Abstract:
A multi-field antenna able to receive a signal over one field selected from a plurality of different fields of the antenna includes an interface to connect the antenna to a signal processing device, such as an RFID reader, to receive and process the signal. The antenna includes a first magnetic loop configured to be tuned by a first tuner to provide a first volume field for reading data; a second magnetic loop configured to be tuned by a second tuner to provide a second volume field for reading data, the second volume field being smaller than the first volume field; and a switch to configure the first tuner and the second tuner to select the one field from the plurality of fields. The multi-field antenna can have a wide volume field selected to detect items within a large area and then the multi-field antenna can be switched to select a smaller volume field to detect items within a substantially smaller area. In a preferred embodiment, the multi-field antenna further includes; a first metallic element configured to cover at least a portion of the second magnetic loop, the first metallic element comprising a slot extending from one end of the first metallic element to a point proximal an opposite end of the first metallic element. Also preferably, the multi-field antenna can also create a point volume field, smaller than the second volume field, to localize detected objects within a still smaller area.

Description:
The present invention relates generally to RFID antennas and, more specifically, to an RFID antenna capable of selectively using one of multiple antenna fields to transmit and receive radio information. 
     BACKGROUND OF THE INVENTION 
     It is known to track and attempt to locate objects, such as sales goods, components, medical samples, documents, produce or other articles of commerce, during their manufacture, storage, transport and/or distribution. Wireless communication transponders may be attached to or associated with such objects to provide information about the objects such as their identification number, expiration date, date of manufacture, lot number, and the like. An example of such a wireless communication transponder is a radio frequency identification (RFID) tag. 
     In order to communicate with the wireless communication transponders, a wireless transmission interrogator is placed in proximity to the objects. An example of such a wireless transmission interrogator is an RFID reader. The RFID reader creates a radio frequency field with appropriate radio circuitry and an antenna to communicate with the RFID tag and to identify the object the tag is associated with. 
     There are generally three different types of RFID tags: active RFID tags; passive RFID tags; and battery assisted passive (BAP) RFID tags. Active RFID tags contain a battery and can transmit signals autonomously. Passive RFID tags have no battery and require an external source, typically a signal transmitted by the interrogator, to power signal transmission. BAP RFID tags require an external source to activate the tag, but their battery powers their transmission resulting in it having a greater range of operation. 
     However, all three types of RFID tags are designed to operate at relatively short range. Accordingly, the RFID reader&#39;s antenna must be placed into relatively close proximity to the RFID tag in order to read it. In order to address this, different antennas have been developed to provide different radio frequency field sizes for reading the RFID tags in different use cases. 
     Unfortunately, antennas that have a large field size typically have a low resolution. That is, for example, an antenna with a large field size could be used to locate a target box from within a plurality of boxes, but it probably could not locate a target item from within the target box. Conversely, an antenna with a relatively small field size could locate a target item from within a box of items, but could not locate the box containing the target item from a collection of possible target boxes. Thus, different antennas, or different RFID readers altogether, may need to be used to locate both the target box and the target item or for other particular use cases. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a novel system and method for locating objects which obviates or mitigates at least one disadvantage of the prior art. 
     In accordance with a first aspect of the present invention, there is provided a multi-field antenna which is able to receive a signal over one field selected from a plurality of different fields of the antenna, the multi-field antenna comprising: a first magnetic loop; a first tuner to tune the first magnetic loop to provide a first volume field for reading data; a second magnetic loop; a second tuner to tune the second magnetic loop to provide a second volume field for reading data, the second volume field being smaller than the first volume field; a first metallic element configured to cover at least a portion of the second magnetic loop; a switch to configure the first tuner and the second tuner to select the one field of the plurality of fields; and an interface to connect the multi-field antenna with a signal processing device operable to receive and process the signal. 
     Preferably, the first metallic element includes a slot extending along a length of the first metallic element from one end of the first metallic element to a point proximal an opposite end of the first metallic element. Also preferably, the slot comprises an aperture at the one end of the first metallic element and the multi-field antenna further comprises a ferrite nub coupled to the second magnetic loop at an end adjacent the aperture, the ferrite nub configured to provide a third volume field, the third volume field being smaller than the second volume field. 
     In accordance with another aspect of the present invention, there is provided a mobile computer device comprising: an RFID reader; memory having stored instructions; a microprocessor configured to implement the stored instructions for receiving and processing a signal from the RFID reader; and a multi-field antenna connected to the RFID reader, the multi-field antenna operable to receive a signal over one field selected from a plurality of different fields of the multi-field antenna and comprising: a first magnetic loop; a first tuner to tune the first magnetic loop to provide a first volume field for reading data from RFID tags; a second magnetic loop; a second tuner to tune the second magnetic loop to provide a second volume field for reading data from RFID tags, the second volume field being smaller than the first volume field; a first metallic element configured to cover at least a portion of the second magnetic loop; and a switch to configure the first tuner and the second tuner to select the one field from the plurality of fields. 
     Preferably, the first metallic element comprises a slot extending along a length of the first metallic element from one end of the first metallic element to a point proximal an opposite end of the first metallic element. Also preferably, the slot comprises an aperture at the one end of the first metallic element and the multi-field antenna further comprises a ferrite nub coupled to the second magnetic loop at an end adjacent the aperture, the ferrite nub configured to provide a third field, the third field being narrower than the second field. 
     Preferably, the switch is controlled by the microprocessor. 
     In accordance with yet another aspect of the present invention, there is provided a method of locating a target object from among a plurality of objects, each object including a wireless communication transponder, comprising the steps of: i) selecting a first field for a multi-field antenna operating with a wireless transmission interrogator, the first field being relatively large in volume; ii) with the selected first field, receiving signals from wireless communication transponders from at least two objects; iii) determining a first estimate of the location of the target object from the received signals within the first field; and iv) selecting a second field for the multi-field antenna, the second field being smaller in volume than the first field and determining a second estimate of the location of the target object within the second field, the second estimate being at least as accurate as the first estimate. 
     Preferably, the method further comprises the step of: v) receiving a signal from the wireless communication transponder of the target object with a third field for the multi-field antenna, the third field having a volume smaller than the second field, to provide a third estimate of the location of the target object. Also preferably, the wireless communication transponders are RFID tags and the wireless transmission interrogator is an RFID reader. Also preferably, the wireless transmission interrogator is operably connected to a mobile computer device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention will now be described, by way of example only, with reference to the attached Figures in which: 
         FIG. 1  shows a perspective view of the top and side of a mobile computer; 
         FIG. 2  is block diagram illustrating components of the mobile computer of  FIG. 1 ; 
         FIG. 3   a  is a schematic view of the top of a multi-field antenna in accordance with the present invention; 
         FIG. 3   b  shows the multi-field antenna of  FIG. 3   a  with a wide field selected; 
         FIG. 3   c  shows the multi-field antenna of  FIG. 3   a  with a narrow field and a point field selected; 
         FIG. 4   a  is a perspective view of the side and end of a test tube including a wireless communication transponder; 
         FIG. 4   b  is an end view of the test tube of  FIG. 4   a  showing the wireless communication transponder; and 
         FIG. 5  shows a perspective view of the top and sides of a box storing the test tubes of  FIGS. 4   a  and  4   b.    
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1  a mobile computer is indicated generally at  100 . Mobile computer  100  comprises a main body  102 , a display  104 , a keyboard  106 , and an external antenna connector (not shown). In the present embodiment, the external antenna connector is preferably located beneath a protected cap or cover  108 . Cap  108  protects the external antenna connector from water, dirt or other foreign elements when the multi-field antenna is not connected. Alternatively, the external antenna can be permanently installed on mobile computer  100  and/or may be integrally formed with main body  102 . 
     Mobile computer  100  can have the capability to wirelessly communicate data and/or voice signals, to and from servers as well as data acquisition sources within a communication network. 
     One or more circuit boards or assemblies are housed within mobile computer  100  for providing the electronic components required to implement functionality provided by the mobile computer  100 . It will be appreciated that various configurations of mobile computers having different internal and external components can be used without affecting the functionality of the invention. 
     Referring now to  FIG. 2 , a block diagram illustrating an example of the logical structure of mobile computer  100  is shown. Mobile computer  100  includes a microprocessor  238  for controlling general operation of the mobile computer  100 . The microprocessor  238  also interacts with functional device subsystems such as: a data capture subsystem  211 ; display  104 ; a flash memory  224 ; random access memory (RAM)  226 ; auxiliary input/output (I/O) subsystems  228 ; serial port  230 ; keyboard  106 ; speaker  234 ; microphone  236 ; WAN communication subsystem  237 ; and a short-range communications subsystem  240 , such as a Bluetooth™ transceiver for example. 
     Mobile computer  100  includes a power source  210 , such as a rechargeable battery which may also be removable and replaceable from the mobile computer. Mobile computer  100  may also include a location device  244 , such as a GPS receiver for example, for receiving location information. 
     Operating system software used by the microprocessor  238  may be stored in a persistent store such as flash memory  224 , which may alternatively be a read-only memory (ROM), disk drive or other suitable storage element (not shown). Those skilled in the art will appreciate that the operating system, specific device applications, or parts thereof, may be temporarily loaded into a volatile store such as RAM  226 . 
     Microprocessor  238 , in addition to its operating system functions, enables execution of software applications on the mobile computer  100 . A predetermined set of applications, which control basic device operations, may be installed on the mobile computer  100  during its manufacture. These basic operations typically include data and voice communication applications, for example. Additionally, applications may also be subsequently loaded onto the mobile computer device  100  through the WAN communication subsystem  237 , an auxiliary I/O subsystem  228 , serial port  230 , USB port  242 , short-range communications subsystem  240 , or any other suitable subsystem, and installed by a user in RAM  226 , or the persistent store  224 , for execution by the microprocessor  238 . Such flexibility in application installation increases the functionality of the mobile computer  100  and may provide enhanced on-device features, communication-related features, or both. 
     As will be apparent to those skilled in field of communications, the particular design of the WAN communication subsystem  237  depends on the communication network in which mobile computer  100  is intended to operate, and may include communication functionalities such as Wi-Fi based on 802.11 standards, 3G standards, Long Term Evolution (LTE), WiMax, 4G standards and the like. 
     Data capture subsystem  211  preferably includes an internal RFID reader  250  which is coupled, via a switch  252 , to antenna connector  254 . 
     As will be apparent to those of skill in the art, switch  252  can be a mechanical switch directly operated by a user of mobile computer  100 , or can be an electronic switch operable by microprocessor  238  in response to software instructions executed thereon and/or input from a user of mobile computer  100 . 
     While in the present embodiment it is preferred that RFID reader  250  be located internal to mobile computer  100 , the present invention is not so limited and data capture subsystem  211  can be external to mobile computer  100 , such as an RFID reader backpack, or other external unit. Whether data capture subsystem  211  is internal or external, an appropriate direct, or indirect, data connection is provided between RFID reader  250  and microprocessor  238  to allow data to be transferred therebetween. 
     The display module  222  is used to visually present an application&#39;s graphical user interface (GUI) to the user. Depending on the type of mobile computer  100 , the user can have access to various types of input devices, such as, for example, a scroll wheel, trackball, light pen and/or a touch sensitive screen. 
     Referring now to  FIG. 3   a , a multi-field antenna in accordance with the present invention is indicated generally at  300 . Multi-field antenna  300  includes a large magnetic loop  302 , a small magnetic loop  304 , a ferrite nub  306 , a first metallic element  308 , a second metallic element  310 , a first tuner  312 , a second tuner  314 , and a mobile computer interface  316  which can include connector  254 . 
     In the present embodiment, the mobile computer interface is configured to couple with the external antenna connector  254  on the mobile computer  100  to connect to RFID reader  250 . The first tuner  312  is configured to provide impedance matching between the RFID reader  250 , which typically has an output impedance of 50 ohms, and the large magnetic loop  302 . Similarly, the second tuner  314  is configured to provide impedance matching between the RFID reader  250  and the small magnetic loop  304 . Which magnetic loop, and its corresponding tuner, is activated depends on the position of the switch  252 . 
     The large magnetic loop  302  is generally rectangular in shape and has one or more turns of wire. The large magnetic loop  302  provides a relatively large volume field ( 380  in  FIG. 3   b ) and can read a large population of RFID tags within its range. As will be apparent to those of skill in the art, the volume of the field can be shaped as a sphere, ovoid or other shape, as desired, by the particular design and arrangement of large magnetic loop  302  and other elements of the multi-field antenna. 
     An example application for which the large magnetic loop  302  could be useful is an inventory application. In the present embodiment, the large magnetic loop  302  is configured to read RFID tags at a distance of up to approximately 5 cm to 15 cm with an ovoid-shaped field. The large volume field activated by the large magnetic loop  302  is shown in  FIG. 3   b.    
     First metallic element  308  is a solid metal element that is generally rectangular in shape and is sized smaller than the large magnetic loop  302  but large enough to cover a substantial portion of the small magnetic loop  304 . Preferably, the first metallic element  308  is not completely closed-off and instead includes a slot  320 . The slot  320  extends along a length of the first metallic element  302  from an aperture  322  at one end of the first metallic element  308  to a point proximal an opposite end of the first metallic element  308 . Thus, the structural integrity of the first metallic element  308  as a single entity is maintained. As will be understood by those of skill in the art, the dimensions of slot  320  helps define the field volume and shape of the small magnetic loop  304 . 
     The small magnetic loop  304  is generally rectangular in shape and has one or more turns of wire. The small magnetic loop  304  provides a smaller volume field than large magnetic loop  302  ( 385  in  FIG. 3   c ) and can read a population of RFID tags within the volume. The size and shape of the smaller volume field is influenced by the dimensions of the slot  320 , as the magnetic field generated by the small magnetic loop  304  radiates therethrough. In a present embodiment, the small magnetic loop  304  is configured to create a field which can read RFID tags at a distance of approximately 2 cm to 3 cm and which has a substantially elongate shaped field. The smaller volume field activated by the small magnetic  304  loop is shown at  385  in  FIG. 3   c.    
     In the illustrated embodiment, the large magnetic loop  302  and the small magnetic loop  304  are in substantially the same plane and the first metallic element  308  is minimally offset, either above or below the small magnetic loop  304 . Alternatively, the large magnetic loop  302  and the first metallic element  308  can be in substantially the same plane and the small magnetic loop  304  can be minimally offset, either above or below the first metallic element  308 . Yet alternatively, each of the large magnetic loop  302 , the small magnetic loop  304  and the first metallic element  308  can be minimally offset, so that each is in a different plane. 
     Ferrite nub  306  is coupled with the small magnetic loop  304  at an end adjacent to aperture  322 . In the illustrated embodiment, ferrite nub  306  is cylindrical in shape and is thereby configured to provide a pointed (e.g.—ellipsoidal) volume field ( 390  in  FIG. 3   c ) which allows interacting with a RFID tag with high accuracy. Further, in a present embodiment, the composition of the ferrite nub  306 , as well as its size and shape, are selected to provide a target frequency. In a present embodiment, this target frequency is 13.56 MHz, although other target frequencies can be selected as desired. 
     Second metallic element  310  is coupled with the ferrite nub  306  to help localize pointed volume field  390 , thereby inhibiting reading RFID tags neighbouring the target RFID tag. In the present embodiment, second metallic element  310  is an annular ring configured to fit snugly about the ferrite nub  306 , proximal the small magnetic loop  304 . Accordingly, the pointed volume field  390  is localized in a direction away from the small magnetic loop  304 , as illustrated in  FIG. 3   c.    
     As will be apparent to those of skill in the art, the ability to use pointed volume field  390  can provide advantages relative to a multi-field antenna which only offers large volume and small volume fields, but it is contemplated that in some circumstances pointed volume field  390 , and the elements used to form it, can be omitted from multi-field antenna  300  without departing from the scope of the present invention. 
     As will be apparent to those of skill in the art, first metallic element  308  acts as a mask, masking large magnetic loop  302  from small magnetic loop  304 . That is, when the large magnetic loop  302  is active, a current can be induced in the small magnetic loop  304 . In turn, the induced current generates a magnetic field which may interfere with the operation of the large magnetic loop  302 . Accordingly, the first metallic element  308  inhibits these effects, thereby masking the large magnetic loop  302  from the small magnetic loop  304 . 
     In operation, only one of large magnetic loop  302  or small magnetic loop  304  is activated at a time. The other magnetic loop is left open circuited, or has a load applied to it, to further inhibit interference and the selection of which magnetic loop is activated is made with switch  252 . 
     As previously mentioned, the illustrated embodiment of the present invention is designed specifically for a frequency of 13.56 MHz used in HF (high frequency) RFID systems. However, it is contemplated that multi-field antenna  300  can be designed to operate at different frequencies, used in other RFID or wireless transponder systems as desired. 
     Further, while the description above only discusses providing a first tuner  312  and a second tuner  314  and the corresponding large magnetic loop  302  and small magnetic loop  304 , it will be apparent to those of skill in the art that multi-field antenna  300  can be constructed with additional tuners, magnetic loops and metallic elements to provide additional selectable field volumes and/or shapes if desired. 
     A sample application of the operation of the multi-field antenna  300 , to locate a target test tube containing a medical specimen is described as follows. In the present example, an operator of a mobile computer  100  desires to locate a target test tube  400   a  amongst a plurality of test tubes  400 . An example of such a test tube  400   a  is illustrated in  FIGS. 4   a  and  4   b . Each of the test tubes  400  includes a unique RFID tag  404  and can be stored in one of an array of compartments in one or more boxes  408  or other storage arrays, as indicated in  FIG. 5 . 
     Before beginning to search for the particular target test tube  400   a , the operator attaches the multi-field antenna  300  to the mobile computer  100 , if it is not already attached, via connector  254  and uses switch  252  to select the large volume field  380  offered by the large magnetic loop  302  (as shown in  FIG. 3   b ). In this case, switch  252 , whether operated manually by the user, or under software control, enables the first tuner  312  for activating the large magnetic loop  302  and, in the present embodiment, the small magnetic loop  304  is open-circuited to inhibit interference with the operation of the large magnetic loop  302 . Alternatively, a load or resistor can be applied to the small magnetic loop  304  to detune it to further inhibit interference with the operation of the large magnetic loop  302 . 
     Once the large magnetic loop  302  has been activated, the operator uses the large volume field  380  of the multi-field antenna  300  to scan two or more boxes  408  to determine in which of the boxes  408  the target test tube  400   a  is located (“the target box”). When mobile computer device  100  and multi-field antenna  300  are adjacent a box  408  which contains target test tube  400   a , mobile computer device  100  will provide to the user a positive indication of the presence of target test tube  400   a  within large volume field  380 . Thus the user will have a first estimate (i.e.—within the target box  408 ) of the location of target test tube  400   a.    
     Once the target box  408  has been located, the switch  252  is used, either under software control or manually by the operator, to switch multi-field antenna  300  from operating with the large volume field  380  to operating with the smaller volume field  385  of the small magnetic loop  304  in order to further narrow the search for the target test tube  400   a . Because of the resolution of the large volume  380  of the large magnetic loop  302 , the operator cannot efficiently determine where in the array within the target box  408  of test tubes  400  the target test tube  400   a  is positioned. 
     Switch  252  enables the second tuner  314  for tuning the small magnetic loop  304  and, in the present embodiment, the large magnetic loop  302  is open-circuited to inhibit interference with the operation of the small magnetic loop  304 . Alternatively, a load or resistor can be applied to the large magnetic loop  302  to further inhibit interference with the operation of the small magnetic loop  304 . 
     Once the small magnetic loop  304  has been enabled, the operator uses the smaller volume field  385  of the multi-field antenna  300  to scan the rows or columns of the array within the located box  408  to determine in which row or column (depending upon the orientation of multi-field antenna  300  as smaller volume field  385  is preferably elongate in one direction and narrower in the other, as seen in  FIG. 3   c ) the target test tube  400   a  is located. Again, mobile computer device  100  will provide to the user a positive indication of the presence of target test tube  400   a  within smaller volume field  385 . Thus the user will have a second, more accurate, estimate (i.e.—within an identified row or column of the target box  408 ) of the location of target test tube  400   a.    
     Once the row or column has been determined, the operator uses the pointed field  390  of the ferrite nub  306  in order to further narrow the search for the target test tube. Because of the resolution of the smaller volume field  385  of the small magnetic loop  304 , the operator may not be able to efficiently determine where the target test tube  400   a  is positioned in the row or column of the array solely with smaller volume field  385 . 
     At this point, it is not required to further activate the switch  252 , because the ferrite nub  306  is coupled with the small magnetic loop  304 . The operator uses the pointed volume field  390  of the ferrite nub  306  to locate the target test tube  400   a  within the row or column. Again, mobile computer device  100  will provide to the user a positive indication of the presence of target test tube  400   a  within pointed volume field  390 . Thus the user will have a third, still more accurate, estimate (i.e.—within a particular storage location of the array of locations in box  408 ) of the location of target test tube  400   a.    
     It will be appreciated by a person of ordinary skill in the art that the time taken to locate a target item, such as a test tube  400 , even in a close packed array of target items can be dramatically reduced using the multi-field antenna  300  as described herein 
     A further sample application of the operation of the multi-field antenna  300  is described as follows. In the present example, an operator of a mobile computer  100  desires to take an inventory of the test tubes  400  stored in an array in each of a plurality of boxes  408 . Each of the test tubes  400 , as well as each of the boxes  408  includes an RFID tag having a unique identifier. Further, each storage array comprises a plurality of predefined rows and columns. In the illustrated embodiment, the array comprises ten rows and ten columns for storage locations for one hundred test tubes  400 . Each position in the array is identified by a unique number from one to one hundred. 
     Before beginning to take inventory, the operator attaches the multi-field antenna  300  to the mobile computer  100 , if it is not already attached, and selects the large volume field  380  offered by the large magnetic loop  302 . Accordingly, the switch  252  enables first tuner  312  for tuning the large magnetic loop  302 . As before, in the present embodiment the small magnetic loop  304  is open-circuited to inhibit interference with the operation of the large magnetic loop  302 . Alternatively, a load or resistor can be applied to the small magnetic loop  304  to further inhibit interference with the operation of the large magnetic loop  302 . 
     Once the large magnetic loop  302  has been activated, the operator uses the large volume field  380  of the multi-field antenna  300  to scan a box  400  to determine its identifier as well as the identifiers of the test tubes  400  contained therein. At this point, mobile computer device  100  can determine the particular test tubes  400  in the scanned box  408 . 
     Once the box  408  has been scanned with the large volume field  380 , the operator switches from the large volume field  380  to the smaller volume field  385  of the small magnetic loop  304  in order to further narrow the search for the target test tube  400   a.    
     Accordingly, the switch  252  enables the second tuner  314  for tuning the small magnetic loop  304 . As before, in the present embodiment the large magnetic loop  302  is open-circuited to inhibit interference with the operation of the small magnetic loop  304 . Alternatively, a load or resistor can be applied to the large magnetic loop  302  to further inhibit interference with the operation of the small magnetic loop  304 . 
     Once the small magnetic loop  304  has been activated, the operator uses the smaller volume field  385 , with its elongate shape, of multi-field antenna  300  to scan each of the rows (or columns) in a predefined order. For example, the rows can be scanned from row one to row ten and, similarly, each of the columns (or rows) are scanned from column one to column ten. As each row, or column is scanned, mobile computer device  100  records the identity of each test tube  400  in turn, in combination with the row or column number. Thus, once the rows and columns have been scanned, software on the mobile computer device  100  can arrange the scanned test tubes  400  into their proper positions within the storage array of the identified box  408 . If desired, the operator can use the pointed volume field  390  of the ferrite nub  306  in order to validate the position of the test tubes  400  as determined by the software. At this point, it is not required to further activate the switch  252 , because the ferrite nub  306  is coupled with the small magnetic loop  304 . 
     Although the invention has been described with reference to certain specific embodiments, various modifications thereof will be apparent to those skilled in the art without departing from the scope of the invention as defined by the appended claims. 
     For example, although both the large metallic loop  302 , the first metallic element  308  and the small metallic loop are described herein as being generally rectangular in shape, other shapes may be effectively employed, if desired. Examples of other possible shapes include circular, oval, and the like. Similarly, the shape of the ferrite nub  306  and the second metallic element  310  may also differ from their described shapes and suitable materials other than ferrite, as will occur to those of skill in the art, can be employed for nub  306 . 
     Further, in the embodiments described above, the switch  252  is implemented on the mobile computer  100 . However, the switch  252  may also be implemented on the multi-field antenna  300 . Further, as mentioned, the switch  252  can be implemented in either hardware or software or a combination of both. 
     Similarly, in the embodiments described above, the first tuner  312  and the second tuner  314  are implemented on the multi-field antenna  300 . However, first tuner  312  and the second tuner  314  may be implemented on the mobile computer  100  instead. 
     Yet further, the multi-field antenna  300  can be an external, paddle antenna or it can be integrated into cap  108 , or other portion of main body  102 , of the mobile computer  100 . These and other implementations will become apparent to a person of ordinary skill in the art.