Rotating-polarization reflector-backed RFID loop antenna apparatus and method

• US 8,659,494 B2
• Filed: 11/07/2011
• Issued: 02/25/2014
• Est. Priority Date: 11/07/2011
• Status: Active Grant

• Current Assignee: Symbol Technologies, LLC (Zebra Technologies Corporation)
• Original Assignee: Symbol Technologies, Inc. (Zebra Technologies Corporation)
• Inventors: Bellows, David E.
• Primary Examiner(s): Ho, Tan
• Application Number:
  US13/290,160
• Publication Number:
  US 20130113669A1
• Time in Patent Office: 841 Days
• Field of Search: 343/741, 343/866, 343/761, 343/764, 340/572.1
• US Class Current: 343/764
• CPC Class Codes: H01Q 1/2216 used in interrogator/reader equipment
• CPC Class Codes: H01Q 19/104 using a substantially flat reflector for deflecting the radiated beam, e.g. periscopic antennas periscopic fed Cassegrain antennas H01Q19/191; passive relays H04B7/145
• CPC Class Codes: H01Q 21/245 provided with means for varying the polarisation polarising devices H01Q15/24; tracking by comparing linear polarisation compounds G01S3/146; reducing depolarisation effects H04B7/00; polarisation diversity H04B7/10
• CPC Class Codes: H01Q 7/00 Loop antennas with a substantially uniform current distribution around the loop and having a directional radiation pattern in a plane perpendicular to the plane of the loop

Abstract

The present disclosure provides a rotating-polarization reflector-backed Radio Frequency Identification (RFID) loop antenna apparatus and method. The loop antenna apparatus and method provides high gain (i.e., maximizing read distances at lowest power), directionality (i.e., ability to focus on specific areas), orientation insensitivity (i.e., ability to read RFID tags in any direction or orientation) while occupying minimal volume in overhead configurations. In an exemplary embodiment, the loop antenna apparatus includes a reflector and a loop element with the reflector configured to reflect downward RF energy from the loop element. Antenna polarization is controlled by a feed location on the loop element and antenna pattern is controlled by the reflector. Thus, orientation insensitivity may be achieved without changing the antenna pattern by rotating the feed location and not the reflector.

Claims

1. An antenna apparatus, comprising:

a rotatable loop element comprising a feed; and

a reflector backing the loop element and configured to reflect radio frequency energy from the loop element in a direction substantially perpendicular to the reflector;

wherein the rotatable loop element and the reflector cooperatively form a rotating-polarization reflector-backed loop antenna with directionality responsive to a position and/or orientation of the reflector and polarization responsive to a position of the feed on the rotatable loop element.

2. The antenna apparatus of claim 1, wherein the rotatable loop element is configured to rotate by at least 90 degrees thereby providing vertical and horizontal polarization coverage with the rotatable loop element without changing a pattern.

3. The antenna apparatus of claim 1, wherein the rotatable loop element comprises a circumference dimensioned responsive to approximately one full wavelength and the reflector comprises a diameter dimensioned responsive to approximately one full wavelength.

4. The antenna apparatus of claim 1, wherein a pattern formed by the rotating-polarization reflector-backed loop antenna is based on the reflector.

5. The antenna apparatus of claim 1, wherein the rotating-polarization reflector-backed loop antenna is rotated for spatial diversity and the rotatable loop element is rotated without rotating the reflector for polarization diversity.

6. The antenna apparatus of claim 1, further comprising:

a housing comprising the rotatable loop element and disposed to the reflector.

7. The antenna apparatus of claim 6, wherein the housing comprises a substantially dome shape with the rotatable loop element formed on, disposed to, or attached on the dome shape.

8. The antenna apparatus of claim 6, wherein the housing is configured to rotate the rotatable loop element thereby providing vertical and horizontal polarization coverage with the rotatable loop element.

9. The antenna apparatus of claim 6, further comprising:

a Radio Frequency Identification (RFID) reader disposed in the housing and communicatively coupled to the rotating-polarization reflector-backed loop antenna.

10. The antenna apparatus of claim 9, further comprising:

a device comprising any of a camera and wireless access point disposed in the housing and located substantially within a center of the rotatable loop element.

11. A Radio Frequency Identification (RFID) reader, comprising:

a housing;

an RFID reader module disposed in the housing; and

a rotating-polarization reflector-backed loop antenna communicatively coupled to the RFID reader module;

wherein the RFID reader is configured to operate in an overhead configuration with respect to a plurality of RFID tags based on the rotating-polarization reflector-backed loop antenna.

12. The RFID reader of claim 11, wherein the rotating-polarization reflector-backed loop antenna comprises:

a rotatable loop element comprising a feed; and

a reflector backing the loop element and configured to reflect radio frequency energy from the loop element in a direction substantially perpendicular to the reflector;

wherein the rotatable loop element and the reflector cooperatively form the rotating-polarization reflector-backed loop antenna with directionality responsive to a position and/or orientation of the reflector and polarization responsive to a position of the feed on the rotatable loop element.

13. The RFID reader of claim 12, wherein the rotatable loop element is configured to rotate by at least 90 degrees thereby providing vertical and horizontal polarization coverage with the rotatable loop element without changing a pattern.

14. The RFID reader of claim 12, wherein the rotatable loop element comprises a circumference dimensioned responsive to approximately one full wavelength and the reflector comprises a diameter dimensioned responsive to approximately one full wavelength.

15. The RFID reader of claim 12, wherein a pattern formed by the rotating-polarization reflector-backed loop antenna is based on the reflector.

16. The RFID reader of claim 12, wherein the rotating-polarization reflector-backed loop antenna is rotated for spatial diversity and the rotatable loop element is rotated without rotating the reflector for polarization diversity.

17. The RFID reader of claim 12, wherein the housing comprises a substantially dome shape with the rotatable loop element formed on, disposed to, or attached on the dome shape.

18. The RFID reader of claim 12, wherein the housing is configured to rotate the rotatable loop element thereby providing vertical and horizontal polarization coverage with the rotatable loop element.

19. The RFID reader of claim 12, further comprising:

a device comprising any of a camera and wireless access point disposed in the housing and located substantially within a center of the rotatable loop element.

20. A method, comprising:

transmitting radio frequency energy using a loop element with a feed in a first position;

reflecting with a reflector substantially all of the radio frequency transmitted from the loop element in a vertical direction;

rotating the feed while keeping the reflector in a same position to achieve polarization diversity; and

rotating the reflector and the loop element with the field cooperatively to achieve spatial diversity.