Virtual short circuit for providing reference signal in RFID tag

• US 7,505,001 B2
• Filed: 12/14/2006
• Issued: 03/17/2009
• Est. Priority Date: 12/14/2005
• Status: Active Grant

• Current Assignee: University of Kansas
• Original Assignee: University of Kansas
• Inventors: Moncombu Ramakrishnan, Karthik Narayanan, Deavours, Daniel D.
• Primary Examiner(s): Ho; Tan
• Application Number:
  US11/610,873
• Publication Number:
  US 20070195003A1
• Time in Patent Office: 824 Days
• Field of Search: 340/572.7, 340/572.8, 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

An RFID tag (10) including a virtual short circuit using a stepped impedance transformation from an open circuit or other known impedance point to provide a reference signal to an integrated circuit (22). The stepped impedance transformer (28) does not consist solely of a quarter wavelength transmission line. The stepped impedance transformer (28) may consist of first and second transmission lines (30,32) having different lengths and widths. The RFID tag (10) may also include an impedance matching circuit (20) which does not consist solely of a three-section transmission line. The matching circuit (20) may include a shorting stub transmission line.

Claims

1. A radio frequency identification transponder comprising:

a microstrip antenna;

an integrated circuit;

an impedance matching circuit coupling the microstrip antenna with the integrated circuit; and

a stepped impedance transformer from a known impedance point for providing a reference signal to the integrated circuit, the stepped impedance transformer including

a first transmission line coupled with the antenna and having a first width and a first length, and

a second transmission line coupled in series with the first transmission line and having a second width and a second length,

wherein the first width is different from the second width and the first length is different from the second length.

2. The radio frequency identification transponder as set forth in claim 1, wherein the known impedance point is an open circuit.

3. The radio frequency identification transponder as set forth in claim 1, wherein the first width is greater than the second width and the first length is less than the second length.

4. The radio frequency identification transponder as set forth in claim 1, wherein the matching circuit is not a three-section microstrip circuit.

5. The radio frequency identification transponder as set forth in claim 1, wherein the matching circuit includes a shorting stub matching circuit.

6. The radio frequency indentification transponder as set forth in claim 1, wherein the matching circuit consists of a single transmission line.

7. 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, an integrated circuit, and an impedance matching circuit coupling the microstrip antenna with the integrated circuit, the improvement comprising:

a stepped impedance transformer from a known impedance point for providing a reference signal to the integrated circuit, the stepped impedance transformer including

a first transmission line coupled with the antenna and having a first width and a first length, and

a second transmission line coupled in series with the first transmission line and having a second width and a second length,

wherein the first width is different from the second width and the first length is different from the second length.

8. The radio frequency identification transponder as set forth in claim 7, wherein the known impedance point is an open circuit.

9. The radio frequency identification transponder as set forth in claim 7, wherein the first width is greater than the second width and the first length is less than the second length.

10. The radio frequency identification transponder as set forth in claim 7, wherein the matching circuit is not a three-section microstrip circuit.

11. The radio frequency identification transponder as set forth in claim 7, wherein the matching circuit includes a shorting stub matching circuit.

12. A radio frequency identification transponder comprising:

a microstrip antenna;

an integrated circuit;

an impedance matching circuit coupling the microstrip antenna with the integrated circuit, wherein the impedance matching circuit is not a three-section microstrip circuit; and

a virtual short circuit from a known impedance point for providing a reference signal to the integrated circuit, the virtual short circuit including a stepped impedance transformer that is not a quarter wavelength transmission line.

13. The radio frequency identification transponder as set forth in claim 12, wherein the known impedance point is an open circuit.

14. The radio frequency identification transponder as set forth in claim 12, wherein the stepped impedance transformer includes

a first transmission line coupled with the antenna and having a first width and a first length, and

a second transmission line coupled in series with the first transmission line and having a second width and a second length,

wherein the first width is different from the second width and the first length is different from the second length.

15. The radio frequency identification transponder as set forth in claim 14, wherein the first width is greater than the second width and the first length is less than the second length.

16. The radio frequency identification transponder as set forth in claim 12, wherein the matching circuit is not a three-section microstrip circuit.

17. The radio frequency identification transponder as set forth in claim 12, wherein the matching circuit includes a shorting stub matching circuit.

18. 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, an integrated circuit, and an impedance matching circuit coupling the microstrip antenna with the integrated circuit, the improvement comprising:

the impedance matching circuit is not a three-section microstrip circuit; and

a virtual short circuit from a known impedance point for providing a reference signal to the integrated circuit, the virtual short circuit including a stepped impedance transformer that is not a quarter wavelength transmission line.

19. The radio frequency identification transponder as set forth in claim 18, wherein the known impedance point is an open circuit.

20. The radio frequency identification transponder as set forth in claim 18, wherein the stepped impedance transformer includes

a first transmission line coupled with the antenna and having a first width and a first length, and

a second transmission line coupled in series with the first transmission line and having a second width and a second length,

wherein the first width is different from the second width and the first length is different from the second length.

21. The radio frequency identification transponder as set forth in claim 20, wherein the first width is greater than the second width and the first length is less than the second length.

22. The radio frequency identification transponder as set forth in claim 18, wherein the matching circuit includes a shorting stub matching circuit.