Cross dipole antenna and tag using the same

• US 20070279311A1
• Filed: 11/29/2006
• Published: 12/06/2007
• Est. Priority Date: 05/30/2006
• Status: Active Grant

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Kai, Manabu, Maniwa, Toru, Yamagajo, Takashi
• Granted Patent: US 7,446,727 B2
• Time in Patent Office: Days
• US Class Current: 343/797
• CPC Class Codes: G06K 19/07786 the antenna being of the HF type, such as a dipole
• 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 1/2225 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 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 9/285 Planar dipole H01Q9/065 takes precedence; patch antenna H01Q9/0407
• CPC Class Codes: H04B 7/10 Polarisation diversity; Directional diversity

Abstract

A compact antenna structure having substantially no directivity independent of a tag direction in an RFID tag is proposed. The antenna structure includes a pair of dipole antennas is provided in a cross dipole antenna to be applied to an RFID system for communicating information between a reader/writer and the tag using a high-frequency radio signal. The above pair of dipole antennas further includes lines extending from a feed point and mutually intersecting crosswise, and also triangularly expanded lines from the bent ends of the above lines. Each total length of the above pair of dipole antennas is longer than 2/λ of a use frequency λ.

Claims

1. A cross dipole antenna to be applied to an RFID system communicating information between a reader/writer and a tag using a high-frequency radio signal, the cross dipole antenna comprising:

a pair of dipole antennas having lines extending from a feed point of the pair of dipole antennas mutually intersecting crosswise; and

ahead of the bent ends of the lines, triangularly expanded lines,

wherein each total length of the pair of dipole antennas is longer than 2/λ

of a use frequency λ

.

2. The cross dipole antenna according to claim 1, further comprising:

extension portions disposed ahead of the respective end portions of the triangularly expanded lines of the pair of dipole antennas,

wherein the impedance is adjusted depending on the lengths of the extension portions.

3. The cross dipole antenna according to claim 2,

wherein the lengths of the extension portions are set according to the dielectric constant and the thickness of the base body having the pair of dipole antennas pasted thereon.

4. The cross dipole antenna according to claim 1, further comprising:

a conductive bar connected to the respective lines extending from the feed point of the pair of dipole antennas,

wherein the impedance is adjusted depending on the connection position of the conductive bar to the lines extending from the feed point.

5. The cross dipole antenna according to claim 1,

wherein the triangle shape is formed of a peripheral contour portion of a conductor the central portion of which is hollowed.

6. A tag to be applied to an RFID system communicating information between a reader/writer and the tag using a high-frequency radio signal, the tag comprising:

a base body;

a pair of dipole antennas formed of conductors on the base body; and

an LSI chip connected to a feed point of the pair of dipole antennas mutually intersecting crosswise,

wherein the pair of dipole antennas further includes;

lines extending from a feed point of the pair of dipole antennas mutually intersecting crosswise; and

ahead of the bent ends of the lines, triangularly expanded lines,

wherein each total length of the pair of dipole antennas is longer than 2/λ

of a use frequency λ

.

7. The tag to be applied to the RFID system according to claim 6,

wherein the base body is formed of PET, film or paper material, and the conductors of the dipole antennas are formed of Cu, Ag or Al.

8. The tag to be applied to the RFID system according to claim 6, further comprising:

extension portions disposed ahead of the respective end portions of the triangularly expanding lines of the pair of dipole antennas,

wherein the impedance is adjusted depending on the lengths of the extension portions.

9. The tag to be applied to the RFID system according to claim 8,

wherein the lengths of the extension portion are set according to the dielectric constant and the thickness of the base body having the pair of dipole antennas pasted thereon.

10. The tag to be applied to the RFID system according to claim 6, further comprising:

a conductive bar connected to the respective lines extending from the feed point of the pair of dipole antennas,

wherein the impedance is adjusted depending on the connection position of the conductive bar to the lines extending from the feed point.

11. The tag to be applied to the RFID system according to claim 6,

wherein the triangle shape is formed of a peripheral contour portion of a conductor the central portion of which is hollowed.