 61 is ｕｎｉｔ The length is 15 cm. Figure 12 illustrates the radio wave intensity within a unit cell 61 and the length L of the unit cell 61. ｕｎｉｔ As can be seen from the relationship, the length L of the unit cell 61 ｕｎｉｔ λ ｕｎｉｔ In the range of 3.75 cm or more, which is 4 or more, an out-of-phase component of the radio wave is generated within the unit cell 61. Therefore, a null point occurs. In this case, the length L of the unit cell 61 is... ｕｎｉｔ By setting this to less than 3.75 cm, no out-of-phase component of radio waves is generated within the unit cell 61. Therefore, the occurrence of null points can be prevented.

[0049] Furthermore, the length L of the transmission line ａｎｔ When the length is 90 cm and the operating frequency f is 1 GHz, the length L of the unit cell 61 is set to satisfy the above conditions. ｕｎｉｔ This is set as follows: The period P in the periodic structure of the transmission line is 3.5 cm, and the capacitance component C Ｒ The capacitance is 8.32 pF, and the inductor component L is... Ｒ The volume component is 6.47 nH, and the volume component is C.Ｌ The capacitance is 4.5 pF, and the inductor component is L. Ｌ The various dimensional parameters of the unit cell 61 are set so that the effective refractive index n of the transmission line is 3.07 nH. ｅｆｆ This is set to 0.076. The absolute value of the effective refractive index set in this way is |n ｅｆｆ Since | is less than 1 and satisfies equation (1) above, the occurrence of null points due to the cancellation of radio waves within the transmission line as described above can be prevented.

[0050] In other words, the absolute value of the effective refractive index of the transmission line |n ｅｆｆ In addition to the condition that | is less than 1 and satisfies equation (1) above, the length L of the unit cell must also satisfy equations (2) and (3) above. ｕｎｉｔ The parameters of the unit cell 61, including the above, are set. This makes it possible to realize an antenna device 40 that operates in the leaky wave region while preventing missed readings of wireless tags not only far from the antenna but also near the antenna.

[0051] As described above, in this embodiment, the effective refractive index of a unit cell is determined according to the operating frequency, the width and thickness of the strip conductor, and the dielectric constant and height of the dielectric substrate, n ｕｎｉｔ , the wavelength of the radio wave in a unit cell is λ ｕｎｉｔ In this case, the length L of the unit cell in the predetermined direction is as follows: ｕｎｉｔ L is set such that it satisfies the following equations (2) and (3). ｕｎｉｔ <λ ｕｎｉｔ / 4...(2) λ ｕｎｉｔ = λ ０ / |n ｕｎｉｔ | ... (3)

[0052] Even within a single unit cell, the length L of the unit cell ｕｎｉｔ Depending on the circumstances, null points may occur. This is because the out-of-phase components of the radio waves generated within the unit cell cancel each other out. Null points generated within individual unit cells do not affect the reading of wireless tags far from the antenna, but they do affect the reading of wireless tags near the antenna. Therefore, in addition to the conditions mentioned above, the length L of the unit cell must satisfy equation (2) above.ｕｎｉｔ This is set. That is, the length L of the unit cell. ｕｎｉｔ This is the wavelength λ of the radio wave within a unit cell, which is obtained by the above equation (3). ｕｎｉｔ It is less than 1 / 4 of that. As a result, no out-of-phase component of the radio wave is generated within the unit cell, and thus the generation of null points caused by out-of-phase components within a single unit cell can also be prevented. That is, the length L of the unit cell is further reduced so that equations (2) and (3) above are also satisfied. ｕｎｉｔ The parameters of the unit cell, including the specified parameters, are set. This makes it possible to realize an antenna device that operates in the leaky wave region while preventing missed readings of wireless tags not only far from the antenna but also in the vicinity of the antenna.

[0053] <Third Embodiment> Next, an antenna device according to the third embodiment will be described with reference to the drawings. The third embodiment mainly differs from the first embodiment in that the edges of the strip conductors forming a predetermined gap are not linear. 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.

[0054] Consider the case of reading a wireless tag T located near an antenna. When the tag tip Tc of the wireless tag T is located near the gap 64 formed between the strip conductors 62, depending on the shape of the gap 64, there is a possibility that the wireless tag T may not be read. This is because, depending on the capacitive coupling state between the unit cells 61, the magnetic field strength in the gap 64 may be weaker than that of the current source on the strip conductor 62, causing the gap 64 to become a region where leakage wave radiation is weakened (i.e., a region where the magnetic field is weakened) from the perspective of the wireless tag T. The wider the gap 64, the weaker the leakage wave radiation becomes. For example, in the example shown in Figure 13, wireless tags T1 and T2 located on the strip conductor 62 may be read, but wireless tag T3 located near the gap 64 may not be read.

[0055] By shortening the width (i.e., length in the Y direction) of the linearly formed gap 64, the tag chip Tc of the wireless tag T becomes more likely to be positioned not only on the gap 64 but also on the strip conductor 62. Therefore, reading errors of the wireless tag can be suppressed. However, the above-mentioned condition (i.e., the absolute value of the effective refractive index of the transmission line |n) ｅｆｆ The various parameters of the unit cell 61 are set such that | is less than 1 and satisfies the above equation (1). Therefore, the width of the gap 64 may not be sufficiently short.

[0056] Therefore, in the antenna device 40 according to this embodiment, the above-mentioned conditions (i.e., the absolute value of the effective refractive index of the transmission line |n) ｅｆｆ Assuming that | is less than 1 and satisfies the above equation (1), the unit cell 71 adopted in place of the unit cell 61 is formed such that the edges of the strip conductor 72 forming the gap 74 are non-linear.

[0057] Specifically, as illustrated in Figure 14A, in the strip conductor 72, a portion of one edge is extended to form an extended portion 72a, and a portion of the other edge is extended to form an extended portion 72b. The extended portions 72a and 72b of two adjacent strip conductors 72 face each other in the X direction via a gap 74. Therefore, the gap 74 includes the portion on the extended end side of the extended portion 72a, the opposing portions of the extended portions 72a and 72b, and the portion on the extended end side of the extended portion 72b. That is, the gap 74 bends at right angles in two places. In Figure 14, the stub conductor is indicated by reference numeral 73.

[0058] By employing a microstrip line in which the unit cells 71 formed as described above are arranged, the tag chip Tc of the wireless tag T is more likely to be positioned on the strip conductor 72 even when it is positioned on the gap 74. As a result, the portion where leakage wave radiation is weakened from the perspective of the wireless tag T is reduced, and reading errors of the wireless tag T caused by predetermined gaps between strip conductors can be suppressed.

[0059] The unit cell 71 is formed such that the extended portions 72a and 72b of the strip conductor 72 face each other in the X direction via a gap 74. This ensures that the gap 74 is non-linear. However, the shape of the gap 74 is not limited to this. For example, the edges of the strip conductors may be formed in a curved shape, thereby creating a non-linear gap between the strip conductors. Even in this case, the tag chip Tc of the wireless tag T is more likely to be positioned on the strip conductor 72 even when it is positioned on the gap 74. Therefore, reading errors of the wireless tag T caused by a predetermined gap between the strip conductors can be suppressed.

[0060] As a modification of this embodiment, a capacitive component C is added between the strip conductors 72. Ｌ A chip capacitor 75 that functions as such may be mounted. Preferably, the chip capacitor 75 is mounted across the extended portion 72a and extended portion 72b in the X direction, as illustrated in Figure 14B. This is to suppress the cancellation of currents caused by current flowing in the reverse direction at the extended portion 72b.

[0061] Furthermore, in this embodiment and its modifications, the length of the unit cell may be set to further prevent the occurrence of null points within the unit cell. This makes it possible to realize an antenna device 40 that further achieves the effects described in the second embodiment.

[0062] As described above, in this embodiment, the edges of the strip conductors forming the predetermined gap may be non-linear.

[0063] Consider the case of reading a wireless tag located near an antenna. When the tag chip of the wireless tag is located near a predetermined gap formed between strip conductors, this location can become a region where leakage wave radiation from the wireless tag is weakened (i.e., a region where the magnetic field is weakened). This can lead to missed readings of the wireless tag. Therefore, in addition to the conditions mentioned above, the edges of the strip conductors forming the predetermined gap are formed to be non-linear. This makes it easier for the tag chip of the wireless tag to be located on the strip conductor even when it is located on the predetermined gap. As a result, the region where leakage wave radiation from the wireless tag is weakened is reduced, and thus missed readings of the wireless tag caused by the predetermined gap between the strip conductors can be suppressed.

[0064] <Fourth Embodiment> Next, an antenna device according to the fourth embodiment will be described with reference to the drawings. The fourth embodiment differs from the first embodiment in that the stub conductor is formed to be located at the boundary between unit cells. 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.

[0065] Depending on the storage conditions of items G with wireless tags T attached, the orientation of the wireless tag T may remain almost constant relative to the antenna device. In such cases, it is desirable to maximize the radiation efficiency of the antenna device by setting boundary conditions at both ends of the antenna according to the orientation of the wireless tag T. Specifically, by setting the boundary at both ends of the antenna to a short circuit condition, the series resonant current flowing through the strip conductor (i.e., the current flowing in the Y direction) increases. Therefore, the radiation efficiency for reading wireless tags T whose polarization direction is the direction of this current can be maximized. On the other hand, by setting the boundary at both ends of the antenna to an open circuit condition, the parallel resonant current flowing through the stub conductor (i.e., the current flowing in the X direction) increases. Therefore, the radiation efficiency for reading wireless tags T whose polarization direction is the direction of this current can be maximized.

[0066] Here, depending on the orientation of the wireless tag T to be read, the boundaries at both ends of the antenna are set to an open condition. If the wireless tag T is located at the boundary between the stub conductors 63 and the boundary between the unit cells 61 (i.e., the line in the X direction passing through the center of the gap 64), depending on the distance between the stub conductors 63, the position of the wireless tag T may become a null point, potentially resulting in the wireless tag T being missed from being read. For example, in the example shown in Figure 15, wireless tags T1 and T2 located on the stub conductors 63 are read even when the antenna is in close proximity. However, wireless tag T3 located between the stub conductors 63 may not be read.

[0067] Therefore, in the antenna device 40 according to this embodiment, the above-mentioned conditions (i.e., the absolute value of the effective refractive index of the transmission line |n) ｅｆｆ Assuming that | is less than 1 and satisfies the above equation (1), a unit cell 81 is adopted in place of the unit cell 61. In the unit cell 81, the stub conductor 83 is extended so as to be located at the boundary between the unit cells 81.

[0068] Specifically, as illustrated in Figure 16A, the stub conductor 83 extends from one end of the strip conductor 82 in the direction of arrangement (i.e., the Y direction) and the X direction (i.e., the diagonal direction). The extended end 83a is located at the boundary between the unit cells 81. In particular, since each stub conductor 83 has the same shape, a distance is ensured between the stub conductors 83, and adjacent stub conductors 83 do not connect. In Figure 16, a predetermined gap interposed between the strip conductors 82 is indicated by reference numeral 84.

[0069] As a result, as can be seen in Figure 16A, even if the wireless tag T3 is located at the boundary between stub conductors 83 and the boundary between unit cells 81, the wireless tag T3 is more likely to receive a magnetic field from at least one of the stub conductors 83. In other words, there is no interruption in the magnetic field relative to the wireless tag T, even if the wireless tag T is located between stub conductors 83. Therefore, reading errors of the wireless tag T caused by the distance between stub conductors can be suppressed.

[0070] In the first modification of this embodiment, the stub conductor 83 is not limited to being located at the boundary between unit cells 81 by extending diagonally from one end of the strip conductor 82. For example, as illustrated in Figure 16B, the stub conductor 85 may be formed to extend in an inverted L-shape from the center of the strip conductor 82, with the inverted L-shaped bend located at the boundary between unit cells 81.

[0071] As a second modification of this embodiment, the unit cell 81 may be formed such that the stub conductor 86 extends in a direction from one end to the other of the strip conductor 82, as illustrated in Figure 17A, and has a plurality of bent portions. As a third modification of this embodiment, the unit cell 81 may be formed such that the width of the stub conductor 87 is approximately the same as the width of the strip conductor 82, as illustrated in Figure 17B.

[0072] Furthermore, in this embodiment and its modifications, the length of the unit cell is set so as to prevent the occurrence of null points within the unit cell. This makes it possible to realize an antenna device 40 that further achieves the effects described in the second embodiment.

[0073] As described above, in this embodiment, the stub conductor may be extended to be located at the boundary between unit cells.

[0074] This prevents any interruptions in the magnetic field from the perspective of the wireless tag, even when the wireless tag is located between stub conductors. Therefore, it is possible to suppress missed readings of wireless tags caused by the distance between stub conductors.

[0075] <Fifth Embodiment> Next, an antenna device according to the fifth embodiment will be described with reference to the drawings. The fifth embodiment differs from the first embodiment in that the unit cells are formed so as to maximize the radiation efficiency of the antenna device according to the boundary conditions at both ends of the antenna that are set. 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.

[0076] Depending on the orientation of the wireless tag T to be read, the boundary between both ends of the antenna may be short-circuited. This is to increase the series resonant current flowing through the strip conductor 62. In this case, the length L of the unit cell shown in Figure 3. ｕｎｉｔ By making the length longer and shortening the length of the stub conductor 63 in the extension direction (i.e., the length in the X direction), the series resonance current becomes larger. As a result, the radiation efficiency can be maximized.

[0077] For example, the length L of a unit cell. ｕｎｉｔ The wavelength λ of the radio wave within the unit cell 61 ｕｎｉｔ By increasing it to a range of 1 / 4 or less, the radiation efficiency can be maximized while achieving the effects of each embodiment described above.

[0078] Furthermore, the series resonant current can be increased by, for example, further shortening the length of the stub conductor 63 in the extension direction while maintaining the required inductance value. As shown in Figure 3, the length of the stub conductor 63 in the extension direction is less than the length of the strip conductor 62 in the arrangement direction (i.e., the length in the Y direction). By narrowing the width of the stub conductor 63 (i.e., the length in the Y direction), the length of the stub conductor 63 in the extension direction can be further shortened while maintaining the inductance value. The length of the stub conductor 63 in the extension direction can also be further shortened while maintaining the inductance value by forming a meander-type stub conductor 63.

[0079] Depending on the orientation of the wireless tag T to be read, the boundary at both ends of the antenna can be set to an open condition. This is to increase the parallel resonant current flowing through the stub conductor 63. In this case, the length of the stub conductor 63 in the extension direction is increased, and the length L of the unit cell is also increased. ｕｎｉｔ By shortening the length, the current during parallel resonance becomes larger. As a result, the radiation efficiency can be maximized.

[0080] For example, the length of the stub conductor 63 in the extension direction is the wavelength λ of the radio wave within the unit cell 61. ｕｎｉｔ By increasing it to a range of 1 / 4 or less, the radiation efficiency can be maximized while achieving the effects of each embodiment described above.

[0081] Furthermore, the parallel resonant current can be increased by, for example, further shortening the length of the strip conductors 62 in the direction of arrangement while maintaining the required inductance value. The length of the strip conductors 62 in the direction of arrangement is less than the extended length of the stub conductor 63. The length of the strip conductors 62 in the direction of arrangement can also be further shortened while maintaining the inductance value by forming meander-type strip conductors 62. The effect of increasing the parallel inductance component can be reduced by forming slits in the strip conductors 62 to reduce the capacitive component of the right-handed system. This has the effect of shortening the length of the strip conductors 62 in the direction of arrangement while maintaining the inductance value, because the inductance value is larger in the thin wire portion of the strip conductors 62.

[0082] This disclosure is not limited to the embodiments described above, and may take the following forms, for example: (1) The antenna device 40 according to each embodiment of this disclosure is installed on the management shelf 10 and used in an item management system 1 in which items G that are moved in and out of the management shelf 10 are managed. However, the use of the antenna device 40 is not limited to this. For example, the antenna device 40 may be used as an antenna device for a reader in which an item with a wireless tag to be read is placed nearby.

Claims

1. An antenna device comprising a dielectric substrate and a transmission line in which a plurality of unit cells are arranged in a predetermined direction on one surface of the dielectric substrate, wherein reflectors are provided at both ends of the transmission line, each of the plurality of unit cells has a strip conductor extending in the predetermined direction and a stub conductor branching off from the strip conductor, and is arranged such that a predetermined gap is interposed between the strip conductor and the strip conductor of an adjacent unit cell, thereby comprising a series branch circuit that equivalently includes a capacitive component due to the predetermined gap and a parallel branch circuit that equivalently includes an inductive component due to the stub conductor, and the length of the transmission line in the predetermined direction is L ａｎｔ λ is the wavelength of radio waves in a vacuum. ０ In this case, the absolute value of the effective refractive index of the transmission line is |n ｅｆｆ An antenna device in which the parameters of each of the plurality of unit cells are set such that | is less than 1 and satisfies the following equation (1). |n ｅｆｆ | <λ ０ / (4L ａｎｔ ) ... (1) 2. The effective refractive index n of each of the plurality of unit cells determined according to the operating frequency, the width and thickness of the strip conductor, and the dielectric constant and height of the dielectric substrate ｕｎｉｔ , when the wavelength of the radio wave in each of the plurality of unit cells is λ ｕｎｉｔ , the length L in the predetermined direction of each of the plurality of unit cells ｕｎｉｔ is set so as to satisfy the following formulas (2) and (3). The antenna device according to claim 1. L ｕｎｉｔ <λ ｕｎｉｔ / 4 ・・・(2) λ ｕｎｉｔ =λ ０ / |n ｕｎｉｔ | ・・・(3) 3. The antenna device according to claim 1, wherein the edges of the strip conductor that form the predetermined gap are non-linear.

4. The antenna device according to claim 1, wherein the stub conductor is extended to be located at the boundary between the plurality of unit cells.

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