Loop antenna

Abstract

To reduce the size and increase the efficiency of loop antennas.SOLUTION: A loop antenna 100 has first and second planar conductors 112, 113 arranged on a substrate 111 through slits 114 of a predetermined width, and a third planar conductor 117 connecting the opposite edges of the slits 114 in the first and second conductors 112, 113, and a power feed 115 is connected near the edge of the slits 114 in the first and second conductors 112, 113.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a loop antenna used in a wireless tag or the like. [Background technology]

[0002] A known loop antenna used in wireless tags is one in which a strip-shaped conductor, one end of which is connected to a wireless communication circuit, is wound around a dielectric and the other ends are overlapped parallel to each other, ensuring stable performance even when placed near metal (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-109552 Summary of the Invention [Problem to be solved by the invention]

[0004] In a loop antenna in which a strip-shaped conductor is wound around a dielectric as described above, the efficiency tends to decrease when an attempt is made to miniaturize the radiator, and it has been difficult to achieve both miniaturization and efficiency.

[0005] In view of the above, an object of the present invention is to provide a sensor that is compact and has stable performance even when placed in close proximity to metal. [Means for solving the problem]

[0006] To achieve the above objectives, The present invention provides A loop antenna having a conductor formed on a substrate, First and second planar conductors are arranged on a substrate via slits of a predetermined width; a planar third conductor connecting edge portions of the first and second conductors opposite to the slit; and The first and second conductors are characterized in that a power supply portion is connected to the slit portion.

[0007] This provides the same effect as when the loop length is increased in accordance with the length of the slit, making it easy to ensure stable performance even when the sensor is small and in close proximity to metal. [Effects of the Invention]

[0008] The present invention can easily achieve miniaturization while maintaining stable performance even when placed in close proximity to metal. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a perspective view showing the configuration of a loop antenna 100 of a first embodiment. [Figure 2] FIG. 10 is an explanatory diagram schematically showing a loop length. [Figure 3] 10 is a graph showing an example of antenna characteristics. [Figure 4] FIG. 10 is a perspective view showing the configuration of a loop antenna 100 of a second embodiment. [Figure 5] FIG. 10 is a perspective view showing the configuration of a loop antenna 100 of a third embodiment. [Figure 6] FIG. 10 is a perspective view showing the configuration of a loop antenna 100 according to a fourth embodiment. [Figure 7] FIG. 10 is a perspective view showing the configuration of a loop antenna 100 of a fifth embodiment. [Figure 8] FIG. 10 is a perspective view showing the configuration of a loop antenna 100 according to a sixth embodiment. [Figure 9] FIG. 10 is a perspective view showing the configuration of a loop antenna 100 of a seventh embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In each of the following embodiments, components having the same functions as those in other embodiments will be denoted by the same reference numerals and will not be described again.

[0011] (Embodiment 1) As shown in FIG. 1 , loop antenna 100 includes first and second conductors 112 and 113 made of copper foil arranged on dielectric substrate 111 with slit 114 in between. The width dimensions of first and second conductors 112 and 113, i.e., the dimensions perpendicular to slit 114, are set such that first conductor 112 is narrower than second conductor 113. In other words, slit 114 is provided at an offset position. A power feed 115 is connected to first and second conductors 112 and 113 near one end of slit 114. Although not essential, matching component 116, such as a capacitor, inductor, or resistor, is connected near the other end of slit 114.

[0012] The edges of the first and second conductors 112 and 113 on the side opposite to the slit 114 are connected to each other by a third conductor 117. More specifically, for example, the third conductor 117 is formed with a U-shaped cross section having a pair of side portions 117a and 117a perpendicular to the substrate 111 and a top portion 117b parallel to the substrate 111, and the edge of the side portion 117a is connected to the edges of the first and second conductors 112 and 113 by soldering or the like. That is, for example, the edges of the conductors 112, 113, and 117 are used as land pads, and the edges of the side portions 117a and 117a of the third conductor 117 are abutted against them and fixed by soldering.

[0013] On the substrate 111, components such as a wireless module 121 and a button battery 122 are also mounted.

[0014] In the loop antenna 100 described above, when a metal plate is placed nearby, a mirror current flows, making it appear as if the loop is larger than the actual loop, thereby achieving high antenna efficiency. In addition, by providing slit 114 between the first and second conductors 112 and 113, in other words, by forming conductors 112, 113, and 117 to the length of slit 114, it is possible to obtain an effect similar to that obtained when the loop length is increased by twice the length along slit 114, as shown schematically in Fig. 2. Therefore, it is easy to obtain high antenna efficiency even with a small size, and in particular, even when a metal plate or the like is placed nearby, it is easy to obtain high antenna efficiency, as shown in Fig. 3, for example.

[0015] In the above example, power supply 115 is connected closest to the ends of conductors 112 and 113, but this is not limiting and power supply 115 may be located at a distance from the ends. That is, when connected to the ends as described above, the loop length can be easily set long, but this can be adjusted in various ways depending on the shape of the board, the position of the circuit components, and various other constraints. For example, power supply 115 may be connected to the center of slit 114 in the longitudinal direction, but connecting it to a position offset from the center can easily lower the resonant frequency or reduce the size while maintaining the same resonant frequency, compared to connecting it to the center.

[0016] Furthermore, by connecting matching component 116 to a position in slit 114 different from the position where power supply 115 is connected, it is possible to easily improve antenna efficiency. In particular, even when a metal plate or the like is nearby, it is possible to easily form a regular mirror image, and it is also possible to easily maintain high antenna efficiency. Furthermore, by connecting power supply 115 near one end of slit 114 and matching component 116 near the other end as described above for impedance matching, it is possible to set the loop length long and easily obtain a stable current density distribution in the loop portion shown in FIG. 2 , i.e., from the slit 114 portion in first and second conductors 112 and 113 to the edges of first to third conductors 112, 113, and 117, and it is therefore possible to easily obtain even higher antenna efficiency.

[0017] Although the above example shows that the first conductor 112 is narrower than the second conductor 113, the width can be set in various ways depending on the characteristics required of the loop antenna 100. Specifically, for example, the bandwidth can be widened by increasing the difference in width, or narrowed by decreasing the difference in width. Furthermore, the total width of the conductors 112, 113, and 117 and / or the slit 114 can be narrowed to increase the resonant frequency or narrow the bandwidth, or vice versa. Furthermore, the width of the slit 114 is not particularly limited; for example, the bandwidth can be narrowed by narrowing the width of the slit 114. The widths of the conductors 112, 113, and 117 can be set depending on the layout and wiring pattern of the wireless module 121 and button battery 122 arranged on the substrate 111.

[0018] (Embodiment 2) The slit 114 is not limited to being formed linearly as described above, but may be provided with a bent portion 114a such as a crank-like portion as shown in FIG. 4, thereby making it possible to further increase the equivalent loop length.

[0019] (Embodiment 3) The third conductor 117 may be soldered to the conductors 112 and 113 by forming the edges of the conductors 112 and 113 as land pads, but may also be soldered to the conductors 112 and 113 by forming through pads 112a on the edges of the conductors 112 and 113, and forming tabs 117c on the sides 117a of the third conductor 117, inserting them into the through pads 112a, as shown in Fig. 5. This makes it possible to easily improve the ease of assembly, the accuracy of assembly positioning, and / or the mechanical strength.

[0020] (Embodiment 4) Furthermore, the connection between the conductors 112 and 113 and the third conductor 117 does not necessarily have to be by soldering. For example, as shown in Fig. 6, the connection may be made by providing elastic terminals 131 near the edges of the conductors 112 and 113 to clamp the side portions 117a of the third conductor 117. This can eliminate the need for soldering and can make it easier to assemble the third conductor 117 after the wireless module 121 is mounted.

[0021] (Embodiment 5) 7, for example, when loop antenna 100 is housed in housing 141 having main body 141a and lid 141b, third conductor 117 may be attached to lid 141b and then attached to main body 141a, thereby connecting first and second conductors 112 and 113 to third conductor 117. In this case, the connection between them may be made by terminal 131 as shown in embodiment 4 (FIG. 6), or may be made by pressure-contacting third conductor 117 to first and second conductors 112 and 113 directly or via a separately provided flexible member due to the pressing force applied when lid 141b is attached to main body 141a.

[0022] Furthermore, a plate member similar to the side portion 117a of the third conductor 117 may be attached to the first and second conductors 112 and 113, while the lid portion 141b may be provided with a flat conductive member or conductive coating corresponding to the top portion 117b, and a loop may be formed by the contact between these.

[0023] (Embodiment 6) 8, a notch 117d may be formed in the top 117b of the third conductor 117 in a direction parallel to the slit 114. This makes it easy to achieve a wider bandwidth and a smaller size.

[0024] (Embodiment 7) The length of third conductor 117 does not necessarily have to be set to the same length as slit 114, and partial conductor 118 having a shorter length may be provided, for example, as shown in Fig. 9. In this case, partial conductor 118 as described above is preferably provided at least near the connection point of power supply unit 115 and at a position furthest from the connection point of power supply unit 115, and may also be provided at an intermediate position. The installation position of partial conductor 118 at the intermediate position may also serve as a matching adjustment.

[0025] Here, the connection between the partial conductor 118 and the first and second conductors 112 and 113 as described above may be performed by various methods as described in the above embodiments, or by a combination of these methods.

[0026] By using such partial conductor 118, it is possible to reduce the weight, improve the workability of installing wireless module 121, and make button battery 122 easier to replace.

[0027] (Other matters) In the above example, the first and second conductors 112 and 113 and the third conductor 117 are provided on the same side of the substrate 111. However, the present invention is not limited to this. The first and second conductors 112 and 113 may be provided on the back side of a double-sided substrate or on an inner layer of a multi-layer substrate. On the other hand, the wireless module 121 and the like may be disposed on the back side of the substrate 111.

[0028] Furthermore, the cross-sectional shape of the third conductor 117 is not limited to a U-shape (i.e., the conductors 112 and 113 as a whole are rectangular), but may be formed into various cross-sectional shapes, such as a circle, an ellipse, an oval, or a triangle, as long as a loop is formed. [Explanation of symbols]

[0029] 100 Loop Antenna 111 Substrate 112 first conductor 112a Through Pad 113 Second Conductor 114 Slit 114a Bend section 115 Power Supply Unit 116 Matching Parts 117 Third Conductor 117a Side 117b Top 117c Tab 117d Notch 118 Partial conductor 121 Wireless Module 122 Button cell battery 131 terminals 141 Case 141a Main body 141b Lid

Claims

1. A loop antenna having a conductor formed on a substrate, First and second planar conductors are arranged on a substrate via slits of a predetermined width; a planar third conductor connecting edge portions of the first and second conductors opposite to the slit; and a power supply portion is connected to the slit portion of the first and second conductors; The loop antenna further comprises a matching component connected to the slit at a position different from the position at which the feeding portion is connected.

2. The loop antenna of claim 1, The loop antenna is characterized in that the power supply portion is connected to a position shifted from the center of the slit in the longitudinal direction.

3. The loop antenna of claim 2, The loop antenna is characterized in that the feeding portion is connected near an end of the slit.

4. The loop antenna of claim 3, The loop antenna is characterized in that the matching component is connected near the end of the slit opposite to the end to which the feeding portion is connected.

5. The loop antenna according to any one of claims 1 to 4, The loop antenna is characterized in that the third conductor is connected to the edges of the first and second conductors by soldering.

6. The loop antenna according to any one of claims 1 to 4, A loop antenna characterized in that a clamping portion is provided on one of the edge portions of the first and second conductors or the edge portion of the third conductor, and the other edge portion is clamped by the clamping portion, thereby connecting the third conductor to the first and second conductors.

7. The loop antenna according to any one of claims 1 to 6, A loop antenna characterized in that a bent portion is formed in the slit.

8. The loop antenna according to any one of claims 1 to 7, A loop antenna characterized in that a notch extending in a direction parallel to the slit is formed on an edge of the third conductor different from the connection portion with the first and second conductors.

9. The loop antenna according to any one of claims 1 to 8, The loop antenna further comprises a circuit component provided on a surface of the substrate opposite to the surface on which the first and second conductors are arranged.

10. The loop antenna according to any one of claims 1 to 9, The loop antenna is characterized in that the first and second conductors are provided on the opposite side of the substrate to the third conductor or on an intermediate layer.

11. The loop antenna according to any one of claims 1 to 10, A loop antenna characterized in that the third conductor is divided into a plurality of strip-shaped conductors spaced apart from each other in the direction of the slit.

12. The loop antenna according to any one of claims 1 to 11, The loop antenna is characterized in that the third conductor is attached to a lid of a housing having a case body and a lid in which the loop antenna is housed.

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