Patent Publication Number: US-2011063081-A1

Title: Antenna device for rf tag communication and rf tag reader and writer

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No, 2009-213086, filed on Sep. 15, 2009; the entire contents of which are incorporated herein by reference. 
     FIELD 
     The embodiments described in this specification relate to an RF tag reader and writer for communicating with an RF tag in a non-contact manner and to an antenna thereof. 
     BACKGROUND 
     The RFID (Radio Frequency Identification) system is attracting attention and is being introduced in the field of distribution, for example. The RFID system includes an IC chip and an antenna, and is constituted by an RF tag (also referred to as a wireless tag or an RFID tag) attached to respective goods and an RF tag reader and writer (hereinafter, also simply referred to as a reader and writer) for reading information stored in a memory within the IC chip of the RF tag in a non-contact manner and writing information in the memory within the IC chip of the RF tag in a non-contact manner. 
     As a process by the RFID system, a collective information reading process from a plurality of RF tags (hereinafter, referred to as a collective reading) in an inventory count in a shop or the like can be exemplified. At this time, the reader and writer radiates radio waves in a range of up to several meters, executes communications with unspecified RF tags each of which is attached to each of a plurality of commercial goods, and collectively reads the information stored in the respective RF tags. In addition, as other processes by the RFID system, it is possible to exemplify reading and writing processes with respect to one or a plurality of specific RF tags (hereinafter, both of which are referred to as selective reading and selective writing, respectively, and referred to as selective communication, collectively). At this time, the reader and writer selectively reads information from specific RF tags or selectively writes information in the RF tags. 
     Here, there are cases where selective writing or the like is performed in the circumstances of a shop or the like, around which a number of commercial goods attached with the RF tags exist. In such circumstances, information may be written to an RF tag different from an RF tag to which a user desires to write the information, as a result of the communication with circumferential RF tags by mistake. Accordingly, in the conventional technique, the user was required to use both a reader and writer for a collective reading and a reader and writer for a selective communication, which has a smaller radio wave transmission output than that of the reader and writer for collective reading and has a narrower range of directionality, depending on the operation. In addition, when performing selective communication, the user was required to perform an action such as keeping RF tags which were not communication targets away from the circumference of the antenna device of the reader and writer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an RF tag reader and writer of a first embodiment; 
         FIG. 2  is a block diagram illustrating a hardware configuration of the RF tag reader and writer of the first embodiment; 
         FIG. 3  is a circuit configuration diagram of a wireless unit included in the RF tag reader and writer of the first embodiment; 
         FIG. 4  is a sectional view of an antenna device taken along a line A-A′ in  FIG. 1 ; 
         FIG. 5  is a plan view of a radiation element and a feeding point according to the first embodiment; 
         FIG. 6  is a graph for illustrating a distribution of field intensity in the first embodiment; 
         FIG. 7  is a graph for illustrating a distribution of field intensity in the first embodiment; 
         FIG. 8  is a diagram illustrating a process flow relating to a communication with an RF tag in the first embodiment; 
         FIG. 9  is a diagram illustrating an example of a process designation screen in the first embodiment; 
         FIG. 10  is a diagram illustrating an example of a result notification screen in the first embodiment; 
         FIG. 11  is a diagram illustrating an example of an RF tag arrangement designation screen in the first embodiment; 
         FIG. 12  is a diagram illustrating an example of a result notification screen in the first embodiment; 
         FIG. 13  is a diagram illustrating an example of a result notification screen in the first embodiment; 
         FIG. 14  is a perspective view of an antenna device with a restriction member mounted thereon according to a second embodiment; and 
         FIG. 15  is a perspective view of an antenna device according to another embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     First Embodiment 
     According to a first embodiment, the RF tag reader and writer includes an antenna device for RF tag communication and a transmission output control unit. The antenna device for RF communication includes a plate-shaped radiation element and an antenna case body which accommodates the radiation element and has an indicating unit at a position corresponding to a region in which the field intensity of the electric field generated by the radiation element reaches its highest. In addition, the transmission output control unit controls the transmission output of the radio wave radiated from the radiation element. 
     Hereinafter, the description will be made of the embodiment with reference to the drawings. The following description will be made while exemplifying an identification ID as the information to be read from or written to the RF tags. In addition, the description will be made while exemplifying as a collective communication a collective reading to be used in operations such as an inventory count and the like. 
       FIG. 1  is a perspective view illustrating a schematic configuration of an RF tag reader and writer  100  according to the first embodiment. The reader and writer  100  of the first embodiment includes an antenna device  10  and a reader and writer main body  30 . The antenna device  10  and the reader and writer main body  30  are connected by a coaxial cable  40 . The antenna device  10  includes an antenna case body  12  and a patch antenna  14  accommodated in the case body. The reader and writer  100  communicates with RF tags (not illustrated) via radio waves radiated from the patch antenna. 
     In the first embodiment, an indicating unit  16  is provided on the outer surface of the case body  12  of the antenna device. In addition, in the first embodiment, the reader and writer  100  has a communication mode relating to selective reading and selective writing, in which the reader and writer can communicate with the RF tags only in the region indicated by the indicating unit  16 , and a communication mode relating to collective reading in which the reader and writer can communicate with the RF tags in a broader range than that for the former communication mode. 
     First, the description will be made of a configuration of hardware provided in the reader and writer main body  30 . As shown in  FIG. 2 , the reader and writer main body  30  includes a control unit  31 , a wireless unit  33 , an input unit  35 , a display unit  37 , and an interface unit  39 . In addition, a power source unit  32 , which controls a battery and the charge and discharge thereof, shown in  FIG. 1  supplies a current to each hardware and the antenna device  10 . Accordingly, the reader and writer  100  of the first embodiment is configured as a mobile reader and writer. 
     The control unit  31  plays a role in performing various processes in the reader and writer  100 , such as communications with the RF tags or communications with external devices such as a personal computer (not illustrated), and the like, via a network, by executing a program stored in a storage unit  311 , which will be described later, based on input from a user. For example, the control unit  31  controls the wireless unit  33  in accordance with a communication protocol such that an identification ID obtained by a PC via the interface unit  39  which will be described later or input by the user via the input unit  35  which will be described later is transmitted from the antenna device  10  to the RF tags via radio waves. In addition, the control unit  31  includes the storage unit  311  and a transmission output control unit  315  which will be described later. 
     The storage unit  311  stores output information as information to be used by the transmission output control unit  315 , which will be described later, regarding the magnitude of the transmission output corresponding to one of collective reading, selective reading, and selective writing, in addition to the obtained identification ID and the communication protocol for transmitting the identification ID via radio waves (a communication protocol for RF tags complying with, for example, ISO18000-6). 
     The transmission output control unit  315  controls the wireless unit  33 , which will be described later, to cause the antenna device to radiate radio waves at a transmission output based on the transmission output information stored in the storage unit  311 . 
     Here, according to the first embodiment, the transmission output control unit  315  causes the antenna device  10  to radiate radio waves at a transmission output capable of communicating only with the RF tags positioned in the region indicated by the indicating unit  16  provided in the antenna case body  12  when controlling the wireless unit  33 , which will be described later, based on the output information relating to selective reading and selective writing (selective reading output information and selective writing output information) In addition, the transmission output control unit  315  causes the antenna device  10  to radiate radio waves at a transmission output greater than that for selective reading or selective writing when controlling the wireless unit  33  based on the collective reading output information relating to collective reading. 
     That is, in the first embodiment, the transmission output control unit  315  switches between the communication mode relating to selective reading and selective writing and the communication mode relating to collective reading. In other words, the transmission output control unit can switch between a first output mode for causing the radio wave to be radiated at a transmission output capable of communicating only with the RF tags positioned in the region indicated by the indicating unit and a second output mode for causing radio waves to be radiated at a greater transmission output than that for the first output mode. 
     Specifically, the control unit  31  of the first embodiment can be configured with a CPU, a RAM, and a ROM mounted on the reader and writer main body  30 . 
     In addition, a suitable value for the transmission output varies depending on the type of the RF tags, and the communication environment where the processes are performed (for example, materials of walls, materials of shelves onto which the RF tags are being mounted, materials of goods to which the RF tags are being attached, the density of the RF tags, and the like) in addition to the process type such as a collective reading and the selective communication. Accordingly, when the transmission output is preset for the respective processes, it is preferable that plural pieces of information are stored for one process, as in the first embodiment, since it is possible to more suitably set the transmission output. If the explanation is made while exemplifying collective reading, three types of output information indicating different transmission outputs of collective reading output information A, B, and C are stored in the first embodiment. 
     The wireless unit  33  is hardware with a function of communicating with the RF tags via the antenna device  10 .  FIG. 3  is a detailed circuit configuration diagram of the wireless unit  33 . 
     Here, if the RF tags are passive tags with no battery, the wireless unit  33  first amplifies a non-modulated carrier with a power amplifier  331 , outputs radio waves from the antenna via a directional coupler  332 , and starts the RF tags. When transmitting data to the RF tags, the wireless unit subjects the signal encoded in accordance with the communication protocol to an amplitude modulation at an amplitude modulator  333 , then amplifies the signal with the power amplifier  331 , subsequently outputs radio waves from the antenna via the directional coupler  332 , and thereby transmits the data. In addition, when a signal is received from the RF tags, the RF tags control (back scatter) impedance at the end of the antenna while the reader and writer  100  is transmitting the non-modulated carrier, thereby the reflection state is changed, and the antenna device of the reader and writer  100  detects the change. The directional coupler  332  performs orthogonal demodulation on the received radio wave signal, and synchronous clock generation units I ( 334 ) and Q ( 335 ) generate a synchronous clock. Then, preamble detection units I ( 336 ) and Q ( 337 ) detect a predetermined preamble to thereby detect the head of the data, and decoding units I ( 338 ) and Q ( 339 ) perform decoding to obtain the received data. In addition, error detection units I ( 341 ) and Q ( 342 ) are configured to detect the existence of errors using an error detection code.  FIG. 3  shows a configuration in which it is determined that the data was appropriately received if there was no error in one of the demodulation of the in-phase component of the orthogonal demodulation and the demodulation of the orthogonal component. In addition, the power amplifier  331  is configured so as to be able to set the transmission output depending on the type of the process based on the control by the transmission output control unit of the control unit  31  (specifically, the transmission of the transmission output setting signal to set the transmission output). 
     The input unit  35  is hardware through which a user inputs an instruction to the reader and writer  100 , and specifically, can be configured with button (keys) capable of inputting instructions by being pressed, a touch pad, and the like. 
     The display unit  37  is hardware to be used to show the user the result of communication with the RF tags and to encourage the user to input instructions, and specifically, can be configured by an LCD (Liquid Crystal Display) or the like. In addition, the display unit  37  may be configured as a graphical display with a touch panel sensor mounted thereon, and the input unit  35  and the display unit  37  may be integrated. 
     The interface unit  39  is hardware for communicating with an external device such as a personal computer, which stores an identification ID, via a network. 
     Next, the description will be made of the antenna device  10  of the first embodiment. 
     As shown in  FIG. 1 , the antenna device  10  includes the substantially rectangular antenna case body  12  and the patch antenna  14  accommodated in the antenna case body  12 . In the first embodiment, the antenna case body  12  is provided with a grip member  19  for facilitating gripping the antenna device  10  when the user uses the reader and writer  100  while carrying it. However, it is needless to say that the antenna case body  12  can be configured without the grip member  19 . 
     In the first embodiment, the patch antenna  14  can be configured in accordance with a known method, and can be configured to be able to communicate with RF tags only with the indicating unit  16  of the antenna case body  12 , as will be described later, and have an antenna gain which receives radio waves radiated to several meters away by adjusting the transmission output. 
     Here,  FIG. 4  shows a sectional view of the antenna device  10  taken along a line AA′ line in  FIG. 1  for easy understanding of the configuration of the patch antenna  14  of the first embodiment. As shown in  FIG. 4 , the patch antenna  14  accommodated in the antenna case body  12  includes a dielectric layer  141 , a plate-shaped earth conductor  143  facing one main surface of the dielectric layer  141 , and a plate-shaped radiation element  145  facing the other main surface of the dielectric layer  141 . The earth conductor  143  and the radiation element  145  can be formed using an arbitrary conductive material such as aluminum, copper, or the like. In addition, the dielectric layer  141  can be formed using a dielectric material such as a ceramic, or the like, and can be formed as an air layer. 
     As shown in  FIG. 4 , the earth conductor  143  and the dielectric layer  141  are formed with a through hole  42 , and the coaxial cable  40  connected to the reader and writer main body  30  is inserted into the through hole  42 . The external conductor (GND) of this coaxial cable  40  is connected to the earth conductor  143 , and the internal conductor (unbraided wire) is electrically connected to the radiation element  145  on the surface of the radiation element  145 , which faces to the dielectric layer  141 . In addition, a feeding point  44  is formed at a contact point with the radiation element  145 , and the radiation element  145  is supplied with current via the feeding point  44 . 
     Here, in the first embodiment, the radiation element  145  has a rectangular shape when seen in a plan view as shown in  FIG. 5 , and a notch portion  15  (slit) is formed at one side of the rectangular plate so as to be recessed toward the center. In addition, the feeding point  44  is positioned at a substantially central position in the extending direction of the notch portion  15  on the plate, and arranged at a position different from a center position M 0  of the plate in the direction perpendicular to the extending direction of the notch portion  15  on the plate. 
     The notch portion  15  and the feeding point  44  are arranged as described above, and thereby it is possible to generate a region in which the field intensity exceeds a predetermined threshold value t, that is, a region in which the field intensity becomes the maximum, in the vicinity of the leading end of the notch portion (a predetermined position at the notch portion) by adjusting the transmission output of the radio waves. The region is smaller than the region in which the radio waves used for the conventional selective communication propagates, and therefore it is possible to perform a more reliable selective communication with the RF tags by communicating with RF tags in this region. 
     It is known that in the patch antenna, more current flows in the vicinity of the outer periphery which is parallel to the central axis if the feeding point  44  is formed at a position which is different from the center position M 0  on the central axis of the radiation element when seen in a plan view (corresponding to a part on the X 0 -X 0 ′ line and on the Y 0 -Y 0 ′ line in the radiation element in  FIG. 5 , for example). In addition, it is also known that more current flows in the vicinity of the end portion of the notch portion which is closest to the center of the radiation element (hereinafter, simply referred to as the leading end of the notch portion) if the notch portion is provided at the outer periphery toward the center of the radiation element. The above operations and effects are obtained by using such characteristics of the patch antenna and changing the transmission output to adjust the range in which the communication with the RF tags is possible. 
     In the first embodiment, the notch portion  15  is formed on one side along the X 0 -X 0 ′ line corresponding to one of the central axes toward the center as shown in  FIG. 5 , and the feeding point  44  is provided at a position which is different from the center position on the Y 0 -Y 0 ′ line corresponding to the other central axes.  FIGS. 6 and 7  show the distributions of the field intensities along the X 0 -X 0 ′ line and the Y 1 -Y 1 ′ line in the first embodiment. As can be understood from FIGS.  5 ,  6 , and  7 , the filed intensity is not less than the predetermined threshold value t in the vicinity of the leading end of the notch portion  15  in the first embodiment by providing the notch portion  15  and the feeding point  44  in the above described arrangement. Moreover, the field intensity on the intersection point M 1  between the X 0 -X 0 ′ line and the Y 1 -Y 1  line is the maximum. 
     In addition, although the feeding point  44  and the notch portion  15  are provided at the positions shown in  FIG. 5  in the first embodiment, these positions can be appropriately set by those skilled in the art based on the known technique because of the reasons described above. That is, the positions of the notch portion  15  and the feeding point  44  are not limited to the positions shown in  FIG. 5 , and may be set differently. Similarly, the number and the size (dimension) of the notch portion  15  can be also appropriately set by those skilled in the art based on the known technique. 
     The threshold value t of the field intensity can be appropriately set by those skilled in the art in accordance with the type, and the like, of the RF tags to be used. 
     Next, a description will be made of the antenna case body  12 . In the first embodiment, the antenna case body  12  is configured as a rectangular compact having a sufficient volume to accommodate the patch antenna  14 . In addition, the antenna case body  12  is provided with an elliptical indicating unit on its outer surface, and the elliptical indicating unit corresponds to the vicinity of the leading end of the notch portion  15  which is provided in the radiation element  145  of the patch antenna  14  accommodated therein. In other words, the indicating unit  16  indicates the position corresponding to the vicinity of the leading end of the notch portion  15 . 
     Here, in the first embodiment, the field intensity can be set to be no less than the predetermined threshold value only in the vicinity of the leading end of the notch portion  15  by adjusting the transmission output of the radio waves, and as a result, the setting can be made such that the communication with the RF tags is possible only in the vicinity of the leading end, as described above. Accordingly, the user can easily recognize the region in which the communication with the RF tags is possible in selective communication by providing the indicating unit  16 , which indicates the position corresponding to the vicinity of the leading end of the notch portion  15 , in the antenna case body  12 . 
     Next, a description will be made of the process flow for the communication with the RF tags relating to collective reading, selective reading, or selective writing by the reader and writer  100  of the first embodiment with reference to  FIG. 8 . In the following description, the magnitude of the transmission output for the respective processes (that is, which output information is to be based on when the transmission output control unit  315  controls the transmission output for the respective processes) and the number of the RF tags to be communicated with in selective communication are preset in the reader and writer main body  30 . 
     First, in Act  101 , the control unit  31  obtains the process designation information indicating which process is to be executed from among collective reading, selective reading, and selective writing, based on input from the user. Specifically, the control unit  31  constructs a process designation screen  51  as shown in  FIG. 9 , and causes the display unit  37  to display the screen. The user designates a desired process via the input unit  35  based on the process designation screen  51  displayed on the display unit  37 . The control unit  31  obtains the process designation information from the user&#39;s designation via the input unit  35 . 
     Next, in Act  102 , the control unit  31  determines whether the obtained process designation information designates collective reading. If the information designates collective reading, the transmission output control unit  315  of the control unit  31  sets the transmission output for the wireless unit  33  based on the collective reading output information stored in the storage unit  311  in Act  103 . 
     Next, in Act  104 , the control unit  31  controls the wireless unit  33  to cause the antenna device  10  to radiate radio waves for collective reading, thereby performing collective reading, and obtains the information (identification ID) held in the RF tags. Then, in Act  105 , the control unit  31  constructs a process result screen  53  ( FIG. 10 ) for informing of the completion of the process and causes the display unit  37  to display the screen, and the process returns to Act  101 . If the executed process is collective reading, described herein, or selective reading, which will be described later, the control unit  31  displays the obtained identification ID along with the notification of the completion of the process on the process result screen for the notification for the user. In addition, if the control unit  31  cannot obtain the identification ID, the control unit displays the notification of the failure of the communication with the RF tags instead of the content shown in  FIG. 10  on the process result screen  53  for the notification for the user. 
     On the other hand, if it is determined that the process designation information does not designate collective reading in Act  102 , the process proceeds to Act  106 , and the control unit  31  determines whether the process designation information designates selective reading. If the information designates selective reading, the process proceeds to Act  107 , and the transmission output setting unit of the control unit  31  sets the transmission output for the wireless unit  33  based on the selective reading output information stored in the storage unit  311 . 
     Next, in Act  108 , the control unit  31  constructs a process start screen  55 , as shown in  FIG. 11 , for encouraging the movement to the region in the respective RF tags, which is indicated by the indicating unit  16 , and obtaining the user&#39;s instruction relating to the reading start, and causes the display unit  37  to display the process start screen  55 . Then, the process proceeds to Act  109 , and the control unit  31  determines whether the information regarding the reading start is obtained. If the user places the RF tag in the region on the antenna case body, which is indicated by the indicating unit  16  (inside the elliptical shape in this embodiment) and inputs the instruction for the reading start via the input unit  35 , the control unit  31  obtains an instruction relating to the reading start, and the process proceeds to Act  110 . In Act  110 , the control unit  31  controls the wireless unit  33  to cause the antenna device  10  to radiate the radio wave for selective reading, performs the selective reading process, and obtains the identification ID held in the respective RF tags. Thereafter, in Act  111 , the control unit  31  causes the display unit  37  to display the process result screen  53  for notifying the obtained identification ID along with the completion of the process ( FIG. 10 ), and the process returns to Act  101 . 
     Here, the RF tags, of which the number is smaller or larger than that preset by the user, are read as a result of the execution of selective reading in some cases. At this time, if the RF tags of which the number was smaller than the set number were read, the control unit  31  constructs a process result screen  57  as shown in  FIG. 12 , causes the display unit  37  to display the screen, and encourages the user to move the RF tags or increase the setting of the transmission output. 
     On the other hand, if the RF tags of which the number was larger than the set number were read, the control unit  31  constructs a process result screen  59  as shown in  FIG. 13 , causes the display unit  37  to display the screen, and encourages the user to decrease the setting of the transmission output. 
     In Act  106 , if it is determined that the process designation information does not designate selective reading, the control unit  31  determines that the process designation information designates selective writing. Then, the process proceeds to Act  112 , and the transmission output setting unit  315  of the control unit  31  sets the transmission output for the wireless unit  33  based on the selective reading output information stored in the storage unit  311 . 
     Next, in Act  113 , the control unit  31  constructs the process start screen as shown in  FIG. 11  for encouraging the movement of the RF tags to the region indicated by the indicating unit  16  and obtaining the user&#39;s instruction regarding the reading start, and causes the display unit  37  to display the screen. Subsequently, the process proceeds to Act  114 , and the control unit  31  determines whether or not the instruction for the reading start is obtained. If the user places the RF tags in the region on the antenna case body, which is indicated by the indicating unit  16 , and inputs the reading start instruction via the input unit  35 , the control unit  31  obtains the instruction for the reading start, and the process proceeds to Act  115 . In Act  115 , the control unit  31  controls the wireless unit  33  to cause the antenna device  10  to radiate the radio waves for selective writing, performs selective writing, and add the identification ID for the respective RF tags. Then, in Act  116 , the control unit  31  confirms that the writing is completed based on the responses from the RF tags, constructs the process result screen  53  in the same manner as in the case of reading process, and causes the display unit  37  to display the screen. 
     Here, writing is performed on the RF tags, of which the number is smaller or larger than that preset by the user in the designation of the process designation information, as a result of the execution of selective writing in some cases. At this time, if writing was performed on RF tags of which the number was smaller than the preset number, the control unit  31  constructs the process result screen  57  as shown in  FIG. 12 , causes the display unit  37  to display the screen, and encourages the user to move the RF tags or increase the setting of the transmission output. On the other hand, if writing was performed on RF tags of which the number was larger than the preset number, the control unit  31  constructs the process result screen  59  as shown in  FIG. 13 , causes the display unit  37  to display the screen, and encourages the user to decrease the setting of the transmission output. 
     As described above, the reader and writer  100  of the first embodiment can perform both collective reading and selective communication by changing the transmission output of the radio wave to be radiated from the antenna device  10 . In addition, it is possible to allow the region in which the field intensity is not less than the predetermined threshold value to correspond the region (the vicinity of the leading end of the slit provided in the radiation element) indicated by the indicating unit by controlling the transmission output. Accordingly, it is possible to reliably communicate with the RF tags, with which the user desires to communicate, in selective communication. 
     Second Embodiment 
     In the second embodiment, the reader and writer  100  further includes a restriction member  60  to be used by being mounted on the antenna device  10  as shown in  FIG. 14  in addition to the configuration described in the first embodiment. It is possible to restrict the radiation of the radio waves from the region other than the region indicated by the indicating unit  16  to the outside of the case body as compared with the radiation of the radio wave from the region indicated by the indicating unit  16  to the outside of the case body, by mounting the restriction member  60  onto the antenna device  10 . The restriction member  60  is configured of a metal material, for example, as shown in  FIG. 14 , and can be a compact provided with an opening portion  62  in the vicinity of the position indicated by the indicating unit  16 . In addition, it is also possible to differently configure the restriction member  60 . For example, the restriction member  60  can be a compact which has a surface facing the outer surface of the antenna case body in the mounted state and configured with plastic processed for radio wave absorption (attached with a radio wave absorption material, for example) as its material, and is provided with an opening portion only at a position corresponding to the vicinity of the position indicated by the indicating unit  16  or constituted by an unprocessed plastic. 
     In the second embodiment, the restriction member  60  is configured to be able to retreat from the position where the radiation of the radio wave from the region other then the region indicated by the indicating unit  16  to the outside of the case body  12  is restricted to the position where the radiation of the radio wave is not restricted, by being detached from the outer surface of the antenna device  10  (antenna case body  12 ). However, the retreat of the restriction member  60  from the antenna device  10  is not limited to detaching from the surface of the antenna case body, and can be configured differently. For example, it is also applicable to configure the restriction member  60  by connecting to the antenna case body  12  via a hinge and allow the restriction member  60  to be movable from a position where the radiation of the radio waves is restricted to a position where the radiation of the radio waves is not restricted (in this specification, “retreat” as a concept includes movement of position). 
     Other Embodiments 
     Although the description was made of the first and second embodiments as above, it is needless to say that another configuration can be applied. 
     For example, although the radiation element  145  of the antenna device  10  has a rectangular shape in the first embodiment, the shape thereof is not particularly limited as long as it is a plate shape formed with a notch portion extending such that a part of the outer line of the radiation element  145  is recessed toward the center, and the radiation element  145  may be shaped differently. In such a case, the feeding point  44  is arranged at a position in the vicinity of the leading end of the notch portion  15  in which more current flows; in other words, the position in the vicinity of the leading end of the notch portion  15 , in which the field intensity is allowed to be not less than the predetermined threshold value when the transmission output is adjusted. 
     In addition, although the indicating unit  16  has an elliptical shape printed on the outer surface of the antenna case body  12  in the first embodiment, the shape thereof is not limited thereto. For example, it is also possible to provide the indicating unit  16  by forming a recess or a protrusion on the outer surface of the case body  12  or by attaching a sticker. In addition, the shape thereof is also not particularly limited, and can be an arrow shape as shown in  FIG. 15 , for example. In  FIG. 15 , a part indicated by the broken line is a position corresponding to the vicinity of the leading end of the notch portion  15 . In this case, the indicating unit  16  is applicable as long as the field intensity is not less than the threshold value t in the region indicated by the arrow, and it is not necessary that the field intensity of the radio wave is not less than the threshold value in the region in the arrow itself. 
     Moreover, the output information for controlling the transmission output is stored in the storage unit  311  constituted by the ROM or the RAM in the reader and writer main body  30  in the first embodiment. However the invention is not limited thereto, and it is also applicable that the output information is stored in a storage unit in the external device and obtained by the control unit  31  via the interface unit  39 , if necessary. 
     Furthermore, although the antenna device  10  (antenna case body  12 ) and the reader and writer main body  30  are separately configured in the first embodiment, it is also applicable to integrally configure the antenna device  10  and the reader and writer main body  30  by connecting two case bodies (antenna case body  12  and the case body of the reader and writer main body  30 ) or by accommodating the patch antenna  14  and the hardware of the reader and writer main body  30  in the respective compartment inside one case body. 
     Moreover, although the transmission output is set based on the output information stored in advance in the first embodiment, it is also applicable that the user sets the transmission output via the input unit  35 . 
     As described above, according to the technique disclosed in this specification, it is possible to collectively communicate with one or a plurality of unspecified RF tags, and reliably communicate with one or a plurality of specific RF tags in selective communication. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of invention. Indeed, the novel apparatus, methods and computer readable media described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the apparatus and methods and computer readable media described herein may be made without departing from the sprit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.