Loop antenna and radio frequency tag

• US 9,563,838 B2
• Filed: 04/22/2016
• Issued: 02/07/2017
• Est. Priority Date: 04/28/2015
• Status: Active Grant

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Ban, Yasumitsu, Kai, Manabu
• Primary Examiner(s): Kim, Ahshik
• Application Number:
  US15/136,633
• Publication Number:
  US 20160321535A1
• Time in Patent Office: 291 Days
• Field of Search: 235/492, 235/451, 343/748, 343/855
• US Class Current: 1/1
• CPC Class Codes: G06K 19/077 Constructional details, e.g. mounting of circuits in the carrier
• CPC Class Codes: G06K 19/07786 the antenna being of the HF type, such as a dipole
• CPC Class Codes: G06K 19/07788 the antenna being of the capacitive type
• 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 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

A loop antenna includes first and second conductors configured to have conductivity, the first conductor including first and second patterns, the first pattern being provided along a first surface and including a first feed point, and the second pattern being coupled to the first pattern at a first end of the first surface and being provided to oppose the first pattern; and a second conductor configured to have conductivity, the second conductor including third and fourth patterns, the third pattern being provided on the first surface with a gap generating a capacitance between the first pattern and including a second feed point, the fourth pattern being electrically coupled to the third pattern at a second end opposing the first end on the first surface, the fourth pattern overlapping the second pattern so as to cause capacitive coupling or being connected to the second pattern.

Claims

1. A loop antenna comprising:

a first conductor configured to have electrically conductivity, the first conductor including a first pattern and a second pattern, the first pattern being provided along a first surface and including a first feed point, and the second pattern being electrically coupled to the first pattern at a first end of the first surface and being provided to oppose the first pattern; and

a second conductor configured to have electrically conductivity, the second conductor including a third pattern and a fourth pattern, the third pattern being provided on the first surface with a gap generating a capacitance between the first pattern and including a second feed point, the fourth pattern being electrically coupled to the third pattern at a second end opposing the first end on the first surface, the fourth pattern overlapping the second pattern so as to cause capacitive coupling or being connected to the second pattern,

wherein at least a part of the first pattern is arranged closer to the second end than at least a part of the third pattern and the first feed point and the second feed point are provided so as to include the at least part of the first pattern in a path of current from the first feed point to the second feed point.

2. The loop antenna according to claim 1,

wherein the first feed point is provided closer to the second end than the second feed point.

3. The loop antenna according to claim 2,

wherein the first feed point is provided on a first side of the at least part of the first pattern, the first side opposing the at least part of the third pattern, and the second feed point is provided on a second side of the at least part of the third pattern, the second side opposing the at least part of the first pattern.

4. The loop antenna according to claim 3,

wherein the first pattern further includes a projection extending from the first side to the first end along the third pattern and

the third pattern further includes a projection extending from the second side to the second end along the first pattern.

5. The loop antenna according to claim 3,

wherein the first pattern includes a first slit, the first slit being formed between the first feed point and a connection portion that connects the at least part of the first pattern and the first end, the first slit extending in a direction from the first side toward the second end.

6. The loop antenna according to claim 3,

wherein the first pattern includes a first slit, the first slit being formed in a direction crossing the path of current, the current flowing between the first feed point and the second feed point through the first conductor and the second conductor.

7. The loop antenna according to claim 5,

wherein the second pattern and the fourth pattern include a second slit, the second slit being formed at a position overlapping the gap when viewed from a direction vertical to the first surface.

8. The loop antenna according to claim 1,

wherein the first pattern is formed such that a first side opposing the second end of the first pattern has a meandering shape, and the third pattern is formed such that a second side opposing the first end of the third pattern has a meandering shape along the first side and that the gap is formed between the first side and the second side.

9. The loop antenna according to claim 1, further comprising:

a substrate formed of a dielectric material, the substrate including the first surface,

wherein the second pattern and the fourth pattern are provided on a surface opposing the first surface of the substrate.

10. The loop antenna according to claim 1,

wherein a width of the gap and a size of portions of the first pattern and the third pattern that vary in size in accordance with variation in the width of the gap are set so that variation in a resonance frequency of the loop antenna caused by the variation in the size of the portions is suppressed by varying the width of the gap.

11. The loop antenna according to claim 10, further comprising:

an attachment pattern having conductivity and configured to attach, to the loop antenna, a circuit to be connected to the loop antenna,

wherein an area of the attachment pattern and the size of the portions of the first pattern and the third pattern are set so that the variation in the resonance frequency of the loop antenna caused by the variation in the size of the portions is suppressed by varying the area of the attachment pattern in accordance with the variation in the size of the portions.

12. A radio frequency tag comprising:

a loop antenna configured to include a first feed point and a second feed point; and

a communication processing circuit configured to be connected to the loop antenna through a feed line that feeds power to the first feed point and the second feed point and configured to transmit or receive a radio signal through the loop antenna,

wherein the loop antenna includes

a first conductor configured to have electrically conductivity, the first conductor including a first pattern and a second pattern, the first pattern being provided along a first surface and including a first feed point, and the second pattern being electrically coupled to the first pattern at a first end of the first surface and being provided to oppose the first pattern; and

a second conductor configured to have electrically conductivity, the second conductor including a third pattern and a fourth pattern, the third pattern being provided on the first surface with a gap generating a capacitance between the first pattern and including a second feed point, the fourth pattern being electrically coupled to the third pattern at a second end opposing the first end on the first surface, the fourth pattern overlapping the second pattern so as to cause capacitive coupling or being connected to the second pattern,

wherein at least a part of the first pattern is arranged closer to the second end than at least a part of the third pattern and the first feed point and the second feed point are provided so as to include the at least part of the first pattern in a path of current from the first feed point to the second feed point.