Antenna using inductively coupled feeding method, RFID tag using the same and antenna impedance matching method thereof

• US 7,545,328 B2
• Filed: 12/07/2005
• Issued: 06/09/2009
• Est. Priority Date: 12/08/2004
• Status: Active Grant

• Current Assignee: Electronics and Telecommunications Research Institute
• Original Assignee: Electronics and Telecommunications Research Institute
• Inventors: Chae, Jong-Suk, Pyo, Cheol-Sig, Choi, Won-Kyu, Yun, Je-Hoon, Son, Hae-Won
• Primary Examiner(s): MANCUSO, HUEDUNG XUAN CAO
• Application Number:
  US11/297,256
• Publication Number:
  US 20060158380A1
• Time in Patent Office: 1,280 Days
• Field of Search: 343/700.MS, 343/748, 343/728, 343/867, 343/895, 455/82, 342/368
• US Class Current: 343/700.0MS
• 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 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

Provided are an antenna using an inductively coupled feeding method, a Radio Frequency Identification (RFID) tag thereof, and an antenna impedance matching method thereof. The antenna includes a resonator for determining a resonance frequency of the antenna and a feeder for providing an RF signal to an element connected to the antenna. An RFID tag includes an antenna which receives an RF signal from the RFID reader, an RF front-end which rectifies and detects the RF signal, and a signal processor which is connected to the RF front-end. Particularly, the antenna includes a resonator for determining a resonance frequency of an antenna and a feeder for providing the RF signal to the RF front-end, wherein mutual inductive coupling between the resonator and the feeder is performed.

Claims

1. An antenna, comprising:

a resonator for determining a resonance frequency of the antenna; and

a feeder for providing a radio frequency (RF) signal to an element connected to the antenna, wherein the resonator has a dipole structure with opposed first and second ends, a first meander structure coupled to the first end, and a second meander structure coupled to the second end,

wherein the feeder has a loop structure that a terminal, connected to the element, is formed onto, and at least a distance between the dipole structure of the resonator and the loop structure of the feeder is varied to control a real number part of the antenna impedance, and

wherein a internal circumference of the loop is less than 30% of a wavelength corresponding to a resonance frequency of the resonator.

4. The antenna as recited in claim 1, wherein the impedance is controlled based on a characteristic that the imaginary number part of the impedance in the antenna is varied according to an internal area of the loop.

5. The antenna as recited in claim 4, wherein the impedance is controlled based on a characteristic that the imaginary number part increases as the internal area of the loop increases.

6. The antenna as recited in claim 1, wherein the impedance is controlled based on a characteristic that the real number part of the impedance in the antenna is varied according to a distance between the resonator and the loop.

7. The antenna as recited in claim 6, wherein the impedance is controlled based on a characteristic that the real number part decreases as the distance between the resonator and the loop increases.

8. The antenna as recited in claim 1, wherein the impedance is controlled based on a characteristic that the real number part of the impedance in the antenna is varied according to height of a loop side which is close to the resonator.

9. The antenna as recited in claim 8, wherein the impedance is controlled based on a characteristic that the real number part increases as the height of the loop side increases.

12. The antenna as recited in claim 1, wherein the loop is a curve including a circle.

13. The antenna as recited in claim 1, wherein the resonator has a trapezoidal flat dipole structure with the opposed first and second ends, the first meander structure coupled to the first end, and the second meander structure coupled to the second end.

14. The antenna as recited in claim 1, wherein the impedance is controlled based on a characteristic that the impedance of the antenna is varied as a connecting position of the resonator and the feeder, i.e., a feed point, is varied.

15. The antenna as recited in claim 1, wherein the resonator and the feeder are open by a Direct Current (DC) method.

16. The antenna as recited in claim 15, wherein the resonator and the feeder are fabricated on a same side of one substrate.

17. The antenna as recited in claim 15, wherein the resonator and the feeder are individually fabricated on different sides of one substrate.

18. The antenna as recited in claim 15, wherein the resonator and the feeder are individually fabricated on different substrates.

19. The antenna as recited in claim 1, wherein the middle part of the resonator has a trapezoid flat dipole structure and both ends of the resonator have a meander structure.

20. The antenna as recited in claim 1, wherein the impedance is controlled based on a characteristic that the real number part of the impedance in the antenna is varied according to mutual inductance between the resonator and the feeder.

21. The antenna as recited in claim 20, wherein the impedance is controlled based on a characteristic that the real number part increases as the inductance between the resonator and the feeder increases.

22. The antenna as recited in claim 1, wherein the impedance is controlled based on a characteristic that the real number part of the impedance in the antenna is varied according to resistance of the resonator.

23. The antenna as recited in claim 22, wherein the impedance is controlled based on a characteristic that the real number part decreases as the resistance increases.

24. The antenna as recited in claim 1, wherein the impedance is controlled based on a characteristic that the imaginary number part of the impedance in the antenna is varied according to controlling inductance of the feeder.

25. The antenna as recited in claim 24, wherein the impedance is controlled based on a characteristic that the imaginary number part increases as the feeder inductance increases.

2. The antenna as recited in c1aim 1, wherein the feeder is controlled based on a characteristic that an imaginary number part of an impedance is varied according to a linewidth of the loop.

3. The antenna as recited in claim 2, wherein the impedance is controlled based on a characteristic that the imaginary number part increases as the linewidth of the loop decreases.

10. The antenna as recited in claim 2, wherein the imaginary number part is an inductive reactance.

11. The antenna as recited in c1aim 1, wherein the loop is a polygon.

26. An impedance matching method of an antenna, the antenna comprising:

a resonator for determining a resonance frequency; and

a feeder for providing an RF signal in a loop structure,

wherein a characteristic that the imaginary number part of impedance in the antenna is varied according to the linewidth of the loop being used,

wherein the resonator has a dipole structure with opposed first and second ends, a first meander structure coupled to the first end, and a second meander structure coupled to the second end,

wherein the feeder has a loop structure that a terminal, connected to the element, is formed onto, and at least a distance between the dipole structure of the resonator and the loop structure of the feeder is varied to control a real number part of the antenna impedance, and

wherein a internal circumference of the loop is less than 30% of a wavelength corresponding to a resonance frequency of the resonator.

27. The method as recited in claim 26, wherein a characteristic that the imaginary number part of the impedance in the antenna is varied according to internal area of the loop is used.

28. The method as recited in claim 27, wherein the characteristic that the real number part of the impedance in the antenna is varied according to distance between the resonator and the loop is used.

29. The method as recited in claim 28, wherein the characteristic that the real number part of the impedance in the antenna is varied according to length of the loop side close to the resonator is used.