Antenna and RFID device

• US 8,424,769 B2
• Filed: 05/16/2012
• Issued: 04/23/2013
• Est. Priority Date: 07/08/2010
• Status: Active Grant

• Current Assignee: Murata Manufacturing Co Limited
• Original Assignee: Murata Manufacturing Co Limited
• Inventors: Kato, Noboru
• Primary Examiner(s): TRAIL, ALLYSON NEEL
• Application Number:
  US13/472,520
• Publication Number:
  US 20120223149A1
• Time in Patent Office: 342 Days
• Field of Search: 235/487, 235/492
• US Class Current: 235/487
• CPC Class Codes: H01Q 1/2216 used in interrogator/reader equipment
• 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 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 5/378 Combination of fed elements with parasitic elements
• 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

In an antenna for an RFID device, a feed coil is coupled to a first booster coil and a second booster coil through an electromagnetic field. In the feed coil, a first region and a second region are disposed so as to overlap with the first booster coil and the second booster coil, respectively. The first region of the feed coil is coupled to the first booster coil through an electromagnetic field, and the second region of the feed coil is coupled to the second booster coil through an electromagnetic field. Accordingly, the antenna has a high degree of coupling between the feed coil and a booster antenna and superior transmission efficiency of an RF signal, and prevents the occurrence of a null point.

Claims

1. An antenna comprising:

a booster antenna including a first booster coil and a second booster coil; and

a feed coil coupled to the booster antenna;

wherein

the first booster coil and the second booster coil are connected in series;

the first booster coil and the second booster coil are adjacent to each other;

the feed coil overlaps with a portion of the first booster coil and with a portion of the second booster coil at a position at which the first booster coil and the second booster coil are adjacent to each other; and

a winding direction of the second booster coil with respect to the first booster coil is a direction in which the feed coil is coupled to the first booster coil and the second booster coil in a same phase through an electromagnetic field.

2. The antenna according to claim 1, wherein the first booster coil and the second booster coil are laminated in a plurality of layers.

3. The antenna according to claim 2, wherein at least one of a pair of the first booster coils adjacent to each other in a layer direction and a pair of the second booster coils adjacent to each other in a layer direction is coupled through capacitance.

4. The antenna according to claim 1, wherein a distance from an inner circumference of the first booster coil to an inner circumference of the second booster coil in a portion in which the first booster coil and the second booster coil are adjacent to each other is larger than a width of an outer circumference of the feed coil.

5. The antenna according to claim 1, wherein a distance between the first booster coil and the second booster coil is greater than a conductor spacing in the first booster coil and the second booster coil.

6. The antenna according to claim 1, wherein a resonance frequency of the feed coil or a resonance frequency of a circuit based on the feed coil and a feed circuit connected to the feed coil is higher than a resonance frequency of the booster antenna.

7. An RFID device comprising:

an antenna according to claim 1; and

a feed circuit connected to the feed coil of the antenna;

wherein

an RFIC is included in the feed circuit.