Antenna equipment

Abstract

The present invention provides an antenna device that operates in the leakage wave region without forward-propagating and backward-propagating radio waves canceling each other out, even when the size is adjusted to match the tag monitoring range. [Solution] Reflectors 53 and 72 are provided at both ends of the microstrip line 60, and the unit cell 61 has a strip conductor 62 and a stub conductor 63, and is arranged so that a predetermined gap 64 is interposed between the strip conductors 62, thereby reducing the capacitance component C caused by the gap 64, etc. L The series branch circuit 61a, which equivalently includes the inductor component L caused by the stub conductor 63, etc. L The system is configured to include a parallel branch circuit 61b that equivalently includes the above, and the length of the transmission line along the predetermined direction is L ant When the wavelength of a radio wave in a vacuum is λ0, 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 equation (1).

Description

[Technical Field]

[0001] This invention relates to an antenna device. [Background technology]

[0002] Traditionally, systems have been in place to manage inventory status in managed shelves by having workers sequentially read barcodes or other information codes displayed on the items, shelves, and work instructions using portable readers when items are placed in or removed from the shelves. However, systems that rely on workers reading information codes for each item have problems such as decreased inventory management accuracy due to human error and high management costs due to the cumbersome reading 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 tags that can be read by 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. This leaky wave antenna device is configured by cascading a pair of unit cells, each having a series branch circuit, a parallel branch circuit, and a transmission line portion, between a pair of ports, and arranging a pair of CRLH transmission lines in close proximity to each other so as to be substantially parallel and electromagnetically coupled to each other. This leaky wave antenna device operates by making the effective refractive index of the transmission line smaller than the refractive index in free space, which is 1, so that 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, and 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 in order to prevent reading errors by improving the radiation efficiency of the leaky waves radiated to the outside as described above. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2024-142998 [Overview of the project] [Problems that the invention aims to solve]

[0005] Incidentally, when installing an antenna device at the entrance / exit of a storage rack through which managed items pass when being moved in and out, it is necessary to match the reading range of the antenna device to the area through which the tags attached to the items being moved in and out (hereinafter also referred to as the tag monitoring range) in order to prevent any missed readings of the tags. As mentioned above, even when installing an antenna device that operates in the leaked wave region, it is necessary to match the length dimension of the antenna device in the direction along the transmission line (main polarization direction of the radiated electric field) to the tag monitoring range, for example, the width dimension of the entrance / exit of the storage rack.

[0006] However, depending on the size of the tag monitoring range to be matched, the length of the antenna device's transmission line may become such that the forward-propagating radio waves and the backward-propagating radio waves reflected by the reflector cancel each other out, potentially creating areas (null spots) within the management rack where wireless tags are difficult to read.

[0007] The present invention was made to solve the above-mentioned problems, and its objective is to provide an antenna device that operates in the leak wave region without forward-propagating and backward-propagating radio waves canceling each other out, even when the size is adjusted to match the tag monitoring range. [Means for solving the problem]

[0008] To achieve the above objective, the present invention Dielectric substrate (50), A transmission line (60) is formed by arranging multiple unit cells (61, 71, 81) along a predetermined direction with respect to one surface (51) of the dielectric substrate, An antenna device (40) comprising, Reflectors (53, 54) are provided at both ends of the aforementioned transmission line. The unit cell has strip conductors (62, 72, 82) extending along the predetermined direction and stub conductors (63, 73, 83, 85, 86, 87) branching off from the strip conductors, and is arranged such that a predetermined gap (64, 74, 84) is interposed between the strip conductors, thereby comprising a series branch circuit (61a) that equivalently includes a capacitive component due to the predetermined gap and a parallel branch circuit (61b) that equivalently includes an inductive component due to the stub conductors. The length of the transmission line along the predetermined direction is L. ant When the wavelength of a radio wave in a vacuum is λ0, the absolute value of the effective refractive index of the transmission line is |n eff The parameters of the unit cell are set such that | is less than 1 and satisfies the following equation (1). |n eff |<λ0 / (4L ant ) ···(1) The symbols within the parentheses above indicate the correspondence with the specific means described in the embodiments described later. [Effects of the Invention]

[0009] In this invention, a transmission line is formed by arranging a plurality of unit cells along a predetermined direction on one surface of a dielectric substrate, and reflectors are provided at both ends of the transmission line. Each unit cell has a strip conductor extending along 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 conductors. This configuration includes 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 along the predetermined direction is L ant When the wavelength of a radio wave in a vacuum is λ0, the absolute value of the effective refractive index of the transmission line is |n eff The parameters of the unit cell are set such that | is less than 1 and satisfies the above equation (1).

[0010] For example, the length L of the transmission line ant The wavelength λ of the radio waves in the transmission line antUnder the conditions that match, L in the transmission line ant / 4 and 3L ant When the forward-propagating wave and the backward-propagating wave reinforce each other at the positions of / 4 and 3L / 4 in the transmission line, at the position of 2L / 4 in the transmission line ant A null point occurs where the forward-propagating wave and the backward-propagating wave cancel each other out. In contrast, when the length L ant of the transmission line is less than the wavelength λ ant / 4 of the radio wave in the transmission line, the forward-propagating wave and the backward-propagating wave do not have opposite phases, so in the transmission line, the forward-propagating wave and the backward-propagating wave do not cancel each other out and no null point occurs. Therefore, since the wavelength λ ant of the radio wave in the transmission line is equal to λ0 (wavelength of the radio wave in vacuum) / n eff (effective refractive index of the transmission line), when the effective refractive index n eff of the transmission line satisfies the above formula (1), the above-described cancellation of the radio waves does not occur. That is, even when the length L ant of the transmission line is sized to match the tag monitoring range such as the width dimension of the entrance and exit of the management shelf, by controlling the effective refractive index n eff of the transmission line so as to satisfy the above formula (1), the generation of null points due to the above-described cancellation of radio waves can be eliminated. Furthermore, by controlling the absolute value |n eff | of the effective refractive index of the transmission line to be less than 1, it is possible to operate in the leaky wave region as described above. Since the effective refractive index n eff of the transmission line can be controlled by the dimensional parameters of the unit cell, etc., by setting the dimensional parameters of the unit cell so that the effective refractive index n eff of the transmission line satisfies the above conditions, it is possible to realize an antenna device that operates in the leaky wave region without the forward-propagating wave and the backward-propagating wave canceling each other out even when sized to match the tag monitoring range.

[0011] The length L of the unit cell along the predetermined direction unit is determined according to the operating frequency, the width and thickness of the strip conductor, the dielectric constant and height of the dielectric substrate, and the effective refractive index n unit of the unit cell, and the wavelength λ of the radio wave in the unit cellunit In this case, the settings may be configured to satisfy the following equations (2) and (3). L unit <λ unit / 4 ···(2) λ unit =λ0 / |n unit | ···(3)

[0012] Even within a single unit cell, the length L of the unit cell unit Depending on the circumstances, null points may occur due to the cancellation of radio waves by the opposite-phase component of the radio waves generated within a unit cell. These null points within individual unit cells do not affect readings far from the antenna, but they do affect readings near the antenna. Therefore, in addition to the conditions mentioned above, the length L of the unit cell must also be considered. unit However, the wavelength λ of the radio wave within the unit cell, which is obtained by equation (3) above, satisfies equation (2) above. unit By making it less than 1 / 4 of the above, the opposite phase component of the radio wave does not occur within the unit cell, and thus the occurrence of null points caused by the opposite phase component within a single unit cell can be eliminated. That is, the length L of the unit cell is further reduced to satisfy equations (2) and (3) above. unit By setting the parameters of the unit cell, including the antenna, it is possible to realize an antenna device that operates in the leakage wave region so as to eliminate reading errors not only at the distance from the antenna but also near the antenna.

[0013] The strip conductor may be formed such that the edges forming a predetermined gap are non-linear.

[0014] When reading near an antenna, if the tag chip of a wireless tag is located directly above a predetermined gap formed between strip conductors, this location becomes an area where leakage wave radiation is weakened (an area where the magnetic field is weakened) from the perspective of the wireless tag, potentially leading to missed readings of that wireless tag. Therefore, in addition to the conditions mentioned above, by forming the edges of the strip conductors forming the predetermined gap in a non-linear shape, the tag chip of the wireless tag becomes more likely to be positioned not only on the predetermined gap but also on the strip conductors. This reduces the area where leakage wave radiation is weakened from the perspective of the wireless tag, thereby suppressing missed readings of wireless tags caused by the predetermined gap between strip conductors.

[0015] The stub conductor may be formed by extending it to cover the boundary between unit cells.

[0016] This eliminates any gaps in the magnetic field between stub conductors from the perspective of the wireless tag, thereby suppressing missed readings of wireless tags caused by the distance between stub conductors. [Brief explanation of the drawing]

[0017] [Figure 1] This is an explanatory diagram illustrating an item management system employing the antenna device according to the first embodiment. [Figure 2] Figure 1 is a perspective view of the storage shelves from the entrance side. [Figure 3] This is a schematic plan view of the antenna device in the first embodiment. [Figure 4] This is an explanatory diagram illustrating the schematic configuration of a unit cell in the first embodiment. [Figure 5] This is a circuit diagram showing the equivalent circuit model of a unit cell in the first embodiment. [Figure 6] This block diagram shows the schematic configuration of the wireless tag reader shown in Figure 1. [Figure 7]Figure 7(A) is an explanatory diagram illustrating the storage state in which items are placed into a storage rack, and Figure 7(B) is an explanatory diagram illustrating the storage state in which items are placed further into the storage state from the state in Figure 7(A). [Figure 8] This is an explanatory diagram illustrating the relationship between the current distribution in a transmission line and the wavelength. [Figure 9] This diagram illustrates the relationship between radio wave intensity and position within the transmission line. Figure 9(A) shows the case where the transmission line length is 90 cm, the operating frequency f is 1 GHz, and the effective refractive index of the transmission line is 1. Figure 9(B) shows the case where the phase of the input power is changed in the same way as in Figure 9(A). Figure 9(C) shows the case where the transmission line length is 90 cm, the operating frequency f is 1 GHz, and the effective refractive index of the transmission line is 0.8. [Figure 10] These are explanatory diagrams showing the relationship between radio wave intensity and position within the transmission line. Figure 10(A) shows the case where the transmission line length is 90 cm, the operating frequency f is 1 GHz, and the effective refractive index of the transmission line is 0.166. Figure 10(B) shows the case where the transmission line length is 90 cm, the operating frequency f is 1 GHz, and the effective refractive index of the transmission line is 0.0833. Figure 10(C) shows the case where the transmission line length is 90 cm, the operating frequency f is 1 GHz, and the effective refractive index of the transmission line is 0.04. [Figure 11] These are explanatory diagrams showing the relationship between radio wave intensity and position within the transmission line. Figure 11(A) shows the case where the transmission line length is 200 cm, the operating frequency f is 1 GHz, and the effective refractive index of the transmission line is 0.04. Figure 11(B) shows the case where the transmission line length is 200 cm, the operating frequency f is 1 GHz, and the effective refractive index of the transmission line is 0.018. [Figure 12] This is an explanatory diagram illustrating the relationship between radio wave intensity within a unit cell and the length of that unit cell. [Figure 13] This diagram illustrates the positional relationship between wireless tags that are less prone to reading errors and those that are prone to reading errors, based on a linear gap. [Figure 14] Figure 14(A) is an explanatory diagram illustrating the unit cell used in the antenna device of the third embodiment, and Figure 14(B) is an explanatory diagram illustrating the unit cell used in the antenna device of a modified example of the third embodiment. [Figure 15] This is an explanatory diagram illustrating the positional relationship between wireless tags that are less prone to reading errors and wireless tags that are prone to reading errors, based on the stub conductor. [Figure 16] Figure 16(A) is an explanatory diagram illustrating the unit cell used in the antenna device of the fourth embodiment, and Figure 16(B) is an explanatory diagram illustrating the unit cell used in the antenna device of the first modified example of the fourth embodiment. [Figure 17] Figure 17(A) is an explanatory diagram illustrating the unit cell used in the antenna device in the second modified example of the fourth embodiment, and Figure 17(B) is an explanatory diagram illustrating the unit cell used in the antenna device in the third modified example of the fourth embodiment. [Modes for carrying out the invention]

[0018] [First Embodiment] Hereinafter, a first embodiment of the antenna device according to the present invention 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. It is 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. As shown in Figures 1 and 2, the item management system 1 is configured to include an antenna device 40 installed on the management shelf 10 and a management device 20 that manages the movement of items G through the entrance / exit 11 of the management shelf 10.

[0019] The item G to be managed is, for example, a packaging box in which predetermined parts are contained and packaged, and a wireless tag T, such as an RF tag with a unique tag ID recorded in a way that can be read via contactless communication, is attached to its side or elsewhere. In this embodiment, the tag ID functions as information that can identify the item G, and is registered in a server or the like to be associated with the item G itself to which the wireless tag T with the recorded tag ID is attached, as well as the type and number of parts contained in the item G. Therefore, by querying the server or the like with the tag ID read from the wireless tag T, the item G to which the wireless tag T with that tag ID is attached can be identified. Note that the item G is not limited to being a packaging box or the like as described above, but may also be the product itself, and the wireless tag T may be attached to the product itself.

[0020] 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 metal material, glass material, wooden material, etc. Note that in Figure 1 and Figure 7 described later, the side wall 15 is omitted from the illustration for convenience.

[0021] As shown in Figures 3 and 4, the antenna device 40 in this embodiment is configured to include a dielectric substrate 50 and a microstrip line 60 as a transmission line formed by arranging a plurality of unit cells 61 along a predetermined direction (y-direction in Figure 3) with respect to one surface of the dielectric substrate 50 which serves as the radio wave radiating surface 51. A reflector 53 connected to a power supply port is provided at one end of the microstrip line 60 which is the power supply side, and a reflector 54 is provided at the other end of the microstrip line 60.

[0022] In this embodiment, the microstrip line 60 is configured as a right-handed / left-handed composite transmission line (CRLH line) that operates in the leakage wave region, with the above-mentioned arrangement direction (y direction in Figure 3) being the main polarization direction of the radiated electric field.

[0023] Each unit cell 61 constituting the microstrip line 60 has a strip conductor 62 extending along the alignment direction (y-direction in Figure 3) and a stub conductor 63 branching off from the strip conductor 62, with a predetermined gap (hereinafter also referred to as gap 64) which is a non-conductive portion interposed between the strip conductors 62. That is, as shown in Figure 4, the unit cell 61 is constructed such that the strip conductor 62 and the stub conductor 63 are sandwiched between one half of the gap 64 (hereinafter also referred to as one-side gap 64a) and the other half of the gap 64 (hereinafter also referred to as other-side gap 64b). Each stub conductor 63 is connected to the ground conductor 52 of the dielectric substrate 50 via a via conductor 65.

[0024] With this arrangement, each unit cell 61 of the antenna device 40 has an inductor component L, as shown in Figure 5. R In addition, the volume component C caused by gap 64, etc. L Circuit 61a of the series branch that also equivalently includes the capacitive component C R In addition, the inductor component L is caused by the stub conductor 63, etc. L The system is configured to include a parallel branch circuit 61b that also equivalently includes the above.

[0025] 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 configured to be smaller than the refractive index in free space, which is "1". The radiation direction of leakage waves radiated to the outside of the transmission line is the effective refractive index n eff It varies according to the effective refractive index n eff The closer this value approaches "0", the closer the direction of leakage wave radiation approaches the direction perpendicular to the radio wave emission surface 51 (the z-direction in Figure 3: perpendicular to the direction of the main polarization of the radiated electric field).

[0026] 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 these factors. L It changes depending on the effective dielectric, etc., which is affected by the following. Therefore, in this embodiment, the effective refractive index n of the transmission line changes according to the setting of various dimensional parameters in the strip conductor 62, stub conductor 63, and gap 64, etc., that constitute the unit cell 61. eff This is controlled as described below.

[0027] The antenna device 40, configured as described above, 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 constitutes the area below the entrance / exit 11 that is within the tag monitoring range. The length of the antenna device 40, more specifically the length of the transmission line L, is adjusted to match the reading range of the tag monitoring range. ant (See Figure 3) The size is set to be slightly smaller than the width of the entrance 11.

[0028] With this configuration, the antenna device 40 operates using predetermined power supplied from the wireless tag reader 30, setting the entrance / exit 11 of the storage shelf 10 as the tag monitoring area and adjusting its reading range to match that area. The antenna device 40 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 incoming items G, or on the inner surfaces of the side walls 14, 15, or the back wall 16.

[0029] The management device 20 is configured to include a wireless tag reader 30 and a management terminal 21. The wireless tag reader 30 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 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 mainly composed of a microcontroller and has a CPU, system bus, input / output interface, etc., and together with the storage unit 32 which consists of semiconductor memory etc., it constitutes an information processing device.

[0030] As shown in Figure 6, the communication processing unit 33 includes a transmitting circuit 33a, a receiving circuit 33b, and the like. The transmitting circuit 33a 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 31. The encoding unit encodes the transmission data output from the control unit 31 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 34 as the transmission signal.

[0031] The input terminal of the receiving circuit 33b is connected to the antenna 34, and the radio signal (received signal) corresponding to the response wave from the wireless tag T received by the antenna 34 is input to the receiving circuit 33b. The receiving circuit 33b is composed of, for example, an amplifier and a demodulator, and the received signal received by the antenna 34 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 31 as received data.

[0032] The external interface 35 is configured as an interface for data communication with external devices such as the management terminal 21, and is configured to perform communication processing in cooperation with the control unit 31.

[0033] The management terminal 21 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 40 from the wireless tag T passing through the entrance and exit 11 by the wireless tag reader 30.

[0034] In the item management system 1 configured in this way, as illustrated in Figure 7(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 40. 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 40 by the wireless tag reader 30 during the inventory management process performed at the management terminal 21. Furthermore, as illustrated in Figure 7(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.

[0035] In the inventory management process, when a tag ID without an inventory flag (indicating an inventory status) is read, an 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 21, along with the inventory time, etc. Also, in the inventory management process, when a tag ID with an inventory flag 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.

[0036] 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 controlling this are explained below. The length L of the transmission line is adjusted to match the reading range of the antenna device 40 to the entrance / exit 11 which is the tag monitoring range. ant If you adjust it to the size of the entrance / exit 11, the length of the transmission line L depends on the size of the tag monitoring range that needs to be adjusted. ant Because the length of the region where the forward-propagating radio waves and the backward-propagating radio waves reflected by the reflector cancel each other out, there is a possibility that areas (null points) will occur within the management shelf 10 where the wireless tag T is difficult to read.

[0037] As can be seen from the relationship between the current distribution and wavelength of the transmission line illustrated in 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, L in the transmission line ant / 4 and 3L ant When forward-propagating and reverse-propagating radio waves reinforce each other at the position of / 4, resulting in maximum amplitude, 2L in the transmission line ant At position / 4, forward-propagating and reverse-propagating radio waves cancel each other out, creating a null point.

[0038] In contrast, the length L of the transmission lineant The wavelength λ of the radio wave in the transmission line ant By setting the value 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 Since it is necessary to match the size of the entrance / exit 11, in order to avoid creating null points, the wavelength λ of the radio waves in the transmission line ant It needs to be controlled.

[0039] Wavelength λ of radio waves in a transmission line ant This is the relationship between the wavelength λ0 of a radio wave in a vacuum and the effective refractive index n of the transmission line. eff Based on the following equation (4), the wavelength λ0 of a radio wave in a vacuum can be determined using the speed of light c and the frequency f of the radio wave, based on the following equation (5). λ ant =λ0| / n eff | ···(4) λ0 = c / f ···(5)

[0040] 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 Since it can be controlled by the transmission line length L ant The wavelength λ of the radio wave in the transmission line ant To keep it less than / 4, the absolute value of the effective refractive index of the transmission line |n eff If | is controlled to satisfy equation (1) below, the aforementioned cancellation of radio waves will not occur. |n eff |<λ0 / (4L ant ) ···(1)

[0041] That is, the length L of the transmission line ant Even when the size is adjusted to match the tag monitoring range, such as the width dimension of the entrance / exit 11 of the management shelf 10, the effective refractive index n of the transmission line must satisfy the above formula (1). eff By controlling this, the generation of null points due to the cancellation of radio waves as described above can be eliminated.

[0042] For example, to match the size of the entrance / exit 11, the length of the transmission line L ant When 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 9(A), multiple locations where the aforementioned radio wave cancellation occurs (locations where null points occur) appear on the transmission line. Even when the phase of the input power is changed, as can be seen from Figure 9(B), there is no change in the locations where null points occur. On the other hand, for example, the length L of the transmission line ant When the length is 90 cm and the operating frequency f = 1 GHz, the effective refractive index n of the transmission line is... eff When the value is 0.8, as can be seen from Figure 9(C), not only do multiple null points appear on the transmission line, but the maximum amplitude also decreases.

[0043] In contrast, the length L of the transmission line ant =90cm, operating frequency f=1GHz, effective refractive index n of the transmission line eff =0.166(λ ant / 2=L ant In the case of ), as can be seen from Figure 10(A), a single null point occurs in the center of the transmission line, and 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 =90cm, operating frequency f=1GHz, effective refractive index n of the transmission line eff =0.0833(λ ant / 4=L ant In this case, as can be seen from Figure 10(B), a null point occurs at the power supply end of the transmission line, and even if the phase of the input power is changed, the position where this null point occurs does not change.

[0044] Therefore, the length L of the transmission line ant When the length is 90 cm and the operating frequency f = 1 GHz, the effective refractive index n of the transmission line should satisfy the above equation (1). eff 0.0833(λ ant / 4=L antBy setting it to a value smaller than , for example, 0.04, as can be seen from Fig. 10(C), the generation of null points due to the cancellation of radio waves described above can be eliminated. And even when the phase of the input power is changed, no null points occur, and the amplitude is almost uniform at each phase.

[0045] Also, for example, in order to match the size of the entrance / exit 11, the length L of the transmission line ant is 200 cm, and when the operating frequency f of the radio wave used is 1 GHz, the effective refractive index n of the transmission line eff is 0.04, the above formula (1) is not satisfied. As can be seen from Fig. 11(A), one null point occurs on the transmission line. In contrast, when the length L of the transmission line ant = 200 cm and the operating frequency f = 1 GHz, by setting the effective refractive index n of the transmission line eff to 0.018, as can be seen from Fig. 11(B), the generation of null points due to the cancellation of radio waves described above can be eliminated.

[0046] Thus, by controlling the effective refractive index n of the transmission line so as to satisfy the above formula (1), the generation of null points due to the cancellation of radio waves described above can be eliminated. Furthermore, by controlling the effective refractive index |n eff | of the transmission line to be less than 1, it can be made to operate in the leaky wave region as described above.

[0047] The effective refractive index n of the transmission line eff can be controlled according to the setting of various dimensional parameters in the strip conductor 62, stub conductor 63, gap 64, etc. that make up 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 x-direction length and y-direction length (line width w) and thickness (electrode thickness t) of the strip conductor 62, the shape dimensions of the stub conductor 63 including the x-direction length and y-direction length and thickness (electrode thickness t) of the stub conductor 63, the width and length of the gap 64, etc. can be adopted.

[0048] ​​For example, the length L of the transmission line ant When = 90 cm and the operating frequency f = 1 GHz, the period p in the periodic structure of the transmission line (see Fig. 5) is 3 cm, and the capacitance component C R is 6.62 pF, and 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. By setting various dimensional parameters of the unit cell 61, the effective refractive index n of the transmission line eff is controlled to be 0.075. The absolute value |n eff | of the thus controlled effective refractive index is less than 1 and satisfies the above formula (1), so that the generation of null points due to the cancellation of radio waves can be eliminated.

[0049] As described above, the antenna device 40 according to this embodiment has reflectors 53 and 54 provided at both ends of a microstrip line 60 formed by arranging a plurality of unit cells 61 along a predetermined direction (the y direction in Fig. 3) on one surface of a dielectric substrate 50. The unit cell 61 has a strip conductor 62 extending along the predetermined direction and a stub conductor 63 branched from the strip conductor 62. By arranging the unit cell such that a predetermined gap 64 is interposed between the strip conductors 62, a series-branch circuit 61a that equivalently includes a capacitance component C L caused by the gap 64, etc., and an inductor component L L caused by the stub conductor 63, etc., are provided. When the length of the transmission line along the predetermined direction is L ant and the wavelength of the radio wave in vacuum is λ0, the absolute value |n eff | of the effective refractive index of the transmission line is less than 1 and satisfies the above formula (1), and various parameters of the unit cell 61 are set.

[0050] Under the above conditions, the effective refractive index n of the transmission line effBy setting the dimensional parameters of the unit cell 61 to satisfy this condition, even when the antenna device 40 is sized to match the tag monitoring range, 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.

[0051] [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 length of the unit cell is set so as to eliminate 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.

[0052] Even within a single unit cell 61, the length L of the unit cell 61 along the predetermined direction (y-direction in Figure 3) unit Depending on the period p (corresponding to the periodic structure of the transmission line), null points may occur due to the cancellation of radio waves by the opposite-phase component of the radio waves generated within the unit cell 61. Null points generated within individual unit cells 61 do not affect readings far from the antenna, but they do affect readings near the antenna. Therefore, if readings near the antenna are also important, it is necessary to prevent null points from occurring within each unit cell 61.

[0053] Therefore, in this embodiment, the above-mentioned condition (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 the above equation (1), the effective refractive index of the unit cell 61 is determined according to the operating frequency f, the width (line width w) and thickness (electrode thickness t) of the strip conductor 62, and the dielectric constant and height (substrate thickness h) of the dielectric substrate 50, n unit The length L of the unit cell 61 is... unit However, the wavelength λ of the radio wave within the unit cell 61, which is obtained by equation (3) below, satisfies equation (2) below. unitThis is set to less than 1 / 4 of the original value. As a result, no out-of-phase component of radio waves is generated within the unit cell 61, and thus the generation of null points due to the cancellation of radio waves within a single unit cell 61 as described above can be eliminated. L unit <λ unit / 4 ···(2) λ unit =λ0 / |n unit | ···(3)

[0054] For example, given that the line width w = 10.2 mm, substrate thickness h = 2.4 mm, electrode thickness t = 0.01 mm, relative permittivity εr = 4.9, and operating frequency f = 1 GHz, the effective refractive index n within the unit cell 61 is... unit When this becomes 2, the wavelength λ of the radio wave within the unit cell 61 can be obtained from equation (3) above. unit = 15 cm. The radio wave intensity within the unit cell 61 and the length L of the unit cell 61 are illustrated in Figure 12. unit As can be seen from the relationship, the length L of the unit cell 61 unit λ unit When the length of the unit cell 61 exceeds 3.75 cm (which is 4 or more), a null point occurs because an out-of-phase component of the radio wave is generated within the unit cell 61. In this case, the length of the unit cell 61 L 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, thus eliminating the occurrence of null points.

[0055] Furthermore, the length L of the transmission line ant Assuming a length of 90cm and an operating frequency of f=1GHz, the length of the unit cell 61 L is determined to satisfy the above conditions. unit That is, the period p in the periodic structure of the transmission line is 3.5 cm, and the capacitance component C R The capacitance is 8.32pF, and the inductor component is L. R 6.47 nH, volume component C L The capacitance is 4.5pF, and the inductor component is L. L By setting the various dimensional parameters of the unit cell 61 to 3.07 nH, the effective refractive index n of the transmission line can be set. eff It is controlled so that it becomes 0.076. The absolute value of the effective refractive index |n| controlled in this way. effSince | 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 eliminated.

[0056] 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 also satisfies equations (2) and (3) above. unit By setting the parameters of the unit cell 61, including the above, it is possible to realize an antenna device 40 that operates in the leakage wave region so as to eliminate reading omissions not only at the distance from the antenna but also near the antenna.

[0057] [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 first embodiment and the like is that the edges of the strip conductors forming a predetermined gap are formed to be non-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.

[0058] When reading near an antenna, if the tag chip Tc of a wireless tag T is located near the gap 64 formed between strip conductors 62, depending on the shape of the gap 64, there is a possibility that the wireless tag T may not be read. Depending on the capacitive coupling state between 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, and the gap 64 may become a region where leakage wave radiation is weakened (a region where the magnetic field is weakened) from the perspective of the wireless tag T. The wider the gap 64, the more pronounced the weakening of leakage wave radiation becomes. For example, in the example shown in Figure 13, even if wireless tags T1 and T2 located on the strip conductor 62 can be read, there is a possibility that wireless tag T3, located near the gap 64, may not be read.

[0059] By shortening the width (length in the y-direction) of the linearly formed gap 64, the tag chip Tc of the wireless tag T can be more easily positioned not only on the gap 64 but also on the strip conductor 62, thereby suppressing missed readings of the wireless tag. However, the above condition (absolute value of the effective refractive index of the transmission line|n eff Since the various parameters of the unit cell 61 are set such that | is less than 1 and satisfies the conditions of equation (1) above, etc., the width of the gap 64 may not be sufficiently shortened.

[0060] Therefore, in the antenna device 40 according to this embodiment, the above-mentioned condition (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), etc., 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.

[0061] Specifically, as illustrated in Figure 14(A), the strip conductor 72 is formed such that an extension portion 72a extending from a part of one edge and an extension portion 72b extending from a part of the other edge of the adjacent strip conductor 72 face each other in the x-direction via a gap 74. Therefore, the gap 74 is formed to bend at right angles in two places, due to the range on the extension end side of extension portion 72a, the range where extension portions 72a and 72b face each other, and the range on the extension end side of extension portion 72b. In Figure 14, the stub conductor is indicated by reference numeral 73.

[0062] By employing a microstrip line with the unit cells 71 arranged as described above, the tag chip Tc of the wireless tag T can be more easily positioned not only on the gap 74 but also on the strip conductor 72. This reduces the portion where leakage wave radiation is weakened from the perspective of the wireless tag T, thereby suppressing reading errors of the wireless tag T caused by predetermined gaps between the strip conductors.

[0063] In the unit cell 71, the extensions 72a and 72b of the strip conductor 72 are formed to face each other in the x-direction via a gap 74, so that the gap 74 is non-linear. However, the unit cell 71 is not limited to this, and for example, the edges of the strip conductors may be formed in a curved shape so that the gap between the strip conductors is non-linear. Even in this way, the tag chip Tc of the wireless tag T is more likely to be caught not only on the gap 74 but also on the strip conductor 72, so that reading errors of the wireless tag T caused by a predetermined gap between the strip conductors can be suppressed.

[0064] 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 installed. In order to suppress the cancellation of current due to the current flowing in the reverse direction at the extension portion 72b, it is desirable to install the chip capacitor 75 so that it extends from the extension portion 72a to the extension portion 72b in the x direction, as illustrated in Figure 14(B).

[0065] Furthermore, in this embodiment and its modifications, by setting the length of the unit cell to eliminate the occurrence of null points within the unit cell, an antenna device 40 that achieves the effects described in the second embodiment can be realized.

[0066] [Fourth Embodiment] Next, the antenna device according to this fourth embodiment will be described with reference to the drawings. In this fourth embodiment, the main difference from the first embodiment and others is that the stub conductor is formed to extend over the boundary portion 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.

[0067] Depending on the warehousing status of items G with wireless tags T attached, the orientation of the wireless tags T may be nearly constant relative to the antenna device. In such cases, it is desirable to maximize the radiation efficiency of the antenna device by setting the boundary conditions at both ends of the antenna to match the orientation of the wireless tags T. Specifically, by setting the boundary conditions at both ends of the antenna to a short circuit, the series resonant current (current flowing in the y direction) flowing through each strip conductor increases, and the radiation efficiency can be maximized for reading wireless tags T whose polarization direction is aligned with the direction of this current. On the other hand, by setting the boundary conditions at both ends of the antenna to an open circuit, the parallel resonant current (current flowing in the x direction) flowing through each stub conductor increases, and the radiation efficiency can be maximized for reading wireless tags T whose polarization direction is aligned with the direction of this current.

[0068] Here, if the boundary at both ends of the antenna is set to open depending on the orientation of the wireless tag T to be read, and the wireless tag T is located in the boundary portion between each stub conductor 63 that is between unit cells 61 (the portion of the line in the x direction passing through the center of the gap 64), then depending on the distance between the stub conductors 63, the position of the wireless tag T may become a null point, and there is a possibility that the wireless tag T will not be read. For example, in the example shown in Figure 15, wireless tags T1 and T2, which are positioned so as to overlap the stub conductor 63, can be read even when the antenna is close, but there is a possibility that the wireless tag T3, which is located between the stub conductors 63, will not be read.

[0069] Therefore, in the antenna device 40 according to this embodiment, the above-mentioned condition (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), etc., a unit cell 81 is adopted in place of the unit cell 61. The unit cell 81 is formed by extending the stub conductor 83 so that it covers the boundary portion between the unit cells 81.

[0070] Specifically, as illustrated in Figure 16(A), the stub conductor 83 extends diagonally from one end of the strip conductor 82 in the direction of arrangement (y-direction), and its extended end 83a is formed to overlap the boundary portion between the unit cells 81. In particular, each stub conductor 83 is formed to have the same shape, ensuring distance between them and preventing them from joining together. In Figure 16, a predetermined gap interposed between the strip conductors 82 is indicated by reference numeral 84.

[0071] As a result, as can be seen in Figure 16(A), even if the wireless tag T3 is located at the boundary between each stub conductor 83 that is also 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, since the parts where the magnetic field is interrupted from the perspective of the wireless tag T can be eliminated even between the stub conductors 83, reading errors of the wireless tag T caused by the distance between stub conductors can be suppressed.

[0072] As a first modification of this embodiment, the unit cell 81 is not limited to being formed such that the stub conductor 83 extends diagonally from one end of the strip conductor 82 and overlaps the boundary portion between the unit cells 81. For example, as illustrated in Figure 16(B), the stub conductor 85 may be formed such that the bent portion extending in an inverted L shape from the center of the strip conductor 82 overlaps the boundary portion between the unit cells 81.

[0073] As a second modification of this embodiment, the unit cell 81 may be formed such that the stub conductor 86 extends from one end to the other of the strip conductor 82 with a plurality of bent portions, as illustrated in Figure 17(A). As a third modification of this embodiment, the unit cell 81 may be formed such that the stub conductor 87 is approximately the same width as the strip conductor 82, as illustrated in Figure 17(B).

[0074] Furthermore, in this embodiment and its modified form, by setting the length of the unit cell to eliminate the occurrence of null points within the unit cell, an antenna device 40 that achieves the effects described in the second embodiment can be realized.

[0075] [Fifth Embodiment] Next, the antenna device according to this fifth embodiment will be described with reference to the drawings. In this fifth embodiment, the main difference from the first embodiment and others is that each unit cell is formed in such a way as to maximize the radiation efficiency of the antenna device in accordance with 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] When the boundary between the ends of the antenna is short-circuited in order to increase the series resonant current flowing through each strip conductor 62 according to the orientation of the wireless tag T to be read, the length L of the unit cell is... unit By making the length longer and shortening the extension length (length in the x-direction) of the stub conductor 63, the series resonance current becomes larger, thereby maximizing the radiation efficiency.

[0077] Therefore, 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 the value to a degree not exceeding 1 / 4 of the above embodiment, 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 extension length of the stub conductor 63, which is less than the length in the arrangement direction (y-direction length) of the strip conductor 62, while maintaining the required inductance value. The extension length of the stub conductor 63 can be further shortened while maintaining the inductance value by narrowing the width (y-direction length) of the stub conductor 63. The extension length of the stub conductor 63 can also be further shortened while maintaining the inductance value by forming the stub conductor 63 in a meander shape.

[0079] When the boundary at both ends of the antenna is kept open in order to increase the parallel resonant current flowing through each stub conductor 63 in accordance with the orientation of the wireless tag T to be read, the extension length of the stub conductor 63 is increased, and the length of the unit cell L is also increased. unit By shortening the length, the current during parallel resonance becomes larger, thus maximizing the radiation efficiency.

[0080] For this reason, for example, the extension length of the stub conductor 63 is set to the wavelength λ of the radio wave within the unit cell 61. unit By increasing the value to a degree not exceeding 1 / 4 of the above embodiment, 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, which is less than the extended length of the stub conductor 63, while maintaining the required inductance value. The strip conductors 62 can also be formed in a meander shape, which further shortens the length of the strip conductors 62 in the direction of arrangement while maintaining the inductance value. By forming slits in the strip conductors 62, the capacitive component of the right-handed system can be reduced, and the effect of increasing the parallel inductance component can be absorbed. Since the inductance value increases in the thinned portion of the strip conductors 62, this has the effect of shortening the length of the strip conductors 62 in the direction of arrangement while maintaining the inductance value.

[0082] The present invention is not limited to the embodiments described above, and may be further embodied as follows, for example. (1) The antenna device 40 according to the present invention is 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 an antenna device for a reading device in which an item with a wireless tag to be read is placed nearby. [Explanation of symbols]

[0083] 1. Inventory Management System 10 Management shelf 11 Entrance / exit 20 Management device 30 Wireless Tag Readers 40 Antenna equipment 50 Dielectric substrate 53,54 reflector 60 Microstrip lines (transmission lines) 61, 71, 81 unit cells 61a Circuit of a series branch 61b Parallel branch circuits 62, 72, 82 strip conductors 63, 73, 83, 85, 86, 87 Stub Conductors 64, 74, 84 gap G Goods L ant Length of transmission line L unit Length of a unit cell n eff Effective refractive index n unit Effective refractive index T Wireless Tag λ0 Wavelength of radio waves in a vacuum λ ant Wavelength of radio waves in a transmission line λ unit Wavelength of radio waves within a unit cell

Claims

1. Dielectric substrate and A transmission line comprising multiple unit cells arranged in a predetermined direction on one surface of the dielectric substrate, An antenna device comprising, A reflector is provided at each end of the aforementioned transmission line. The unit cell has a strip conductor extending along 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 conductors, 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. The length of the transmission line along 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 characterized in that the parameters of the unit cell are set such that | is less than 1 and satisfies the following formula (1). |n ｅｆｆ |<λ ０ / (4), ａｎｔ ) ・・・(1)

2. The length L of the unit cell along the predetermined direction ｕｎｉｔ is the effective refractive index n of the unit cell determined according to the operating frequency, the width and thickness of the strip conductor, the dielectric constant and height of the dielectric substrate ｕｎｉｔ , the wavelength of the radio wave in the unit cell is λ ｕｎｉｔ When it is set so as to satisfy the following formulas (2) and (3), the antenna device according to claim 1, characterized in that L ｕｎｉｔ <l ｕｎｉｔ / 4 ・・・(2) l ｕｎｉｔ =λ ０ / |n ｕｎｉｔ |・・・(3)

3. The antenna device according to claim 1, characterized in that the strip conductor is formed such that the edges forming the predetermined gap are non-linear.

4. The antenna device according to claim 1, characterized in that the stub conductor is formed by extending it so as to extend over the boundary portion between the unit cells.

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