Abstract:
A reader antenna includes dipole antennas, the dipole antennas including: a horizontal dipole antenna having the characteristic of horizontal polarization; and a dipole antenna perpendicular to the horizontal dipole antenna and including a vertical dipole antenna having the characteristic of vertical polarization, wherein the horizontal dipole antenna and the vertical dipole antenna may both have the characteristic of circular polarization. The reader antenna can be easily stored in an electronic shelf because it is realized in an ultrathin structure using a single-layered dielectric substrate.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2012-0016593 filed in the Korean Intellectual Property Office on Feb. 17, 2012, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     (a) Field of the Invention 
     The present invention relates to a reader antenna and an RFID electronic shelf including the same, and more particularly, to a reader antenna capable of simultaneously recognizing many individual items (item level tagging), and an RFID electronic shelf including the same. 
     (b) Description of the Related Art 
     The application field of radio frequency identification (RFID) in the ultra-high frequency (UHF) band has been extending from case or box unit recognition to individual item recognition as it has been recently used for an RFID electronic shelf. 
     The material and shape of items to be mounted on an RFID electronic shelf, the shape of a packaging material, the method of displaying items, and so on may be diversified according to application fields. Thus, a reader antenna for an RFID electronic shelf is emerging as one of the methods for simultaneously recognizing a plurality of items displayed on the RFID electronic shelf. 
     Recently, active research has been conducted on RFID electronic shelf applications in the field of RFID technology in the high frequency (HF) band and the field of RFID technology in the ultra-high frequency (UHF) band. The RFID technology of the HF band employing magnetic coupling is being studied in the RFID electronic shelf field, placing stress on excellent field characteristics for liquids and metals compared to the UHF band, but the recognition rate is drastically degraded due to interference between RFID tags, interference between tags and readers, and the like. The UHF band RFID technology using backscattering of electromagnetic waves, having advantages in that it has a relatively long recognition distance and similar field characteristics to those in the UHF band in a near field zone, is being studied in the RFID electronic shelf field. However, there is still a problem of recognition rate degradation due to a fading zone, caused by a change made to items to be displayed and a display method, and a polarization mismatch caused by the direction of tags to be displayed. Particularly, a conventional fixed reader antenna is directly applied to an electronic shelf in most cases because little research has been conducted regarding a reader antenna for an RFID electronic shelf in the UHF band. This leads to poor mountability of the reader antenna on the shelf. 
     Moreover, some reader antennas being studied for RFID electronic shelf applications in the UHF band cannot solve the problem of misrecognition caused by a polarization mismatch with tags, and a fading zone. 
     That is, in order to simultaneously recognize a plurality of tags in an item display environment where a plurality of items having different physical properties and shapes may be arbitrarily displayed on an RFID electronic shelf, the reader antenna for the RFID electronic shelf has to be easily mounted on the electronic shelf, and has to be capable of transmission and reception of polarization of arbitrary tags. Further, a technique of forming a near field on the RFID electronic shelf is required to avoid tag misrecognition caused by a fading zone. However, there are many difficulties in designing a reader antenna for an RFID electronic shelf having the above-mentioned characteristics by the conventional HF band antenna technology and the UHF band antenna technology. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in an effort to provide a reader antenna which is easy to install because of its ultrathin profile and that offers an improved recognition rate, and an RFID electronic shelf including the same. 
     An exemplary embodiment of the present invention provides a reader antenna including dipole antennas, the dipole antennas including: a horizontal dipole antenna having the characteristic of horizontal polarization; and a dipole antenna perpendicular to the horizontal dipole antenna and including a vertical dipole antenna having the characteristic of vertical polarization, wherein the horizontal dipole antenna and the vertical dipole antenna may both have the characteristic of circular polarization. 
     The horizontal dipole antenna may include: a dielectric layer; a first horizontal unipole antenna formed in a first direction on the top surface of the dielectric layer; and a second horizontal unipole antenna formed on the bottom surface of the dielectric layer and coupled to the first horizontal unipole antenna to form the dipole antennas. 
     The horizontal dipole antenna may further include: a first horizontal feed line formed on the top surface of the dielectric layer and connected to the first horizontal unipole antenna; and a second horizontal feed line formed on the bottom surface of the dielectric layer and connected to the second horizontal unipole antenna, wherein a first horizontal impedance matching slot may be formed at a connecting portion of the first horizontal unipole antenna connected to the first horizontal feed line, and a second horizontal impedance matching slot may be formed at a connecting portion of the second horizontal unipole antenna connected to the second horizontal feed line. 
     The first horizontal unipole antenna may be symmetrical to the second horizontal unipole antenna with respect to the first horizontal feed line. 
     The vertical dipole antenna may include: the dielectric layer; a first vertical unipole antenna formed in a second direction perpendicular to the first direction on the top surface of the dielectric layer; and a second vertical unipole antenna formed in the second direction on the bottom surface of the dielectric layer and coupled to the first vertical unipole antenna to form the dipole antennas. 
     The vertical dipole antenna may further include: a first vertical feed line formed on the top surface of the dielectric layer and connected to the first vertical unipole antenna; and a second vertical feed line formed on the bottom surface of the dielectric layer and connected to the second vertical unipole antenna, wherein a first vertical impedance matching slot may be formed at a connecting portion of the first vertical unipole antenna connected to the first vertical feed line, and a second vertical impedance matching slot may be formed at a connecting portion of the second vertical unipole antenna connected to the second vertical feed line. 
     The first vertical unipole antenna may be symmetrical to the second vertical unipole antenna with respect to the first vertical feed line. 
     The first horizontal impedance matching slot, the second horizontal impedance matching slot, the first vertical impedance matching slot, and the second vertical impedance matching slot may each have a horizontal slot portion and a vertical slot portion, and impedance matching may be performed by adjusting the lengths of the horizontal and vertical slot portions. 
     Another embodiment of the present invention provides a reader antenna including a patch antenna, the patch antenna including: a dielectric layer; and a polygonal antenna formed on the top surface of the dielectric layer and having the characteristic of circular polarization. 
     The patch antenna may further include a patch feed line formed on the top surface of the dielectric layer and connected to the polygonal antenna, wherein the patch feed line may be spaced a predetermined length apart from the central axis of the polygonal axis. 
     The patch feed line may be inserted a predetermined length into the polygonal antenna. 
     Yet another embodiment of the present invention provides an RFID electronic shelf including a reader antenna, the RFID electronic shelf including: a shelf portion including a horizontal shelf for displaying items and a vertical shelf perpendicular to the horizontal shelf; and the reader antenna including a plurality of patch antennas and a plurality of dipole antennas formed on the horizontal shelf and the vertical shelf, respectively. 
     The RFID electronic shelf may further include a phase shifter block connected to the plurality of patch antennas and forming a time-varying near field. 
     Each of the patch antennas may include: a dielectric layer; and a polygonal antenna formed on the top surface of the dielectric layer and having the characteristic of circular polarization. 
     Each of the patch antennas may further include a patch feed line formed on the top surface of the dielectric layer and connected to the polygonal antenna, wherein the patch feed line may be spaced a predetermined length apart from the central axis of the polygonal axis. 
     The patch feed line may be inserted a predetermined length into the polygonal antenna. 
     The RFID electronic shelf may further include a bent impedance transformer connected to the patch feed line. 
     The RFID electronic shelf may further include a patch current phase delay unit connected to the patch feed line. 
     The plurality of patch antennas may include four patch antennas of two rows and two columns connected to the patch feed line and gathering to form a unit patch antenna, and the patch feed line of the unit patch antenna may be connected to a unit feed port. 
     The phase shifter block may be connected to the unit feed port. 
     The dipole antennas may include: a horizontal dipole antenna having the characteristic of horizontal polarization; and a dipole antenna perpendicular to the horizontal dipole antenna and including a vertical dipole antenna having the characteristic of vertical polarization, wherein the horizontal dipole antenna and the vertical dipole antenna may both have the characteristic of circular polarization. 
     The horizontal dipole antenna may include: a dielectric layer; a first horizontal unipole antenna formed in a first direction on the top surface of the dielectric layer; and a second horizontal unipole antenna formed on the bottom surface of the dielectric layer and coupled to the first horizontal unipole antenna to form the dipole antennas. 
     The horizontal dipole antenna may further include: a first horizontal feed line formed on the top surface of the dielectric layer and connected to the first horizontal unipole antenna; and a second horizontal feed line formed on the bottom surface of the dielectric layer and connected to the second horizontal unipole antenna, wherein a first horizontal impedance matching slot may be formed at a connecting portion of the first horizontal unipole antenna connected to the first horizontal feed line, and a second horizontal impedance matching slot may be formed at a connecting portion of the second horizontal unipole antenna connected to the second horizontal feed line. 
     The first horizontal unipole antenna may be symmetrical to the second horizontal unipole antenna with respect to the first horizontal feed line. 
     The vertical dipole antenna may include: the dielectric layer; a first vertical unipole antenna formed in a second direction perpendicular to the first direction on the top surface of the dielectric layer; and a second vertical unipole antenna formed in the second direction on the bottom surface of the dielectric layer and coupled to the first vertical unipole antenna to form the dipole antennas. 
     The vertical dipole antenna may further include: a first vertical feed line formed on the top surface of the dielectric layer and connected to the first vertical unipole antenna; and a second vertical feed line formed on the bottom surface of the dielectric layer and connected to the second vertical unipole antenna, wherein a first vertical impedance matching slot may be formed at a connecting portion of the first vertical unipole antenna connected to the first vertical feed line, and a second vertical impedance matching slot may be formed at a connecting portion of the second vertical unipole antenna connected to the second vertical feed line. 
     The first vertical unipole antenna may be symmetrical to the second vertical unipole antenna with respect to the first vertical feed line. 
     The first horizontal impedance matching slot, the second horizontal impedance matching slot, the first vertical impedance matching slot, and the second vertical impedance matching slot each may have a horizontal slot portion and a vertical slot portion, and impedance matching may be performed by adjusting the lengths of the horizontal and vertical slot portions. 
     The reader antenna according to an exemplary embodiment of the present invention can be easily stored in an electronic shelf because it is realized in an ultrathin structure using a single-layered dielectric substrate. 
     The RFID electronic shelf according to an exemplary embodiment of the present invention can stably recognize items, even if a plurality of items are displayed in an arbitrary form on the electronic shelf, by arranging a reader antenna on the electronic shelf according to the mounting position of the antenna and the display form of items. 
     The RFID electronic shelf according to an exemplary embodiment of the present invention can offer an improved recognition rate because a fading zone can be eliminated from an electronic shelf by forming a time-varying near field on the electronic shelf by the use of both an antenna and a phase shifter block. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top plan view of a reader antenna according to a first exemplary embodiment of the present invention. 
         FIG. 2  is a perspective view of a horizontal dipole antenna of the reader antenna according to the first exemplary embodiment of the present invention. 
         FIG. 3  is a cross-sectional view taken along line III-III of  FIG. 2 . 
         FIG. 4  is a top plan view of a first horizontal unipole antenna and a first vertical unipole antenna formed on the top surface of a dielectric layer of the reader antenna according to the first exemplary embodiment of the present invention. 
         FIG. 5  is a top plan view of a second horizontal unipole antenna and a second vertical unipole antenna formed on the bottom surface of the dielectric layer of the reader antenna according to the first exemplary embodiment of the present invention. 
         FIG. 6  is a perspective view of a reader antenna according to a second exemplary embodiment of the present invention. 
         FIG. 7  is a perspective view of a unit patch antenna having reader antennas arranged in two rows and two columns according to the second exemplary embodiment of the present invention. 
         FIG. 8  is a perspective view of an RFID electronic shelf including the reader antenna according to the first exemplary embodiment and the reader antenna according to the second exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The present invention will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the principles for the present invention. 
     In order to clarify the present invention, elements extrinsic to the description are omitted from the details of this description, and like reference numerals refer to like elements throughout the specification. 
     Now, a reader antenna according to a first exemplary embodiment of the present invention will be described in detail with reference to  FIGS. 1 to 5 . 
       FIG. 1  is a top plan view of a reader antenna according to a first exemplary embodiment of the present invention,  FIG. 2  is a perspective view of a horizontal dipole antenna of the reader antenna according to the first exemplary embodiment of the present invention,  FIG. 3  is a cross-sectional view taken along line III-III of  FIG. 2 ,  FIG. 4  is a top plan view of a first horizontal unipole antenna and a first vertical unipole antenna formed on the top surface of a dielectric layer of the reader antenna according to the first exemplary embodiment of the present invention, and  FIG. 5  is a top plan view of a second horizontal unipole antenna and a second vertical unipole antenna formed on the bottom surface of the dielectric layer of the reader antenna according to the first exemplary embodiment of the present invention. 
     As shown in  FIG. 1 , the reader antenna according to the first exemplary embodiment of the present invention includes dipole antennas  3 , the dipole antennas  3  including a horizontal dipole antenna  1  having the characteristic of horizontal polarization and a vertical dipole antenna  2  perpendicular to the horizontal dipole antenna  1  and having the characteristic of vertical polarization. 
     The horizontal dipole antenna  1  and the vertical dipole antenna  2  both have the characteristic of circular polarization. 
     As shown in  FIG. 2  and  FIG. 3 , the horizontal dipole antenna  1  includes a single dielectric layer  100 , a radiation-type first horizontal unipole antenna  10  formed in a first direction, i.e., the horizontal direction, on the top surface of the dielectric layer  100 , and a radiation-type second horizontal unipole antenna  20  formed on the bottom surface of the dielectric layer  100  and coupled to the first horizontal unipole antenna  10  to form the dipole antennas. 
     A first horizontal feed line  50  connected to the first horizontal unipole antenna  10  and supplying current to the first horizontal unipole antenna  10  is formed on the top surface of the dielectric layer  100 , and a second horizontal feed line  60  connected to the second horizontal unipole antenna  20  and supplying current to the second horizontal unipole antenna  20  is formed on the bottom surface of the dielectric layer  100 . Using the first horizontal feed line  50  and the second horizontal feed line  60 , the first horizontal unipole antenna  10  and the second horizontal unipole antenna  20  can be easily arranged. The first horizontal unipole antenna  10  is symmetrical to the second horizontal unipole antenna  20  with respect to the first horizontal feed line  50 . 
     A first horizontal impedance matching slot  15  for impedance matching between the first horizontal feed line  50  and the first horizontal unipole antenna  10  is formed at a connecting portion of the first horizontal unipole antenna  10  connected to the first horizontal feed line  50 , and a second horizontal impedance matching slot  25  for impedance matching between the second horizontal feed line  60  and the second horizontal unipole antenna  20  is formed at a connecting portion of the second horizontal unipole antenna  20  connected to the second horizontal feed line  60 . 
     The first horizontal impedance matching slot  15  and the second horizontal impedance matching slot  25  are T-shaped slots, each having a vertical slot portion  15   b  and  25   b  connected to an intermediate portion of a horizontal slot portion  15   a  and  25   a . Impedance matching can be made easy by adjusting the length d 1  of the horizontal slot portion and the length d 2  of the vertical slot portion. 
     Like the horizontal dipole antenna  1 , the vertical dipole antenna  2  may include the dielectric layer  100 , a first vertical unipole antenna  30  formed in a second direction perpendicular to the first direction, i.e., the vertical direction, on the top surface of the dielectric layer  100 , and a second vertical unipole antenna  40  formed in the second direction on the bottom surface of the dielectric layer  100  and coupled to the first vertical unipole antenna  30  to form the dipole antennas. 
     A first vertical feed line  70  connected to the first vertical unipole antenna  30  is formed on the top surface of the dielectric layer  100 , and a second vertical feed line  80  connected to the second vertical unipole antenna  40  is formed on the bottom surface of the dielectric layer  100 . 
     A first vertical impedance matching slot  35  for impedance matching between the first vertical feed line  70  and the first vertical unipole antenna  30  is formed at a connecting portion of the first vertical unipole antenna  30  connected to the first vertical feed line  70 , and a second vertical impedance matching slot  45  is formed at a connecting portion of the second vertical unipole antenna  40  connected to the second vertical feed line  80 . 
     The first vertical unipole antenna  30  is symmetrical to the second vertical unipole antenna  40  with respect to the first vertical feed line  70 . 
     The first horizontal impedance matching slot  15 , the second horizontal impedance matching slot  25 , the first vertical impedance matching slot  35 , and the second vertical impedance matching slot  45  each have a horizontal slot portion and a vertical slot portion, and impedance matching can be performed by adjusting the lengths d 1  and d 2  of the horizontal and vertical slot portions. 
     The configuration of the horizontal dipole antenna and the vertical dipole antenna will be concretely described below. 
     The first horizontal unipole antenna  10  and first vertical unipole antenna  30  shown in  FIG. 4  and the second horizontal unipole antenna  20  and second vertical unipole antenna  30  shown in  FIG. 5  can be used to exhibit the characteristic of circular polarization. 
     As shown in  FIG. 4 , the first horizontal unipole antenna  10  and the first vertical unipole antenna  30  are formed on the top surface of the dielectric layer  100 . The first horizontal impedance matching slot  15  and the first vertical impedance matching slot  35  are formed in the first horizontal unipole antenna  10  and the first vertical unipole antenna  30 , respectively, to achieve impedance matching. 
     The first horizontal unipole antenna  10  is horizontally formed to transmit and receive horizontal polarization, and the first vertical unipole antenna  30  is vertically formed to transmit and receive vertical polarization. The first horizontal feed line  50  feeds electric power to the first horizontal unipole antenna  10 , and the first vertical feed line  70  feeds electric power to the first vertical unipole antenna  30 . The first horizontal feed line  50  and the first vertical feed line  70  are divided from the first feed line  80 . 
     A dipole current phase delay unit  71  is formed on the first vertical feed line  70  so that the phase of the current fed to the first vertical unipole antenna  30  is delayed by 90 degrees relative to the phase of the current fed to the first horizontal unipole antenna  1 . 
     With the phase difference of 90 degrees between the currents respectively fed to the first vertical unipole antenna  30  and the first horizontal unipole antenna  10 , circular polarization is radiated through the first vertical unipole antenna  30  and the first horizontal unipole antenna  10 . 
     As shown in  FIG. 5 , the second horizontal unipole antenna  20  and the second vertical unipole antenna  40  are formed on the bottom surface of the dielectric layer  100 . The second horizontal impedance matching slot  25  and the second vertical impedance matching slot  45  are formed in the second horizontal unipole antenna  20  and the second vertical unipole antenna  40 , respectively, to achieve impedance matching. 
     The second horizontal unipole antenna  20  is horizontally formed to transmit and receive horizontal polarization, and the second vertical unipole antenna  40  is vertically formed to transmit and receive vertical polarization. The second horizontal feed line  20  feeds electric power to the second horizontal unipole antenna  60 , and the second vertical feed line  80  feeds electric power to the second vertical unipole antenna  40 . The second horizontal feed line  60  and the second vertical feed line  80  are divided from a second feed line  90 . 
     A tapered ground  81  is formed by tapering the second horizontal feed line  60  and the second vertical feed line  80  at a junction between them, so that current is divided into two exact halves and fed to the second horizontal unipole antenna  20  and the second vertical unipole antenna  40 , respectively. 
     As shown in  FIG. 1 , the first horizontal unipole antenna  10  and the first vertical unipole antenna  30  are formed on the top surface of the dielectric layer  100 , and the second horizontal unipole antenna  20  and the second vertical unipole antenna  40  are formed on the bottom surface of the dielectric layer  100 , thereby forming a dipole antenna  3  having the characteristic of circular polarization. 
     Although the reader antenna is a dipole antenna in the first exemplary embodiment, the reader antenna may be a patch antenna in a second exemplary embodiment. 
     Hereinafter, referring to  FIGS. 6 and 7 , a reader antenna according to the second exemplary embodiment of the present invention will be described in detail. 
       FIG. 6  is a perspective view of a reader antenna according to a second exemplary embodiment of the present invention. 
     As shown in  FIG. 6 , the reader antenna according to the second exemplary embodiment of the present invention is a patch antenna  4  including a dielectric layer  100  and a radiation-type polygonal antenna  200  formed on the top surface of the dielectric layer  100  and having the characteristic of circular polarization. 
     The polygon antenna  200  is an antenna which is symmetrical with respect to a symmetrical axis C. 
     A patch feed line  400  connected to the polygonal antenna  200  and supplying current to the polygonal antenna  200  is formed on the top surface of the dielectric layer  100 . 
     The patch feed line  400  uses an offset feeding method so as to be spaced a predetermined length P 1  apart from the central axis C of the polygonal antenna  2 , thereby achieving the characteristic of circular polarization. 
     The patch feed line  400  may use an inset feeding method so as to be inserted a predetermined length P 2  into the polygonal antenna  200 , thereby efficiently achieving impedance matching in various ways. 
       FIG. 7  is a perspective view of a unit patch antenna having reader antennas arranged in two rows and two columns according to the second exemplary embodiment of the present invention. 
     As shown in  FIG. 7 , a plurality of patch antennas  4 , i.e., four patch antennas of two rows and two columns connected to the patch feed line  400 , gather to form a unit patch antenna  210 . 
     The unit patch antenna  210  includes a pair of first unit patch antennas  211  and  212  and a pair of second unit patch antennas  213  and  214  facing each other with respect to the central axis A of the arrangement. 
     Current fed from a unit feed port  410  is divided into halves and fed, and the impedance of the divided current is transformed by a bent impedance transformer  420  and fed to the pair of first unit patch antennas  211  and  212  and the pair of second unit patch antennas  213  and  214 , respectively. 
     Moreover, a patch current phase delay unit  430  is formed at the patch feed line  400  to improve the impedance bandwidth of the unit patch antenna  210  and the axial ratio of circular polarization. 
     Hereinafter, an RFID electronic shelf including the reader antenna according to the first exemplary embodiment and the reader antenna according to the second exemplary embodiment will be described in detail. 
       FIG. 8  is a perspective view of an RFID electronic shelf including the reader antenna according to the first exemplary embodiment and the reader antenna according to the second exemplary embodiment. 
     As shown in  FIG. 8 , the RFID electronic shelf includes a shelf portion  1000  including a horizontal shelf  1100  for displaying items and a vertical shelf  1200  perpendicular to the horizontal shelf  1100 , and a reader antenna  2000  formed on the shelf portion  1000 . 
     The reader antenna  2000  includes a plurality of patch antennas  4  formed on the horizontal shelf  1100  and a plurality of dipole antennas  3  formed on the vertical shelf  1200 . 
     Although the present exemplary embodiment has been described with respect to, but is not limited to, three unit patch antennas  210  spaced apart from each other and two dipole antennas  3  being symmetrical with respect to a feeding point  5 , the RFID electronic shelf may be scaled up or down according to its structure. 
     Since the two dipole antennas  3  are formed on the vertical shelf  1200  behind a plurality of items to be stored and delayed, the items can be stably recognized. 
     Moreover, a plurality of items displayed in a single layer can be stably recognized because the three unit patch antennas  210  are formed on the horizontal shelf  1100 , spaced apart from each other. 
     Meanwhile, a phase shifter block  3000  connected to a plurality of patch antennas may be installed to form a time-varying near field. That is, a time-varying near field can be formed by installing a phase shifter block  3000  connected to three unit patch antennas  210 . The time-varying near field can eliminate a fading zone that may be formed on the RFID electronic shelf. At this point, the phase shifter block  3000  is able to cause a current having a sequential phase difference that varies with time to be fed to unit feed ports  410  of the three unit patch antennas  210 , respectively. 
     While the present invention has been shown and described in connection with the exemplary embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims. 
     
       
         
               
             
               
               
               
             
           
               
                   
               
               
                 &lt;Description of Symbols&gt; 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                   3: dipole antenna 
                   4: patch antenna 
               
               
                   
                  10: first horizontal unipole antenna 
               
               
                   
                  20: second horizontal unipole antenna 
               
               
                   
                  30: first vertical unipole antenna 
               
               
                   
                  40: second vertical unipole antenna 
               
               
                   
                  100: dielectric layer 
                  200: polygonal antenna 
               
               
                   
                  210: unit patch antenna 
                  400: temperature sensor 
               
               
                   
                 1000: shelf portion 
                 2000: reader antenna 
               
               
                   
                 3000: phase shifter block