Antenna device, RFID tag, and communication terminal apparatus

• US 8,814,056 B2
• Filed: 09/19/2013
• Issued: 08/26/2014
• Est. Priority Date: 07/19/2011
• Status: Active Grant

• Current Assignee: Murata Manufacturing Co Limited
• Original Assignee: Murata Manufacturing Co Limited
• Inventors: Kato, Noboru
• Primary Examiner(s): Marshall, Christle I
• Application Number:
  US14/031,270
• Publication Number:
  US 20140027520A1
• Time in Patent Office: 341 Days
• Field of Search: 235/492, 235/494
• US Class Current: 235/494
• CPC Class Codes: G06K 19/07783 the coil being planar
• CPC Class Codes: G06K 19/07794 the record carrier comprising a booster or auxiliary antenna in addition to the antenna connected directly to the integrated circuit
• 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 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
• CPC Class Codes: H01Q 9/0457 electromagnetically coupled to the feed line
• CPC Class Codes: H04B 5/24 Inductive coupling
• CPC Class Codes: H04B 5/77 for interrogation

Abstract

An RFIC element includes a capacitance therein. By this capacitance and an inductance of a loop-shaped conductor, an LC resonant circuit is provided. When UHF-band high-frequency power is supplied to the loop-shaped conductor from the RFIC element, the loop-shaped conductor is coupled to a flat conductor in an electromagnetic field by a current flowing through the loop-shaped conductor, and induced currents flow through the flat conductor. By propagation of the induced currents through the flat conductor, the flat conductor acts as a radiation element. It is preferred that the dimension in the longitudinal direction of the flat conductor be a half wavelength of the used frequency band. Accordingly, the flat conductor acts as a half-wave radiation element.

Claims

1. An antenna device comprising:

an antenna module including a loop-shaped conductor to which a feed circuit is connected or coupled, and a magnetic sheet provided in parallel or substantially in parallel to the loop-shaped conductor; and

a flat conductor disposed so as to face the antenna module, and having an area larger than the loop-shaped conductor;

wherein

the loop-shaped conductor includes a first portion facing the flat conductor with the magnetic sheet therebetween, and a second portion directly electrically connected or coupled in an electromagnetic field to the flat conductor without the magnetic sheet therebetween;

the loop-shaped conductor includes a feed point connected or coupled to the feed circuit, and a current maximum point spaced away from the feed point, and the second portion is a region including the current maximum point;

the loop-shaped conductor is disposed close to the flat conductor such that a surface defined by the loop-shaped conductor extends along a surface of the flat conductor; and

the loop-shaped conductor is disposed at a location where the second portion is closer to an end edge portion side of the flat conductor than a center or approximate center of the flat conductor.

2. The antenna device according to claim 1, wherein the second portion of the loop-shaped conductor is linear, and the loop-shaped conductor is parallel or substantially parallel to a linear end edge portion of the flat conductor.

3. The antenna device according to claim 1, wherein the flat conductor is a ground conductor located on a printed wiring board.

4. An RFID tag comprising:

the antenna device according to claim 1; and

an RFIC element directly connected or coupled in an electromagnetic field to the loop-shaped conductor of the antenna device.

5. The RFID tag according to claim 4, wherein the first portion the loop-shaped conductor is located on a top surface of a first ferrite sheet, and the second portion of the loop-shaped conductor is located on an under surface of a second ferrite sheet, and the first and second portions are connected to each other by via conductors.

6. The RFID tag according to claim 4, wherein the first portion the loop-shaped conductor is located on a top surface of a first non-magnetic sheet, and the second portion of the loop-shaped conductor is located on a top surface of a second non-magnetic sheet, and the first and second portions are connected to each other by via conductors.

7. A communication terminal apparatus comprising:

the antenna device according to claim 1; and

an RFIC element directly connected or coupled in an electromagnetic field to the loop-shaped conductor.

8. The communication terminal apparatus according to claim 7, wherein the flat conductor is a ground conductor located on a printed wiring board.

9. The communication terminal apparatus according to claim 7, wherein the RFIC element is configured to operate in a UHF-band RFID system where the RFIC element achieves matching with the loop-shaped conductor in a UHF band.

10. The communication terminal apparatus according to claim 7, wherein the loop-shaped conductor includes a base sheet and a rectangular or substantially rectangular loop-shaped conductive pattern located on the base sheet, a portion of the base sheet including the rectangular or substantially rectangular loop-shaped conductor is folded from a first main surface of the magnetic sheet over a second main surface thereof.

11. The communication terminal apparatus according to claim 7, wherein the loop-shaped conductor includes a first auxiliary conductor and a second auxiliary conductor coupled to each other by at least one capacitance.

12. The communication terminal apparatus according to claim 7, wherein the loop-shaped conductor includes a base sheet and a loop-shaped conductor patterned on an under surface of the base sheet, the first portion of the loop-shaped conductor faces the flat conductor with the magnetic sheet therebetween, and the second portion of the loop-shaped conductor is electrically connected to the flat conductor without the magnetic sheet therebetween.

13. The antenna device according to claim 1, wherein the loop-shaped conductor includes a base sheet and a rectangular or substantially rectangular loop-shaped conductive pattern located on the base sheet.

14. The antenna device according to claim 13, wherein the base sheet is a PET film or a polyimide film and conductive pattern is a patterned metal foil.

15. The antenna device according to claim 1, wherein the flat conductor is a half-wave radiation element.

16. The antenna device according to claim 1, wherein

the second portion of the loop-shaped conductor is provided at only substantially one side of a rectangle defining a shape of the loop-shaped conductor.

17. The antenna device according to claim 1, wherein

the second portion of the loop-shaped conductor includes a narrowed portion and the first portion of the loop-shaped portion extends throughout both sides of one side of a rectangle that defines a shape of the loop-shaped conductor.

18. The antenna device according to claim 1, wherein

the magnetic sheet is interposed only at substantially one side of a rectangle that defines a shape of the loop-shaped conductor, and three remaining sides of the rectangle define the second portion of the loop-shaped conductor.