Antenna and wireless tag

• US 9,159,019 B2
• Filed: 01/16/2014
• Issued: 10/13/2015
• Est. Priority Date: 07/20/2011
• Status: Active Grant

• Current Assignee: Fujikura Limited
• Original Assignee: Fujikura Limited
• Inventors: Takigahira, Masato
• Primary Examiner(s): Savusdiphol, Paultep
• Application Number:
  US14/157,005
• Publication Number:
  US 20140131455A1
• Time in Patent Office: 635 Days
• Field of Search: 235/492, 235/487
• US Class Current: 1/1
• CPC Class Codes: G06K 19/07792 the antenna adapted for extending in three dimensions
• 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 9/36 with top loading
• CPC Class Codes: H01Q 9/42 with folded element, the folded parts being spaced apart a small fraction of the operating wavelength

Abstract

An antenna (1) in accordance with the present invention includes a ground plate (11) and an antenna element (12) provided on an identical plane or on different planes parallel to each other, and is suitable for use in a wireless tag (2). The antenna (1) in accordance with the present invention further includes a shortening capacitor (14) that bridges the ground plate (11) and an end part (12B) of the antenna element (12), the end part (12B) being opposite to the power feed-side end part.

Claims

1. An antenna comprising:

a ground plate provided on a first plane;

an antenna element at least part of which is provided on a second plane, the second plane being identical to the first plane or being a plane parallel to the first plane; and

a capacitor that bridges the ground plate and a first end part of the antenna element, the first end part being opposite to a second end part that is a power feed-side end part,

wherein;

the antenna element is a ribbon-shaped conductor; and

the capacitance of the capacitor is set so as to be not less than 0.5×

Co but not greater than 1.5×

Co, where Co [F] is C obtained by substituting d=W into the following Equation (A);

2. The antenna according to claim 1, wherein a capacitance of the capacitor is set so that the total length of the antenna element is equal to or less than λ

/8, where λ

is the resonant wavelength of the antenna.

3. The antenna according to claim 1, wherein the ground plate and the antenna element are provided on a single planar substrate.

4. The antenna according to claim 3, wherein one of the first and second planes is a back surface of the planar substrate and the other is a front surface of the planar substrate.

5. The antenna according to claim 4, wherein:

the planar substrate has a size of equal to or smaller than 85.6 mm×

54.0 mm; and

the resonant frequency of the antenna is equal to or lower than 322 MHz.

6. The antenna according to claim 3, wherein:

the planar substrate is a multilayer substrate;

the first plane is a plane included in a first layer that is an inner layer or an outer layer of the planar substrate; and

the second plane is a plane included in a second layer that is an inner layer or an outer layer of the planar substrate, the second layer being other than the first layer.

7. The antenna according to claim 1, wherein the second plane is identical to the first plane.

8. The antenna according to claim 7, wherein:

the ground plate and the antenna element are provided within a rectangular region of equal to or smaller than 85.6 mm×

54.0 mm; and

the resonant frequency of the antenna is equal to or lower than 322 MHz.

9. The antenna according to claim 7, wherein:

the ground plate has a recess at its edge; and

the second end part of the antenna element is positioned in an area defined by the recess.

10. An antenna according to claim 7, further comprising a short-circuit section that short-circuits an intermediate part of the antenna element and an edge of the ground plate,

wherein a power feed line part of the antenna element, the power feed line part extending from the second end part to the intermediate part, is positioned within a region defined by the ground plate, the short-circuit section, and a main part of the antenna element which main part extends from the intermediate part to the first end part.

11. The antenna according to claim 10, wherein at least one of (i) an end part, which is opposite to an intermediate part-side end part, of the short-circuit section and (ii) the first end part of the antenna element is connected to a side constituting the edge of the ground plate in a position between an end and middle of the side.

12. An antenna according to claim 7, further comprising a short-circuit section that short-circuits the second end part of the antenna element and an edge of the ground plate,

wherein a region defined by the edge of the ground plate, the antenna element and the short-circuit section is divided into two regions by a line connecting power feed points.

13. A wireless tag comprising an antenna recited in claim 1.

14. A wireless tag according to claim 13, further comprising a battery, wherein the ground plate and the battery are provided within a rectangular region of equal to or smaller than 85.6 mm×

54.0 mm such that they do not overlap each other.

15. The wireless tag according to claim 13, which has a shape of a card.