Antenna using proximity-coupled feed method, RFID tag having the same, and antenna impedance matching method thereof

• US 20070080867A1
• Filed: 09/25/2006
• Published: 04/12/2007
• Est. Priority Date: 09/26/2005
• Status: Active Grant

• Current Assignee: Electronics and Telecommunications Research Institute
• Original Assignee: Electronics and Telecommunications Research Institute
• Inventors: Choi, Gil-Young, Pyo, Cheol-Sig, Shin, Chan-Soo, Choi, Won-Kyu, Son, Hae-Won
• Granted Patent: US 7,629,929 B2
• Time in Patent Office: Days
• US Class Current: 343/700.MS
• 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 1/38 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 9/0407 Substantially flat resonant element parallel to ground plane, e.g. patch antenna dipole H01Q9/285; monopole H01Q9/40
• CPC Class Codes: H01Q 9/0421 with a shorting wall or a shorting pin at one end of the element H01Q9/0414 takes precedence
• CPC Class Codes: H01Q 9/0457 electromagnetically coupled to the feed line

Abstract

An antenna, a RFID tag using the same, and an antenna impedance matching method thereof are provided. The antenna includes: a radiation patch for deciding a resonant frequency of the antenna; a ground plate disposed in parallel to the radiation patch; and a feeder disposed between the radiation patch and the ground plate in parallel for providing a RF signal to an element connected to the antenna, wherein the feeder includes a microstrip feed line proximately coupled to the radiation patch by being formed perpendicularly to the resonant length direction of the radiation patch.

Claims

1. An antenna, comprising:

a radiation patch for deciding a resonant frequency of the antenna;

a ground plate disposed in parallel to the radiation patch; and

a feeder disposed between the radiation patch and the ground plate in parallel for providing a RF signal to an element connected to the antenna,

wherein the feeder includes a microstrip feed line proximately coupled to the radiation patch by being formed perpendicularly to the resonant length direction of the radiation patch.

2. The antenna as recited in claim 1, wherein the feeder includes:

a dielectric substrate disposed between the radiation patch and the ground plate;

a microstrip feed line proximately coupled to the radiation patch by being formed perpendicularly to the resonant length direction of the radiation patch; and

a ground side disposed to be separated in the ground plate direction from the feed line in parallel.

3. The antenna as recited in claim 2, wherein the ground side of the feeder is shorted from the ground plate in a direct current (DC) manner.

4. The antenna as recited in claim 2, wherein the ground side of the feeder is shorted from the ground plate in an alternating current (AC) manner through a capacitive coupling.

5. The antenna as recited in claim 2, wherein the ground plate is used as the ground side of the feeder.

6. The antenna as recited in claim 1, wherein a terminal for connecting the element connected to the antenna is formed on one end of the feed line.

7. The antenna as recited in claim 6, wherein the other end of the feed line is opened or shorted.

8. The antenna as recited in claim 6, wherein a load is connected to the other end of the feed line.

9. The antenna as recited in claim 8, wherein the load is a lumped element or a distributed element.

10. The antenna as recited in claim 1, further comprising a shorting means for shorting the radiation patch and the ground plate.

11. The antenna as recited in claim 10, wherein the shorting means is a shorting plate or a shorting pin.

12. The antenna as recited in claim 1, wherein the feed line has a meander structure.

13. The antenna as recited in claim 1, wherein a slot is formed at the radiation patch.

14. The antenna as recited in claim 1, wherein the space between the radiation patch and the ground plate is filled with dielectric.

15. The antenna as recited in claim 1, wherein the impedance of the antenna is controlled using a characteristic that a real number part of antenna impedance varies according to a coupling capacitance between the radiation patch and the feed line where the coupling capacitance decides a coupling amount of the feed line and an equivalent impedance between the radiation patch and the ground plate.

16. The antenna as recited in claim 15, wherein the impedance of the antenna is controlled using a characteristic that the real number part of the antenna impedance increases as the coupling capacitance increases.

17. The antenna as recited in claim 15, wherein the impedance of the antenna is controlled using a characteristic that the coupling capacitance increases as the width of the feed line is widened.

18. The antenna as recited in claim 15, wherein the impedance of the antenna is controlled using a characteristic that the coupling capacitance increases as a distance between the radiation patch and the feed line is reduced.

19. The antenna as recited in claim 1, wherein the impedance of the antenna is controlled using a characteristic that the real number part of the antenna impedance changes according to a distance from a center of the resonant length direction of the radiation patch to the feed line.

20. The antenna as recited in claim 19, wherein, wherein the impedance of the antenna is controlled using a characteristic that the real number part of the antenna impedance increases as a distance from a center of the resonant length direction of the radiation patch to the feed line increases.

21. The antenna as recited in claim 19, wherein the impedance of the antenna is controlled using a characteristic that the real number part of the antenna impedance varies according to a distance from the shorting means to the feed line.

22. The antenna as recited in claim 21, wherein the impedance of the antenna is controlled using a characteristic that the real number part of the antenna impedance increases as a distance from the shorting means to the feed line increases.

23. The antenna as recited in claim 1, wherein the impedance of the antenna is controlled using a characteristic that an imaginary number part of the antenna impedance varies according to a characteristic impedance of the feed line.

24. The antenna as recited in claim 8, wherein the impedance of the antenna is controlled using a characteristic that an imaginary number part of the antenna impedance varies according to an impedance of the load.

25. The antenna as recited in claim 1, wherein the impedance of the antenna is controlled using a characteristic that an imaginary number part of the antenna impedance varies according to the length of the feed line.

26. An antenna, comprising:

a radiation patch for deciding a resonant frequency of the antenna;

a ground plate disposed in parallel to the radiation patch; and

a feeder disposed between the radiation patch and the ground plate in parallel for providing a RF signal to an element connected to the antenna,

wherein the feeder includes a microstrip feed line proximately coupled to the grand plate by being formed perpendicularly to the resonant length direction of the radiation patch.

27. The antenna as recited in claim 26, wherein the feeder includes:

a dielectric substrate disposed between the radiation patch and the ground plate;

a microstrip feed line proximately coupled to the ground plate by being formed perpendicularly to the resonant length direction of the radiation patch; and

a ground side disposed to be separated in the ground plate direction from the feed line in parallel.

28. The antenna as recited in claim 27, wherein the ground side of the feeder is shorted from the radiation path in a direct current (DC) manner.

29. The antenna as recited in claim 27, wherein the ground side of the feeder is shorted from the radiation patch in an alternating current (AC) manner through a capacitive coupling.

30. The antenna as recited in claim 27, wherein the radiation patch is used as the ground side of the feeder.

31. The antenna as recited in claim 26, wherein a terminal for connecting the element connected to the antenna is formed on one end of the feed line, and a load is connected to other end of the feed line.

32. The antenna as recited in claim 26, further comprising a shorting means for shorting the radiation patch and the ground plate.

33. The antenna as recited in claim 26, wherein the feed line has a meander structure.

34. The antenna as recited in claim 26, wherein the space between the radiation patch and the ground plate is filled with dielectric.

35. The antenna as recited in claim 26, wherein the impedance of the antenna is controlled using a characteristic that a real number part of antenna impedance varies according to a coupling capacitance between the ground plate and the feed line where the coupling capacitance decides a coupling amount of the feed line and an equivalent impedance between the radiation patch and the ground plate.

36. The antenna as recited in claim 26, wherein the impedance of the antenna is controlled using a characteristic that the real number part of the antenna impedance changes according to a distance from a center of the resonant length direction of the radiation patch to the feed line.

37. The antenna as recited in claim 32, wherein the impedance of the antenna is controlled using a characteristic that the real number part of the antenna impedance varies according to a distance from the shorting means to the feed line.

38. The antenna as recited in claim 26, wherein the impedance of the antenna is controlled using a characteristic that an imaginary number part of the antenna impedance varies according to a characteristic impedance of the feed line.

39. The antenna as recited in claim 31, wherein the impedance of the antenna is controlled using a characteristic that an imaginary number part of the antenna impedance varies according to an impedance of the load.

40. The antenna as recited in claim 26, wherein the impedance of the antenna is controlled using a characteristic that an imaginary number part of the antenna impedance varies according to the length of the feed line.

41. A radio frequency identification (RFID) tag, comprising:

an antenna for receiving a radio frequency (RF) signal transmitted from a RFID reader;

a front-end for rectifying and detecting the RF signal; and

a signal processor connected to the RF front-end, wherein the antenna includes;

a radiation patch for deciding a resonant frequency of the antenna;

a ground plate disposed in parallel to the radiation patch; and

a feeder disposed between the radiation patch and the ground plate for providing a RF signal to the RF front-end through a microstrip feed line proximately coupled to the radiation patch by being formed perpendicularly to the resonant length direction of the radiation patch.

42. The RFID tag as recited in claim 41, wherein the feeder includes:

a dielectric substrate disposed between the radiation patch and the ground plate;

a microstrip feed line proximately coupled to the radiation patch by being formed perpendicularly to the resonant length direction of the radiation patch; and

a ground side disposed to be separated in the ground plate direction from the feed line in parallel.

43. The RFID tag as recited in claim 41, wherein a terminal for accessing the front end is formed at one end of the feed line, and a load is connected to the other end of the feed line.

44. The RFID tag as recited in claim 41, further comprising a shorting means for shorting the radiation patch and the ground plate.

45. The RF tag as recited in claim 41, wherein the feed line includes a meander structure.

46. The RFID tag as recited in claim 41, wherein the impedance of the antenna is controlled using a characteristic that a real number part of antenna impedance varies according to a distance from the center of the resonant length direction of the radiation patch to the feed line, and according to a coupling capacitance that decides the coupling amount of the feed line and the equivalent impedance between the radiation patch and the ground plate.

47. The RFID tag as recited in claim 44, wherein the impedance of the antenna is controlled using a characteristic that a real number part of antenna impedance varies according to a distance from the shorting means to the feed line, and according to a coupling capacitance that decides the coupling amount of the feed line and the equivalent impedance between the radiation patch and the ground plate.

48. The RFID tag as recited in claim 41, wherein the impedance of the antenna is controlled using a characteristic that an imaginary number part of antenna impedance varies according to a characteristic impedance of the feed line and a length of the feed line.

49. The RFID tag as recited in claim 43, wherein the impedance of the antenna is controlled using a characteristic that an imaginary number part of antenna impedance varies according to impedance of the load.

50. An impedance matching method for an antenna having a radiation patch for deciding a resonant frequency of the antenna, a ground plate disposed in parallel to the radiation patch, and a microstrip feed line proximately coupled to the radiation patch by being disposed between the radiation patch and the ground plate to be perpendicular to the resonant length direction of the radiation patch, the method comprising the step of:

matching impedance using a characteristic that a real number part of an antenna impendence varies according to a location of the feed line in the resonant length direction of the radiation patch.

51. The impedance matching method as recited in claim 50, wherein the impedance matching method a characteristic that the real number part of the antenna impedance varies according to the coupling capacitance between the ground plate and the feed line, where the coupling capacitance decides a coupling amount of the feed line and an equivalent impedance between the radiation patch and the ground plate.

52. The impedance matching method as recited in claim 51, wherein the impedance matching method uses a characteristic that the coupling capacitance varies according to a line width of the feed line and a distance between the radiation patch and the feed line.

53. The impedance matching method as recited in claim 50, wherein the impedance matching method uses a characteristic that the real number part of the antenna impedance is reduced as the distance from the center of the resonant length of the radiation patch to the feed line is shortened.

54. The impedance matching method as recited in claim 50, wherein the impedance matching method uses a characteristic that the real number part of the antenna impedance is reduced as the distance from the shorting means for shorting the radiation patch and the ground plate to the feed line is shortened.

55. The impedance matching method as recited in claim 50, wherein the impedance matching method uses a characteristic that the imaginary number part of the antenna impedance varies according to the characteristic impedance of the feed line.

56. The impedance matching method as recited in claim 50, wherein the impedance matching method uses a characteristic that the imaginary number part of the antenna impedance varies according to impedance of a load connected to one end of the feed line.

57. The impedance matching method as recited in claim 50, wherein the impedance matching method uses a characteristic that the imaginary number part of the antenna impedance varies according to the length of the feed line.