Inductively coupled feed structure and matching circuit for RFID device

• US 7,557,757 B2
• Filed: 12/13/2006
• Issued: 07/07/2009
• Est. Priority Date: 12/14/2005
• Status: Active Grant

• Current Assignee: University of Kansas
• Original Assignee: University of Kansas
• Inventors: Eunni, Madhuri Bharadwaj, Deavours, Daniel D.
• Primary Examiner(s): Ho; Tan
• Application Number:
  US11/610,288
• Publication Number:
  US 20070194993A1
• Time in Patent Office: 937 Days
• Field of Search: 340/572.7, 343/700.MS, 343/850, 343/860
• US Class Current: 343/700.0MS
• CPC Class Codes: G06K 19/07749 the record carrier being capable of non-contact communication, e.g. constructional details of the antenna of a non-contact smart card
• CPC Class Codes: G06K 19/07786 the antenna being of the HF type, such as a dipole
• CPC Class Codes: H01Q 1/22 by structural association with other equipment or articles
• 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 1/2216 used in interrogator/reader equipment
• CPC Class Codes: H01Q 1/2225 used in active tags, i.e. provided with its own power source or in passive tags, i.e. deriving power from RF signal
• CPC Class Codes: H01Q 1/38 formed by a conductive layer on an insulating support patch antennas H01Q9/0407; microstrip dipole antennas H01Q9/065; microstrip slot antennas H01Q13/106; transmission line microstrip antennas H01Q13/206; manufacturing reflecting surfaces using insulating material for supporting the reflecting surface H01Q15/142
• CPC Class Codes: H01Q 1/48 Earthing means; Earth screens; Counterpoises
• CPC Class Codes: H01Q 23/00 Antennas with active circuits or circuit elements integrated within them or attached to them
• CPC Class Codes: H01Q 5/35 using two or more simultaneously fed points
• CPC Class Codes: H01Q 5/40 Imbricated or interleaved structures; Combined or electromagnetically coupled arrangements, e.g. comprising two or more non-connected fed radiating elements
• CPC Class Codes: H01Q 9/0407 Substantially flat resonant element parallel to ground plane, e.g. patch antenna dipole H01Q9/285; monopole H01Q9/40
• CPC Class Codes: H01Q 9/0442 with particular tuning means
• CPC Class Codes: H01Q 9/28 Conical, cylindrical, cage, strip, gauze, or like elements having an extended radiating surface; Elements comprising two conical surfaces having collinear axes and adjacent apices and fed by two-conductor transmission lines waveguide horns or mouths H01Q13/00; slot antennas H01Q13/00
• CPC Class Codes: H01Q 9/30 with feed to end of elongated active element, e.g. unipole H01Q9/44 takes precedence
• CPC Class Codes: H01Q 9/40 Element having extended radiating surface

Abstract

A feed structure (18) and matching circuit (20) for inductively coupling an antenna (16) with an IC (22) in an RFID tag (10). The tag (10) includes first and second feed structures (26,28) coupled with the antenna (16), a first transmission line (30) coupling the feed structures (26,28), and a matching circuit (20) including a second transmission line (32) having a portion that is substantially parallel to and spaced apart from the first transmission line (30) such that the first and second transmission lines (30,32) inductively couple. Where two or more antenna elements (56,57) are used, the elements (56,57) are sufficiently loosely coupled by inductive coupling that they can operate at nearly the same frequency without forming a single resonant antenna. Thus, for example, different elements can operate at approximately 905 MHz and approximately 925 MHz, respectively, to effectively cover the FCC range of 900-930 MHz.

Claims

1. A radio frequency identification transponder comprising:

a microstrip antenna;

first and second feed projections coupled with the microstrip antenna;

a first transmission line coupling the first feed projection with the second feed projection; and

an impedance matching circuit including a second transmission line having a portion that is substantially parallel to and spaced apart from the first transmission line such that the first and second transmission lines inductively couple.

2. The radio frequency identification transponder as set forth in claim 1, wherein the first and second transmission lines are spaced apart a distance approximately between 0.1 mm and 1.5 mm.

3. The radio frequency identification transponder as set forth in claim 1, wherein the first and second feed structures and the first transmission line form a U-shaped structure.

4. A radio frequency identification transponder comprising:

a first microstrip antenna;

first and second feed projections coupled with the first microstrip antenna;

a first transmission line coupling the first feed projection with the second feed projection;

a second microstrip antenna;

third and fourth feed projections coupled with the second microstrip antenna;

a second transmission line coupling the third feed projection with the fourth feed projection; and

an impedance matching circuit including;

a third transmission line having a portion that is substantially parallel to and spaced apart from the first transmission line such that the first and third transmission lines inductively couple, and

a fourth transmission line having a portion that is substantially parallel to and spaced apart from the second transmission line such that the second and fourth transmission lines inductively couple.

5. The radio frequency identification transponder as set forth in claim 4, wherein the first microstrip antenna resonates at a first resonance frequency and the second microstrip resonates at a second resonance frequency.

6. The radio frequency identification transponder as set forth in claim 5, wherein the first and second resonance frequencies are between approximately 900 MHz and 930 MHZ.

7. The radio frequency identification transponder as set forth in claim 4, wherein the parallel transmission lines are spaced apart a distance approximately between 0.1 mm and 1.5 mm.

8. The radio frequency identification transponder as set forth in claim 4, wherein the first and second feed structures and the first transmission line form a first U-shaped structure, and the third and fourth feed structures and the second transmission line form a second U-shaped feed structure.

9. In a radio frequency identification transponder for physical association with an object and for storing and communicating data about the object, the radio frequency identification transponder having a microstrip antenna and an integrated circuit, the improvement comprising:

first and second feed projections coupled with the microstrip antenna;

a first transmission line coupling the first feed projection with the second feed projection;

an impedance matching circuit including a second transmission line having a portion that is substantially parallel to and spaced apart from the first transmission line such that the first and second transmission lines inductively couple.

10. The radio frequency identification transponder as set forth in claim 9, wherein the first and second transmission lines are spaced apart a distance approximately between 0.1 mm and 1.5 mm.

11. In a radio frequency identification transponder for physical association with an object and for storing and communicating data about the object, the radio frequency identification transponder having an integrated circuit, the improvement comprising:

a first microstrip antenna;

first and second feed projections coupled with the first microstrip antenna;

a first transmission line coupling the first feed projection with the second feed projection;

a second microstrip antenna;

third and fourth feed projections coupled with the second microstrip antenna;

a second transmission line coupling the third feed projection with the fourth feed projection; and

an impedance matching circuit including;

a third transmission line having a portion that is substantially parallel to and spaced apart from the first transmission line such that the first and third transmission lines inductively couple, and

a fourth transmission line having a portion that is substantially parallel to and spaced apart from the second transmission line such that the second and fourth transmission lines inductively couple.

12. The radio frequency identification transponder as set forth in claim 11, wherein the first microstrip antenna resonates at a first resonance frequency and the second microstrip resonates at a second resonance frequency.

13. The radio frequency identification transponder as set forth in claim 12, wherein the first and second resonance frequencies are between approximately 900 MHz and 930 MHZ.

14. The radio frequency identification transponder as set forth in claim 11, wherein the parallel transmission lines are spaced apart a distance approximately between 0.1 mm and 1.5 mm.

15. The radio frequency identification transponder as set forth in claim 11, wherein the first and second feed structures and the first transmission line form a first U-shaped structure, and the third and fourth feed structures and the second transmission line form a second U-shaped feed structure.