RFID tag system

Abstract

To provide an RFID tag system which can improve accuracy in detection of a direction in which a management target is moved, and can make the system lower in costs and in size.SOLUTION: The present invention is directed to an RFID tag system 1 having a reader device 20 for communicating with an RFID tag 31 fitted to a movable management target 30. The system has an antenna apparatus 10 having a transmission antenna 11 for transmitting a radio wave generated by the reader device 20 to the RFID tag 31, and reception antennas 12a, 12b, 12c for receiving a radio wave transmitted from the RFID tag 31.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to an RFID tag system that reads or writes an IC tag, and more particularly to an RFID tag system having a fixed installation type antenna for unmanned operation applications or a gate type antenna with self - contained installation thereof.

Background Art

[0002] There are various solutions related to RFID tags. In recent years, in particular, solutions related to article management and movement management within or across enterprises, such as automating the management of taking out articles using RFID tags and automating the movement management of handled goods in a logistics warehouse, have attracted attention. What is common in this case is that the fixed installation type antenna or gate antenna is used to manage the passage of articles, parcels, etc. that are moved by people, transport robots, or conveyors without human intervention.

[0003] When performing movement management of articles by an RFID tag system having a fixed installation type antenna and a reader device, it is important to reliably read the RFID tag with the fixed installation antenna and to reliably grasp when and what has passed through a predetermined point of the fixed installation type antenna (moved in the direction of incoming or outgoing). This is because it is necessary to confirm whether it is a correct passage along predetermined business processes, such as taking out or returning articles from a shelf, or carrying in or out of a warehouse. Conventionally, a method of detecting the movement direction of a moving object to be managed by installing a plurality of antennas is known (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the above-described prior art, a phased array antenna that arranges a plurality of antenna elements and controls their phases is used, and an adaptive array that can control the beam of radio waves (the range where radio waves can be transmitted and received) with high precision must be adopted, resulting in a complicated configuration and an expensive device. Generally, when trying to enhance the processing in a system using radio waves in the UHF band or higher frequency bands, it is necessary to perform signal processing by dedicated hardware at high speed, increasing the manufacturing cost.

[0006] An object of the present invention is to provide an RFID tag system that can improve the accuracy of detecting the moving direction of a management target, reduce the cost, and miniaturize the system by eliminating the need for radio wave beam control (radio wave direction control).

Means for Solving the Problems

[0007] (1) An RFID tag system according to an embodiment for achieving the above object is an RFID tag system having a reader device that communicates with an RFID tag attached to a movable management target, the RFID tag system including an antenna device including a transmission antenna that transmits radio waves generated by the reader device to the RFID tag and a reception antenna that receives radio waves transmitted from the RFID tag, and the antenna device is characterized in that at least two or more reception antennas are arranged. (2) In an RFID tag system according to another embodiment, preferably, the reader device switches the reception timing of radio waves received by each of at least two or more reception antennas, acquires in order the time when at least an RFIC tag is read and the reception intensity at that time received by each reception antenna, and detects the moving direction of the management target based on the read time and reception intensity. (3) In the RFID tag system according to another embodiment, preferably, the reader device simultaneously receives radio waves for each of at least two or more receiving antennas, and acquires in the order of the time when at least the RFIC tag is read and the reception intensity at that time at each antenna, and detects the moving direction of the object to be managed based on the read time and the reception intensity. (4) In the RFID tag system according to another embodiment, preferably, it has a host computer connected to the reader device, and the host computer creates a reception intensity distribution based on the read time and the reception intensity in the reception data constituting the radio wave for each antenna, calculates the peak value of the reception intensity for each antenna, compares the occurrence times of the peak values among the antennas, and detects the moving direction of the object to be managed based on the comparison result. (5) In the RFID tag system according to another embodiment, the receiving antenna device desirably has at least a receiving antenna arranged such that the central axis of the beam of the radiated radio wave overlaps with the central axis of the beam of the radiated radio wave of the transmitting antenna, and a receiving antenna arranged such that the central axis of the beam of the radiated radio wave is inclined by a predetermined angle with respect to the central axis of the beam of the radiated radio wave of the transmitting antenna. (6) In the RFID tag system according to another embodiment, the predetermined angle is preferably an angle at which radio waves from the RFID tag can be received within the directivity range of the radio waves radiated from the transmitting antenna.

Advantages of the Invention

[0008] According to the present invention, it is possible to provide an RFID tag system that can improve the accuracy of detecting the moving direction of an object to be managed, reduce the cost of the system, and miniaturize the system by eliminating the need for direction control of the radio wave beam.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

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Figure 9

Embodiments for Carrying Out the Invention

[0010] Hereinafter, the RFID tag system according to the embodiments of the present invention will be described with reference to the drawings. In each drawing, the same reference numerals are assigned to the same elements, and for the sake of clarity of explanation, duplicate explanations are omitted as necessary.

[0011] <RFID tag system> [First Embodiment]: When there are multiple receiving antennas and antenna operation switching is performed The RFID tag system 1 includes RFID tags 31 respectively attached to management objects 30 such as a plurality of packages that are warehoused and shipped in a warehouse, an antenna device 10 that transmits radio waves of a predetermined wavelength and performs communication processing with each RFID tag 31, a reader device (interrogator) 20 connected to the antenna device 10, and a host computer (management terminal) 40 connected to the reader device 20 via a communication network. Note that the RFID tag (Figure 3) side does not hold a power source necessary for operation such as a battery, performs necessary processing using the energy of radio waves radiated from the reader device, and has a configuration in which a signal is returned to the reader device using the same frequency as the radio waves received from the reader device. At this time, since the operation of the RFID tag 31 transmitting a signal toward the reader device 20 actually applies the principle of radio waves being reflected and returning, this signal is called a backscatter signal. Hereinafter, embodiments will be described on the premise of the above-described passive RFID tag system.

[0012] The RFID tag 31 stores at least predetermined identification information different for each RFID tag 31, and transmits an identification signal including this identification information to the antenna device 10 non-contact via radio waves of a predetermined wavelength. Each RFID tag 31 may be an active tag (with built-in operating power source) or a passive tag (without built-in operating power source), and repeatedly transmits the identification signal of the tag. Also, the RFID tag 31 may be attached to any position of the management object 30 as long as it is in a position where the radio waves radiated from the transmission unit 21 of the reader device 20 can reach and be received, but it is preferably attached to a position facing the antenna surfaces of the transmission antenna 11, reception antennas 12a, 12b, 12c that constitute the antenna device described later (see Figure 5(a)), but for example, it may be attached to the left side surface (see Figure 5(b)) or the right side surface (see Figure 5(c)).

[0013] [Antenna device] The antenna device 10 is configured to include a transmitting antenna 11 and three receiving antennas 12a, 12b, and 12c, and is built into a plastic housing. The transmitting antenna 11 is electrically connected by wire to the transmitting unit 21 of the reader device 20. The antenna surface of the transmitting antenna 11 is arranged such that when the object 30 to be managed passes in front of the antenna device 10, the central axis (reference numeral 14 in FIG. 4) of the radiation beam (query wave) of the transmitting antenna 11 is orthogonal to the RFID tag 31. Here, the transmitting antenna 11 and the three receiving antennas 12a, 12b, and 12c are preferably so-called patch antennas. The transmitting antenna 11 radiates the query wave generated by the reader device 20, which will be described later, as a radiation beam in front of the antenna surface with respect to the RFID tag 31.

[0014] On the other hand, regarding the receiving antennas, the receiving antenna 12b is arranged at the center, and the receiving antennas 12a and 12c are arranged on the left and right of the receiving antenna 12b. In other words, the receiving antennas 12a and 12c are arranged so as to sandwich the receiving antenna 12b. The receiving antennas 12a, 12b, and 12c receive the response wave (response signal to the above query wave) transmitted from the RFID tag 31. Further, the receiving antennas 12a, 12b, and 12c are each electrically connected by wire to the receiving unit 25 of the reader device 20.

[0015] Regarding the receiving antenna 12b located at the center, it is arranged below the transmitting antenna 11 (on the lower side in the Y-axis direction in FIG. 4) so that the central axis of the radiation beam of the receiving antenna 12b overlaps with the central axis of the radiation beam (radiated radio wave) of the transmitting antenna 11. The receiving antenna 12a located on the left side of the receiving antenna 12b (on the left side in the X-axis direction in FIG. 6) is arranged by being inclined at a predetermined angle (shifted by a predetermined shift angle) with respect to the antenna surface of the transmitting antenna 11. The receiving antenna 12c located on the right side of the receiving antenna 12b (on the right side in the X-axis direction in FIG. 6) is arranged by being inclined at a predetermined angle (shifted by a predetermined shift angle) with respect to the antenna surface of the transmitting antenna 11. This shift angle is the directivity shift angle, and it is an angle indicating how much the central axes 16a, 16c of the radiation beams radiated from the antennas are inclined with respect to the antenna surface of the transmitting antenna 11. Also, this shift angle is an angle at which the receiving antennas 12a, 12c can receive the signal (backscatter signal) from the RFID tag 31 within the directivity range of the transmitting antenna 11.

[0016] The receiving antenna 12a is fixedly arranged by shifting the central axis 16a of the radiation beam, for example, in the moving direction of the object 30 to be managed (the approaching direction for the moving direction of arrow A in FIG. 6, and the departing direction for the moving direction of arrow B). The receiving antenna 12c is fixedly arranged by shifting the central axis 16c of the radiation beam, for example, in the moving direction of the object 30 to be managed (the departing direction for the moving direction of arrow A in FIG. 6, and the approaching direction for the moving direction of arrow B). In addition, this shift is performed so that the directivities of the receiving antennas 12a, 12c whose central axes of the radiation beams are shifted overlap with the directivity of the transmitting antenna 11.

[0017] As a specific example, the shift angles of the central axes 16a, 16c of the respective radiation beams of the receiving antennas 12a, 12c with respect to the central axis of the radiation beam of the transmitting antenna 11 are set to 30 degrees. According to the configuration of this example, it was confirmed that the signal (backscatter signal) from the RFID tag 31 was received.

[0018] Note that the transmitting antenna and the receiving antenna have been described by taking a patch antenna as an example. However, for the purpose of miniaturizing the antenna, a high dielectric constant material such as ceramic may be used instead. This is particularly effective when the increase in the thickness of the antenna housing due to the setting of the shift angle becomes a demerit, and it contributes to the miniaturization of the antenna device. Further, since the separation of the transmitting and receiving antennas suppresses the leakage of the transmitted radio waves from the transmitting antenna 11 to the receiving antennas 12a, 12b, and 12c, it is possible to compensate for the decrease in the gain of the receiving antennas 12a, 12b, and 12c. Therefore, a ceramic patch antenna in which the antenna element is mounted on a ceramic material can also be applied.

[0019] [Reader device] The reader device 20 reads the identification information and the like of the RFID tag 31 by receiving a response signal (a signal that responds to the interrogation signal) transmitted from the RFID tag 31. The reader device 20 includes a transmission unit 21, a reception unit 25, and a reception data processing unit 29. The transmission unit 21 includes an encoding processing unit 22 that encodes transmission data including command information for the RFID tag 31, a modulation processing unit 23 that modulates a transmission carrier with a transmission baseband signal by modulation processing and frequency conversion processing of the encoded transmission data to generate transmission data (backscatter signal) in the UHF (Ultra High Frequency) band, and an amplification processing unit 24 that amplifies the modulated transmission data. The reception unit 25 includes a reception antenna switching unit 28 that switches the operations of the reception antennas 12a, 12b, and 12c, a direct conversion reception unit 27 that receives a reception signal (backscatter signal) obtained by mixing a signal having the same frequency as a reception signal generated by an internal oscillator (not shown), and a reception signal baseband processing unit 26 that performs baseband processing and demodulation on the reception signal from the direct conversion reception unit 27.

[0020] The received data processing unit 29 acquires data such as the reception time when the RFID tag 31 is received based on the demodulated signal, the ID (antenna identification ID) for identifying the received antennas 12a, 12b, 12c, the ID (RFID tag identification ID) for identifying the RFID tag 31, and the RSSI (Received Signal Strength Indicator) value at the time of reception (refer to the data structure in Fig. 6(b)), and outputs it to the host computer 40.

[0021] [Host computer] The host computer 40 is configured to execute the moving direction detection process of the RFID tag 31 based on the data from the received data processing unit 29, that is, the received time, the ID for identifying the received antenna, the ID for identifying the RFID tag 31, and the RSSI value at the time of reception. The frame of the transmission signal generated by the transmission unit 21 has "question content" and "antenna operation switching command", and the antenna operation switching command includes a time slot for determining the antenna switching timing. When the time of this time slot elapses, a command to switch to the next antenna is output from the host computer 40, and an operation command indicating which received antenna to switch to next is output from the host computer 40.

[0022] [Moving direction detection process of RFID tag] Next, a detailed description will be given of an embodiment of the moving direction detection process of the RFID tag with reference to FIGS. 6 to 8. The host computer 40 determines whether there is received data (received signal) (step S101). If it is determined that there is received data, the host computer 40 refers to the antenna ID included in the received data, acquires the received data for each antenna ID, and stores it in a memory (not shown) (step S102). If it is determined in step S101 that there is no received data, the process returns to step S101. Next, the host computer 40 creates an RSSI distribution based on the RSSI values and reception times in the received data for each acquired antenna (step S103). Next, the host computer 40 calculates, as the median value, the peak value of the RSSI value for each antenna by an integral detection type method described later (step S104). Next, the host computer 40 compares the median generation times between the antennas (step S105), and detects the moving direction of the management target 30 based on the comparison result (step S106). Note that, if a histogram is applied, in the generation time distribution of the peak values of the histograms of the RSSI values received from the respective receiving antennas 12a, 12b, 12c, the moving direction can also be obtained by comparing them in the same manner as described above.

[0023] The RSSI distribution is the time distribution of RSSI values as shown in, for example, FIG. 7, and is created by sampling based on the RSSI values extracted (acquired) from the received signals from the receiving antennas 12a, 12b, 12c and the RSSI value acquisition times by operating the receiving antennas 12a, 12b, 12c by switching them every predetermined time. Here, the time distribution is created with the maximum value of the slope of the sampled RSSI values with respect to the elapsed time as the median value. According to the time distribution shown in FIG. 7, for example, for the receiving antenna 12a, the RSSI value increases (rises) with the passage of time and decreases (falls) with the median value (peak value: time t1) as the boundary. This is because the measurement target is a moving object. Similarly for the receiving antenna 12b, the RSSI value increases (rises) with the passage of time and decreases (falls) with the median value (peak value: time t2) as the boundary. Similarly for the receiving antenna 12c, the RSSI value increases (rises) with the passage of time and decreases (falls) with the median value (peak value: time t3) as the boundary.

[0024] Analyzing the time distribution in FIG. 7, it can be seen that the peak values visit (appear) in the order of the receiving antennas 12a, 12b, 12c (t1 → t2 → t3) as time passes. This means that the object 30 with the RFID tag 31 attached moves from the left side to the right side of the paper (in the direction of arrow B). That is, as shown in FIG. 6, when the object 30 to be managed moves in the direction of arrow B and approaches the receiving antenna 12a, the RFID tag 31 enters the beam (irradiation range of the interrogation signal) E1 irradiated from the transmitting antenna 11, and the receiving antenna 12a receives a response signal with a peak value at time t1 in FIG. 7. After that, when the object 30 to be managed moves in the direction of arrow B and approaches the receiving antenna 12b, the RFID tag 31 enters the beam E2 irradiated from the transmitting antenna 11, and the receiving antenna 12b receives a response signal with a peak value at time t2 in FIG. 7. After that, when the object 30 to be managed moves in the direction of arrow B and moves away from the receiving antenna 12c, the RFID tag 31 enters the beam E3 irradiated from the transmitting antenna 11, and the receiving antenna 12c receives a response signal with a peak value at time t3 in FIG. 7.

[0025] On the other hand, although not shown, when the peak value visits in the order of the receiving antennas 12c, 12b, 12a (t1 → t2 → t3) as time elapses, it means that the object 30 with the RFID tag 31 attached moves from the right side to the left side (in the direction of arrow A) of the paper. That is, as shown in FIG. 6, when the object 30 to be managed moves in the direction of arrow A and approaches the receiving antenna 12c, the RFID tag 31 enters the beam (irradiation range of the interrogation signal) E1 irradiated from the transmitting antenna 11, and the receiving antenna 12c receives a response signal having a peak value at time t1. Thereafter, when the object 30 to be managed moves in the direction of arrow B and approaches the receiving antenna 12b, the RFID tag 31 enters the beam E2 irradiated from the transmitting antenna 11, and the receiving antenna 12b receives a response signal having a peak value at time t2 in FIG. 7. Thereafter, when the object 30 to be managed moves in the direction of arrow B and moves away from the receiving antenna 12a, the RFID tag 31 enters the beam E3 irradiated from the transmitting antenna 11, and the receiving antenna 12a receives a response signal having a peak value at time t3.

[0026] As described above, according to the RFID tag system according to the first embodiment, by analyzing the RSSI time distribution based on the received data from the three receiving antennas 12a, 12b, and 12c, it is possible to accurately grasp whether the object 30 to be managed approaches from the left side or the right side of the movement line, for example. And since it is not necessary to separately provide, for example, a plurality of detection sensors for the object 30 to determine the moving direction of the RFID tag 31, it is possible to improve the accuracy of detecting the moving direction of the object 30 and to reduce the cost and size of the system.

[0027] [Second Embodiment]: When there are a plurality of receiving antennas and no antenna operation switching is performed This second embodiment is configured such that a direct conversion receiving unit is provided independently for each antenna, eliminating the need to switch the operations of multiple receiving antennas. Since it is the same as the first embodiment described above except for the configuration of the receiving unit, only the different parts will be described below, and the same parts will be omitted. Note that the same parts as those in the first embodiment will be described using the same reference numerals.

[0028] [Reader device] The reader device 120 reads the identification information and the like of the RFID tag 31 by receiving a response signal (a signal responding to the interrogation signal) transmitted from the RFID tag 31. The reader device 120 includes a transmission unit 121, a reception unit 125, and a reception data processing unit 29. The transmission unit 121 includes an encoding processing unit 22 that encodes transmission data including command information for the RFID tag 31, a modulation processing unit 23 that modulates a transmission carrier with a transmission baseband signal by modulating and frequency-converting the encoded transmission data to generate transmission data (backscatter signal) in the UHF band, and an amplification processing unit 24 that amplifies the modulated transmission data. The reception unit 125 includes direct conversion receiving units 27a, 27b, and 27c corresponding to the reception antennas 12a, 12b, and 12c respectively, and reception signal baseband processing units 26a, 26b, and 26c that perform baseband processing and demodulation on the reception signals from the direct conversion receiving units 27a, 27b, and 27c respectively. The direct conversion receiving unit 27a receives a reception signal (backscatter signal) obtained by mixing a reception signal (a reception signal received via the antenna 12a) with a signal having the same frequency as the reception signal generated by an internal oscillator (not shown). The direct conversion receiving unit 27b receives a reception signal (backscatter signal) obtained by mixing a reception signal (a reception signal received via the reception antenna 12b) with a signal having the same frequency as the reception signal generated by an internal oscillator (not shown). The direct conversion receiving unit 27c receives a reception signal (backscatter signal) obtained by mixing a reception signal (a reception signal received via the reception antenna 12c) with a signal having the same frequency as the reception signal generated by an internal oscillator (not shown).

[0029] The received signal baseband processing unit 26a performs baseband processing on the received signal from the direct conversion receiving unit 27a and demodulates it. The received signal baseband processing unit 26b performs baseband processing on the received signal from the direct conversion receiving unit 27b and demodulates it. The received signal baseband processing unit 26c performs baseband processing on the received signal from the direct conversion receiving unit 27c and demodulates it. The received data processing unit 29 acquires data such as the time when the RFID tag 31 was received, the ID for identifying the received antenna, the ID for identifying the RFID tag 31, and the RSSI value at the time of reception (see FIG. 6(b)) based on the signals demodulated by the direct conversion receiving units 27a, 27b, and 27c.

[0030] [Host computer] The host computer 40 is configured to execute the moving direction detection process of the RFID tag 31 based on each data from the received data processing unit 29, that is, the time received by each of the receiving antennas 12a, 12b, and 12c, the ID for identifying the received antenna, the ID for identifying the RFID tag 31, and the RSSI value at the time of reception.

[0031] [Moving direction detection process of RFID tag] In the second embodiment, all of the receiving antennas 12a, 12b, and 12c are operated simultaneously, and RSSI distribution is created by performing simultaneous sampling, which is different from the above-described first embodiment. Other points are the same. According to the second embodiment, since simultaneous sampling is possible, there is no receiving antenna switching period according to the moving speed of the RFID tag 31, so data acquisition is possible for the movement into the reception area of the managed movement target. Therefore, a more accurate moving direction detection process is possible.

[0032] Note that the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention. For example, the above-described embodiment is an example using three receiving antennas. However, for example, a configuration with two receiving antennas in which a first receiving antenna is arranged at the center and a second receiving antenna is arranged on the right or left side thereof may be used. For the first receiving antenna, it is arranged below the transmitting antenna so that the central axis of the radiation beam of the first receiving antenna overlaps the central axis of the radiation beam of the transmitting antenna. The shift angle of the second receiving antenna is set to an angle at which the second receiving antenna can receive a signal (backscatter signal) from the RFID tag within the directivity range of the transmitting antenna. Even with this configuration, the moving direction of the object to be managed can be detected by analyzing the above-described RSSI time distribution based on the received data.

[0033] Also, for example, a configuration using five receiving antennas may be used. First, a first receiving antenna is arranged at the center, a second and a third receiving antenna are arranged on the left side of the first receiving antenna, and a fourth and a fifth receiving antenna are arranged on the right side of the first receiving antenna. At this time, for the first receiving antenna, it is arranged below the transmitting antenna so that the central axis of the radiation beam of the first receiving antenna overlaps the central axis of the radiation beam of the transmitting antenna. The shift angles of the second to fifth receiving antennas are set to angles at which the second to fifth receiving antennas can receive a signal (backscatter signal) from the RFID tag within the directivity range of the transmitting antenna. In this example, by increasing the number of antennas, the received data from the first to fifth receiving antennas can be more reliably extracted. Therefore, by analyzing the RSSI time distribution based on the extracted received data, it is possible to more accurately grasp whether the object to be managed approaches from the left side or the right side of the moving line.

Explanation of Reference Numerals

[0034] 1 RFID tag system 10 Antenna device 11 Transmitting antenna 12a, 12b, 12c Receiving antenna Central axes 16a, 16b, 16c Reader devices 20, 120 Transmitting units 21, 121 Encoding processing unit 22 Modulation processing unit 23 Amplification processing unit 24 Receiving units 25, 125 Received signal baseband processing units 26, 26a, 26b, 26c Direct conversion receiving units 27, 27a, 27b, 27c Receiving antenna switching unit 28 Received data processing unit 29 Object to be managed 30 RFID tag 31 Host computer 40

Claims

1. An RFID tag system having a reader device that communicates with an RFID tag attached to a movable object to be managed, having an antenna device including a transmission antenna that transmits radio waves generated by the reader device to the RFID tag and a reception antenna that receives radio waves transmitted from the RFID tag, wherein at least two or more reception antennas are arranged in the antenna device, characterized by an RFID tag system.

2. The reader device switches the reception timing of radio waves received by each of the at least two or more reception antennas, and acquires in the order in which the RFID tag is read at least at the time when the RFID tag is read and the reception intensity at that time in each reception antenna, and detects the moving direction of the object to be managed based on the read time and reception intensity. The RFID tag system according to claim 1, characterized in that.

3. The reader device simultaneously receives radio waves for each of the at least two or more reception antennas, acquires in the order in which the RFID tag is read at least at the time when the RFID tag is read and the reception intensity at that time in each antenna, and detects the moving direction of the object to be managed based on the read time and reception intensity. The RFID tag system according to claim 1, characterized in that.

4. having a host computer connected to the reader device, The host computer creates a reception intensity distribution based on the read time and reception intensity in the reception data constituting the radio waves for each antenna, calculates the peak value of the reception intensity for each antenna, compares the occurrence times of the peak values among the antennas, and detects the moving direction of the object to be managed based on the comparison result. The RFID tag system according to claim 1 or 2, characterized in that.

5. The reception antenna device has at least a reception antenna arranged such that the central axis of the beam of the radiated radio wave overlaps with the central axis of the beam of the radio wave radiated by the transmission antenna, and a reception antenna arranged such that the central axis of the beam of the radiated radio wave is inclined by a predetermined angle with respect to the central axis of the beam of the radio wave radiated by the transmission antenna. The RFID tag system according to claim 1 or 2, characterized in that.

6. The predetermined angle is an angle at which radio waves from the RFID tag can be received within the directivity range of the radio waves radiated from the transmission antenna. The RFID tag system according to claim 5, characterized in that.

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