System and method of estimating true bearings of radio frequency identification (RFID) tags associated with items located directly underneath an overhead antenna array in a controlled area

• US 9,361,494 B2
• Filed: 05/09/2014
• Issued: 06/07/2016
• Est. Priority Date: 12/13/2013
• Status: Active Grant

• Current Assignee: Symbol Technologies, LLC (Zebra Technologies Corporation)
• Original Assignee: Symbol Technologies, LLC (Zebra Technologies Corporation)
• Inventors: Swope, Charles B, Faraone, Antonio, Jacques, Alexander M
• Primary Examiner(s): Brainard, Timothy A
• Application Number:
  US14/274,141
• Publication Number:
  US 20150323662A1
• Time in Patent Office: 760 Days
• Field of Search: 342/158
• US Class Current: 1/1
• CPC Class Codes: G01S 13/75 using transponders powered from received waves, e.g. using passive transponders , or using passive reflectors
• CPC Class Codes: G01S 13/751 wherein the responder or reflector radiates a coded signal
• CPC Class Codes: G01S 13/825 with exchange of information between interrogator and responder
• CPC Class Codes: G01S 3/16 using amplitude comparison of signals derived sequentially from receiving antennas or antenna systems having differently-oriented directivity characteristics or from an antenna system having periodically-varied orientation of directivity characteristic
• CPC Class Codes: G01S 3/46 using antennas spaced apart and measuring phase or time difference between signals therefrom, i.e. path-difference systems
• CPC Class Codes: G06K 7/10099 the directional field being used for pinpointing the location of the record carrier, e.g. for finding or locating an RFID tag amongst a plurality of RFID tags, each RFID tag being associated with an object, e.g. for physically locating the RFID tagged object in a warehouse
• CPC Class Codes: G06K 7/10128 the step consisting of detection of the presence of one or more record carriers in the vicinity of the interrogation device
• CPC Class Codes: G06K 7/10366 the interrogation device being adapted for miscellaneous applications
• CPC Class Codes: G06K 7/10415 the interrogation device being fixed in its position, such as an access control device for reading wireless access cards, or a wireless ATM banking machines in general G07F19/00

Abstract

An RFID tag reading system and method estimate true bearings of RFID tags associated with items located in a scan zone directly underneath an overhead array of antenna elements. A controller energizes a plurality of diametrically opposite antenna elements to yield electric fields having polarizations, and switches each antenna element between mutually orthogonal polarizations. A primary transmit beam and a primary receive beam are steered at a primary steering angle over the scan zone, and a plurality of secondary receive beams are steered over the scan zone at different secondary steering angles that are offset from the primary steering angle by receiving secondary receive signals from each tag, and by processing the secondary receive signals to estimate a true bearing for each tag.

Claims

1. A radio frequency (RF) identification (RFID) tag reading system for estimating true bearings of RFID tags associated with items in a controlled area, comprising:

an RFID reader having an overhead array of antenna elements arranged about a vertical axis, and a plurality of RF transceivers; and

a controller operatively connected to the transceivers, and operative for controlling the transceivers by executing an antenna processing module operative for energizing a plurality of the antenna elements at opposite sides of the vertical axis to yield electric fields having polarizations, and for switching each antenna element between mutually orthogonal polarizations,

the controller being further operative for controlling the transceivers by executing a tag processing module operative for steering a primary transmit beam throughout the controlled area, including a scan zone directly underneath the overhead array, by transmitting a primary transmit signal via the plurality of the antenna elements to each tag, and for steering a primary receive beam throughout the controlled area, including the scan zone, at a primary steering angle by receiving a primary receive signal via the plurality of the antenna elements from each tag,

the controller being further operative for controlling the transceivers by executing a bearing processing module operative for steering a plurality of secondary receive beams throughout the controlled area, including the scan zone, at different secondary steering angles that are offset from the primary steering angle by receiving a plurality of secondary receive signals via the first and second pairs of the antenna elements from each tag, and by processing the secondary receive signals to determine a true bearing for each tag throughout the controlled area, including the scan zone.

2. The system of claim 1, wherein the controller is further operative for energizing a first pair of the antenna elements at opposite sides of the vertical axis to yield an electric field having one of the mutually orthogonal polarizations, and for energizing a different second pair of the antenna elements at different opposite sides of the vertical axis to yield an electric field having the other of the mutually orthogonal polarizations.

3. The system of claim 2, wherein the first pair of the antenna elements are diametrically opposite to each other along a first path across the axis, wherein the second pair of the antenna elements are diametrically opposite to each other along a second path across the axis, and wherein the first and second paths intersect and are mutually orthogonal.

4. The system of claim 2, and a switch for each antenna element, and wherein the controller is further operative for controlling each switch to switch the respective antenna element between the mutually orthogonal polarizations.

5. The system of claim 1, wherein the controller is further operative for energizing one pair of the antenna elements at opposite sides of the vertical axis to yield an electric field having one of the mutually orthogonal polarizations, and for energizing another pair of the antenna elements at the same opposite sides of the vertical axis to yield an electric field having the same one of the mutually orthogonal polarizations as that of the first pair of the antenna elements.

6. The system of claim 5, wherein the one pair of the antenna elements are diametrically opposite to each other along a first path across the axis at one elevation, wherein the other pair of the antenna elements are diametrically opposite to each other along a second path across the axis at another elevation, and wherein the first and second paths are generally parallel.

7. The system of claim 1, wherein the scan zone extends over a three-dimensional spatial sector that subtends a solid angle whose vertex is centered on the vertical axis, that extends downwardly away from the vertex, and that measures about 30 degrees in elevation on each side of, and upwardly away from, the vertical axis, and 360 degrees in azimuth around the vertical axis.

8. The system of claim 1, wherein the bearing processing module is operative for steering a first pair of the secondary receive beams at opposite sides of at least one of the primary transmit beam and the primary receive beam in elevation, and for processing a first pair of the secondary receive signals to obtain a pair of elevation offset signals;

and wherein the bearing processing module is further operative for steering a second pair of the secondary receive beams at opposite sides of the at least one of the primary transmit beam and the primary receive beam in azimuth, and for processing a second pair of the secondary receive signals to obtain a pair of azimuth offset signals.

9. The system of claim 8, wherein the bearing processing module is operative for processing the elevation offset signals by dividing their difference by their sum to obtain an elevation error signal as an elevation correction to the primary steering angle, and wherein the bearing processing module is operative for processing the azimuth offset signals by dividing their difference by their sum to obtain an azimuth error signal as an azimuth correction to the primary steering angle.

10. A radio frequency (RF) identification (RFID) tag reading system for estimating true bearings of RFID tags associated with items in a controlled area, comprising:

an RFID reader mounted at an overhead location in the controlled area above a scan zone, and having an overhead array of antenna elements arranged about a vertical axis, and a plurality of RF transceivers;

a server operatively connected to the RFID reader; and

a controller located in at least one of the RFID reader and the server and operatively connected to the transceivers, the controller being operative for controlling the transceivers by executing an antenna processing module operative for energizing a plurality of the antenna elements at opposite sides of the vertical axis to yield electric fields having polarizations, and for switching each antenna element between mutually orthogonal polarizations,

the controller being further operative for controlling the transceivers by executing a tag processing module operative for steering a primary transmit beam throughout the controlled area, including the scan zone directly underneath the overhead array, by transmitting a primary transmit signal via the plurality of the antenna elements to each tag, and for steering a primary receive beam throughout the controlled area, including the scan zone, at a primary steering angle by receiving a primary receive signal via the plurality of the antenna elements from each tag,

the controller being further operative for controlling the transceivers by executing a bearing processing module operative for steering a plurality of secondary receive beams throughout the controlled area, including the scan zone, at different secondary steering angles that are offset from the primary steering angle by receiving a plurality of secondary receive signals via the plurality of the antenna elements from each tag, and by processing the secondary receive signals to determine a true bearing for each tag throughout the controlled area, including the scan zone.

11. The system of claim 10, wherein the controller is further operative for energizing a first pair of the antenna elements at opposite sides of the vertical axis to yield an electric field having one of the mutually orthogonal polarizations, and for energizing a different second pair of the antenna elements at different opposite sides of the vertical axis to yield an electric field having the other of the mutually orthogonal polarizations.

12. The system of claim 11, wherein the first pair of the antenna elements are diametrically opposite to each other along a first path across the axis, wherein the second pair of the antenna elements are diametrically opposite to each other along a second path across the axis, and wherein the first and second paths intersect and are mutually orthogonal.

13. The system of claim 10, wherein the controller is further operative for energizing one pair of the antenna elements at opposite sides of the vertical axis to yield an electric field having one of the mutually orthogonal polarizations, and for energizing another pair of the antenna elements at the same opposite sides of the vertical axis to yield an electric field having the same one of the mutually orthogonal polarizations as that of the first pair of the antenna elements.

14. The system of claim 13, wherein the one pair of the antenna elements are diametrically opposite to each other along a first path across the axis at one elevation, wherein the other pair of the antenna elements are diametrically opposite to each other along a second path across the axis at another elevation, and wherein the first and second paths are generally parallel.

15. A radio frequency (RF) identification (RFID) tag reading method of estimating true bearings of RFID tags associated with items in a controlled area, comprising:

mounting an RFID reader at an overhead location in the controlled area above a scan zone;

arranging an overhead array of antenna elements for the reader about a vertical axis;

operatively connecting a plurality of RF transceivers to a controller;

controlling the transceivers by having a controller execute an antenna processing module operative for energizing a plurality of the antenna elements at opposite sides of the vertical axis to yield electric fields having polarizations, and for switching each antenna element between mutually orthogonal polarizations;

controlling the transceivers by having the controller execute a tag processing module operative for steering a primary transmit beam throughout the controlled area, including the scan zone directly underneath the overhead array, by transmitting a primary transmit signal via the plurality of the antenna elements to each tag, and for steering a primary receive beam throughout the controlled area, including the scan zone, at a primary steering angle by receiving a primary receive signal via the plurality of the antenna elements from each tag; and

controlling the transceivers by having the controller execute a bearing processing module operative for steering a plurality of secondary receive beams throughout the controlled area, including the scan zone, at different secondary steering angles that are offset from the primary steering angle by receiving a plurality of secondary receive signals via the plurality of the antenna elements from each tag, and by processing the secondary receive signals to determine a true bearing for each tag throughout the controlled area, including the scan zone.

16. The method of claim 15, wherein the energizing is performed by energizing a first pair of the antenna elements at opposite sides of the vertical axis to yield an electric field having one of the mutually orthogonal polarizations, and by energizing a different second pair of the antenna elements at different opposite sides of the vertical axis to yield an electric field having the other of the mutually orthogonal polarizations.

17. The method of claim 16, and arranging the first pair of the antenna elements to be diametrically opposite to each other along a first path across the axis, arranging the second pair of the antenna elements to be diametrically opposite to each other along a second path across the axis, and configuring the first and second paths to intersect and be mutually orthogonal.

18. The method of claim 15, wherein the energizing is performed by energizing one pair of the antenna elements at opposite sides of the vertical axis to yield an electric field having one of the mutually orthogonal polarizations, and by energizing another pair of the antenna elements at the same opposite sides of the vertical axis to yield an electric field having the same one of the mutually orthogonal polarizations as that of the first pair of the antenna elements.

19. The method of claim 18, and arranging the one pair of the antenna elements to be diametrically opposite to each other along a first path across the axis at one elevation, arranging the other pair of the antenna elements to be diametrically opposite to each other along a second path across the axis at another elevation, and configuring the first and second paths to be generally parallel.

20. The method of claim 15, and configuring the scan zone to extend over a three-dimensional spatial sector that subtends a solid angle whose vertex is centered on the vertical axis, that extends downwardly away from the vertex, and that measures about 30 degrees in elevation on each side of, and upwardly away from, the vertical axis, and 360 degrees in azimuth around the vertical axis.