Patent Publication Number: US-7899425-B2

Title: Multi-band wireless communication device and method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 11/514,436, filed Aug. 31, 2006, which is a continuation of U.S. patent application Ser. No. 11/302,416, filed Dec. 12, 2005, which is a continuation of U.S. patent application Ser. No. 09/678,630, filed Oct. 3, 2000, now U.S. Pat. No. 6,975,834, issued Dec. 13, 2005, the entire disclosures of which are hereby incorporated by reference herein. 
    
    
     FIELD OF INVENTION 
     The present invention relates to a wireless communication device and communication of information concerning an item containing the wireless communication device, and particularly to a wireless communication device supporting multi-frequency usage. 
     BACKGROUND 
     It is often desired to track and identify items, such as packages, containers, and the like, and to communicate information concerning such items wirelessly. One method of tracking and providing information concerning packages is to attach a wireless communication device, such as a radio frequency identification (RFID) transponder or other identification device, to packages or items. The information communicated concerning the packages or items may include expiration dates, “born on” dates, lot numbers, manufacturing information, and the like. A wireless communication device may be attached to an individual package, to a container containing multiple packages, or other item as the situation merits. 
     Different countries have allocated different portions of the electromagnetic spectrum for use with such wireless communication devices. For example, some countries may use frequency bands centered on 2.45 GHz and others may use bands centered on 13.56 MHz, 868 MHz, or 915 MHz. It is desirable to be able to communicate at a plurality of these frequencies to increase the functionality and utility of the wireless communication device. For each of these frequencies, the wireless communication device may need a different antenna. Multiple antennas inherently take up space in the wireless communication device that is considered valuable in this era of miniaturization. This situation is compounded when the needed electrical length for antennas operating at these different frequencies is taken into account. 
     SUMMARY 
     The present invention relates to a wireless communication device, such as a transponder, that has a plurality of antennas for operation at multiple frequencies. The wireless communication device comprises a control system, communication electronics, memory, and the aforementioned antennas. 
     In a first embodiment, a dipole antenna is positioned across one or more nested loop conductor antennas to achieve multiple operating frequencies. Two conductive tabs are coupled to the wireless communication device to provide the dipole antenna. This dipole antenna provides a first operating frequency to the wireless communication device. The conductive tabs are also coupled across the nested loop conductor antenna through capacitive coupling. A second wireless communication circuit is also coupled to the nested loop conductor antenna. As the frequency increases, the conductive tabs across the nested loop conductor antenna become closer to a short. Therefore, different loop conductor antenna configurations in the nested loop conductor antenna resonate depending upon the frequency to provide multiple operating frequencies to the wireless communication device. 
     In a second embodiment, a pole antenna is coupled to the wireless communication device that serves as one antenna for a first operating frequency. At least one additional loop conductor antenna is placed in proximity to the pole antenna to provide at least one additional operating frequency. 
     By way of example, the pole antenna may be a dipole antenna that is comprised of two conductive tabs coupled to the wireless communication device. Two loop conductor antennas are placed in close proximity to the tabs for capacitive coupling. Each of the loop conductor antennas resonate at their own design frequency. Since the tabs that serve as a dipole antenna are also coupled to the loop conductor antennas, the wireless communication device is capable of operating at three frequencies. The first operating frequency is achieved through the dipole antenna. The second operating frequency is achieved through capacitive coupling between the wireless communication device and one of the loop conductor antennas. The third frequency is achieved through capacitive coupling between the wireless communication device and the other loop conductor antenna. 
     The above embodiment is also applicable to a monopole antenna arrangement whereby one conductive tab is coupled to the wireless communication device. A ground plane is additionally provided and coupled to the wireless communication device. 
     Variations on the second embodiment comprise using an asymmetrical dipole antenna that is coupled to loops of differing shapes and sizes. Likewise, manipulating the ground plane may also provide desired variations. In a first variation, an asymmetrical dipole antenna is coupled to differently sized loop antennas and a ground plane positioned underneath the dipole antenna. In another variation, the ground plane is slotted to minimize interaction between the loop antennas. In another variation, one of the loops includes a nested loop. In still another variation, the loop comprises a low frequency loop antenna. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  illustrates a schematic diagram of a wireless communication device and an interrogation reader; 
         FIG. 2  illustrates a wireless communication device attached to an automobile; 
         FIG. 3  illustrates a prior art antenna arrangement for a wireless communication device; 
         FIG. 4  illustrates a first embodiment of an antenna arrangement for a wireless communication device; 
         FIGS. 5A-5F  illustrate a number of different effective antennas in the embodiment of  FIG. 4 ; 
         FIG. 6  illustrates a second embodiment of an antenna arrangement for a wireless communication device; 
         FIG. 7  illustrates a first variation of the second embodiment of  FIG. 6 ; 
         FIG. 8  illustrates a second variation of the second embodiment of  FIG. 6 ; 
         FIG. 9  illustrates a third variation of the second embodiment of  FIG. 6 ; 
         FIG. 10  illustrates a fourth variation of the second embodiment of  FIG. 6 ; 
         FIG. 11  illustrates a fifth variation of the second embodiment of  FIG. 6 ; 
         FIG. 12  illustrates a schematic diagram of a tracking and information system; 
         FIG. 13  illustrates a schematic diagram of a synchronization device for dual chip wireless communication devices; and 
         FIG. 14  illustrates a flow chart for the synchronization of data for dual chip wireless communication devices. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention is directed to providing multi-frequency functionality for a wireless communication device, such as a transponder. Referring now to the drawings in general, and to  FIG. 1  in particular, it will be understood that the illustrations are for the purpose of describing specific embodiments of the present invention and are not intended to limit the invention thereto. A wireless communication device  130  is connected or attached to a device or article of manufacture or other material to communicate information electronically and wirelessly concerning the device, article of manufacture, or other material. 
     One embodiment of the present invention uses a specific type of wireless communication device  130  called a radio frequency transponder. Herein, “transponder” is used interchangeably with “wireless communication device”  130 ; however, the present invention is not limited to using a transponder as the wireless communication device  130 . Some wireless communications devices  130 , such as that described in U.S. Pat. No. 5,585,953, entitled “IR/RF Radio Transceiver and Method,” incorporated herein by reference in its entirety, have both transmit and receive capability and can be used in the present invention. Other wireless communication devices  130  have receive capability and use the energy received to communicate back, such as described in U.S. Pat. No. 6,078,259, entitled “Radio Frequency Identification Tag,” incorporated herein by reference in its entirety. Such passive devices may likewise be used with the present invention. The wireless communication device  130  in the present invention can be any type of device that allows reception of wireless, electronic communications and is able to communicate in response thereto. 
     The transponder  130  may be made out of plastic or other suitable material and comprises a control system  134 , wireless communication electronics  132 , antenna assembly  136 , and memory  138 . 
     The wireless communication electronics  132  receive information wirelessly through at least one of the antennas in antenna assembly  136 . The wireless communication electronics  132  assimilate the received information and communicate it to the control system  134 . The control system  134  receives this information and controls the operation of the transponder  130 . In one embodiment, the control system  134  is an integrated circuit or other type of microprocessor or micro-controller electronics that controls the operations of the transponder  130 . The control system  134  is connected to the wireless communication electronics  132  to communicate and receive transmissions. 
     The transponder  130  may also contain a magnet  142  to aid in the transponder&#39;s  130  attachment to the magnetic surface portion of an article if so desired. The magnetic surface portion may be a conductive material or may be a non-conductive material. The transponder  130  may also contain its own power source  140 , such as a battery or reservoir capacitor, for needed power to carry out operations within the transponder  130  that are discussed later. U.S. Pat. No. 4,857,893 (hereinafter “&#39;893 patent”), entitled “Single Chip Transponder Device,” incorporated hereby by reference in its entirety, discusses a transponder having its own battery as a power source for a variety of functions. In this &#39;893 patent, the battery allows the transponder to be converted into a self-powered beacon device that periodically transmits its identifying encoded data word without the need for the presence of a carrier signal. 
       FIG. 1  also depicts how communication is achieved with the transponder  130 . An interrogation reader  100  contains interrogation communication electronics  102  and an interrogation antenna  104 . Interrogation readers  100  are also referred to herein as interrogators. As used herein, the term “interrogator” refers to a wireless communications device capable of establishing communications with a plurality of corresponding wireless communication devices, herein referred to as “transponders,” for the purpose of discriminating among and identifying individual transponders, e.g., by receiving and decoding an identification code. The interrogation reader  100  communicates to the transponder  130  by emitting a signal or command modulated in a signal  106  through the interrogation antenna  104 . The interrogation antenna  104  may be any type of antenna that can radiate the modulated signal  106  through a field  108  so that a compatible device such as a transponder  130  can receive such signal  106  through antenna assembly  136 . The field  108  could be any of a variety of different types used in the communication industry including electric, magnetic, or electromagnetic. The signal  106  is a message containing information and/or specific instructions for the transponder  130 . The range of interrogation reader  100  is designed and configured so as to encompass the area in the immediate vicinity of interrogation reader  100 . 
     When the transponder antenna assembly  136  is in the presence of the field  108  emitted by the interrogation antenna  104 , the wireless communication electronics  132  are energized, thereby energizing the transponder  130 . The transponder  130  remains energized so long as its antenna  136  is in the field  108  of the interrogation reader  100 . The wireless communication electronics  132  demodulate the signal  106  and send a message containing information and/or specific instructions to the control system  134  for appropriate actions. For example, the request in the message maybe for the transponder  130  to send back information stored in memory  138  about the article to which the transponder  130  is attached, including but not necessarily limited to its date of manufacture, place of manufacture, “born-on” date, expiration date, tracking information, status information, type of article, temperature of the article or its surroundings (if a temperature sensor is provided), or other distinguishing characteristics of the article. The transponder  130  communicates information to the interrogation reader  100  by altering the contents of the signal  106  in its return path to the interrogation reader  100 . 
     Alternative forms exist for communicating with a wireless communication device  130 . For instance, the wireless communication device  130  may have a transmitter so that it can send information to a remote source without having to use the signal  106  return as a means for communication. The wireless communication device  130  may contain its own power source  140  if it transmits information separately from its reception. It is understood to one of ordinary skill in the art that there are many other manners to provide a wireless communication device  130  to communicate wirelessly for use with the present invention, such as a transponder  130 , and that the present invention includes but is not limited to the particular manners described above. 
       FIG. 2  illustrates a particular embodiment of the transponder  130  attached to a particular article or article of manufacture, namely, an automobile  160 . The transponder  130  is mounted to a magnetic surface portion  162  of the automobile  160  using magnetic force for attraction. Magnet  142  associated with the transponder  130  may be used to provide an attractive force, causing the wireless communication device  130  to attract to and attach to the magnetic surface portion  162  of the automobile  160 . Magnet  142  may be a permanent magnet or electromagnet. Magnet  142  may be provided by constructing the transponder  130  and/or its elements, such as antenna assembly  136 , out of magnetic material. Such embodiments are disclosed in commonly owned U.S. patent application Ser. No. 09/618,506, filed Jul. 18, 2000, now U.S. Pat. No. 6,646,555, issued Nov. 11, 2003, entitled “Wireless Communication Device Attachment and Detachment Device and Method,” and incorporated herein by reference in its entirety. The transponder  130  may also be attached to an article using a fastener or an adhesive material between the transponder  130  and the article. 
     Through any appropriate attachment techniques, such as those described above, the transponder  130  may be attached to articles for tracking or information purposes. For instance, the location of the automobile  160  may be tracked through use of the transponder  130  if the transponder  130  contains an identification means, such as a number, relating to the particular automobile  160  to which the transponder  130  is attached. Additional information concerning the automobile  160 , including its make, model, etc., can be communicated and/or tracked wirelessly. Other devices or items may be tracked instead of an automobile  160 . For example, packages or containers may be tracked as described in commonly owned U.S. patent application Ser. No. 09/618,505, filed Jul. 18, 2000, now U.S. Pat. No. 6,483,473, issued Nov. 19, 2002, entitled “Wireless Communication Device and Method,” which is hereby incorporated by reference in its entirety. Examples include chip bags, chewing gum packages, beer kegs, and the like. 
     A presently existing wireless communication device is illustrated in  FIG. 3 . In particular, the wireless communication device  200  conforms to an international standard, ISO-15693-2. Wireless communication device  200  operates at 13.56 MHz by using magnetic field coupling, involving the use of tuned coils  202  as a loop conductor antenna  204  on a first side of a substrate  206 . Typically, an integrated chip  208  is mounted on the opposite side of the substrate  206 . Electrical connections extend from the integrated chip  208 , through the substrate  206  to provide an electrical connection between the wireless communication electronics  132  ( FIG. 1 ) and the antenna  204 . 
     Note that while this is an example of a prior art device, other prior art devices also exist which operate at another standard for 125 kHz. The present invention is also adapted for use with such devices. 
     As alluded to above, different interrogation readers  100  may interrogate a wireless communication device  130  at different frequencies. To that end, it may be necessary to add antennas to the wireless communication device  130 . One embodiment is illustrated in  FIG. 4 . Wireless communication device  130  is substantially similar to wireless communication device  200 . However, in addition to the loop antenna  204 , a dipole antenna  250  is placed across the coils  202 . Dipole antenna  250  comprises a first tab  252 , a second tab  254 , each of which may be approximately a quarter wavelength long relative to a desired operating frequency, and an integrated circuit  256 . The tabs  252 ,  254  are constructed out of any type of material desired so long as the material is conductive. Such material may be a ferrous material, including metal, steel, and iron, or the material may be aluminum or other type of conducting material. In another embodiment, a conductor made from metal loaded ink may be used as described in U.S. Pat. No. 5,566,441, entitled “Attaching an electronic circuit to a substrate,” incorporated herein by reference in its entirety. In particular, a multi-layer screen or other printing method may be used to create the entire tag while the chips  208 ,  256  are inserted in the ink whilst still wet. As used herein, the terms chips and circuits are used interchangeably. 
     In one implementation, the dipole antenna  250  is operative at 2.45 GHz. The integrated chip  256  may contain the wireless communication electronics  132 , control system  134 , and other desired components. An example of an appropriate integrated circuit comprises those used by INTERMEC in the Intellitag® labels and those used by SCS in the DL100 label. Note that the loops  202  act to load capacitively the tips of the dipole antenna  250 . While not shown explicitly, a dielectric material may be placed between the tabs  252 ,  254  and the coils  202  to preclude the creation of an outright short thereacross. An effective short at higher frequencies (i.e., above the operative frequency of the loop antenna  204 ) is permissible. 
     This arrangement creates a plurality of effective antennas that may be used with an interrogation reader  100 .  FIGS. 5A-5F  illustrate a number of different effective antennas that are present within the wireless communication device  130  of  FIG. 4 . The arrows within the loops of  FIGS. 5A-5F  illustrate the effective loop.  FIG. 5A  illustrates the effective antenna formed by the dipole antenna  250 . Even coupled to the wireless communication device  130 , the dipole antenna  250  still operates at its desired frequency, which, in an exemplary embodiment, is 2.45 GHz.  FIG. 5B  illustrates the loop conductor antenna  204 , which likewise operates at its desired frequency, which, in an exemplary embodiment is 13.56 MHz.  FIG. 5C  illustrates a first created loop conductor antenna  260  that enables reception in a third band. In particular, the capacitance between the tip of the tabs  252 ,  254  and the coils  202  effectively shorts the coils  202  together at higher frequencies, treating them as a single conductor. This coupling links the integrated chip  256  to two additional loops formed by the intersection of loop  204  with the dipole antenna  250 . A first created loop antenna  260  is formed by the top half of the loop  204 , the tabs  252 ,  254  of the dipole antenna  250 , and the integrated chip  256 . In an exemplary embodiment, this may operate at 915 MHz. 
     As illustrated in  FIG. 5D , a second created loop antenna  262  is formed by the lower half of the loop  204 , the tabs  252 ,  254  of the dipole antenna  250 , and the integrated chips  208 ,  256 . If the UHF capacitance of the integrated chip  208  is correctly selected, it is possible to tune the second loop  262  to a different UHF frequency from the first loop  260 , such as the desirable 868 MHz. 
     It should be appreciated that both the first and second loops  260 ,  262  can be made to act as UHF antennas by ensuring that the net inductance of these loops at the UHF frequency, the impedance of the chip  256  (and chip  208  in loop  260 ), and the series capacitances formed by the parallel plate coupling of the tab  252 ,  254  tips to the coils  202  collectively resonate at the desired frequencies. This can be controlled by varying the size of the tabs  252 ,  254  and the position of the dipole antenna  250  on the wireless communication device  130 . In one embodiment, the transponder  130  operates at a 0.5 meter range at 13.56 MHz, 3 meters at 915 MHz, and 0.5 meters at 2.45 GHz. 
     The tabs  252 ,  254  capacitively couple to the coils  202 , and create an effective short thereacross at UHF frequencies. It may also be possible that the tabs  252 ,  254  may be used as feed lines that capacitively couple to the coils  202  and drive the same at still other frequencies. Since the coils are effectively shorted at some frequencies, but not at others, a loop  264  ( FIG. 5E ) may be generated and used as a loop conductor antenna. Likewise, at other frequencies, the integrated chip  208  may still be part of the electrical length of a loop  266  ( FIG. 5F ), allowing yet another operative frequency. 
     It may also be possible to vary how the coils are capacitively shorted together by the tabs  252 ,  254 , by varying the size and shape of the tabs  252 ,  254 . For example, flaring or tapering the tabs  252 ,  254  may make it more likely that only a portion of the coils are shorted together at certain frequencies. This allows still other frequencies to be used as needed or desired. 
     Note that, for the purposes of the present invention, this wireless communication device  130  has two or more loop conductor antennas, they just happen to share at least portions of the same conductor coil. 
     For wireless communication devices  130  that contain two chips  208 ,  256  coupled to common antennas, there may be a desire to synchronize the data carried in each chip  208 ,  256 , so that when they are interrogated at any of the operational frequencies, the same data is returned. A simple method of achieving this desired result is a dual reader/writer device  700 , as illustrated in  FIG. 13 . Dual reader/writer device  700  comprises a controller  702  controlling two or more interrogation readers  100  by data flow connections  704 . Dual reader/writer device  700  may include an optional communicative link  706  to a remote source. Wireless communication device  130  is brought into the communicative fields of the at least two interrogation readers  100  and data exchanged therebetween. 
     It may be advantageous to have all the data written to memory  138  of the wireless communication device  130  to be time and date stamped. In use, information may be read and written by the interrogation readers  100  operating at only a single frequency, allowing memory  138  on the different chips  208 ,  256  to be modified in different manners at different times by different readers. This creates different outputs from the different chips  208 ,  256 . Understandably, this situation is undesirable. 
     The methodology is illustrated as a flow chart in  FIG. 14 . One of the interrogation readers  100  reads the data from the first chip (for example, chip  208 ) (block  800 ). The second interrogation reader  100  reads the data from the second chip (for example, chip  256 ) (block  802 ). The controller  702  compares the data returned from the two chips  208 ,  256  (block  804 ). If the data is synchronous, no action is required and the process ends (block  806 ). If, however, the data is not synchronous, the controller  702  may archive all the data from both chips  208 ,  256  (block  808 ). The controller  702  may then instruct the appropriate interrogation reader  100  to write the data from the chip  208 ,  256  with the newest date stamp to the chip  208 ,  256  carrying the older date stamp (block  810 ). The data is now synchronous between the two chips  208 ,  256  and the process ends (block  812 ). Other techniques of synchronization are also possible. 
     A second embodiment of a multi-band wireless communication device is illustrated in  FIG. 6 . In particular, the wireless communication device  130  comprises a dipole antenna  250  and a pair of loop conductor antennas  302 ,  304  oppositely positioned from one another on either side of the dipole antenna  250 . Dipole antenna  250  comprises a first tab  252 , a second tab  254 , and an integrated chip  256  as previously described and may be operative at 2.45 GHz. Loop conductor antennas  302 ,  304  may comprise multiple coils (not shown) or a single coil of microstrip and may be sized as needed to achieve a desired operating frequency. Note that the gaps  306  between the tabs  252 ,  254  and the loop conductor antennas act as series capacitors, forming resonant circuits between the integrated chip  256  and the two loop conductor antennas  302 ,  304 . In one version of this embodiment, the loop conductor antennas  302 ,  304  operate at 868 MHz and 915 MHz, respectively. An alternate way to tune the loop conductor antennas  302 ,  304  is to move the relative placement of the dipole antenna  250 . If the dipole antenna  250  were closer to one loop ( 302  or  304 ) than the other, there would be an increased coupling capacitance between the dipole  250  and the closer loop ( 302  or  304 ), impacting the operating frequency. Likewise, there would be a lower coupling capacitance between the dipole and the farther loop ( 302  or  304 ), also impacting the operating frequency of that loop ( 302  or  304 ) as well. These antennas  250 ,  302 ,  304  may likewise be positioned on a substrate  206 . In other versions of the present embodiment, the antennas  250 ,  302 ,  304  may be positioned on different sides of the substrate  206 . Variations in which side of the substrate  206  on which the antennas are placed, the thickness of the substrate, and the like may also be used to tune the antennas  250 ,  302 ,  304  to the desired frequencies. Likewise, variations in the dimensions of the loop, the number of coils, and even the material used may impact the operating frequencies of the loops. 
     Also note that one tab  252 ,  254  may be used with this embodiment to create a monopole-type antenna if a ground plane (not shown) is provided that is coupled to transponder  130 . Likewise, only one loop conductor antenna  302 ,  304  may be used to create a device that operates at two different frequencies; one through the pole-type antenna and the other through the loop conductor antenna  302 ,  304 . 
     A number of the variations just discussed, as well as some others, are presented in  FIGS. 7-11 . In  FIGS. 7-11 , the coils are illustrated as microstrip antennas. Other arrangements are possible. Specifically,  FIG. 7  illustrates a transponder  400  comprising an asymmetrical dipole antenna  402  coupled to a pair of asymmetrical loop antennas  410 ,  412 . As illustrated in  FIG. 7 , the dipole antenna  402  is positioned such that loop antenna  410  is smaller than loop antenna  412 . Dipole antenna  402  comprises asymmetrical tabs  404 ,  406  as illustrated. Variations in the nature of the asymmetry to achieve the desired operating frequencies are considered within the skill of those in the industry. A further discussion of asymmetrical dipole antennas may be found in commonly owned, concurrently filed U.S. patent application Ser. No. 09/678,271, entitled “Wireless Communication Device and Method,” now U.S. Pat. No. 6,501,435, issued Dec. 31, 2002, which is hereby incorporated by reference in its entirety. A ground plane  408  is further used to tune the antennas  402 ,  410 ,  412 . Chip  414  controls all the antennas  402 ,  410 ,  412 . Further tuning may be achieved by varying the position of the various elements on the substrate  206 . For example, some elements may be on one side, some embedded, and some on the other side; all the elements may be embedded; all the elements on one side; or other arrangement as needed or desired. It should be appreciated that the ground plane  408  may be isolated from the other elements to provide the desired grounding effect, but such may be done with a dielectric tape or the like as is well understood. Again, this wireless communication device  400  has multi-frequency functionality in that the dipole antenna  402  may operate at a first frequency, the first loop antenna  410  may operate at a second frequency, and the second loop antenna  412  may operate at a third frequency. 
       FIG. 8  illustrates a second variant wireless communication device  400 A, wherein the ground plane  408 A is slotted behind the dipole  402  to minimize interaction between the loop antennas  410 ,  412 . This is a function of the fact that at UHF frequencies, the gap will appear as a high impedance gap. At the microwave frequencies of the dipole  402 , the gap has a relatively low impedance and looks like a continuous ground plane, allowing the dipole  402  to operate normally. 
       FIG. 9  illustrates a third variant with nested loops for improved bandwidth response. In particular, wireless communication device  450  comprises an asymmetrical dipole antenna  402 , a ground plane  408 , a first loop  412 , a second loop  452 , and a chip  414 . Second loop  452  comprises a first part  454  and a second part  456 , which are nested and coupled to the dipole  402 . If the loops are similarly sized, but not identical, the overall circuit behaves like two coupled tuned circuits, giving an overall wider receive bandwidth than would be achieved with one loop. 
       FIG. 10  illustrates a fourth variant wireless communication device  500 . Wireless communication device  500  comprises a dipole antenna  402 , a ground plane  408 , a first loop antenna  412 , and a second loop antenna  502 . Second loop antenna  502  is electrically longer at low frequencies such as 13.56 MHz. Additionally, it should be noted that the coils of the second loop antenna  502  may be separated by a dielectric tape, or even by having an opposite surface connection. 
       FIG. 11  illustrates a fifth variant wireless communication device  550 . Wireless communication device  550  comprises a dipole antenna  402 , a slotted ground plane  408 B, a first loop antenna  412 , and a second loop antenna  502 A. The first loop antenna  412  is operative at UHF frequencies, the dipole antenna  402  at microwave frequencies, and the second loop antenna  502 A is operative at low frequencies akin to second loop antenna  502 . The second loop antenna  502 A is coupled to the chip  414  via capacitance between the two plates  552 ,  554  of the slotted ground plane  408 B. In this variant, a thin substrate  206  allows increases in the capacitive coupling between the dipole antenna  402  and the second loop antenna  502 A. The narrow gap in the ground plane  408 B is seen as a relatively low impedance gap at microwave frequencies, allowing the dipole antenna  402  to function normally. 
     The variants and embodiments of  FIGS. 6-11  are designed more from a fresh perspective than with an eye towards retrofitting. That does not mean that these variations may not be used in a retrofit context, but the present commercially available wireless communication devices  200  are not designed to accommodate these variations as easily. To that end, the embodiments of  FIGS. 6-11  are designed to operate with a single RFID chip,  256  or  414 . Chip  256  or  414  can sense in a simple way which frequency at which the interrogation is occurring. If the chip  256 ,  414  has an input port connected to the antenna terminals prior to the internal rectifier, it will “see” 13.56 MHz when being interrogated at this frequency, but not when being interrogated at higher frequencies. This is useful because when operating at 13.56 MHz, the standard requires that the chip  256 ,  414  clock off the received field. This may also be helpful because the chip  256 ,  414  may change modulation methods, data rates or the like depending on the received frequency. Alternatively, the interrogator  100  may simply send an identifier as part of the interrogation message. The identifier may identify the frequency at which the interrogator  100  is operating. This identifier may be in the form of amplitude modulation of the signal or other technique as desired. 
       FIG. 12  illustrates one type of tracking system whereby the transponder  130  attached to articles  161 , for example, automobile  160 , can be tracked through an environment such as a factory, distribution facility, or storage facility. For example, the transponder  130  connected to article  161  passes a first interrogation point  150  that includes an interrogation reader  100 . When the article  161  and its attached transponder  130  are in the presence of the interrogation reader  100  as described previously, a message containing information and/or a specific request for information may be transmitted by the interrogation reader  100  and received by the transponder  130 . This process continues as the article  161  moves to a second interrogation point  152 , a third interrogation point  154 , a fourth interrogation point  156 , and on to a last interrogation point  158 . 
     A central control system  159  maintains the information from interrogation readers  100  and monitors the movement of the articles  161  through the facility. The information received by each of the interrogation readers  100  may be forwarded to the central control system  159  in a variety of architectures such as parallel or serial communication or through use of a local area network (LAN) or wide area network (WAN). Such architecture may include wiring between the interrogation readers  100  and the central control system  159  or may be wireless communication. The central control system  159  may also send information to the interrogation reader  100  to be transmitted back to the transponder  130  attached to the article  161  for a variety of purposes, including for identification. If the central control system  159  is designed to have knowledge of anticipated or expected whereabouts of the articles  161 , then an alarm may be generated if the control system  159  expects to receive information about a particular article  161  and does not. Other situation-based alarms may also be possible, such as when an item appears at the same station twice or if some other unexpected situation occurs. 
     Note that wireless communication devices  130  having their own transmission capability may still be used for tracking and communicating information concerning articles  161  without the use of interrogation readers  100 . In its simplest form, a receiver to receive communication from the wireless communication device  130  would be needed. Alternatively, multiple receivers may be used to triangulate the position of the tracked article  161 . If the system tracks and/or receives information from more than one wireless communication device  130 , the system may need to have the ability to receive and transmit on different frequencies in order to distinguish wireless communication devices  130 . However, an identification stored in memory  138  of the transponder  130  may also be used to distinguish wireless communication devices  130 . During commissioning of each transponder  130 , it may be necessary to place the transponder  130  in range of an interrogation reader  100  to erase previously stored information in memory  138  or to store particular data or configuration information about the article  161  in memory  138  for later use. 
     It should be appreciated that while the present invention is phrased as being operative at certain frequencies, the intended interpretation of such comments is that some bandwidth centered about the operative frequencies is used. Thus, for example, stating that the dipole antenna  250  may be operative at 2.45 GHz is intended to mean that the dipole antenna  250  operates on a channel having a bandwidth centered at 2.45 GHz. This is true for the other operative frequencies as well. 
     The present invention may, of course, be carried out in other specific ways than those herein set forth without departing from the scope and the essential characteristics of the invention. The present embodiments are therefore to be construed in all aspects as illustrative and not restrictive and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.