Antenna structures for RFID devices

• US 7,262,701 B1
• Filed: 05/23/2005
• Issued: 08/28/2007
• Est. Priority Date: 05/23/2005
• Status: Active Grant

• Current Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Original Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Inventors: Nguyen, Thanh Huu
• Primary Examiner(s): Lee; Benjamin C.
• Assistant Examiner(s): TANG, SON M
• Application Number:
  US11/135,055
• Time in Patent Office: 827 Days
• Field of Search: None
• US Class Current: 340/572.7
• 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 21/205 providing an omnidirectional coverage turnstile aerials H01Q21/26
• CPC Class Codes: H01Q 9/16 with feed intermediate between the extremities of the antenna, e.g. centre-fed dipole H01Q9/44 takes precedence

Abstract

An improved antenna structure for RFID tags uses a pair of bent dipole antennas having arms that extend substantially about an outer edge of an RFID substrate. The antennas can be adjusted to resonance at about a half-wavelength of an applied electromagnetic field in the conductive material of the antennas. The antennas can be shorted together using a shorting path, the position of which can be adjusted to adjust an input impedance of the antenna structure. A shorting stub can be used to couple the antenna structure to a supply voltage connection of an RFID device used for the tag. The overall length of the shorting stub can be adjusted to match the impedance of the antenna structure to the impedance of the RFID device. These antenna structures can be used with RFID devices such as CDIP devices and bumped die packages.

Claims

1. An antenna structure for a wireless communication device, comprising:

a pair of antennas formed on a substrate, each antenna having two arms formed along adjacent edges of the substrate such that the antenna arms extend substantially about an outer edge of the substrate, each antenna further having a base section connecting the respective antenna to a connection point for the wireless communication device;

a shorting path connecting the pair of antennas in order to electrically couple the antennas; and

a shorting stub connecting one of the pair of antennas to a voltage connection point for the wireless communication device, the length of the shorting stub being selected so as to match an impedance of the antenna structure with an input impedance of the wireless communication device.

2. An antenna structure according to claim 1, wherein:

a position of the shorting path is selected to control a relative impedance of the antenna structure and the wireless communication device.

3. An antenna structure according to claim 1, wherein:

the wireless communication device is a ceramic dual inline package.

4. An antenna structure according to claim 1, wherein:

the wireless communication device includes a temperature sensor.

5. An antenna structure according to claim 1, wherein:

the wireless communication device is a bumped die package.

6. An antenna structure according to claim 1, wherein:

the antenna structure and wireless communication device form a Radio Frequency Identification (RFID) tag.

7. An antenna structure according to claim 1, wherein:

a length of each of the pair of antennas is selected to be approximately equal to one-half of the wavelength of an external electromagnetic field used to provide power to the wireless communication device.

8. An antenna structure according to claim 7, wherein:

each of the pair of antennas is tuned to resonance with respect to the electromagnetic field.

9. An antenna structure according to claim 7, wherein:

the pair of antennas is formed from copper.

10. A method of forming an antenna structure for a wireless communication device, comprising the steps of:

forming a pair of conductive antennas on a substrate, each of the pair of antennas having two arms formed along adjacent edges of the substrate such that the antenna arms extend substantially about an outer edge of the substrate, each antenna further having a base section connecting the respective antenna to a connection point for the wireless communication device;

forming a conductive shorting path connecting the pair of antennas in order to electrically couple the antennas;

forming a shorting stub connecting one of the pair of antennas to a voltage connection point for the wireless communication device; and

adjusting a length of the shorting stub in order to match an impedance of the antenna structure with an input impedance of the wireless communication device.

11. A method according to claim 10, further comprising:

adjusting a position of the shorting path in order to adjust an impedance of the antenna structure relative to an input impedance of the wireless communication device when a difference in impedance between the wireless communication device and the antenna structure is outside an adjustable range of the shorting stub.

12. A method according to claim 10, further comprising:

tuning the pair of antennas to resonance relative to an external electromagnetic field.

13. A method according to claim 10, wherein:

the step of forming a pair of antennas includes forming each antenna to have a length approximately equal to one-half of the wavelength of an external electromagnetic field used to provide power to the wireless communication device.

14. A method according to claim 10, further comprising:

connecting the wireless communication device to the antenna structure.

15. A method according to claim 10, wherein:

the wireless electronic device is one of a ceramic dual inline package and a bumped die package.

16. A method according to claim 10, wherein:

the antenna structure and the wireless communication device form a Radio Frequency Identification (RFID) tag.

17. A Radio Frequency Identification tag, comprising:

a wireless communication device;

a substrate for supporting the wireless communication device;

a pair of antennas forming formed on the substrate, each antenna having two arms formed along adjacent edges of the substrate such that the antenna arms extend substantially about an outer edge of the substrate, each antenna further having a base section connecting the respective antenna to a connection point for the wireless communication device;

a shorting path connecting the pair of antennas in order to electrically couple the antennas; and

a shorting stub connecting one of the pair of antennas to a voltage connection point for the wireless communication device, the length of the shorting stub being selected so as to match an impedance of the antenna structure with an input impedance of the wireless communication device.

18. A Radio Frequency Identification tag according to claim 17, wherein:

a length of the shorting stub can be adjusted in order to match an impedance of the antenna structure to an input impedance of the wireless communication device.

19. A Radio Frequency Identification tag according to claim 17, wherein:

a position of the shorting path can be adjusted in order to adjust an impedance of the antenna structure relative to an input impedance of the wireless communication device.

20. A Radio Frequency Identification tag according to claim 17, wherein:

the wireless communication device is one of a ceramic dual inline package and a bumped die package.