JP5864295B2 - Compound antenna - Google Patents

Description

  The composite antenna of the present invention is a combination of a triaxial antenna for LF band used in a keyless entry device for locking and unlocking a vehicle or a house, and an RFID antenna for HF band used for data communication such as RFID. It relates to a composite antenna.

  A keyless entry device that locks and unlocks a vehicle uses a LF band of, for example, 135 KHz, and a three-axis antenna that is miniaturized by combining and arranging the winding axes of three coils to be orthogonal to the antenna. An antenna is used. FIG. 6A is a perspective view showing an embodiment of a conventional triaxial antenna.

  As shown in FIG. 6 (a), the triaxial antenna 100 includes grooves 121a and 121b perpendicular to the center of the top surface and bottom surface of the core, and grooves 121c on the outer periphery of the side surface of the core. Resin in which the metal terminal 151 is insert-molded and disposed on the lower surface of the triaxial core 120, the coils 130a, 130b, and 130c wound around the grooves 121a, 121b, and 121c, respectively. And a base 150 made of metal.

  Since the coil 121a has reception sensitivity in the X-axis direction, the coil 121b has reception sensitivity in the Y-axis direction, and the coil 121c has reception sensitivity in the Z-axis direction, the triaxial antenna 100 has reception sensitivity in all directions. Have Moreover, since it is wound by the single core so that the winding axis of three coils may orthogonally cross, it is very small. For example, the size of the triaxial antenna is 13.8 mm × 13.8 mm × 3.6 mm.

  On the other hand, RFID devices used in product tags and electronic money use, for example, a 13.56 MHz HF band as a frequency, and a printed antenna that can be applied to a product or applied to a card is used as an antenna. ing. FIG. 6B is a perspective view showing an embodiment of a conventional RFID antenna.

As shown in FIG. 6B, the RFID antenna 200 has a spiral coil RFID coil 230 formed along the outer periphery of the substrate 210. An IC chip for processing the received signal is disposed on the inner periphery of the RFID coil 230.
The RFID antenna 200 has reception sensitivity in the surface direction of the substrate 210. Such an RFID antenna is very thin.

Japanese Patent Laid-Open No. 2005-124013

When trying to make a device with two functions, the keyless entry device using the above-mentioned triaxial antenna and the RFID device using the RFIF antenna, the frequency differs greatly between the triaxial antenna and the RFID antenna. A separate antenna was required for each function.
However, while the RFID antenna is thin, it occupies a large area. On the other hand, the triaxial antenna is thick, but small, and when both antennas are combined, the advantages of each antenna can be fully utilized. could not.

  An object of the present invention is to provide a small composite antenna having two functions of a triaxial antenna and an RFID antenna and having a small exclusive area.

The composite antenna of the present invention is
The first winding and the second winding are wound around the core so as to be orthogonal to each other, and the third winding orthogonal to the first and second windings is wound around the outer periphery of the core. A 3-axis antenna,
A resin bobbin around which a fourth winding is wound is disposed on the upper surface of the core,
A base in which a part of a metal terminal is embedded in a resin base is disposed on the lower surface of the core.

  According to the composite antenna of the present invention, the composite antenna having two functions of the triaxial antenna and the RFID antenna can be reduced in size by reducing the area occupied by the antenna on the RFID side. As a result, a device having two functions of a keyless entry device and an RFID device can be reduced in size.

It is a perspective view of one Example of the composite antenna of this invention. It is a figure for demonstrating in detail the composite antenna of FIG. FIG. 2 is an equivalent circuit diagram of the composite antenna of FIG. 1. A graph showing the frequency characteristics when changing the coupling coefficient K ₃₄ of the composite antenna of FIG. It is a perspective view which shows another Example of the composite antenna of this invention. It is a perspective view which shows the example of the conventional triaxial antenna and an RFID antenna.

Hereinafter, an embodiment of the composite antenna of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view showing an embodiment of the composite antenna of the present invention, FIG. 2 (a) is an exploded perspective view of FIG. 1, and FIG. 2 (b) is a perspective view of the triaxial core of FIG. Show.
As shown in FIGS. 1 and 2, the composite antenna 10 includes a triaxial antenna 20, an air-core coil 40 disposed on the upper surface of the triaxial antenna 20, and a base 50 disposed on the lower surface of the triaxial antenna 20. . The air core coil 40 functions as an RFID antenna.

  The triaxial antenna 20 is provided with grooves 20a and 20b intersecting at the center between the upper surface and the bottom surface of the core, and grooves 20c on the outer periphery of the side surface of the core. And the coils 30a, 30b, and 30c wound around the grooves 21a, 21b, and 21c, respectively.

  The triaxial core 21 is formed with an X winding axis by the groove 21a, a Y winding axis by the groove 21b, and a Z winding axis by the groove 21c. The coil 30a is wound around the X winding axis, and the coil 30b is wound around the Y winding axis. Since the coil 30c is wound around the Z winding axis, the triaxial antenna 20 has reception sensitivity in all directions.

The coil 30c is wound on the outer periphery of the coil 30a, so as not to contact with 30b 3-axis core 21, so that the coil 30a and the coil 30b are not in contact, the thickness _{h x} of X winding shaft is, Y wound It is thinner than the shaft thickness _hy . The air-core coil 40 is wound around a flat bobbin 41 made of resin. The diameter of the bobbin 41 and the diameter of the triaxial core 21 are substantially equal. A hole 42 penetrating the winding shaft is provided on the flange surface.

  The base 50 is made of resin and is insert-molded so that a part of the metal terminal is embedded in the resin. The side surface of the metal terminal 51 is provided with a locking portion 52 for binding the end of the coil, and the terminal portions of the coils 30a, 30b, 30c and the terminal portion of the air-core coil 40 are respectively locked. It is entangled with the part 52 and electrically connected. In FIG. 2, the base 50 is shown separately, but at the time of assembly, the base 50 has a plurality of bases connected in series by a lead frame, and is separated from the lead frame after assembly.

The bobbin 41 is disposed on the upper surface of the triaxial antenna 21 and is fixed by injecting an adhesive into the hole 41. The base 40 is fixed to the lower surface of the triaxial antenna 21 by applying an adhesive to the resin of the base 40.
The composite antenna 10 may further have an exterior embedded in a resin for the purpose of improving vibration resistance and environmental resistance.

With the configuration described above, the triaxial core 21 functions as the core of the air-core coil 40, the Q of the air-core coil 40 can be increased, the composite antenna can be downsized, and the RFID antenna has high reception sensitivity. It can be an antenna.
The air-core coil 40 is preferably arranged in parallel with the coil in the Z-axis direction in which the cross-sectional area of the triaxial core 21 is the largest.

  The Q of the RFID antenna can be increased by reducing the distance between the triaxial core 21 and the air-core coil 40. However, if it is too close, the coupling between the coil 30c and the air-core coil 40 becomes too large, causing a problem that the resonance frequency of the air-core coil 40 is shifted.

FIG. 3 is an example of an equivalent circuit diagram including the composite antenna shown in FIG. 1 and a resonant capacitor.
As shown in FIG. 3, resonant capacitors C1, C2, and C3 are connected in parallel to the coils 30a, 30b, and 30c, and a resonant capacitor C4 is connected in parallel to the air-core coil 40.
A portion surrounded by a dotted line is the triaxial antenna 20.
The inductance value of the coil 30a is 4700 [μH],
The inductance value of the coil 30b is 4700 [μH],
The inductance value of the coil 30c is 7200 [μH],
The inductance value of the air-core coil 40 is 1 [μH],
The capacitance value of the resonance capacitor C1 is 370 [μF],
The capacitance value of the resonant capacitor C2 is 360 [μF],
The capacitance value of the resonant capacitor C3 is 238 [μF],
The capacitance value of the resonant capacitor C4 is 150 [pF],
Coupling coefficient between the coil 30a and the coil 30b _{K 12} 0.2,
Coupling coefficient _{K 23} between the coil 30b and the coil 30c are 0.2,
Coupling coefficient _{K 13} between the coil 30c and the coil 30a is 0.2,
Air-core coil 40 and the coupling coefficient _{K 14} between the coil 30a is 0.2,
Air-core coil 40 and the coupling coefficient _{K 24} between the coil 30b is 0.2,
Air-core coil 40 and the coupling coefficient _{K 34} between the coil 30c is 0.3,
It is.

Figure 4 is a graph showing frequency characteristics when changing the coupling coefficient K ₃₄ of the composite antenna shown in FIG. 3, the horizontal axis represents the frequency [MHz], the vertical axis represents the impedance [Omega].
The resonance frequency of the coils 30a, 30b, and 30c of the triaxial antenna is 125 kHz, and the resonance frequency of the air-core coil 40 is 13.56 MHz.
In the figure, 80 is a frequency characteristic of the coil 30c of the three-axis antenna 20 (Z-axis coils), 81-87, the coupling coefficient _{K 34} of 0.20,0,30,0.50,0.70, The frequency characteristics when 0.80, 0.90, and 0.95 are set are shown. The frequency characteristics of the coils 30a and 30b are omitted because they are substantially the same as those of the coil 30c.

FIG. 4 shows that the resonance frequency of the air-core coil 40 shifts as the coupling coefficient k is increased. For example, if the wound is in a groove provided the air-core coil 40 on the same core as the coils 30c, the coupling coefficient K ₃₄ is becomes close to 1, the resonance frequency of the air-core coil 40 is used in RFID As the frequency deviates from the resonance frequency, the impedance decreases, and the reception sensitivity of the RFID antenna decreases.

To accommodate the shift of the resonance frequency of the air-core coil 40 within 5%, the coupling coefficient K ₃₄ between the air-core coil 40 and the coil 30c so as to be substantially 0.3 or less, the air-core coil 40 and the coil 30c Adjust between. In order to adjust the distance, for example, the thickness of the collar of the bobbin 41 may be adjusted. In FIG. 1, the thickness of the collar of the bobbin 41 is about 0.1 mm.

FIG. 5 is an exploded perspective view for explaining another embodiment of the composite antenna of the present invention.
As shown in FIG. 5, the composite antenna 11 includes a triaxial antenna 60, an air core coil 40 disposed on the upper surface of the triaxial antenna 60, and a base 50 disposed on the lower surface of the triaxial antenna 22. The air-core coil 40 and the base 50 are the same as the embodiment shown in FIG.

As shown in FIG. 5, the triaxial antenna 60 includes coils 61a and 61b wound around each rod-shaped core of a cross-shaped core 61 in which two rod-shaped cores are orthogonal to each other, and a cross-shaped antenna. The coil 61c is disposed on the outer periphery of the end portion of the core 61.
The coils 61a, 61b, 61c may be wound using a bobbin.
Thus, the triaxial antenna combined with the air-core coil 40 may use a cross-shaped core as well as a flat columnar core.

10, 11 Composite antenna 20, 60, 100 Triaxial antenna 200 RFID antenna 21, 61, 121 Triaxial core 21a, 21b, 21c, 121a, 121b, 121c Groove 30a, 30b, 30c, 31a, 31b, 31c, 121a, 121b, 121c, 230 Coil 40 Air-core coil 41 Bobbin 50, 150 Base 51 Metal terminal 52 Locking part 210 Substrate 220 IC chips C1, C2, C3, C4 Resonance capacitor

Claims (5)

The first winding and the second winding are wound around the core so as to be orthogonal to each other, and the third winding orthogonal to the first and second windings is wound around the outer periphery of the core. A 3-axis antenna,
A composite antenna, wherein a resin bobbin around which a fourth winding is wound is disposed on an upper surface of the core. Composite antenna according to claim 1, wherein the lower surface of the core, wherein the base in the base made of resin is embedded a portion of the metal terminal is disposed. The composite antenna according to claim 1, wherein an exterior of the composite antenna is embedded in a resin. The core is a flat columnar core,
A first groove and a second groove intersecting at the center of the upper surface and the bottom surface of the core on the outer periphery passing through the upper surface and the lower surface of the core;
A third groove is provided on the outer periphery of the side surface of the core;
A first winding is applied to the first groove;
A second winding is applied to the second groove;
The composite antenna according to any one of claims 1 to 3, wherein a third winding is provided in the third groove. The core is composed of a cross-shaped core in which two rod-shaped cores are orthogonal to each other,
The first winding and the second winding wound around each rod-shaped core are applied,
The composite antenna according to any one of claims 1 to 3, wherein the third winding is disposed on an outer periphery of an end portion of the core.

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