JP2008199316A - Wireless tag communication device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wireless tag communication device capable of appropriately detecting the direction of a wireless tag in an environment where a multipath is generated. <P>SOLUTION: The wireless tag communication device is provided with: a transmission PAA control section 58 for controlling directivity of a transmission array antenna; a reception weight processing section 60 for controlling the directivity of a reception array antenna; a preliminary direction detecting section 64 for changing the directivity of the transmission array antenna and/or the directivity of the reception array antenna, and preliminarily detecting the direction of the wireless tag, based on a direction with the largest communication sensitivity with the wireless tag; and a direction detecting section 66 for performing control, so as to allow the center direction of the directivity of the transmission array antenna to be the direction which is preliminarily detected by the preliminary direction detecting section 64, changing the directivity of the reception array antenna, and also formally detecting the direction of the wireless tag, based on a direction with the smallest communication sensitivity with the wireless tag. Thus, the direction is appropriately detected, while achieving reliable communication with the wireless tag to be an object. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a wireless tag communication apparatus that performs communication with a wireless tag that can wirelessly write and read information, and more particularly to an improvement in technology for detecting the direction of a wireless tag that is a communication target.

  2. Description of the Related Art An RFID (Radio Frequency Identification) system is known in which information is read out in a non-contact manner by a predetermined wireless tag communication device (interrogator) from a small wireless tag (responder) in which predetermined information is stored. This RFID system is capable of reading information stored in a wireless tag by communication with the wireless tag communication device even when the wireless tag is dirty or disposed at an invisible position. Therefore, practical use is expected in various fields such as merchandise management and inspection processes.

  As one use form of such a wireless tag communication device, a technique for detecting the direction of the wireless tag by changing the directivity of communication with the wireless tag that is a communication target is known. For example, general BFA (Beam Forming Antenna) processing, direction detection technology using MUSIC method, ESPRIT method, and the like. However, while the direction detection by BFA processing requires a small amount of calculation, there is a problem that the direction of the wireless tag that is a communication target cannot be detected in detail because the resolution is low. Further, direction detection with high resolution, such as the MUSIC method and the ESPRIT method, has a disadvantage that the processing is complicated and the amount of calculation increases. Therefore, a technique using a null scanning method that estimates the arrival direction of radio waves based on the direction in which the communication sensitivity is minimized has been proposed. For example, this is the tag communication device described in Patent Document 1.

JP 2006-10345 A

  By the way, depending on the environment in which the RFID tag communication system is applied, there is a possibility that a so-called multipass in which a plurality of radio wave reception paths are formed due to reflection or diffraction caused by an obstacle may occur. However, in the conventional technique, when a radio wave, that is, a reflected wave by such a multipath is received by the RFID tag communication device, a difference in signal intensity between the reflected wave and the direct wave is small, so that the target wireless There was an adverse effect that it was difficult to detect the tag direction. In addition, when detecting the direction in which the wireless tag is present by the null scanning method, since communication sensitivity is relatively lowered in the null direction, it becomes impossible to perform suitable communication with the target wireless tag, Multiple directions could be detected. That is, development of a wireless tag communication device that suitably detects the direction of the wireless tag in an environment where multipath can occur has been demanded.

  The present invention has been made against the background of the above circumstances, and an object of the present invention is to provide a wireless tag communication device that suitably detects the direction of a wireless tag in an environment where multipath can occur. is there.

  In order to achieve such an object, the gist of the present invention is that a transmission signal is transmitted to a predetermined wireless tag by a transmission array antenna having a plurality of antenna elements, and a reply is returned from the wireless tag. A wireless tag communication device for receiving a signal by a reception array antenna having a plurality of antenna elements and communicating information with the wireless tag, wherein the transmission directivity control controls the transmission directivity of the transmission array antenna A reception directivity control unit for controlling the reception directivity of the reception array antenna, and the transmission directivity and / or reception array antenna of the transmission array antenna by the transmission directivity control unit and / or the reception directivity control unit. A direction spare that preliminarily detects the direction of the wireless tag based on the direction in which the communication sensitivity with the wireless tag is maximized by changing the reception directivity of the wireless tag The output unit and the transmission directivity control unit control the central direction of the transmission directivity of the transmission array antenna to be the direction preliminarily detected by the direction preliminary detection unit, and the reception directivity control unit A direction detecting unit that detects the direction of the wireless tag based on a direction in which the reception directivity of the reception array antenna is changed to minimize the communication sensitivity with the wireless tag. is there.

  According to this configuration, the transmission directivity control unit that controls the transmission directivity of the transmission array antenna, the reception directivity control unit that controls the reception directivity of the reception array antenna, the transmission directivity control unit, and / or Alternatively, the directionality of the wireless tag can be determined based on the direction in which the communication sensitivity with the wireless tag is maximized by changing the transmission directivity of the transmission array antenna and / or the reception directivity of the reception array antenna by the reception directivity control unit. Preliminary detection direction preliminary detection unit and the transmission directivity control unit control so that the central direction of transmission directivity of the transmission array antenna is the direction preliminarily detected by the direction preliminary detection unit, and the reception directivity Direction of the wireless tag based on a direction in which the communication sensitivity with the wireless tag is minimized by changing the reception directivity of the reception array antenna by the control unit Since the main detection direction detecting unit is provided, the transmission directivity is directed to the direction in which the pre-detected wireless tag exists, and null scanning in the reception directivity is performed corresponding to the direction. Thus, it is possible to preferably detect the direction in which the wireless tag exists while maintaining the state in which the target wireless tag operates reliably. That is, it is possible to provide a wireless tag communication device that suitably detects the direction of the wireless tag in an environment where multipath can occur.

  Here, preferably, a signal strength detection unit that detects a signal strength of a reception signal received by the reception array antenna is provided, and the direction preliminary detection unit is configured to transmit the transmission directivity control unit and / or the reception directivity control. The transmission directivity of the transmission array antenna and / or the reception directivity of the reception array antenna is changed by the unit, and the radio tag of the wireless tag is based on the direction in which the signal strength of the reception signal detected by the signal strength detection unit is maximized. The direction detection unit changes the reception directivity of the reception array antenna by the reception directivity control unit, and the signal strength of the reception signal detected by the signal strength detection unit is minimal. The direction of the wireless tag is detected based on the direction of In this way, it is possible to perform preliminary detection and main detection in the direction in which the target wireless tag exists in a practical manner.

  Preferably, when the direction preliminary detection unit detects a plurality of directions in which the communication sensitivity with the wireless tag is maximized, the transmission directivity control unit detects the transmission array antenna. The center direction of the transmission directivity is sequentially controlled to be the plurality of directions, and the reception directivity of the reception array antenna is changed by the reception directivity control unit corresponding to each direction, and the wireless tag The direction of the wireless tag is detected based on the direction in which the communication sensitivity is minimized. In this way, even when a multipath is formed, the directivity null direction is directed to the direct wave direction where the path is the shortest and the response signal is strong, and thus the direction of the wireless tag can be detected suitably. .

  Preferably, the direction detection unit is a target wireless tag when the reception directivity control unit changes the reception directivity of the reception array antenna so that communication sensitivity with the wireless tag is minimized. Is designated to perform communication with the wireless tag. In this way, it is possible to suitably prevent the occurrence of communication overlap.

  Preferably, the direction detection unit is configured by the reception directivity control unit to minimize communication sensitivity with the wireless tag when a plurality of wireless tags are detected by the direction preliminary detection unit. When changing the reception directivity of the receiving array antenna, the target wireless tags are sequentially specified to communicate with the plurality of wireless tags. In this way, it is possible to suitably prevent the occurrence of communication overlap, and it is possible to preferably detect the direction in which each of the plurality of pre-detected wireless tags exists.

  Preferably, the direction detection unit is configured to control the reception directivity control unit so that communication sensitivity with the wireless tag is minimized only when at least one wireless tag is detected by the direction preliminary detection unit. Thus, the reception directivity of the reception array antenna is changed. In this way, unnecessary null scanning can be avoided.

  Preferably, the direction detecting unit changes the receiving array antenna when the receiving directivity control unit changes the receiving directivity of the receiving array antenna so that the communication sensitivity with the wireless tag is minimized. Of the plurality of antenna elements, two antenna elements communicate with the target wireless tag. In this way, the degree of freedom of reception directivity control is 1, and directivity can be directed only in the direction in which the received signal is the largest.

  Preferably, the direction detection unit performs control for changing the reception directivity of the reception array antenna by the reception directivity control unit by digital signal processing so that communication sensitivity with the wireless tag is minimized. Is what you do. In this way, for example, a received signal converted into a digital signal is stored in a memory, and the received signal is read and processed, so that communication with the target wireless tag is not repeated. Null scanning can be suitably performed.

  Preferably, in the communication when the reception directivity of the reception array antenna is changed by the reception directivity control unit so that the communication sensitivity with the wireless tag is minimized, A transmission signal having a frequency substantially equal to the communication with the wireless tag by the direction preliminary detection unit is used. In this way, since the frequency of the transmission signal is made substantially equal between the preliminary detection and the main detection, the multipath state does not change, and the main detection can be performed with the tag responding reliably. The direction in which the wireless tag exists can be detected more suitably.

  Preferably, the direction detection unit is configured to perform communication in changing the reception directivity of the reception array antenna by the reception directivity control unit so that communication sensitivity with the wireless tag is minimized. The first communication using the transmission signal having the same frequency as the communication with the wireless tag by the preliminary detection unit, and the second communication using the transmission signal having a frequency different from the frequency are performed. Based on the first communication result and the second communication result, the direction of the target wireless tag is detected. In this way, it is possible to more suitably detect the direction in which the wireless tag exists based on the possibility that the target wireless tag does not respond due to a change in the multipath state.

  Preferably, in the communication when the reception directivity of the reception array antenna is changed by the reception directivity control unit so that the communication sensitivity with the wireless tag is minimized, A transmission signal having a strength higher than that of communication with the wireless tag by the direction preliminary detection unit is used. In this way, by making the transmission output larger than the preliminary detection, the response from the target wireless tag in the main detection can be made more reliable.

  Preferably, the transmitting array antenna and the receiving array antenna share a part or all of the antenna elements. In this way, the configuration of the apparatus can be made as simple as possible.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a diagram for explaining an RFID tag communication system 10 in which the RFID tag communication apparatus of the present invention is preferably used. The RFID tag communication system 10 includes an RFID tag communication device 12 according to an embodiment of the present invention, and a single or plural (single in FIG. 1) RFID tags 14 that are communication targets of the RFID tag communication device 12. It is a so-called RFID (Radio Frequency Identification) system, and the RFID tag communication device 12 functions as an interrogator of the RFID system, and the RFID tag 14 functions as a responder. That is, when the interrogation wave F _c (transmission signal) is transmitted from the radio tag communication device 12 toward the radio tag 14, a predetermined information signal (data) is received in the radio tag 14 that has received the interrogation wave F _c. As a result, the interrogation wave F _c is modulated and sent back as a response wave F _r (reply signal) to the RFID tag communication apparatus 12, so that information is transmitted between the RFID tag communication apparatus 12 and the RFID tag 14. Communication takes place. The wireless tag communication system 10 is used, for example, for managing articles in a predetermined communication area. The wireless tag 14 is preferably attached to an article to be managed, for example. And are provided integrally.

FIG. 2 is a diagram illustrating the configuration of the wireless tag communication device 12. As shown in FIG. 2, the wireless tag communication device 12 according to the present embodiment communicates with the wireless tag 14 in order to read and write information with respect to the wireless tag 14 and detect the direction of the wireless tag 14. A DSP that performs communication of information and executes digital signal processing such as outputting transmission data as a digital signal and reading response data from the wireless tag 14 based on a reply signal from the wireless tag 14. a Digital Signal Processor) 16, an antenna element 18a of a plurality (four in FIG. 2) that is shared in the reception of the transmission and the response wave F _r of the interrogating wave F _c, 18b, 18c, 18 d (hereinafter, unless otherwise specified Is simply referred to as an antenna element 18), and a transmission array antenna 22 (see FIG. 4) composed of a part or all of the plurality of antenna elements 18. A transmission process for transmitting the interrogation wave F _c and a reception process of a reception signal received by the reception array antenna 24 (see FIG. 6) configured by a part or all of the plurality of antenna elements 18 And a transmission / reception circuit 20 for performing the above.

The transmission / reception circuit 20 outputs a predetermined frequency signal corresponding to the carrier wave of the interrogation wave F _c to the frequency signal output from the carrier wave output unit 26 corresponding to each antenna element 18. A plurality (four in FIG. 2) of transmission data multipliers 28a, 28b, 28c, and 28d (hereinafter simply referred to as transmission data multipliers 28 unless otherwise distinguished) that multiply transmission data supplied from the DSP 16; A plurality (four in FIG. 4) of transmission phase shifters 30a, 30b, 30c, and 30d (hereinafter referred to as “four” in FIG. 4) that control the phase of the signal output from each transmission data multiplier 28 in accordance with the command value supplied from the DSP 16. When not particularly distinguished, they are simply referred to as transmission phase shift units 30), and a plurality (four in FIG. 4) of transmission amplification units 32a that amplify signals output from the transmission phase shift units 30; 2b, 32c, 32d (hereinafter simply referred to as a transmission amplification unit 32 unless otherwise distinguished) and a signal output from each transmission amplification unit 32 is supplied to the corresponding antenna element 18 and A plurality of (four in FIG. 2) transmission / reception separators 34a, 34b, 34c, and 34d (hereinafter referred to simply as transmission / reception separators 34 unless otherwise specified) that supply the received signals to the corresponding orthogonal transform units 38. ) And a plurality of (four in FIG. 2) filters 36a, 36b, 36c, 36d (hereinafter, referred to as “passage”) provided between each antenna element 18 and the corresponding transmission / reception separation unit 34. Unless otherwise distinguished, simply referred to as a filter 36). In general, a directional coupler or a circulator is preferably used as the transmission / reception separating unit 34.

  The transmission / reception circuit 20 converts a reception signal received by each antenna element 18 into an I-phase signal (in-phase component) and a Q-phase signal (orthogonal component) (four in FIG. 2) orthogonal transform units 38a. , 38b, 38c, 38d (hereinafter simply referred to as the orthogonal transform unit 38 unless otherwise distinguished), and a plurality of (four in FIG. 2) I-phase signals that are output from each orthogonal transform unit 38. Phase amplifiers 40a, 40b, 40c, 40d (hereinafter simply referred to as I-phase amplifiers 40 unless otherwise distinguished) and I-phase signals output from the respective I-phase amplifiers 40 are converted into digital signals. A plurality of I-phase A / D converters 42a, 42b, 42c, 42d (hereinafter simply referred to as I-phase A / D converters 42 unless otherwise specified) to be supplied to the DSP 16, and each orthogonal converter 38 Q-phase signal to be output A plurality of (four in FIG. 2) Q-phase amplifiers 44a, 44b, 44c, 44d (hereinafter simply referred to as Q-phase amplifiers 44 unless otherwise distinguished), A plurality of Q-phase A / D converters 46a, 46b, 46c, and 46d that convert the output Q-phase signal into a digital signal and supply it to the DSP 16 (hereinafter, simply Q-phase A / D conversion unless otherwise distinguished) (Referred to as section 46).

  The DSP 16 includes a CPU, a ROM, a RAM, and the like, and is a so-called microcomputer that performs signal processing according to a program stored in advance in the ROM while using a temporary storage function of the RAM, and each I-phase A / D conversion unit 42. And a reception memory unit 48 for storing a signal supplied from the Q-phase A / D conversion unit 46. In addition, as a control function for performing communication control of information with the wireless tag 14, direction detection control of the wireless tag 14, etc., a transmission bit string generation unit 50, an encoding unit 52, a decoding unit 54, a response bit string interpretation 56, a transmission PAA (Phased Array Antenna) control unit 58, a reception weight processing unit 60, a signal strength detection unit 62, a preliminary direction detection unit 64, a direction detection unit 66, and a carrier wave control unit 68.

  The transmission bit string generation unit 50 generates a command bit string corresponding to a transmission signal to the wireless tag 14. The encoding unit 52 encodes the bit string generated by the transmission bit string generation unit 50 using the FSK method or the like and supplies the encoded bit string to each transmission data multiplication unit 28. The decoding unit 54 decodes the reception signal whose weight has been processed by the reception weight processing unit 60 using the FSK method or the like. The response bit string interpretation unit 56 interprets the signal decoded by the decoding unit 54 and reads an information signal (response data) related to the modulation of the wireless tag 14.

  The transmission PAA controller 58 supplies a command value to the plurality of transmission phase shifters 30 to control the amount of phase shift in each transmission phase shifter 30. By controlling the phase of the signal supplied to each antenna element 18 via the transmission phase shift unit 30 according to such a command value, the antenna element 18 consists of a part or all (preferably all) of the antenna element 18. Phased array control of the transmission array antenna 22 is performed. That is, the transmission PAA control unit 58 functions as a transmission directivity control unit that controls the transmission directivity of the transmission array antenna 22.

  The reception weight processing unit 60 controls the phases and / or amplitudes of the I-phase signal and the Q-phase signal corresponding to the reception signals received by the antenna elements 18 read from the reception memory unit 48, thereby Adaptive array control or phased array control of the receiving array antenna 24 comprising a part or all (preferably two) of the antenna elements 18 is performed. That is, the reception weight processing unit 60 functions as a reception directivity control unit that controls the reception directivity of the reception array antenna 24 by digital signal processing.

  The signal strength detector 62 detects the signal strength of the received signal received by the receiving array antenna 24. Specifically, based on the I-phase signal and the Q-phase signal read from the reception memory unit 48 and controlled in phase and / or amplitude by the reception weight processing unit 60, the I-phase signal and the Q-phase signal are controlled. The signal strength of the received signal corresponding to the signal is calculated.

  The direction preliminary detection unit 64 changes the transmission directivity of the transmission array antenna 22 and / or the reception directivity of the reception array antenna 24 by the transmission PAA control unit 58 and / or the reception weight processing unit 60 to change the radio tag. The direction of the wireless tag 14 is preliminarily detected based on the direction in which the communication sensitivity with the network 14 becomes maximum. Further, the direction detection unit 66 causes the transmission PAA control unit 58 to make the direction of the transmission directivity of the transmission array antenna 22 (main lobe direction) the direction preliminarily detected by the direction preliminary detection unit 64. In addition to the control, the reception weight processing unit 60 changes the reception directivity of the reception array antenna 24 to detect the direction of the wireless tag 14 based on the direction in which the communication sensitivity with the wireless tag 14 is minimized. . The preliminary detection control of the direction of the wireless tag 14 by the preliminary direction detection unit 64 and the actual detection control of the direction of the wireless tag 14 by the direction detection unit 66 will be described later with reference to FIGS.

  The carrier wave control unit 68 controls the carrier wave output by the carrier wave output unit 26. Specifically, the frequency and / or intensity of the carrier wave output from the carrier wave output unit 26 is controlled by supplying a command value to the carrier wave output unit 26. Since the frequency and intensity of the carrier wave correspond to the frequency and intensity of the transmission signal transmitted from the transmission array antenna 22, the carrier wave control unit 68, in other words, is transmitted from the transmission array antenna 22. It controls the frequency and / or intensity of the transmitted signal.

FIG. 3 is a diagram illustrating the configuration of the RFID circuit element 72 provided in the RFID tag 14. As shown in FIG. 3, the RFID circuit element 72 has an antenna unit 74 for transmitting and receiving signals to and from the RFID tag communication device 12, and the RFID tag connected to the antenna unit 74. An IC circuit unit 76 for performing information communication processing with the communication device 12 is provided. The IC circuit unit 76 rectifies the interrogation wave F _c received from the RFID tag communication device 12 received by the antenna unit 74 and the energy of the interrogation wave F _c rectified by the rectification unit 78. Functions as a power supply unit 80 for accumulation, a clock extraction unit 82 that extracts a clock signal from the carrier wave received by the antenna unit 74 and supplies the clock signal to the control unit 88, and an information storage unit that can store a predetermined information signal The RFID circuit element 72 via the memory unit 84, the modulation / demodulation unit 86 that is connected to the antenna unit 74 and modulates and demodulates the signal, the rectification unit 78, the clock extraction unit 82, the modulation / demodulation unit 86, and the like. And a control unit 88 for controlling the operation of. The control unit 88 performs control to store the predetermined information in the memory unit 84 by communicating with the RFID tag communication device 12, and transmits the interrogation wave F _c received by the antenna unit 74 to the modulation / demodulation unit 86. Then, basic control such as control for reflecting and returning the response wave _Fr as the response wave _Fr is executed based on the information signal stored in the memory unit 84.

  FIG. 4 is a diagram for explaining transmission directivity control of the transmission array antenna 22 by the transmission PAA control unit 58, where θ is an angle formed with the front direction of the transmission array antenna 22, and θ = 40 [°]. The case where the wireless tag 14 which is a communication object is located is illustrated. As shown in FIG. 4, the transmission array antenna 22 is preferably composed of four antenna elements 18a, 18b, 18c, and 18d, and the transmission PAA control unit 58 performs phased array processing. Thus, the transmission directivity is changed at every predetermined angle (every 30 ° in FIG. 4). In such a directivity pattern, generally, the portion where the communication sensitivity is maximum is referred to as a main lobe, the other maximum portion is referred to as a side lobe (not shown), and the minimum point between lobes (see FIG. 6) is referred to as a null point. . That is, the transmission PAA control unit 58 changes the angle θ of the transmission directivity in the main lobe direction at every predetermined angle by the phased array process.

  Preferably, the direction preliminary detection unit 64 maximizes the communication sensitivity with the wireless tag 14 by changing the transmission directivity of the transmission array antenna 22 for each predetermined angle by the transmission PAA control unit 58 as described above. The direction of the wireless tag 14 is preliminarily detected on the basis of the direction. More preferably, the direction of the target wireless tag 14 is preliminarily detected based on the direction in which the signal strength of the received signal detected by the signal strength detector 62 is maximized corresponding to each transmission directivity. For example, by applying a predetermined weight to each transmission phase shifter 30 sequentially, the main lobe direction is changed 5 times by 30 [°] between −60 and 60 [°] as shown in FIG. Thus, the received signal strength in each main lobe direction is detected. FIG. 5 shows the transmission directivity direction controlled by the transmission PAA control 58 and the received signal strength detected by the signal strength detector 62 in the preliminary direction detection of the wireless tag 14 by the control of the main lobe direction. It is a figure which shows the relationship. As shown in FIG. 5, it can be seen that the received signal strength detected by the signal strength detector 62 is maximum at θ = 30 [°]. Here, as described above, the wireless tag 14 to be communicated is actually positioned in the direction of θ = 40 [°]. That is, in the direction detection by controlling the main lobe, it is difficult to detect in detail the direction of the wireless tag 14 that has a low resolution and is a communication target. It can be suitably used for rough direction detection, that is, preliminary detection. The preliminary direction detection unit 64 changes the reception directivity of the reception array antenna 24 for each predetermined angle by the reception weight processing unit 60, and based on the direction in which the communication sensitivity with the wireless tag 14 is maximized. The direction of the wireless tag 14 may be preliminarily detected. In this case, the reception directivity is changed by adding the weights determined for each direction in the reception weight processing unit 60 to the reception signals received by the antenna elements 18 of the reception array antenna 24 and adding them together. The Further, the direction of the target wireless tag 14 may be preliminarily detected by changing both the transmission directivity of the transmission array antenna 22 and the reception directivity of the reception array antenna 24.

  FIG. 6 is a diagram for explaining a state in which null is controlled by the reception weight processing unit 60, and illustrates a case where the wireless tag 14 to be communicated is located in the direction of θ = 40 [°] as in FIG. is doing. As shown in FIG. 6, the reception array antenna 24 is preferably composed of two antenna elements 18b and 18c (or 18a and 18d), and the reception weight processing unit 60 is adaptive. The null direction in the reception directivity of the reception array antenna 24 is controlled by array processing at every predetermined angle (for example, every 10 °). In the receiving array antenna 24 including the two antenna elements 18, the degree of freedom of receiving directivity control is 1, and the direction of the null point is determined to be one. Therefore, in the control of changing the reception directivity of the reception array antenna 24 so that the reception weight processing unit 60 controls the reception directivity in the null direction, that is, the communication sensitivity with the wireless tag 14 is minimized. The reception array antenna 24 is preferably constituted by two antenna elements 18 of the plurality of antenna elements 18. In the present embodiment, the reception array antenna 24 is the target antenna element 18 among the reception signals corresponding to the respective antenna elements 18 (four antenna elements 18) stored in the reception memory unit 48. (For example, it is comprised by reading the received signal corresponding to the antenna elements 18b and 18c).

  The direction detection unit 66 preferably changes the reception directivity of the reception array antenna 24 at every predetermined angle by the reception weight processing unit 60 as described above, thereby minimizing the communication sensitivity with the wireless tag. Based on the direction, the direction of the wireless tag is fully detected. More preferably, the direction of the target wireless tag 14 is detected based on the direction in which the signal intensity of the received signal detected by the signal intensity detector 62 corresponds to each reception directivity. In communication with the target wireless tag 14 in the main detection, the transmission PAA control unit 58 determines that the transmission directivity center direction (main lobe direction) of the transmission array antenna 22 is the direction preliminary detection unit 64. Is controlled so as to be in the direction detected in advance. For example, as shown in FIG. 6, while θ = 30 [°] in which the communication sensitivity was maximum in the preliminary detection by the direction preliminary detection unit 64 is controlled to be the main lobe direction of the transmission directivity of the transmission signal. The angle θ is changed (weight to be multiplied) by an angle smaller than the change angle by the preliminary detection described above, for example, 10 [°], between 20 and 40 [°] around the angle (error range in the preliminary detection). And the null control in the reception directivity by the reception weight processing unit 60 is performed three times to detect the detailed direction of the wireless tag 14 to be communicated. In general, the characteristics of the null are very steep and narrow compared to the main lobe, so that a relatively high resolution can be obtained by controlling the null direction. When controlling the null direction of the reception directivity, since the main lobe direction of the transmission directivity is the central angle direction of the null scanning angle range, reliable communication with the target wireless tag 14 is achieved. The direction in which the wireless tag 14 exists can be detected in detail while being realized. FIG. 7 shows the reception directivity direction controlled by the reception weight processing unit 60 and the received signal strength detected by the signal strength detection unit 62 in the direction detection of the wireless tag 14 by controlling null. It is a figure which shows a relationship. As shown in FIG. 7, it can be seen that the received signal strength detected by the signal strength detector 62 is minimal (minimum) at θ = 40 [°], and this direction is the wireless communication target. It coincides with the direction in which the tag 14 is located.

  Here, the direction detection unit 66 preferably uses the transmission PAA control unit 58 when the direction preliminary detection unit 64 detects a plurality of directions in which the communication sensitivity with the wireless tag 14 is maximized. The central direction of the transmission directivity of the transmission array antenna 22 is controlled so as to sequentially become the plurality of directions, and the reception directivity of the reception array antenna 24 is set by the reception weight processing unit 60 corresponding to each direction. The direction of the wireless tag 14 is finally detected based on the direction in which the communication sensitivity with the wireless tag 14 is minimized. Preferably, when a plurality of wireless tags 14 are detected by the direction preliminary detection unit 64, the reception weight processing unit 60 causes the reception array to minimize communication sensitivity with the wireless tags 14. When the reception directivity of the antenna 24 is changed, in order to prevent the occurrence of communication superimposition, the target wireless tags 14 are sequentially designated to perform communication with the plurality of wireless tags 14. Preferably, in order to avoid unnecessary null scanning, the communication sensitivity with the wireless tag 14 is minimized only when at least one wireless tag 14 is detected by the direction preliminary detection unit 64. Thus, the reception weight processing unit 60 changes the reception directivity of the reception array antenna 24. In other words, when one wireless tag 14 is not detected in the preliminary detection by the direction preliminary detection unit 64, the direction detection (main detection) by the direction detection unit 66 is not performed.

  In addition, the direction detection unit 66 preferably controls a carrier wave used for communication with the target wireless tag 14 so as not to change the multipath state between the preliminary detection and the main detection. To do. Specifically, in the main detection, that is, in the communication when the reception directivity of the reception array antenna 24 is changed by the reception weight processing unit 60 so that the communication sensitivity with the wireless tag 14 is minimized, the preliminary direction detection is performed. A transmission signal having a frequency substantially equal to the communication with the wireless tag 14 by the unit 64 is used. That is, the frequency of the carrier wave output from the carrier wave output unit 26 is controlled to be substantially equal between the preliminary detection and the main detection via the carrier wave control unit 68. Preferably, in the communication at the time of the main detection, the first communication using the transmission signal having the same frequency as the communication with the wireless tag 14 by the direction preliminary detection unit 64 and the transmission having the same frequency as the first communication. The second communication using the signal is performed, and the direction of the target wireless tag 14 is finally detected based on the second communication result. Preferably, in order to make the response from the target wireless tag in the main detection more reliable, in the communication at the time of the main detection, the communication with the wireless tag 14 by the direction preliminary detection unit 64 is performed. A transmission signal having a strength higher than that of communication is used. That is, the carrier wave control unit 68 performs control so that the intensity of the carrier wave output from the carrier wave output unit 26 is larger than that in the preliminary detection during the main detection.

  FIG. 8 is a flowchart for explaining a main part of RFID tag direction detection control by the DSP 16 of the RFID tag communication apparatus 12 and is repeatedly executed at a predetermined cycle.

  First, in step (hereinafter, step is omitted) S1, the transmission directivity of the transmission array antenna 22 and / or the reception directivity of the reception array antenna 24 is controlled, and communication with the wireless tag 14 is performed. The preliminary detection of the target wireless tag 14 is performed. Next, in S2, it is determined whether or not the target wireless tag 14 has been detected in the preliminary detection in S1. If the determination at S2 is negative, the routine is terminated accordingly. If the determination at S2 is affirmative, at S3, reception is performed in communication with the wireless tag 14 in the preliminary detection at S1. The direction in which the signal strength of the signal is maximized is detected. Next, in SA, null scanning control as shown in FIG. 9 described later is performed. Next, in SB, after tag direction determination control as shown in FIG. 10 described later is performed, this routine is terminated.

FIG. 9 is a flowchart for explaining a main part of null scanning control in the above-described RFID tag direction detection control of FIG. In this control, first, in SA1, I _max is set to the number in the maximum direction detected in S2, and i is set to 1. Next, in SA2, a target wireless tag 14 is specified, information is communicated (reading information) with the wireless tag 14, and a reception signal (I) corresponding to each antenna element 18 in the communication is performed. Phase signal and Q phase signal) are stored in the reception memory unit 48. In communication with the wireless tag 14 at this time, the main lobe direction of the transmission directivity of the transmission signal is controlled to be the maximum direction detected in S2 described above. Next, in SA2 ′, j indicating the number of divisions in one direction of preliminary detection is set to zero. Next, in SA3, a reception weight that directs null to the j-th region in the i-th maximum direction is selected. Next, in SA4, the received signal strength (combined signal strength) when the reception weight selected in SA3 is applied is calculated. Next, j is whether greater than J _max is determined at SA4 '. If the determination at SA4 'is negative, 1 is added to j at SA4 ", and then the processing after SA3 is executed again. If the determination at SA4' is affirmative, at SA5 I is greater than I _{max If the} determination at SA5 is negative, 1 is added to i at SA6, and then the processing from SA2 'is executed again. If the determination at SA5 is affirmative, the control returns to the RFID tag direction detection control of FIG.

  FIG. 10 is a flowchart for explaining a main part of tag direction determination control in the above-described RFID tag direction detection control of FIG. In this control, first, in SB1, the null direction when the received signal strength calculated in SA4 is minimized is detected. Next, in SB2, after the direction corresponding to the null direction detected in SB1 is detected as the direction in which the target wireless tag 14 exists, the process returns to the wireless tag direction detection control in FIG. In the above control, S1 to S3 correspond to the operation of the direction preliminary detection unit 64.

FIG. 11 is a flowchart for explaining a main part of another example of the null scanning control in the above-described RFID tag direction detection control of FIG. In the following description, steps common to the embodiments are denoted by the same reference numerals and description thereof is omitted. In this control, first, after the processing of SA2 described above is performed, in SA7, J1 _max is set to a predetermined number of amplitude scans, and J1 is set to 1. Next, in SA8, J2 _max is set to a predetermined number of phase scans, and J2 is set to 1. Next, in SA9, the weight corresponding to the antenna element 18 constituting the reception array antenna 24 is set to the weight defined by J1∠J2, that is, the amplitude J1 and the phase J2. Then, after the processing of SA4 described above is performed, in SA10, J2 whether greater than J2 _max is determined. If the determination at SA10 is negative, 1 is added to J2 at SA11, and then the processing below SA2 is executed again. If the determination at SA10 is affirmative, J1 is performed at SA12. Is greater than J1 _max . If the determination of SA12 is negative, after SA1 is incremented by 1, 1 is executed again after SA8. If the determination of SA12 is affirmative, The process returns to the RFID tag direction detection control of FIG. In the above control, SA3 and SA4 correspond to the operation of the reception weight processing unit 60.

  FIG. 12 is a flowchart for explaining a main part of another example of the tag direction determination control in the above-described RFID tag direction detection control of FIG. 8, and is executed corresponding to the above-described null scanning control of FIG. is there. In this control, following the process of SB1, the radiation pattern using the weight detected in SB1 is calculated in SB3. Next, in SB4, after the null direction of the radiation pattern calculated in SB3 is detected as the direction in which the target wireless tag 14 exists, the process returns to the wireless tag direction detection control in FIG. At this time, the process of SB1 corresponds to a process of so-called PIAA (Power Inversion Adaptive Array).

FIG. 13 is a flowchart for explaining a main part of another example of the RFID tag direction detection control by the DSP 16 of the RFID tag communication apparatus 12, and is repeatedly executed at a predetermined cycle. In this control, following the process of S3 described above, in S4, N _max is set to the number in the maximum direction detected in S2, and n is set to 1. Next, in S5, control is performed such that the nth maximum direction among the maximum directions detected in S2 is the main lobe direction of the directivity of the transmission signal. Next, after the above-described SA processing is executed, 1 is added to n in S6. Next, in S7, it is determined whether n is larger than N _max . When the determination at S7 is negative, the above-described processing after S5 is executed again. However, when the determination at S7 is positive, this routine is executed after the above-described processing at SB is executed. Be terminated.

FIG. 14 is a flowchart for explaining a main part of still another example of RFID tag direction detection control by the DSP 16 of the RFID tag communication apparatus 12 and is repeatedly executed at a predetermined cycle. In this control, when the determination of S2 described above is affirmed, that is, when the target wireless tag 14 is detected, in S8, M _max is set to the number of detected wireless tags 14, and m Is set to 1. Next, in S9, the direction in which the signal strength of the received signal corresponding to the mth wireless tag 14 is maximized is detected. Next, in S10, N _{max —} m is set to the number in the maximum direction detected corresponding to the m-th wireless tag 14, and after n is set to 1, the processing in S5 and subsequent steps described above is executed. Further, following the process of SB described above, 1 is added to m in S11. Next, in S12, it is determined whether m is larger than _Mmax . If the determination in S12 is negative, the above-described processing from S9 is executed again. If the determination in S12 is affirmative, the routine is terminated accordingly.

FIG. 15 is a flowchart for explaining a main part of still another example of the RFID tag direction detection control by the DSP 16 of the RFID tag communication apparatus 12, and is repeatedly executed at a predetermined cycle. In this control, following the process of S3 described above, after S is set to 1 in S14, the process of S4 and subsequent steps described above is executed. If the determination in S7 described above is affirmative, that is, if it is determined that n is greater than N _max , whether or not k is 2 is determined in S15. If the determination in S15 is negative, after k is set to 2 in S16, the frequency used for communication with the target wireless tag 14 in S13, that is, output from the carrier output unit 26. After the frequency of the carrier wave is changed, the processes after S4 are executed. However, when the determination at S15 is affirmed, the processes after SB described above are executed.

  FIG. 16 is a flowchart for explaining a main part of still another example of RFID tag direction detection control by the DSP 16 of the RFID tag communication apparatus 12 and is repeatedly executed at a predetermined cycle. In this control, following the process of S3 described above, in S17, the transmission output in communication with the target wireless tag 14, that is, the strength of the carrier wave output from the carrier wave output unit 26 is changed (increased). Thereafter, the processing from S4 onward is executed. In the above control, S1, S5, and SA2 are operations for the transmission PAA control unit 58, S3 and S9 are operations for the signal strength detection unit 62, S13 and S17 are operations for the carrier wave control unit 68, and S4. Through S12, S14 through S16, SA, and SB correspond to the operation of the direction detection unit 66, respectively.

  Thus, according to the present embodiment, the transmission PAA control unit 58 (S1, S5, and SA2) as a transmission directivity control unit that controls the transmission directivity of the transmission array antenna 22 and the reception array antenna 24. The reception weight processing unit 60 (SA3 and SA4) as a reception directivity control unit that controls the reception directivity of the transmission array antenna 22 by the transmission PAA control unit 58 and / or the reception weight processing unit 60. And / or a preliminary direction detection unit 64 (S1 to S3) that preliminarily detects the direction of the wireless tag 14 based on the direction in which the communication sensitivity with the wireless tag 14 is maximized by changing the reception directivity of the reception array antenna 24. ), And the transmission PAA control unit 58 determines that the transmission directivity center direction of the transmission array antenna 22 is reserved by the direction auxiliary detection unit 64. The reception weight processing unit 60 changes the reception directivity of the reception array antenna 24 so that the communication sensitivity with the wireless tag 14 is minimized. Since the direction detection unit 66 (S4 to S12, S14 to S16, SA, and SB) for main detection of the direction of the tag 14 is provided, transmission is performed in the direction in which the pre-detected wireless tag 14 exists. By directing the directivity and performing null scanning in the reception directivity corresponding to the direction, the direction in which the wireless tag 14 exists is preferable while realizing reliable communication with the target wireless tag 14. Can be detected. That is, it is possible to provide the wireless tag communication device 12 that suitably detects the direction of the wireless tag 14 in an environment where multipath can occur.

  Further, a signal strength detection unit 62 (S3 and S9) for detecting the signal strength of the reception signal received by the reception array antenna 24 is provided, and the direction preliminary detection unit 64 includes the transmission PAA control unit 58 and / or the reception. The weight processing unit 60 changes the transmission directivity of the transmission array antenna 22 and / or the reception directivity of the reception array antenna 24 so that the signal strength of the reception signal detected by the signal strength detection unit 62 is maximized. The direction of the wireless tag 14 is preliminarily detected, and the direction detection unit 66 changes the reception directivity of the reception array antenna 24 by the reception weight processing unit 60 and the signal strength detection unit 62 Since the direction of the wireless tag 14 is detected based on the direction in which the signal strength of the detected received signal is minimized, Presence direction of the pre-detection and the detection of the wireless tag 14 to be in use manner can be performed.

  In addition, when the direction preliminary detection unit 64 detects a plurality of directions in which the communication sensitivity with the wireless tag 14 is maximized, the direction detection unit 66 uses the transmission PAA control unit 58 to transmit the transmission array antenna 22. The central direction of the transmission directivity is controlled so as to sequentially become the plurality of directions, and the reception directivity of the reception array antenna 24 is changed by the reception weight processing unit 60 corresponding to each direction. Since the direction of the wireless tag 14 is detected based on the direction in which the communication sensitivity with the tag 14 is minimized, the direction of the wireless tag 14 is preferably detected even when a multipath is formed. be able to.

  In addition, the direction detection unit 66 is a target wireless in the main detection in which the reception weight processing unit 60 changes the reception directivity of the reception array antenna 24 so that the communication sensitivity with the wireless tag 14 is minimized. Since the tag 14 is designated and communication is performed with the wireless tag 14, it is possible to suitably prevent the occurrence of communication superimposition.

  In addition, when the plurality of wireless tags 14 are detected by the preliminary direction detection unit 64, the direction detection unit 66 uses the reception weight processing unit 60 so that the communication sensitivity with the wireless tags 14 is minimized. In the main detection for changing the reception directivity of the reception array antenna 24, since the target wireless tags 14 are sequentially designated to communicate with the plurality of wireless tags 14, superimposition of communication occurs. This can be suitably prevented, and the direction in which each of the plurality of pre-detected wireless tags 14 is present can be suitably detected.

  In addition, the direction detection unit 66 is configured to receive the reception weight processing unit 60 so that the communication sensitivity with the wireless tag 14 is minimized only when at least one wireless tag 14 is detected by the direction preliminary detection unit 64. Therefore, since the main detection for changing the reception directivity of the reception array antenna 24 is performed, unnecessary null scanning can be avoided.

  In addition, the direction detection unit 66 uses the reception array antenna in the main detection in which the reception weight processing unit 60 changes the reception directivity of the reception array antenna 24 so that the communication sensitivity with the wireless tag 14 is minimized. 24, the two antenna elements 18 among the plurality of antenna elements 18 perform communication with the target wireless tag 14, so that the degree of freedom in receiving directivity control is 1, and the received signal is Directivity can be directed only in the largest direction.

  The direction detection unit 66 includes a reception memory unit 48 that stores a reception signal received by the reception array antenna 24, and the wireless tag 14 and the wireless tag 14 based on the reception signal read from the reception memory unit 48. Control for changing the reception directivity of the reception array antenna 24 by the reception weight processing unit 60 so as to minimize the communication sensitivity is performed by digital signal processing. Thus, it is possible to suitably perform null scanning without repeatedly performing communication.

  In the communication at the time of the main detection, the direction detection unit 66 changes the reception directivity of the reception array antenna 24 by the reception weight processing unit 60 so that the communication sensitivity with the wireless tag 14 is minimized. Since the transmission signal having the substantially same frequency as the communication with the wireless tag 14 by the direction preliminary detection unit 64 is used, the frequency of the transmission signal is substantially equal between the preliminary detection and the main detection. Since the main detection can be performed in a situation where the target wireless tag 14 operates reliably without causing a change in the state, the direction in which the target wireless tag 14 exists can be detected more suitably.

  In addition, in the communication at the time of main detection in which the reception weight processing unit 60 changes the reception directivity of the reception array antenna 24 so that the communication sensitivity with the wireless tag 14 is minimized, the direction detection unit 66 The first communication using a transmission signal having the same frequency as the communication with the wireless tag 14 by the direction preliminary detection unit 64 and the second communication using a transmission signal having a frequency different from that frequency. Since the direction of the target wireless tag 14 is detected based on the first communication result and the second communication result, the target wireless tag 14 is caused by the change in the multipath state. Based on the possibility of not responding, the direction in which the wireless tag 14 exists can be detected more suitably.

  In the communication at the time of the main detection, the direction detection unit 66 changes the reception directivity of the reception array antenna 24 by the reception weight processing unit 60 so that the communication sensitivity with the wireless tag 14 is minimized. Since the transmission signal having a strength higher than that of the communication with the wireless tag 14 by the direction preliminary detection unit 64 is used, the wireless tag to be the target in the main detection is increased by increasing the transmission output compared with the preliminary detection. The response from 14 can be made more reliable.

  Further, since the transmitting array antenna 22 and the receiving array antenna 24 share a part or all of the antenna elements 18, the configuration of the apparatus can be made as simple as possible.

  The preferred embodiments of the present invention have been described in detail with reference to the drawings. However, the present invention is not limited to these embodiments, and may be implemented in other modes.

  For example, in the above-described embodiment, the RFID tag communication device 12 includes the antenna element 18 for both transmission and reception for transmitting the transmission signal and receiving the return signal. The present invention is not limited, and a transmission antenna element for transmitting the transmission signal and a reception antenna element for receiving a return signal may be provided individually.

  In the above-described embodiment, all of the control functions of the transmission PAA control unit 58, the reception weight processing unit 60, the signal strength detection unit 62, the direction preliminary detection unit 64, the direction detection unit 66, the carrier wave control unit 68, etc. Although the DSP 16 is functionally provided, these may be provided as individual control devices. Also, it does not matter whether these controls are based on digital signal processing or analog signal processing.

  In the above-described embodiment, the RFID tag communication apparatus 12 controls the transmission directivity of the transmission array antenna 22 by analog signal processing, and controls the reception directivity of the reception array antenna 24 by digital signal processing. However, a mode in which the transmission directivity of the transmission array antenna 22 is controlled by digital signal processing and a mode in which the reception directivity of the reception array antenna 24 is controlled by analog signal processing are also conceivable.

  In the above-described embodiment, the RFID tag communication apparatus 12 has a structure having a plurality of transmission data multipliers 28. However, the output of a single transmission data multiplier 28 is used as a transmission phase shift of a plurality of transmission antennas. You may make it distribute to the part 30. FIG.

  In addition, although not illustrated one by one, the present invention is implemented with various modifications within a range not departing from the gist thereof.

It is a figure explaining the communication system in which the radio | wireless tag communication apparatus of this invention is used suitably. It is a figure explaining the structure of the RFID tag communication apparatus which is one Example of this invention. It is a figure explaining the structure of the wireless tag which is a communication object of the wireless tag communication apparatus of FIG. It is a figure explaining a mode that the transmission PAA process part of FIG. 2 controls the main lobe of the transmission directivity of a transmission array antenna. FIG. 5 is a diagram illustrating a relationship between a reception directivity direction and reception signal strength in the direction detection of a wireless tag by controlling a main lobe in the configuration illustrated in FIG. 4. It is a figure explaining a mode that the reception directivity null of a receiving array antenna is controlled by the receiving weight process part of FIG. FIG. 7 is a diagram illustrating a relationship between a reception directivity direction and reception signal strength in detecting a direction of a wireless tag by controlling null in the configuration illustrated in FIG. 3 is a flowchart illustrating a main part of RFID tag direction detection control by a DSP of the RFID tag communication apparatus in FIG. 2. It is a flowchart explaining the principal part of the null scanning control in the RFID tag direction detection control of FIG. It is a flowchart explaining the principal part of tag direction determination control in the radio | wireless tag direction detection control of FIG. It is a flowchart explaining the principal part of another example of the null scanning control in the RFID tag direction detection control of FIG. FIG. 13 is a flowchart for explaining a main part of another example of tag direction determination control in the RFID tag direction detection control of FIG. 8, and is executed corresponding to the null scanning control of FIG. 11. 6 is a flowchart for explaining a main part of another example of RFID tag direction detection control by the DSP of the RFID tag communication apparatus of FIG. 2. 6 is a flowchart for explaining a main part of still another example of RFID tag direction detection control by the DSP of the RFID tag communication apparatus of FIG. 2. 6 is a flowchart for explaining a main part of still another example of RFID tag direction detection control by the DSP of the RFID tag communication apparatus of FIG. 2. 6 is a flowchart for explaining a main part of still another example of RFID tag direction detection control by the DSP of the RFID tag communication apparatus of FIG. 2.

Explanation of symbols

12: RFID tag communication device 14: RFID tag 18: antenna element 22: transmission array antenna 24: reception array antenna 58: transmission PAA control unit (transmission directivity control unit)
60: Reception weight processing unit (reception directivity control unit)
62: Signal intensity detection unit 64: Preliminary direction detection unit 66: Direction detection unit

Claims (12)

A transmission signal is transmitted to a predetermined radio tag by a transmission array antenna having a plurality of antenna elements, and a reply signal returned from the radio tag is received by a reception array antenna having a plurality of antenna elements. A wireless tag communication device that communicates information with
A transmission directivity control unit for controlling the transmission directivity of the transmission array antenna;
A reception directivity control unit for controlling the reception directivity of the reception array antenna;
The transmission directivity control unit and / or the reception directivity control unit changes the transmission directivity of the transmission array antenna and / or the reception directivity of the reception array antenna so that the communication sensitivity with the wireless tag is maximized. A preliminary direction detecting unit for preliminary detecting the direction of the wireless tag based on;
The transmission directivity control unit controls the center direction of the transmission directivity of the transmission array antenna to be a direction preliminarily detected by the direction preliminary detection unit, and the reception directivity control unit controls the reception array antenna. A wireless tag communication, comprising: a direction detection unit that detects the direction of the wireless tag based on a direction in which reception directivity is changed and communication sensitivity with the wireless tag is minimized. apparatus.   A signal strength detection unit that detects a signal strength of a reception signal received by the reception array antenna, and the direction preliminary detection unit is configured to detect the transmission array antenna by the transmission directivity control unit and / or the reception directivity control unit. The direction of the wireless tag is preliminarily detected based on the direction in which the signal strength of the received signal detected by the signal strength detector is maximized by changing the transmission directivity and / or the reception directivity of the receiving array antenna. And the direction detection unit changes the reception directivity of the reception array antenna by the reception directivity control unit, and based on the direction in which the signal strength of the reception signal detected by the signal strength detection unit is minimized. The wireless tag communication apparatus according to claim 1, which detects the direction of the wireless tag.   The direction detection unit, when the direction preliminary detection unit detects a plurality of directions in which the communication sensitivity with the wireless tag is maximized, the transmission directivity control unit controls the center of the transmission directivity of the transmission array antenna. The direction is controlled so that the direction becomes a plurality of directions sequentially, and the reception directivity control unit changes the reception directivity of the reception array antenna corresponding to each direction, thereby minimizing the communication sensitivity with the wireless tag. The wireless tag communication device according to claim 1 or 2, wherein the direction of the wireless tag is detected based on the direction to be.   The direction detection unit designates a target wireless tag when the reception directivity control unit changes the reception directivity of the reception array antenna so that communication sensitivity with the wireless tag is minimized. 4. The wireless tag communication device according to claim 1, wherein communication is performed with a tag.   When the plurality of wireless tags are detected by the direction preliminary detection unit, the direction detection unit receives the reception array antenna by the reception directivity control unit so that communication sensitivity with the wireless tag is minimized. 5. The wireless tag communication apparatus according to claim 4, wherein when directivity is changed, communication is performed among the plurality of wireless tags by sequentially specifying target wireless tags.   Only when at least one wireless tag is detected by the preliminary direction detection unit, the direction detection unit causes the reception directivity control unit to minimize the sensitivity of the reception array antenna so that the communication sensitivity with the wireless tag is minimized. 6. The wireless tag communication device according to claim 1, wherein the reception directivity is changed.   A plurality of antennas provided in the receiving array antenna when the receiving directivity control unit changes the receiving directivity of the receiving array antenna so that communication sensitivity with the wireless tag is minimized; The RFID tag communication apparatus according to any one of claims 1 to 6, wherein communication is performed with a target RFID tag by using two antenna elements among the elements.   The direction detection unit performs digital signal processing to control the reception directivity of the reception array antenna to be changed by the reception directivity control unit so that communication sensitivity with the wireless tag is minimized. The wireless tag communication device according to any one of 1 to 7.   In the communication when changing the reception directivity of the reception array antenna by the reception directivity control unit so that the communication sensitivity with the wireless tag is minimized, the direction detection unit performs the direction detection unit by the direction preliminary detection unit. 9. The wireless tag communication device according to claim 1, wherein a transmission signal having a frequency substantially equal to that of communication with the wireless tag is used.   The direction detection unit is configured to perform the wireless communication by the direction preliminary detection unit in communication when the reception directivity control unit changes the reception directivity of the reception array antenna so that communication sensitivity with the wireless tag is minimized. A first communication using a transmission signal having a frequency equal to the communication with the tag and a second communication using a transmission signal having a frequency different from the frequency, and the first communication result and 9. The wireless tag communication device according to claim 1, wherein the direction of the target wireless tag is detected based on the second communication result.   In the communication when changing the reception directivity of the reception array antenna by the reception directivity control unit so that the communication sensitivity with the wireless tag is minimized, the direction detection unit performs the direction detection unit by the direction preliminary detection unit. 11. The wireless tag communication device according to claim 1, wherein a transmission signal having a strength higher than that of communication with the wireless tag is used.   12. The RFID tag communication apparatus according to claim 1, wherein the transmission array antenna and the reception array antenna share a part or all of the antenna elements.

Images