Antenna array

• US 20060017634A1
• Filed: 07/21/2005
• Published: 01/26/2006
• Est. Priority Date: 07/22/2004
• Status: Active Grant

• Current Assignee: FEIG ELECTRONIC GmbH
• Original Assignee: FEIG ELECTRONIC GmbH
• Inventors: Meissner, Wolfgang
• Granted Patent: US 7,432,874 B2
• Time in Patent Office: Days
• US Class Current: 343/742
• CPC Class Codes: G06K 7/10356 using a plurality of antennas, e.g. configurations including means to resolve interference between the plurality of antennas
• CPC Class Codes: H01Q 1/2216 used in interrogator/reader equipment

Abstract

An antenna array for RFID antennas for large cohesive detection spaces, having an operating frequency between 100 kHz and 30 MHz. This antenna array can be connected with at least one reader. There can be at least one antenna consisting of an antenna loop having at least one winding. The antenna array can include at least two antennas that are disposed in a plane, in such a manner that the antenna loops of the individual antennas overlap. With this design, at least one multiplexer can be disposed between the at least one reader and the antennas of the antenna array, for selected activation of the antennas.

Claims

1. An antenna array for a RFID antenna having an operating frequency between 100 kHz and 30 MHz, which is coupled to at least one reader, comprising:

a) at least one antenna system comprising at least two antennas each having at least one loop having at least one winding wherein said at least two antennas are disposed approximately in a plane and wherein said at least two antenna loops overlap each other at least partially; and

b) at least one multiplexer disposed between the reader and the antenna system, for selected activation of the antennas wherein a degree or position of an overlap of the antenna loops is set so that the electromagnetic coupling between said antenna loops assumes a minimal value.

3. The antenna array as in claim 1, wherein only one antenna of said antenna array is activated at the same time.

4. The antenna array as in claim 1, wherein said antenna array comprises at least three antennas and at least one power splitter disposed between said at least one reader and said at least one antenna array, and wherein at least two antennas of said antenna array are activated at the same time.

5. The antenna array as in claim 4, wherein a current in directly adjacent antennas has the same current direction.

6. The antenna array as in claim 4, wherein said antenna array comprises at least three antennas including at least two directly adjacent antennas that can be activated at the same time as an antenna group.

7. The antenna array as in claim 6, wherein adjacent antenna groups can be activated one after the other, in each instance wherein a first antenna of a subsequent group corresponds to a last antenna of a previous group.

8. The antenna array as in claim 4, wherein said antenna array comprises at least three antennas wherein at least two antennas are activated at the same time in each instance, and wherein at least one antenna is not activated between at least two remaining antennas, and wherein said activated antenna has a counter-phase current direction at least part of the time.

9. The antenna array as in claim 8, wherein at least two directly adjacent antennas of said at least three antennas are activated at least part of the time and have a same-phase current direction.

10. The antenna array as in claim 4, wherein said antenna array comprises at least three antennas, wherein at least two antennas are activated at the same time, wherein at least one antenna is not activated between said at least two activated antennas, wherein the device further comprises a phase shifter which can shift a phase position of a current of a first antenna relative to a phase position of a current of a second antenna by an amount of 45 degrees to 135 degrees.

11. The antenna array as in claim 1, further comprising a transponder, wherein said antenna loop has at least one side and wherein at least one side of said antenna loop has an angle deviating from 0 degrees to 90 degrees relative to a movement direction of said transponder.

12. The antenna array as in claim 11, wherein said antenna loop has a pentagonal shape.

13. The antenna array as in claim 1, wherein said antenna loop has a rectangular shape with at least one constriction, wherein there are at least an odd number of constrictions and wherein said antenna further comprises a feed in point which is disposed in a symmetrical center of said antenna loop.

14. The antenna array as in claim 1, wherein said antenna array comprises a plurality of antennas including at least two antenna loops that are at least partially overlapping each other in a first plane but spaced apart from at least two other antennas including at least two antenna loops that are at least partially overlapping each other in a second plane, and wherein said antennas can be individually activated one after the other by said at least one multiplexer.

15. The antenna array as in claim 1, wherein said antenna array comprises at least two antenna loops that are at least partially overlapping each other in a first plane but spaced apart from each other, and wherein there are at least two additional at least partially overlapping antenna loops extending in a second plane, wherein said at least one antenna in said first plane and said at least one antenna in said second plane can be activated at the same time via said at least one power splitter and said at least one multiplexer.

16. The antenna array as in claim 15, wherein said antenna disposed in said first plane has a current direction which is in a same phase as said antenna disposed in said second plane.

17. The antenna array as in claim 15, wherein said antenna disposed in said first plane has a current direction which is in a counter phase with said antenna disposed in said second plane.

18. The antenna array as in claim 15, wherein the current direction for said antennas can be switched so that said antenna in said first plane is in either a same phase or in a counter phase with respect to said antenna in said second plane.

19. The antenna array as in claim 15, further comprising a phase shifter, which can shift the phases between said antennas by between approximately 45 degrees and 135 degrees for continuous changing between the same current direction and opposite current direction.

2. An antenna array for a RFID antenna having an operating frequency between 100 kHz and 30 MHz, which is coupled to at least one reader, comprising:

a) at least one antenna system comprising at least two antennas each having at least one loop having at least one winding wherein said at least two antennas are disposed approximately in a plane and wherein said at least two antenna loops overlap at each other at least partially;

b) at least one multiplexer disposed between said at least one reader and said at least one antenna system, wherein said at least one multiplexer is for selected activation of the antennas; and

c) at least one device for opening an inactively switched antenna loop.

31. The antenna array as in claim 2, wherein only one antenna of said antenna array is activated at the same time.

32. The antenna array as in claim 2, wherein said antenna array comprises at least three antennas and at least one power splitter disposed between said at least one reader and said at least one antenna array, and wherein at least two antennas of said antenna array are activated at the same time.

33. The antenna array as in claim 32, wherein a current in directly adjacent antennas has the same current direction.

34. The antenna array as in claim 32, wherein said antenna array comprises at least three antennas including at least two directly adjacent antennas that can be activated at the same time as an antenna group.

35. The antenna array as in claim 34, wherein adjacent antenna groups can be activated one after the other, in each instance wherein a first antenna of a subsequent group corresponds to a last antenna of a previous group.

36. The antenna array as in claim 32, wherein said antenna array comprises at least three antennas wherein at least two antennas are activated at the same time in each instance, and wherein at least one antenna is not activated between at least two remaining antennas, and wherein said activated antenna has a counter-phase current direction at least part of the time.

37. The antenna array as in claim 36, wherein at least two directly adjacent antennas of said at least three antennas are activated at least part of the time and have a same-phase current direction.

38. The antenna array as in claim 32, wherein said antenna array comprises at least three antennas, wherein at least two antennas are activated at the same time, wherein at least one antenna is not activated between said at least two activated antennas, wherein the device further comprises a phase shifter which can shift a phase position of a current of a first antenna relative to a phase position of a current of a second antenna by an amount of 45 degrees to 135 degrees.

39. The antenna array as in claim 2, further comprising a transponder, wherein said antenna loop has at least one side and wherein at least one side of said antenna loop has an angle deviating from 0 degrees to 90 degrees relative to a movement direction of said transponder.

40. The antenna array as in claim 39, wherein said antenna loop has a pentagonal shape.

41. The antenna array as in claim 2, wherein said antenna loop has a rectangular shape with at least one constriction, wherein there are at least an odd number of constrictions and wherein said antenna further comprises a feed in point which is disposed in a symmetrical center of said antenna loop.

42. The antenna array as in claim 2, wherein said antenna array comprises a plurality of antennas including at least two antenna loops that are at least partially overlapping each other in a first plane but spaced apart from at least two other antennas including at least two antenna loops that are at least partially overlapping each other in a second plane, and wherein said antennas can be individually activated one after the other by said at least one multiplexer.

43. The antenna array as in claim 2, wherein said antenna array comprises at least two antenna loops that are at least partially overlapping each other in a first plane but spaced apart from each other, and wherein there are at least two additional at least partially overlapping antenna loops extending in a second plane, wherein said at least one antenna in said first plane and said at least one antenna in said second plane can be activated at the same time via said at least one power splitter and said at least one multiplexer.

44. The antenna array as in claim 43, wherein said antenna disposed in said first plane has a current direction which is a same phase as said antenna disposed in said second plane.

45. The antenna array as in claim 43, wherein said antenna disposed in said first plane has a current direction which is in a counter-phase with said antenna disposed in said second plane.

46. The antenna array as in claim 43, wherein the current direction for said antennas can be switched so that said antenna in said first plane is in either a same phase or in a counter-phase with respect to said antenna in said second plane.

47. The antenna array as in claim 43, comprising a phase shifter, which can shift the phases between said antennas by between approximately 45 degrees and 135 degrees for continuous changing between the same current direction and opposite current direction.

20. A method for determining the overlap position of at least two antenna loops of an antenna array to reduce or minimize the reciprocal influence of the antennas comprising the following steps:

coupling a first antenna with a reader to supply said antenna with RF power;

providing a second antenna which is coupled to a voltmeter; and

moving in an overlapping manner said first antenna or said second antenna until an induced voltage in said antenna loop approaches zero.

21. A method for determining the overlap position of at least two antenna loops of an antenna array to reduce or minimize the reciprocal influence of the antennas comprising the following steps:

positioning at least two antennas so that they do not influence each other, and tuning said at least two antennas to a resonance frequency and input impedance;

coupling a first antenna of said at least two antennas with a reader and supplying said first antenna with RF power; and

pushing said antenna loops over one another until an input impedance of the first antenna assumes the value determined in a non influenced position.

22. The method as in claim 21, further comprising the step of using a standing wave ratio measurement device to measure said input impedance of said at least two antennas.

23. An antenna array for a RFID antenna having an operating frequency between 100 kHz and 30 MHz, which is coupled to at least one reader, comprising:

a) at least one antenna system comprising at least two antennas each having at least one antenna loop having at least one winding wherein said at least two antennas are disposed approximately in a plane and wherein said at least two antenna loops overlap each other at least partially; and

b) at least one power splitter disposed between said at least one reader and said at least one antenna system, wherein a degree or position of an overlap of the antenna loops is set so that the electromagnetic coupling between said antenna loops assumes a minimal value.

24. The antenna array as in claim 23, further comprising a transponder, wherein said antenna loop has at least one side and wherein said at least one side of said antenna loop has an angle deviating from 0 degrees to 90 degrees relative to a movement direction of said transponder.

25. The antenna array as in claim 24, wherein said antenna loop has a pentagonal shape.

26. The antenna array as in claim 23, wherein said antenna loop has a rectangular shape with at least one constriction, wherein there are at least an odd number of constrictions and wherein said antenna loop further comprises a feed in point which is disposed in a symmetrical center of said antenna loop.

27. The antenna array as in claim 23, wherein said antenna array comprises at least two antenna loops that are at least partially overlapping each other in a first plane but spaced apart from each other, and wherein there are at least two additional at least partially overlapping antenna loops extending in a second plane, wherein said at least one antenna in said first plane and said at least one antenna in said second plane can be activated at the same time via said at least one power splitter.

28. The antenna array as in claim 27, wherein said antenna disposed in said first plane has a current direction which is in a same phase as said antenna disposed in said second plane.

29. The antenna array as in claim 27, wherein said antenna disposed in said first plane has a current direction which is in a counter-phase with said antenna disposed in said second plane.

30. The antenna array as in claim 27, further comprising a phase shifter which can shift the phases between said antennas by between approximately 45 degrees and 135 degrees for continuous changing between the same current direction and opposite current direction.