Abstract:
Methods and apparatus are provided for locating one among many items equipped with RFID tags. The apparatus comprises a portable system interrogating the RFID tags and receiving responses therefrom that depend at least on their bearing angle. A comparator selects responses from the one item and ignores others. An annunciator indicates the presence of the one item in the interrogator field of view and, desirably but not essentially, its relative proximity. A directional antenna whose beam pattern is limited in azimuth and/or elevation provides bearing angle information. Its field of view becomes progressively smaller as the antenna approaches the one item so that a user can substantially pinpoint its location without needing any of the usual RFID infrastructure. Tag response hit rate and/or signal strength provides range related information to the interrogator. Optionally, the presence of each new tag is announced until all new tags have been identified.

Description:
TECHNICAL FIELD 
   The present invention generally relates to remotely identifying and locating objects, and more particularly relates to remotely identifying and locating objects using RF signaling. 
   BACKGROUND 
   There are many applications today where it is desired to sense the presence and location of a specific object, as for example, a package stored in a warehouse or on a pallet or in a shipping container. For example, a warehouse attendant or shipping clerk may need to determine whether a particular package or item is present and where it is located. When there are many packages or items that are similar in appearance this can be a daunting and very time consuming task. Ordinarily, the attendant would have to examine the label on every package or item looking for the desired item or package. The advent of bar-code identification has somewhat simplified such tasks, but suffers from the limitation that each bar code label must be located and physically scanned at close range by a bar code reader. Every item or package in the pile may have to be scanned before the user can even be sure whether or not the desired package or item is or is not present. This can be extremely time consuming and inefficient. 
   Radio frequency identification (RFID) tags are now in common use with many goods or items. An RFID tag is an electronic device attached to an item or package and contains a unique identifier (e.g., an ID number) that can be read remotely using a radio frequency (RF) signal. When the RFID tag is interrogated by an RFID tag reader, the tag responds with at least its unique identifier. Many different types of RFID tags are now in use. For example, and not intended to be limiting: (i) some tags are substantially passive, that is, they don&#39;t emit a signal but their presence in the antenna field of the interrogator dynamically alters the impedance of the interrogator&#39;s RF antenna allowing their presence to be detected; (ii) some are semi-passive, that is, they receive a signal from the interrogator on a first frequency and use the received energy to reply on a second frequency; and (iii) some are active, that is, they have an on-board power source for the tag circuit, which is turned on by the interrogation signal so that the tag can broadcast a response. Any of these and other types of tags can be used with the present invention provided that the RFID interrogator can determine the unique tag identifiers. The tag identifier is therefore associated with the item to which the tag is attached. When the tags are within radio frequency (RF) signaling distance of the interrogator they respond. If the unique identifier (e.g., the ID number) of the desired item is among those scanned by the interrogator, then the user will know that it is present within the signaling range of the RFID interrogator, but may still not know its exact location. If the warehouse or other storage location is equipped with tag range measuring infrastructure, then the infrastructure system may also be able to determine the location of the tagged object or package. However, not all package or item storage locations have such infrastructure. So, a need continues to exist for a means and method that will determine the presence and location of a particular item or package without such RFID ranging infrastructure. 
   Accordingly, it is desirable to provide an improved means and method for remotely determining the presence and position of tagged items or packages. It is desirable that such system and method be capable of working with the many types of RFID tags that already exist. In addition, it is desirable that such system and method be simple, rugged and reliable. It is further desirable that such system and method not require fixed infrastructure but be portable and self-contained so that it can be used anywhere. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background. 
   BRIEF SUMMARY 
   An apparatus is provided for locating a particular item from among many items. The apparatus comprises a portable communication system employing a directional antenna for interrogating the many items and receiving individual responses therefrom that depend upon whether they are within the beam pattern of the directional antenna. A comparator is coupled to the communication system for comparing the identifiers in the received responses with a unique identifier for the particular item. The tag&#39;s response is also desirably analyzed to determine proximity information, but this is not essential. An annunciator is coupled to the communication system and the comparator for indicating relative proximity and angle of bearing of the item having the desired identifier. In a further embodiment, the apparatus gives a signal to the user when each new item is identified. The new item signal stops when all new items in the field of view have been identified. The apparatus optionally sends the unique identifiers so identified to a base station. 
   A method is provided for locating a particular item from among a plurality of items, using an RFID tag interrogator in a find mode, wherein each item has an RFID tag containing a unique identifier. The method comprises obtaining and storing the unique identifier for the particular item desired to be located, interrogating the plurality of items to determine their unique identifiers, comparing the unique identifiers thereby obtained to the unique identifier for the particular item stored in memory and, if there is a match, presenting relative position dependant data for the tag having the unique identifier for the particular item, to a user, and repeating the interrogating, comparing steps and presenting steps for different locations of the interrogator, thereby obtaining position dependant data pointing to the particular item. In a further embodiment in a search mode, all tags in the field of view are read and for each newly detected tag a signal is presented to the user and the unique identifier of each newly detected tag is, optionally, sent to a bases station. When all new tags have been identified, the signal to the user stops indicating that no new tags remain in the field of view. In a further embodiment, if a desired tag identifier has already been entered, the method then switches to the find mode already described. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and 
       FIGS. 1A–C  are simplified side views of the item identification and locator system of the present invention for three different locator-item separations, and  FIG. 1D  is a plan or top view of the system of  FIGS. 1A–C  showing further details; 
       FIG. 2  is a simplified electrical block diagram of the item identification and locator system of  FIGS. 1A–D  according to the present invention, interacting with several RFID tagged objects or items; 
       FIG. 3  is a simplified flow chart of the method of the present invention for remotely identifying and locating objects or items having ID tags thereon; 
       FIG. 4  is a simplified electrical block diagram of an item identification and locator system similar to that of  FIG. 2  but according to a further embodiment; and 
       FIG. 5  is a simplified flow chart of the method of the present invention according to a further embodiment. 
   

   DETAILED DESCRIPTION 
   The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description. 
     FIGS. 1A–C  are simplified side views of item identification and locator system  20  of the present invention, interacting with items  30  having thereon RFID tags  32 , for three different locator-item separations  22 A,  22 B,  22 C.  FIG. 1D  is a plan or top view of system  20  interacting with the same items and tags at locator-item separation  22 D. Persons of skill in the art will understand that  FIGS. 1A–C  are two dimensional side views and  FIG. 1D  is a two-dimensional top view of, in this example, a three-dimensional pile of objects or items  30  and associated RFID tags  32 . System  20  comprises RF interrogator  24  with associated antenna  25  and annunciator  33 . Annunciator  33  can include one or both of visual indicator  33 - 1  and audible indicator  33 - 2  to alert the user when a desired object is detected. The details of interrogator  24  and associated annunciator  33  are explained more fully in connection with  FIG. 2 . A suitable antenna is described in commonly owned, co-pending application entitled “Directional Antenna Array” Ser. No. 10/661,652 filed Sep. 12, 2003. 
   Interrogator  24  transmits via antenna  25 , RF signal  29  directed toward objects  30  and associated tags  32  and receives signal  29 ′ in response. In this example, it is assumed merely for convenience of description that transmission signal  29  and reception signals  29 ′ are both handled by antenna  25 , but this is not essential and not intended to be limiting. Separate transmit and receive antennas can also be used (e.g., see  FIG. 2 ). Signal  29  is localized and desirably has approximately cone-shaped RF beam or pattern  26  with outer perimeter  28 . RF beam or pattern  26  has vertical angle or extent  27  (see  FIGS. 1A–C ) and azimuthal angle or extent  27 ′ (see  FIG. 1D ). Three-dimensional perimeter  28  of RF beam or pattern  26  substantially defines the spatial boundary within which interrogator  24  can detect the presence of an RFID tag and determine its unique identifier. For convenience of description it is assumed that the unique identifier is a number, that is, a unique series of digits (abbreviated as ID # or ID # XXXX). However, this is not intended to be limiting and persons of skill in the art will understand that the unique identifier can be any combination of alpha-numeric, binary, or other characters in any convenient representation system, of which decimal, hexi-decimal, binary, etc., are non-limiting examples. Also, while RF beam pattern  26  of perimeter  28  is illustrated herein as being approximately cone-shaped, this is merely for convenience of explanation and is not essential, and any spatially limited antenna pattern may be used. As used herein, the words “RF beam pattern” are intended to include an RF radiation/reception pattern of any shape, that is spatially limited in azimuth or elevation or, preferably both. Further, beam pattern  26  of perimeter  28  is not limited merely to transmitted signal  29  but can also apply to received signal  29 ′ or both, since it is generally a property of most antennas that their transmit and received signal beam patterns have about the same spatially limited shape, albeit of different size depending upon the interrogator&#39;s sensitivity. 
   For item-interrogator separations  22  that are within the sensitivity range of the interrogator, it is desirable that beam pattern  26  have approximately constant angular aperture  27 ,  27 ′ so that the number of items being exposed to beam pattern  26  varies with item-interrogator separation or range  22 . For example, in  FIG. 1A , separation distance  22 A is sufficiently large that beam pattern  26  of perimeter  28  includes substantially all of items  30  (and associated tags  32 ), e.g., items have ID #&#39;s 4321, 6259, 3472, 0027, 5514, 9827, 0312, and 1035. In  FIG. 1B , separation distance  22 B is smaller and beam pattern  26  covers only some of items  30 , for example, items with ID #&#39;s 3472, 0027, 5514 and 9827. In  FIG. 1D  separation distance or range  22 D is such that beam pattern  26  covers, for example, items with ID #&#39;s 2798, 1455, 2700, and 1108. In  FIG. 1C , separation distance  22 C is even smaller and beam pattern  26  covers, substantially, only item  30 -C with ID # 5514. Annunciator  33  desirably gives an audio and/or visual indication whenever interrogator  24  receives a return signal corresponding to the item being sought. By scanning the interrogator back and forth while approaching a pile of objects, the user can narrow the field of search to particularly locate the desired object. 
   Beam pattern  26  is spatially limited, not only in elevation and azimuth but also in distance  23  from interrogator  24 . Beyond perimeter  28  of beam pattern  26 , the transmit and/or receive signal strength drop off such that detection of an RF tag is unlikely. Thus, perimeter  28  of beam pattern  26  can be thought of as defining the “field of view” of interrogator  24 . If item or object  30  lies within field of view  28 , then its on-board RFID tag can be irradiated by interrogator  24  with sufficient signal strength that the RFID tag response can detected by interrogator  24  and indication thereof given by annunciator  33 . Thus, an item or object  30  in this field of view can in effect be “seen” by interrogator  24 . Because field of view  28  is spatially limited, it can be used in cooperation with interrogator  24  to determine the location of a particular item or object. By ‘scanning’ interrogator  24  as shown by arrows  37 ,  37 ′, different portions of objects  30  can be brought into the field of view of interrogator  24 . This provides angle of bearing information about the location of the particular item being sought. As the user moves interrogator  24  closer and closer to objects or items  30 , portion  21  of overall field of view  28  of interrogator  24  intersecting objects  30  narrows in three dimensions so that fewer and fewer of objects or items  30  are effectively within field of view portion  21 . By scanning the interrogator back and forth while approaching a pile of objects, the user can narrow the field of search to particularly locate the desired object. No tag ranging infrastructure is required. However, the task of locating a particular object is made easier by taking advantage of range information that is inherent in signal  29 ′ being returned from the tag. 
     FIG. 2  is a simplified electrical block diagram of item identification and locator system  20  of  FIGS. 1A–D  according to the present invention, interacting with several RFID tags  32  associated with several objects  30 . In the example of  FIG. 2 , objects  30  comprise items or objects  30 - 1 ,  30 - 2 ,  30 - 3  . . .  30 -N with associated RFID tags  32 - 1 ,  32 - 2 ,  32 - 3  . . .  32 -N. Antennas  31 - 1 ,  31 - 2 ,  31 - 3  . . .  31 -N associated with tags  32 - 1 ,  32 - 2 ,  32 - 3  . . .  32 -N are also illustrated. Item identification and locator system  20  has antenna  25  that may handle both transmission of RF interrogation signal  29  and reception of tag response signal  29 ′, or separate receiving antenna(s)  25 ′ may be provided. Either or both arrangements are useful. For example, interrogator  24  may be provided with multiple antennas, where one or more serve different types of tags. Persons of skill in the art will understand which arrangement better suits their needs depending upon the types of tags  32  intended to be interrogated. Interrogator  24  is moveable with respect to objects  30  and tags  32  as indicated by arrows  22 ,  37 . Distance or range  22  to objects  30  can be varied and lateral position with respect to objects  30  can also be varied as shown by arrows  37 . Lateral position can be varied by translating or swinging interrogator  24  back and forth in front of objects  30  (and tags  32 ) so that beam pattern  26  intersects a different portion  21  of objects  30  and tags  32 . As used herein the words “scan” or “scanning” or “sweep” or “sweeping”, present or past tense, are intended to include all types of relative motion of interrogator  24  with respect to objects  30  and associated tags  32 . 
   Interrogator  24  comprises RFID transceiver  40 , processor  42 , memory  44 , data input  46 , annunciator  33  and power supply  48 . Transceiver  40 , processor  42 , memory  44 , data input  46  and annunciator  33  are coupled and intercommunicate by bus or leads  41 . Power supply  48  is coupled to transceiver  40  by power leads  47  and to processor  42 , memory  44 , data input  46  and annunciator  33  by power leads  49 . It is desirable that power supply  48  be self-contained, as for example, using batteries, so that interrogator  24  is freely portable but this is not essential. Power supply  48  can be connected to external power mains by an extension cord (not shown), but this is less desirable since it limits the overall mobility of interrogator  24 . In the preferred embodiment, interrogator  24  is powered by a battery. However, other types of portable energy sources can be used, for example and not intended to be limiting, a fuel cell, high-energy capacitor or a combination thereof. As used herein, the word “battery” is intended to include these and any other kind of portable power source of suitable voltage and current capacity. 
   The ID #(s) of the objects desired to be located are input by the user via data input  46 , as for example, via key pad  35 , but this is not essential. Any means of entering one or more ID #(s) for objects(s) desired to be located may be used. A non-limiting example of an alternate data input method is a touch pad and/or via a Bluetooth™ equipped portable data terminal. The entered ID #(s) are stored in memory  44  or equivalent. It is preferable that memory  44  contain non-volatile memory (as well as transient memory) for this and other purposes. 
   Once interrogator  24  is powered-up, RFID transceiver  40 , desirably but not essentially acting under the direction of processor  42 , broadcasts RFID interrogation signal  29  toward objects  30  and tags  32 . Those of tags  32  that are within RF beam pattern perimeter  28  (the overall interrogator “field of view”) will respond with signal  29 ′. It is desirable but not essential that transceiver  40  be capable of measuring at least the relative strength of received signals  29 ′. Signal  29  can be a repetitive signal so that a series of responses  29 ′ is received by transceiver  40  from tags  32  within field of view  28 . The received signals are referred to in the art as “hits” and include the unique identifier (e.g., the ID #) of the interrogated tags. Depending upon the relative RF signal strength at different locations, the relative position of interrogator  24  and tags  32  and the presence of any intervening items, interrogator  24  may or may not receive a hit each time interrogation signal  29  is sent out by interrogator  24 . However, it is generally the case that the frequency of hits increases as interrogator  24  is brought closer to tags  32 . Processor  42  receives the hits and compares the ID #&#39;s received from tags  32  with ID #&#39;s stored in memory  44 , that is, with the ID #(s) of the one or more objects or items desired to be located and, optionally, with the ID#(s) previously received. When there is a match with the ID#(s) of the item(s) being sought, processor  42  causes a visual or audible and/or other signal to be emitted by annunciator  33 . For example, light  33 - 1  may illuminate or flash, speaker  33 - 2  may emit a beep or tone (continuous or intermittent or frequency varying) and/or alpha-numeric display  33 - 3  may display the located ID #(s) or other alert message, or a vibrator (not shown) may alert the user, depending upon his or her needs. In the preferred embodiment, the signal (audible, visual and/or other) emitted by annunciator  33  is keyed to the hit rate and/or the signal strength of received RFID tag response  29 ′. Thus, the closer that interrogator  24  is to the object or item being looked for, the more rapid and/or the more intense the signals being emitted by annunciator  33 . In this mode of operation, interrogator  24  functions in a manner analogous to a Geiger counter for detecting radiological material. 
   For example, when the object being sought is just barely within RF field of view  28  of interrogator  24 , annunciator  33  beeps or flashes (or both) very slowly. By sweeping or scanning interrogator  24  back and forth and/or up and down or both over the pile or array of objects, the annunciator output may stop and start as the interrogator field of view excludes or includes the object(s) being sought. This tells the user the general direction or angle of bearing of the object(s) being sought. The user continues to sweep or scan interrogator  24  while moving toward the objects. As the distance between the interrogator and the object(s) being sought decreases, the annunciator output rate desirably increases. When interrogator  24  is close enough so that portion  21  of beam pattern  26  is directed primarily at the object being sought, the output of annunciator  33  is, preferably, substantially continuous. While this is the preferred mode of operation any form of annunciator operation that permits the user to determine when interrogator  24  is pointing substantially directly at the item being sought and not others, is useful. While other objects not being sought may also be within beam pattern  26  and are sending hits back to interrogator  24 , they do not interfere with the locating function since they are ignored by processor  42  because their ID#&#39;s do not match the sought-after ID#(s) stored in memory  44 . 
     FIG. 3  is a simplified flow chart of method  100  of the present invention for identifying and locating items having RFID tags thereon. Method  100  begins with START  102  that desirably occurs on system power-up. System  20  may be capable of other functions beside the identify-and-locate (FIND MODE) function described herein. Hence optional ENTER FIND MODE step  104  is initially executed. Step  104  may be initiated by the user via data entry input module  46  or may occur automatically after a predetermined time interval or other default or maybe set by a simple switch (not shown). ID # ENTERED ? query  106  is then executed where it is determined whether or not the user has input (e.g., via keypad  35 ) a unique identifier. If the outcome of query  106  is NO (FALSE), abbreviated as “N”, then method  100  executes OBTAIN and STORE ITEM ID # step  108 , wherein the ID # is obtained in sub-step  108 - 1  and stored in sub-step  108 - 2 . If the outcome of query  106  is YES (TRUE), abbreviated as “Y” or method  100  has proceeded via step  108 , then step  110  is executed wherein those of tags  32  in field of view portion  21  are interrogated by signals  29  and their responses  29 ′ received by RFID transceiver  40 . ITEM ID # IN FIELD OF VIEW ? query  112  is then executed wherein it is determined whether the ID #s received from the various tags in field of view  21  match the stored tag ID #(s). If the outcome of query  112  is NO (FALSE), then optional TIME-OUT LIMIT EXCEEDED ? query  114  is executed wherein it is determined whether or not the time that has passed without a YES (TRUE) outcome of step  112  exceeds a predetermined value. If the outcome of query  114  is NO (FALSE) then method  100  proceeds to optional PROMPT FIELD OF VIEW SWEEP step  116 . In optional step  116  the user is desirably prompted to make a different or further scan or sweep with interrogator  24 . The prompt can be given by, for example, a visual message on output screen  33 - 3  or an audible announcement via speaker  33 - 2  (e.g., a voice message saying “scan other objects” or the like) or by a warning tone or a light output or a combination thereof by annunciator  33 . READ TAGS step  110  is then repeated until query  112  yields a YES (TRUE) output or the TIME-OUT LIMIT in query  114  is exceeded. If the outcome of query  114  is YES (TRUE) indicating that the time-out limit has been exceeded, then as shown by path  115 , method  100  optionally proceeds to END  124 . 
   If the outcome of query  112  is YES (TRUE) indicating that the desired item ID # is in portion  21  of field of view  28  of interrogator  24 , then OBTAIN RANGE DEPENDANT DATA FOR DESIRED ID# step  118  is desirably executed, wherein the proximity of the desired object is estimated from the returned signal hit rate and/or the returned signal strength or a combination thereof. In following step  120 , the range dependant output data obtained in step  118  is presented to the user via annunciator  33 , as has been previously described in connection with  FIG. 2 . For example and not intended to be limiting, the closer the object or item, the more rapid and/or intense the signals presented to the user by annunciator  33 . Following step  116 , FIND MODE STILL ACTIVE ? query  122  is executed wherein system  20  determines whether the FIND MODE is still set or switched on or whether it has been terminated by the user. If the outcome of query  122  is YES (TRUE) meaning that the FIND MODE is still active, then method  100  returns to step  118  as shown by path  121  or optionally returns to step  112  as shown by path  123 . Either arrangement is useful. Steps  118 ,  120 ,  122  repeat so that the user is provided with further indication of the range and bearing of the desired object until the user shuts off the FIND MODE, whereupon query  122  yields (NO (FALSE) outcome and method  100  advances to END  124 . 
     FIG. 4  is a simplified electrical block diagram of item identification and locator system  20 ′ similar to that of  FIG. 2  but according to a further embodiment. Like reference numbers are used for like or analogous elements. System  20 ′ differs from system  20  of  FIG. 2  in that interrogator  24 ′ of system  20 ′ includes system transceiver  50  with antenna  52 . System transceiver  50  is logically coupled to the other elements of interrogator  24 ′ via bus  41 . For convenience of description, the extension of power lead  49  to system transceiver  50  has been omitted in  FIG. 4 , but persons of skill in the art will understand that such power connection is needed. System transceiver  50  communicates with system base station  54  via wireless connection  53 . Any appropriate signaling means may be used for wireless connection  53 . Non-limiting examples are WiFi, 802.11, Bluetooth, Zigbee and so forth. The function of system transceiver  50  acting under the direction of processor  42 , is to transmit to system base station  54  the ID#s of each tag newly identified by system  20 ′. This will be more fully understood in connection with the flow chart of  FIG. 5  where system  20 ′ is acting in a search mode or both a search mode and find mode. 
     FIG. 5  is a simplified flow chart of method  200  of the present invention according to a further embodiment and adapted to be carried out by system  20 ′ of  FIG. 4 . Method  200  begins with START  202  that desirably occurs on system power-up. System  20 ′ is capable of other functions beside the identify and locate function described in connection with  FIGS. 2–3 , hence optional ENTER SEARCH MODE step  204  is initially executed. In subsequent step  206 , all of the tags in the field of view of system  20 ′ are interrogated and in step  208  their unique ID#s determined. It is desirable that such unique ID#s be temporarily stored in interrogator  24 ′. NEW ID #s FOUND ? query  210  is then executed wherein it is determined whether the ID#s identified in step  208  have been previously identified or not. If the outcome of query  210  is YES (TRUE), then method  200  proceeds to step  212  wherein, in either order, sub-step  212 - 1  is executed so that the appearance of a new item (e.g., new ID#) is announced to the user in some convenient manner (audibly, visually, and/or a combination thereof) and, optionally, sub-step  212 - 2  is executed such that the new item ID# is sent by system transceiver  50  to base station  52  over wireless link  53 . In this way, base station system  52  accumulates a list of the items present in the field of view of interrogator  24 ′. This information is very useful since it allows base station system  52  to keep track of the items entering or leaving or remaining in a particular area. Following step  212 , method  200  loops back to step  206  as shown by path  213 , where the tags in the field of view are re-interrogated and steps  208 – 212  repeated until no new tags are detected. 
   For example, in carrying out steps  206 – 212  processor  42  causes annunciator  33  to provide an output while the unknown tags are being scanned, e.g., one beep or flash or other indication for each new tag being detected. When all of the tags have been scanned without finding further new items (further new tags), step  210  yields NO (FALSE)) and processor  42  desirably shuts off the output of annunciator  33 , thereby alerting the user that the scan is complete and that all new items (tags) have been identified. 
   If the outcome of query  210  is NO (FALSE) indicating that no new items are detected, then method  200  optionally proceeds to DESIRED ITEM ID# ENTERED ? query  214  wherein it is determined whether or not the ID# of a desired item has been entered into system  20 ′. In other words, method  200  and system  20 ′ tests to see whether the user desires to automatically enter the FIND mode discussed in connection with  FIG. 3 . If the outcome of query  214  is NO (FALSE) then method  200  proceeds to END  216 . If the outcome of query  214  is YES (TRUE) meaning that the user has already entered the ID# of an item desired to be located, then method  200  can automatically enter the FIND mode as shown in step  218 . Subsequent to step  218  then, as shown by block  220 , method  200  executes steps  110 – 124  of method  100  of  FIG. 3 , wherein the user is able to locate the desired item. In a further embodiment, an additional query can be executed before or after step  218  wherein interrogator  24 ′ checks the desired ID# against the detected ID#s found in step  208  to see whether the desired ID# is present among the already scanned items and announce such to the user, but this is not essential. 
   The present invention has been described for an antenna that has a beam pattern that is spatially limited in both elevation and azimuth. This preferred but not essential. If the interrogator has a beam pattern that is spatially limited even in only one dimension, the user can make use of this to obtain both azimuth and elevation angle information by rotating the interrogator ninety degrees. 
   While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing the exemplary embodiment or exemplary embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope of the invention as set forth in the appended claims and the legal equivalents thereof.