Multi-band RFID encoder

• US 7,342,499 B2
• Filed: 01/26/2006
• Issued: 03/11/2008
• Est. Priority Date: 01/26/2006
• Status: Expired due to Fees

• Current Assignee: TSC Auto ID Technology Co., Ltd.
• Original Assignee: Printronix
• Inventors: Cao, Hai, Kinley, John, Chiu, Lihu M.
• Primary Examiner(s): TRIEU, VAN THANH
• Application Number:
  US11/340,234
• Publication Number:
  US 20070171071A1
• Time in Patent Office: 775 Days
• Field of Search: 340/572.1, 340/572.4, 340/572.7, 340/572.8, 340/568.1, 343/700.MS, 343/895, 333/26, 333/33, 607/36, 607/60
• US Class Current: 340/572.7
• CPC Class Codes: H01Q 1/2208 associated with components used in interrogation type services, i.e. in systems for information exchange between an interrogator/reader and a tag/transponder, e.g. in Radio Frequency Identification [RFID] systems methods or arrangements for sensing record carriers, e.g. for reading patterns G06K7/00; record carrier for use with machines and with at least a part designed to carry digital markings G06K19/00
• CPC Class Codes: H01Q 1/52 Means for reducing coupling between antennas; Means for reducing coupling between an antenna and another structure absorbing means H01Q17/00
• CPC Class Codes: H01Q 5/371 Branching current paths
• CPC Class Codes: H01Q 9/0407 Substantially flat resonant element parallel to ground plane, e.g. patch antenna dipole H01Q9/285; monopole H01Q9/40

Abstract

In one embodiment, a multi-band near-field antenna for an RFID encoder includes a substrate; an internal coil antenna defined within the substrate; an annular ground plane defined on a first surface of the substrate; a second ground plane defined on an opposing second surface of the substrate, wherein the annular ground plane and the second ground plane form a Faraday cage for the internal coil antenna; and a second antenna disposed on the opposing second surface within the annulus defined by the annular ground plane.

Claims

1. A multi-band near-field RFID encoder, comprising:

a substrate;

an internal coil antenna defined within the substrate;

an annular ground plane defined on a first surface of the substrate;

a second ground plane defined on an opposing second surface of the substrate, wherein the annular ground plane and the second ground plane form a Faraday cage for the internal coil antenna; and

a second antenna disposed on the opposing second surface within the annulus defined by the annular ground plane.

2. The multi-band near-field RFID encoder of claim 1, further comprising:

a coaxial feed coupled to the internal coil antenna and the second antenna.

3. The multi-band near-field RFID encoder of claim 2, wherein the annular ground plane and the second ground plane couple to a ground within the coaxial feed.

4. The multi-band near-field RFID encoder of claim 1, wherein the second antenna includes:

a first plurality of serially-connected stripline conductors on the second surface of the substrate, the serially-connected stripline conductors in the first plurality being arranged within a first area of the second surface, and

a second plurality of serially-connected stripline conductors on the second surface of the substrate, the serially-connected stripline conductors in the second plurality being arranged within a second area of the second surface, the encoder being configured to drive the first plurality of serially-connected stripline conductors with an RF signal and to drive the second plurality of serially-connected stripline conductors with a phase-shifted version of the RF signal.

5. The multi-band near-field RFID encoder of claim 4, wherein each of the stripline conductors in the first and second plurality is arranged in parallel with the remaining stripline conductors.

6. The multi-band near-field RFID encoder of claim 4, wherein the first and second plurality of stripline conductors are each arranged in a fractal pattern.

7. The multi-band near-field RFID encoder of claim 1, further comprising:

a stripline feed on the second surface for receiving the RF signal;

a first connector stripline connecting the stripline feed to the first plurality of stripline conductors so that the first plurality of stripline conductors is driven with the RF signal; and

a second connector stripline connecting the stripline feed to the second plurality of stripline conductors, wherein the second connector stripline has a different length than the first connector stripline so that the second plurality of stripline conductors is driven with the phase-shifted version of the RF signal.

8. The multi-band near-field RFID encoder of claim 4, further comprising a variable phase shifter for providing the phase-shifted version of the RF signal.

9. The capacitive encoder of claim 4, wherein a spacing between each of the stripline conductors in the first plurality is at least as large as a thickness of the substrate, and wherein a spacing between each of the stripline conductors in the second plurality is at least as large as the thickness of the substrate.

10. The capacitive encoder of claim 4, wherein a characteristic impedance for the stripline conductors in the first and second plurality is at least 50 Ω

.

11. A system comprising:

a bar code printer;

a capacitive near-field RFID encoder integrated with the bar code printer, wherein the capacitive RFID encoder includes;

a substrate having a first ground plane on a first surface;

a plurality of capacitive elements on an opposing second surface of the substrate, each capacitive element including a plurality of serially-connected stripline conductors, the RFID encoder being configured to drive a first selected one of the capacitive elements with an RF signal and to drive a second selected one of the capacitive elements with a phase-shifted version of the RF signal; and

an annular ground plane on the opposing second surface, the annular ground plane surrounding the capacitive elements.

12. The system of claim 11, wherein the annular ground plane is symmetrically arranged with regard to plurality of capacitive elements.

13. The system of claim 11, wherein the annular ground plane is substantially rectangular, and wherein one side of the annular ground plane has a first width and the remaining sides of the annular ground plane have a second width.

14. The system of claim 11, further comprising:

a coil antenna defined within the substrate, wherein the annular ground plane and the first ground plane form a Faraday shield for the coil antenna.