Abstract:
An interrogator with an antenna that allows information exchanges with multiple transponders in a shorter distance of communication, by securing an intensified and uniform electromagnetic energy concentrated on areas near antenna elements. The interrogator is furnished with a sleeve antenna that includes a monopole conductor of ¼ wavelength (free space wavelength) continuously connected to a core wire of a coaxial cable on one end thereof, and a feed point on the other end, in which the sleeve antenna is grounded at the feed point. The interrogator has a plurality of the transponders arrayed near the antenna, and a plurality of the antennas selected by RF signal selectors. The interrogator antenna allows movable body identification such as in a goods management system for identifying multiply arrayed goods.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to an interrogator that exchanges information with transponders by using an RF signal of the microwave band, specifically to an interrogator provided with antennas suitable for exchanging RF signals with multiple transponders. 
   Movable body identification equipment (identification system by radio waves) is composed of an interrogator and plural transponders responding to the interrogator. The interrogator radiates an RF signal of the microwave band (including the quasi-microwave band) from an antenna to the transponders not having the cells, and exchanges information with the transponders. The transponders receive the RF signal from the interrogator with small antennas, and rectify the RF signal to attain the DC power supply, clocks and data, and in response to the data, answer the information of the memory to the interrogator from the small antennas. 
   The exchange of information includes, for example, discrimination of identification numbers different in each of the transponders. In this case, applying the transponders on articles such as packages will achieve a system that discriminates the packages being carried on a belt conveyer, without using human hands (for example, refer to International Publication No. WO98/21691). 
   The distance of communication within which the information exchange is possible between the interrogator and the transponders is determined depending on the antenna and the power of an RF transmitting signal that the interrogator generates, in case of the capability and the shape and size of the transponders being constant. If the antenna is a phased array antenna that is synthesized with multiple antenna elements, the distance of communication will be prolonged. If the antenna is an antenna with single element, the communication area will be limited within an area near the antenna; thus, the antenna structure of the interrogator limits the range of the distance of communication. A traveling wave antenna is used, for example, in equipment having the transponders applied to the examination of tickets, which discriminates the transponders one by one (refer to Japanese Utility Model Laid-open (Kokai) No. Hei 2-32174). 
   SUMMARY OF THE INVENTION 
   In a case where a single interrogator is desired to secure communications with as many transponders as possible, an antenna configuration for the interrogator that allows an array of multiple transponders within a communication area becomes essential. 
   However, in a quasi-microwave band, for example, a phase synthesis of an electromagnetic wave radiated from the interrogator and electromagnetic waves radiated from the transponders in the space is apt to create fluctuations of the electromagnetic waves; and it is difficult to realize a uniform electromagnetic field over a wide range. Further, if plural transponders are arrayed close to each other, the mutual coupling between the antennas will disturb the radiation characteristic to thereby deteriorate the antenna characteristic, which makes it difficult to attain the power that the transponders need. 
   The present invention has been made in view of the foregoing circumstances, and it provides an interrogator having an antenna that secures an intensified and uniform electromagnetic energy concentrated on areas near antenna elements and thereby achieves an array of multiple transponders in a shorter distance of communication, and a goods management system applying the same. 
   In order to solve the problem of the invention, the interrogator is furnished with a sleeve antenna that includes a monopole conductor of ¼ wavelength (free space wavelength) continuously connected to a core wire of a coaxial cable on one end thereof, and a feed point on the other end, in which the sleeve antenna is grounded at the feed point. An antenna having such a physical makeup generates an electromagnetic field on an outer conductor of the coaxial cable, and by setting the part of the coaxial cable to a length of some wavelengths, the part functions as an antenna. Accordingly, it becomes possible to array plural transponders in an area covering a length of some wavelengths from the open end of the sleeve antenna. 
   First, the general characteristic of a sleeve antenna will be discussed.  FIG. 1  illustrates a basic configuration of the monopole antenna. The antenna includes a monopole in which the coaxial cable having a core wire  1  and a dielectric substance  3  and an outer conductor  2  extends the core wire  1  from the open end by a length of about ¼ wavelength of the free space wavelength, which is excited by a signal source  5 . And, it is idealistic that an infinite ground plane  4  is formed vertically to the monopole antenna including the open end. 
   The radio wave radiated from a monopole antenna having this sort of configuration has a voltage distribution V, a current distribution Cl, and a radiation pattern P between the core wire  1  (monopole antenna) and the ground plane  4 , as shown in  FIG. 2 . The radiation pattern P is formed at the symmetric position to the monopole antenna  1 . 
   Here, as shown in  FIG. 3 , if the grounding is made at a feed point  14 , the ground plane will move to the feed point  14 , and varies the voltage and current distributions on the antenna. The signal from the signal source  5  is transmitted through the coaxial cable, and resonates at the signal source frequency on the monopole portion  1  to radiate an electromagnetic wave. At that moment, the outer conductor  2  of the coaxial cable has a voltage or current excited, which forms a current distribution C 2  shown in  FIG. 4 .  FIG. 4  illustrates an equivalent characteristic of the antenna shown in  FIG. 3 . In the monopole antenna shown in  FIG. 1 , only the equivalent portion to the ¼ wavelength functions as an antenna; however, in the sleeve antenna shown in  FIG. 3 , on the portion of the outer conductor  2  of the coaxial cable is created a voltage or current distribution, whereby the electromagnetic wave is radiated from the outer conductor  2  as well. That is, the whole structure including the monopole antenna and the coaxial cable portion functions as an antenna. The invention adopts the sleeve antenna shown in  FIG. 3 . 
   Thus, in the sleeve antenna shown in  FIG. 3 , an intensified and uniform electromagnetic energy is securely attained to be concentrated on areas near the monopole antenna and the coaxial cable portion. Accordingly, multiple transponders can be arrayed in that area. In other words, even if the antenna characteristics of the transponders are deteriorated, or even if the electromagnetic distributions are different in the fluctuations, the areas adjacent to the antenna elements attain an intensified electromagnetic field, which makes it possible to secure the electromagnetic energy over a wide area that the individual transponders need. 
   Here, the electromagnetic wave radiated by the antenna shown in  FIG. 3  is spread all around the circumference of the coaxial cable. Therefore, in case of using the microwave band, it is effective to form a physical makeup such that the antenna is disposed close to a ground plane though a thin dielectric layer (or film) less than few millimeters, and the electromagnetic wave radiated toward the ground plane is reflected by the ground plane to radiate on the other side of the ground plane. In consequence, the electromagnetic energy supplied to the transponders can be increased. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of the present invention will be described in detail based on the followings, wherein: 
       FIG. 1  is a chart explaining a configuration of a monopole antenna; 
       FIG. 2  is a chart explaining a current/voltage distribution of the monopole antenna and a radiation pattern of an electromagnetic wave; 
       FIG. 3  is a chart explaining a configuration of a sleeve antenna; 
       FIG. 4  is a chart explaining a current distribution of the sleeve antenna; 
       FIG. 5(   a ) illustrates a plan view that explains an interrogator as the first embodiment relating to the invention; 
       FIG. 5(   b ) illustrates a side view that explains an interrogator as the first embodiment relating to the invention; 
       FIG. 6(   a ) illustrates a plan view that explains an interrogator as the second embodiment relating to the invention; 
       FIG. 6(   b ) illustrates a side view that explains an interrogator as the second embodiment relating to the invention; 
       FIG. 7(   a ) illustrates a plan view that explains an interrogator as the third embodiment relating to the invention; 
       FIG. 7(   b ) illustrates a side view that explains an interrogator as the third embodiment relating to the invention; 
       FIG. 8  is a side view that explains an interrogator as the forth embodiment relating to the invention; 
       FIG. 9  is a chart explaining a configuration of an interrogator as the fifth embodiment of the invention; 
       FIG. 10  is a block diagram explaining an example of an RF signal line controller used in the interrogator in  FIG. 9 ; 
       FIG. 11  is a block diagram explaining an example of a switching signal generation circuit used in the RF signal line controller in  FIG. 10 ; 
       FIG. 12  is a block diagram explaining another example of the RF signal line controller used in the interrogator in  FIG. 9 ; 
       FIG. 13  is a perspective view explaining a stock control system applying the interrogator antennas as the sixth embodiment of the invention; 
       FIG. 14  is a perspective view explaining managed goods in the sixth embodiment in  FIG. 13 ; 
       FIG. 15(   a ) illustrates a plan view that explains an interrogator as the seventh embodiment relating to the invention; 
       FIG. 15(   b ) illustrates a side view that explains an interrogator as the seventh embodiment relating to the invention; 
       FIG. 16(   a ) illustrates a plan view that explains an interrogator as the eighth embodiment relating to the invention; and 
       FIG. 16(   b ) illustrates a side view that explains an interrogator as the eighth embodiment relating to the invention. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   An interrogator relating to the invention and a goods management system applying the same will be discussed further in detail with reference to some embodiments shown in the accompanying drawings. 
     FIGS. 5(   a ) and  5 ( b ) illustrate an interrogator as the first embodiment of the invention, which includes plural sleeve antennas switched by selectors and plural transponders arrayed near each of the sleeve antennas, and manages multiple transponders as a whole.  FIG. 5(   a ) is the plan view and  FIG. 5(   b ) is the side view. In  FIGS. 5(   a ) and  5 ( b ),  16   a – 16   e  denote the sleeve antennas as shown in  FIG. 3 ,  113  denotes an interrogator body,  111  an RF signal line that supplies the sleeve antennas  16   a – 16   e  with an RF signal from the interrogator body  113  through an input/output terminal  112 , and  17   a – 17   e  denote RF signal selectors that switch the connections between each of the sleeve antennas and the RF signal line  111 . Each of the sleeve antennas has the outer conductor grounded at the feed point. Further,  19  denotes a dielectric plate, and  18  a conductive plate (ground plane) stuck on the rear side of the dielectric plate  19 . The above construction forms an interrogator antenna incorporated with the interrogator body  113 . 
   Further, in  FIGS. 5(   a ) and  5 ( b ),  110  denotes a transponder group disposed on the front side of the dielectric plate  19 , very close to the sleeve antennas  16   a – 16   e . Each of the transponders forms a long and narrow plane rectangle, and in a practical use, it is stuck on the side face of an article in stock control, for example.  FIGS. 5(   a ) and  5 ( b ) omit to illustrate the articles, and shows the state that the rectangular transponders put on all the articles in stock control are arranged. 
   Each of the rectangular transponders incorporates a rectangular-shaped antenna and an IC chip. The IC chip includes a rectifier that rectifies an RF signal from the antenna to generate a DC voltage, a receiving circuit that extracts clocks and data, etc., from the RF signal, a memory that stores information such as the identification number of its own, and a transmitting circuit that transmits the information of the memory in accordance with the received data, using the received RF signal. 
   Further, the interrogator body  113  includes a transmitting circuit that modulates data for interrogation into an RF signal, and a receiving circuit that receives a signal transmitted from a transponder and extracts information. 
   The sleeve antennas  16   a – 16   e  are disposed inside the dielectric plate  19 , with such a degree of spacing that the antennas do not come in direct contact with the transponder group  110  electrically mechanically. 
   The ground plane  18  is placed close to the sleeve antennas  16   a – 16   e , on the side opposite to the transponder group  110 ; and, it reflects the radio waves that the sleeve antennas radiate to the transponder group  110  so as to increase the power supplied thereto. 
   As shown in  FIGS. 5(   a ) and  5 ( b ), the sleeve antennas  16   a – 16   e  are disposed slant to the dielectric plate  19 . When the sleeve antennas  16   a – 16   e  have such an angle in the layout, and each of the transponder antennas has the linearly polarized wave, the plane of vibration of the linearly polarized wave of the transponder antennas moves in close to the plane of vibration of the linearly polarized wave of the sleeve antennas  16   a – 16   e  (to the longitudinal direction of the antennas), which raises the power for exchanging the RF signals. 
   When each of the transponder antennas has the plane of vibration of the linearly polarized wave in the longitudinal direction along the rectangular shape of the transponder, the RF signal can be exchanged at the maximum efficiency by bringing the plane of vibration into coincidence with the longitudinally directional plane of vibration of the sleeve antennas. However, since the number of the transponders that one sleeve antenna can communicate with decreases in that case, it is effective to lay out the sleeve antennas with an angle as shown in  FIGS. 5(   a ) and  5 ( b ), thereby increase the number of the transponders, even with a slight decrease of the efficiency. 
   This embodiment achieves an interrogator with antennas that enables multiple arrangements of the transponders. 
     FIGS. 6(   a ) and  6 ( b ) illustrate an interrogator as the second embodiment of the invention, in which the sleeve antennas are arranged in the longitudinal direction of the dielectric plate.  FIG. 6(   a ) and  FIG. 6(   b ) are the plan view and the side view, respectively. In  FIGS. 6(   a ) and  6 ( b ),  26   a – 26   e  denote the sleeve antennas disposed in parallel to the longitudinal direction of a dielectric plate  29 . The other configuration is the same as in the first embodiment. That is, the sleeve antennas  26   a – 26   e , RF signal selectors  27   a – 27   e , RF signal line  211 , RF signal input/output terminal  212 , and ground plane  28  configure an interrogator antenna, and a transponder group  210  is disposed very close to the sleeve antennas  26   a – 26   e . Here, the interrogator body is omitted in the drawing. 
   The sleeve antennas  26   a – 26   e  in the second embodiment have the plane of vibration perpendicular to the plane of vibration of the rectangular transponder antennas. This configuration of the plane of vibration of the transponders being perpendicular to that of the sleeve antennas weakens the impedance coupling between the sleeve antennas and the transponder antennas, and decreases the power to be supplied. However, in reverse, the load is apt to be lessened each other, and thereby the optimization of the distance between them will realize an interrogator with the sleeve antennas capable of communicating multiple transponders. 
     FIGS. 7(   a ) and  7 ( b ) illustrate an interrogator as the third embodiment of the invention, in which the sleeve antennas are disposed to shorten the RF signal line for the power distribution.  FIG. 7(   a ) and  FIG. 7(   b ) are the plan view and the side view, respectively. To shorten the RF signal line is to decrease the loss of the RF signal generated. 
   In  FIGS. 7(   a ) and  7 ( b ),  36   a – 36   e  denote the sleeve antennas disposed with the orientations reversed each other, in parallel to the longitudinal direction of a dielectric plate  39 .  311  denotes an RF signal line that feeds the RF signal to the antennas arranged in that manner,  312  an RF signal input/output terminal arranged virtually on the center of the RF signal line  311 . The other configuration is the same as in the second embodiment. That is, the sleeve antennas  36   a – 36   e , RF signal selectors  37   a – 37   e , RF signal line  311 , RF signal input/output terminal  312 , and ground plane  38  configure an interrogator antenna, and a transponder group  310  is disposed very close to the sleeve antennas  36   a – 36   e . Here, the interrogator body is omitted in the drawing. 
   The third embodiment has the advantage of reducing the RF signal loss generated in the RF signal line  311 , by arranging the sleeve antennas  36   a – 36   e  with the orientations changed so as to shorten the length of the RF signal line  311 , and integrating the RF signal selectors  37   a  and  37   b , and  37   c  and  37   d  each into one IC package. 
     FIG. 8  illustrates an interrogator as the fourth embodiment of the invention, in which the interrogator antennas of the first, the second, or the third embodiment are connected in parallel. In  FIG. 8 ,  65 ,  66 ,  67  each denote the interrogator antenna as shown in either of  FIGS. 5(   a ) and  5 ( b )– FIGS. 7(   a ) and  7 ( b ) (hereafter, this will be mentioned as antenna group).  68  denotes an RF signal line  311 ,  69  an RF signal input/output terminal of the interrogator antenna in this embodiment. The interrogator antenna in this embodiment uses a plurality of the antenna groups shown in either of  FIGS. 5(   a ) and  5 ( b )– FIGS. 7(   a ) and  7 ( b ), so that the processable number of the transponders can further be increased. 
   Here, to increase of the number of the parallel connections elongates the RF signal line  68 , and increases the RF signal loss; however, if the output power of the RF signal of the interrogator body is high, or if the receiving sensitivity of each transponder is high, the permissible RF signal loss will be high, and the number of the parallel connections will become possible to increase, without being limited to three in  FIG. 8 . 
     FIG. 9  illustrates an interrogator as the fifth embodiment of the invention, which is provided with the RF signal selectors for each of the antenna groups. In  FIG. 9 ,  70 – 77  signify antenna groups shown in either of  FIGS. 5(   a ) and  5 ( b )– FIGS. 7(   a ) and  7 ( b ), ANTk 0 –ANTk 07  (k=0–7) sleeve antennas that the antenna group  7   k  includes, a 0 –a 7  RF signal selectors furnished with each of the sleeve antennas, b 0 –b 7  RF signal selectors furnished with each of the antenna groups  70 – 77 ,  78  an RF signal line that supplies the RF signal to the RF signal selectors b 0 –b 7 ,  79  an RF signal line controller that controls the connection/disconnection of the RF signal selectors a 0 –a 7  and the RF signal selectors b 0 –b 7 , and  80  an RF signal input/output terminal of the interrogator antenna of this embodiment. 
   The interrogator antenna of this embodiment uses 64 sleeve antennas in total, one of which is selected in accordance with the operation of the RF signal selectors a 0 –a 7  and the RF signal selectors b 0 –b 7  and is connected to the RF signal line  78 , which is controlled by the RF signal line controller  79 . 
   In this embodiment, since each antenna group has the RF signal selector, the load of the interrogator body is reduced in comparison to the forth embodiment, and more antenna groups can be installed. Accordingly, the processable number of the transponders can be increased to a great extent. 
     FIG. 10  illustrates an example of the RF signal line controller  79 . Since the antenna switching circuits and the peripheral circuits thereof, which constitute each RF signal selector, are disposed close to each of the antennas, the supply voltage that drives a switching control signal and each circuit is preferably supplied through one RF signal line together with the RF signal. The line controller  79  in  FIG. 10  is configured in view of the above. 
   In  FIG. 10 ,  89  signifies a switching signal superposing circuit tat superposes a dc voltage from a power supply terminal  90  and a control signal from a control terminal  91  on an RF signal from an RF signal input/output terminal  98 , and  92  signifies a transmission line. Further,  93  signifies a switching signal separation circuit that separates the RF signal, control signal, and supply voltage from the signal sent by the transmission line  92 ,  94  a low pass filter that omits undesired RF components from the supply voltage that the switching signal separation circuit  93  has separated,  95  a switching signal generation circuit that generates switching signals to the RF signal selectors a 0 –a 7  and the RF signal selectors b 0 –b 7 , on the basis of the control signal that the switching signal separation circuit  93  has separated, and  96  an antenna switching circuit, which is composed of the selectors a 0 –a 7  and the selectors b 0 –b 7 . 
   The low pass filter  94  supplies the supply voltage to the switching signal generation circuit  95  and the antenna switching circuit  96 . The RF signal to the antenna to be switched is inputted/outputted through the RF signal input/output terminal  97 . Only one of the sleeve antennas of the interrogator antenna is selectively connected to the RF signal line  78  (transmission line  92 ), by the switching, whereby communications between plural transponders become possible. 
     FIG. 11  illustrates an example of the switching signal generation circuit  95 . In  FIG. 11 ,  107  signifies a switching signal input terminal,  108 ,  109  signify a 4-bit binary counter,  110 ,  111  a 3-to-8 line decoder, and  112 ,  113  an octal D-type latch. 
   As an arbitrary number of pulses are inputted as the control signal from the switching signal input terminal  107 , the switching signal input terminal  108  counts the number of the pulses, and the output signal at the third bit is inputted to the clock input CLK of the 4 bit binary counter  109 . The 3-bit outputs QA, QB, QC of the 4-bit binary counter  108  pass through the 3-to-8 line decoder  110  and the octal D-type latch  112  to be converted into the switching signals that drive the selectors a 0 –a 7  provided to the sleeve antennas. The switching signals are capable of switching plural (8, at the maximum) sleeve antennas. 
   The 4-bit binary counter  109  increments one count every 8 counts of the 4-bit binary counter  108 . The 3-bit outputs QA, QB, QC of the 4-bit binary counter  109  pass through the 3-to-8 line decoder  111  and the octal D-type latch  113  to be converted into the switching signals that drive the selectors b 0 –b 7  provided to the antenna groups. The switching signals are capable of switching plural ( 8 , at the maximum) antenna groups. 
   Next,  FIG. 12  illustrates another example of the RF signal line controller  79 . In this example, rectifying a part of the RF signal generates the power supply voltage. In  FIG. 12 ,  100  signifies a switching signal superposing circuit tat superposes a control signal from the control terminal  91  on the RF signal from the RF signal input/output terminal  98 .  103  signifies a switching signal separation circuit that supplies an RF signal to the antenna switching circuit  96  and a rectifying circuit  104  by an internal coupling circuit thereof, and separates the control signal superposed on the RF signal. The rectifying circuit  104  rectifies an inputted RF signal to generate a dc supply voltage to be supplied to the switching signal generation circuit  95  and the antenna switching circuit  96 . The other circuits are the same as those shown in  FIG. 10 , and the explanation will be omitted. Also in this example, only one of the sleeve antennas of the interrogator antenna is selectively connected to the RF signal line  78 , by the switching, whereby communications between plural transponders become possible. 
     FIG. 13  illustrates a stock control system as the sixth embodiment of the invention, in which the interrogator antennas shown in  FIG. 9  are applied to a rack of plural shelves that controls the reception and stock of managed goods. The managed goods includes a file and document, CD (Compact Disk), DVD (Digital Versatile Disk), etc., and a control terminal controls the goods using an identified result by the interrogator. 
     FIG. 13  illustrates the shelves up to two. In  FIG. 13 ,  121 ,  128  each denote a shelf board on the lower shelf, and a shelf board on the upper shelf; the antenna group is installed on each shelf board, and an interrogator  115  is installed on the right near side of the lower shelf board  121 . The interrogator  115  has a control terminal  132  connected thereto, through a control line  114 . 
   The antenna group installed on the shelf board  121  possesses a board  120 , four sleeve antennas  119  embedded in the board  120 , an RF signal selector  118  for the sleeve antennas  119 , and an RF signal selector  117  for the antenna group. The managed goods are placed on the antenna group, which are illustrated with the symbol  123  in  FIG. 13 , and as described later, rectangular transponders  122  are applied on the managed goods  123 . And, the RF signal line and the ground plane are formed on the board  120 , which are not illustrated in the drawing. 
   Similarly, the antenna group installed on the shelf board  128  possesses a board  127 , four sleeve antennas  125  embedded in the board  127 , an RF signal selector  134  for the sleeve antennas  125 , and an RF signal selector  126  for the antenna group. The managed goods are placed on the antenna group, which are illustrated with the symbol  124  in  FIG. 13 , and rectangular transponders  133  are applied on the managed goods  124 . And, the RF signal line and the ground plane are formed on the board  127 , which are not illustrated in the drawing. The board  127  and the RF signal line thereon are connected to the interrogator  115  through RF coaxial cables  129 ,  131  connected to RF coaxial connectors  116 ,  130 . In this embodiment, the interrogator  115  includes the function of the switching signal superposing circuit of the RF signal line controller. 
     FIG. 14  illustrates a form of the managed goods  123 ,  124 . The managed goods  123  ( 124 ) has the form, such as a file, document, CD, DVD, and the like. The rectangular transponders  122  ( 133 ) are applied on the underside of the managed goods  123  ( 124 ) so as to face to the sleeve antennas  119 ,  125 . 
   In this embodiment, the RF signal selectors  117 ,  126  select either of the antenna groups installed on the shelf boards  121 ,  128 ; further, the RF signal selectors  118 ,  134  select either one of the sleeve antennas  119 ,  125 . And, the number of the antennas  119 ,  125  installed and the location thereof recognizes that a managed goods of which identification number stays at which location of which shelf board. Thus, a further subdivided location becomes possible, and a fine stock control becomes possible accordingly. 
   And, in view of the distinctive features of the invention, it is widely applicable to the control of goods, such as a goods control in a shop, a files and books control in an office, etc., in addition to the above stock control. 
   Now, if an optical indicator such as an LED is used which lights or flickers by the switching signal in combination with the RF signal selectors  117 ,  126 , and the RF signal selectors  118 ,  134 , it will be possible to confirm by visual observation the location of a managed goods on which a rectangular transponder for exchanging data is attached. 
     FIGS. 15(   a ) and  15 ( b ) illustrate an interrogator using such an optical indicator, as the seventh embodiment of the invention.  FIG. 15(   a ) and  FIG. 15(   b ) are the plan view and the side view, respectively. The basic structure of the interrogator antenna is the one from the second embodiment shown in  FIGS. 6(   a ) and  6 ( b ); and indicators  145 – 149  are each connected to the sleeve antenna sides of the RF signal selectors  27   a – 27   e . Naturally, any of the interrogator antennas in the first through third embodiments and the antenna groups in the fourth through sixth embodiments can be the basic structure of the interrogator antenna to which the indicators  145 – 149  are connected. 
   One of the indicators  145 – 149  lights or flickers, when one of the RF signal selectors  27   a – 27   e  corresponding to the indicator is selected, whereby the selected sleeve antenna can be confirmed by visual observation. 
   Further, the indicators can be attached to the RF signal selectors b 0 –b 7  in  FIG. 9 , as well as to the RF signal selectors  117 ,  126  in  FIG. 13 , in addition to the RF signal selectors  27   a – 27   e . When one of the selectors is selected, the corresponding indicator lights or flickers, which enables the confirmation of a selected antenna group by visual observation. 
   Next,  FIGS. 16(   a ) and  6 ( b ) illustrate an interrogator using a sound source instead of an optical indicator, as the eighth embodiment of the invention.  FIG. 16(   a ) and  FIG. 16(   b ) are the plan view and the side view, respectively. Sound sources  165 – 169  are each connected to the sleeve antenna sides of the RF signal selectors  27   a – 27   e.    
   The sound sources  165 – 169  are made up with piezoelectric buzzers that emit audible sounds, and so forth. When any one of the RF signal selectors  27   a – 27   e  is selected, the sound source corresponding to the selected one of the selectors emits an audible sound; accordingly, it becomes possible to confirm the selected sleeve antenna by hearing the sound. Naturally, any of the interrogator antennas in the first through third embodiments and the antenna groups in the fourth through sixth embodiments can be the basic structure of the interrogator antenna to which the sound sources  165 – 169  are connected. 
   Further, the sound sources can be attached to the RF signal selectors b 0 –b 7  in  FIG. 9 , as well as to the RF signal selectors  117 ,  126  in  FIG. 13 , in addition to the RF signal selectors  27   a – 27   e . When one of the selectors is selected, confirming the sound of the sound source connected to the selected selector permits the confirmation of a selected antenna group. 
   Further, it is also possible to combine the indicators and the sounds source. It is possible to properly use the indicators and the sound sources, in a case suitable for making sounds and a case suitable for emitting lights, and also possible to use both at the same time. 
   According to the invention, the antenna group is able to secure an intensified and uniform electromagnetic energy concentrated on the areas near the antenna elements, which accomplishes an interrogator that enables information exchange with multiple transponders in a shorter distance of communication. Using the interrogator of the invention will achieve movable body identification equipment such as a goods management system that identifies multiply arrayed goods, and so forth. 
   It should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Therefore, the present examples and embodiments are to be considered as illustrative and not restrictive and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalence of the appended claims.