Antenna equipment

Abstract

The goal is to change the resonant frequency of the antenna device and improve its characteristics. [Solution] The antenna device 1 comprises an antenna element 10. The antenna element 10 extends with a width. The antenna element 10 has element sections 11 and 12. Element section 12 is narrower than element section 11. The ratio of the element length of element section 12 to the element length of antenna element 10 is less than or equal to a predetermined threshold corresponding to a gain of 0.2 dB.

Description

Technical Field

[0001] The present invention relates to an antenna device.

Background Art

[0002] Conventionally, it is known that an antenna can radiate radio waves most efficiently when in a resonant state. The resonant frequency of an antenna can be adjusted by changing the element length of the antenna. However, in a small antenna such as an RFID (Radio Frequency IDentification) tag antenna, adjusting the resonant frequency by the element length hinders miniaturization. Also, when the location where the antenna can be placed is limited, it is not easy to change the element length and the design effort increases.

[0003] Also, an antenna device having a meander-shaped conductor as an antenna element with the width of both end portions larger (thicker) than the width of the central portion is known (see Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In a conventional antenna device, when changing the width of a part of the antenna element, the resonant frequency changes compared to the antenna element that is not changed. However, when changing the width of a part of the antenna element, not only the resonant frequency but also the antenna characteristics change, and there is a possibility that good antenna characteristics cannot be obtained.

[0006] An object of the present invention is to change the resonant frequency of an antenna device and improve the antenna characteristics. [Means for solving the problem]

[0007] To solve the above problems, the antenna device of the present invention is It has an antenna element that extends with width, The aforementioned antenna element is The first element section, It has a second element portion that is narrower than the first element portion, The ratio of the element length of the second element to the element length of the antenna element is less than or equal to a predetermined threshold corresponding to a gain of 0.2 dB. [Effects of the Invention]

[0008] According to the present invention, the resonant frequency of the antenna device can be changed, and the antenna characteristics can be improved. [Brief explanation of the drawing]

[0009] [Figure 1] This is a plan view showing an antenna device according to an embodiment of the present invention. [Figure 2] This is a plan view showing an antenna device of comparative example to the antenna device of the embodiment. [Figure 3] This figure shows the gain of the antenna device in relation to the proportion of the thin element section. [Figure 4] This figure shows the radiation efficiency of the antenna device in relation to the proportion of the thin element section. [Figure 5] This is a schematic diagram showing a modified antenna device. [Figure 6] This is a schematic diagram showing the antenna device of the comparative example compared to the modified antenna device. [Modes for carrying out the invention]

[0010] Hereinafter, embodiments and modifications of the present invention will be described in detail with reference to the attached drawings. However, the scope of the invention is not limited to the illustrated examples.

[0011] (Embodiment) Embodiments of the present invention will be described with reference to Figures 1 to 4. First, the device configuration of this embodiment will be described with reference to Figures 1 and 2. Figure 1 is a plan view showing the antenna device 1 of this embodiment. Figure 2 is a plan view showing an antenna device 3 as a comparative example to antenna device 1.

[0012] As shown in Figure 1, the antenna device 1 of this embodiment is a small antenna device for RFID tags. However, the application of the antenna device 1 is not limited to RFID tags, and it may be used in other devices that have an antenna device. Also, Figure 1 shows the three-dimensional X, Y, and Z axes, and the same applies to other device configuration diagrams.

[0013] The antenna device 1 comprises an antenna element 10 and a substrate 20. The antenna element 10 is a conductive pattern such as copper foil mounted on the plane of the substrate 20 and is formed in a meander line structure. The antenna element 10 has element sections 11 and 12 and a feed point P1.

[0014] Element sections 11 and 12 have a line pattern structure that is symmetrical in the X-axis direction, with the Y-axis passing through the feed point P1 as the axis of symmetry. Element section 11 is the conductor portion of a meander line pattern with a normal element width W11, located at both the +X and -X ends of the antenna element 10. Element section 12 is the conductor portion of a meander line pattern with an element width W12, connected to the feed point P1 and located between the feed point P1 and either the +X-side element section 11 or the -X-side element section 11. The element width W12 is smaller (narrower) than the element width W11. Thus, the antenna element 10 has a structure in which some element sections 12 have a smaller element width than the normal element section 11. The feed point P1 is connected to an impedance-matched path, and via that path, it is connected to the RFID tag signal transmission and reception circuit (IC (Integrated Circuit), etc.). The feed point P1 is supplied with antenna current and grounded. Strictly speaking, the antenna element 10 is separated in the X-axis direction at the feed point P1.

[0015] The substrate 20 is a substrate made of an insulating material such as R-1566. R-1566 is a halogen-free glass epoxy multilayer substrate material. On the XY plane of the substrate 20, the length in the X-axis direction of the rectangular portion including the antenna element 10 is defined as the antenna length Lx, and the length in the Y-axis direction is similarly defined as the antenna width Ly.

[0016] Referring to FIG. 2, a conventional antenna device 3 will be described as a comparative example of the antenna device 1. The antenna device 3 is also a small antenna device for an RFID tag. However, in the antenna device 3, the same parts as those in the antenna device 1 are assigned the same numbers and their descriptions are omitted. The antenna device 3 includes an antenna element 30 and a substrate 20.

[0017] The antenna element 30 is a conductor pattern such as a copper foil mounted on the plane of the substrate 20 and is formed in a meander line structure. The antenna element 30 has an element portion 31 and a feeding point P1. The element portion 31 has a line pattern structure that is line-symmetric in the X-axis direction with the Y-axis passing through the feeding point P1 as the target axis. The element portion 31 is a conductor portion of a meander line pattern with a normal element width W31. Thus, the antenna element 10 has an element portion 31 in which all meander lines have a normal width.

[0018] On the XY plane of the substrate 20, the length in the X-axis direction of the rectangular portion including the antenna element 30 is defined as the antenna length Lx, and the length in the Y-axis direction is similarly defined as the antenna width Ly.

[0019] Next, referring to FIGS. 3 and 4, the antenna characteristics of the antenna device 1 will be described. FIG. 3 is a diagram showing the gain of the antenna device 1 with respect to the ratio of the narrow element portion 12. FIG. 4 is a diagram showing the radiation efficiency of the antenna device 1 with respect to the ratio of the narrow element portion 12.

[0020] In antenna device 1, as an example, the substrate thickness of the substrate 20 was set to 1 mm, the antenna length Lx to 36 mm, the antenna width Ly to 20 mm, the element width W11 to 1 mm, and the element width W12 to 0.5 mm. The antenna element 10 was made of copper foil. The substrate 20 was made of R-1566. Under these conditions, the antenna characteristics of antenna device 1 were simulated and confirmed using HFSS (High Frequency Structure Simulator) simulation (Ansys' 3D high-frequency structure simulation software).

[0021] In order to obtain a gain [dB] of the antenna device 1 above a predetermined threshold, the element length (total length) of the antenna element 10 was set to 269.5 [mm]. That is, the element length on one side of the antenna element 10, with the feed point P1 as the boundary, was set to 134.75 [mm]. Also, the element length of one side of the element section 12, with the feed point P1 as the boundary, was set to 6.5 [mm]. That is, the element length of both sides of the element section 12 was set to 13 [mm]. The predetermined threshold was the gain required for use as an antenna, and was set to 0.2 [dB]. The resonant frequency of the antenna device 1 was adjusted to 907 [MHz].

[0022] Here, in antenna device 1, with the antenna length Lx and antenna width Ly constant, the relationship between the ratio of the element length of element section 12 to the total element length of antenna element 10 [%] and the peak gain [dB] at the resonant frequency of antenna device 1 was simulated. This simulation was performed by connecting a thin element section 12 to the feed point P1 and connecting an element section 11 of normal width to element section 12. The simulation results for this peak gain are shown in Figure 3. Similarly, the relationship between the ratio of the element length of element section 12 to the total element length of antenna element 10 [%] and the radiation efficiency [%] at the resonant frequency of antenna device 1 was simulated. The simulation results for this radiation efficiency are shown in Figure 4.

[0023] From the results in Figure 3, it was found that in order to obtain a gain of 0.2 dB or higher for the antenna device 1, the ratio of the element length of element section 12 to the total element length [%] needs to be 30% or less. Furthermore, from the results in Figure 4, it was found that the radiation efficiency of the antenna device 1 can be obtained at a high value of 63% or higher within the range of the ratio of the element length of element section 12 [%] (30% or less).

[0024] In antenna device 1, the number of element sections 12 can be increased if a decrease in gain or radiation efficiency is acceptable. When all of the antenna element 10 is changed from element section 11 to element section 12, the resonant frequency changes from 920 [MHz] to 813 [MHz], the peak gain at the resonant frequency decreases from 0.67 [dB] to -0.27 [dB], and the radiation efficiency decreases from 70 [%] to 57 [%]. In this way, the resonant frequency can be adjusted by reducing the element width W12 of some of the element sections 12 of the antenna element 10, thereby adjusting the reactance component.

[0025] Here, the antenna characteristics of antenna device 3 were simulated under the same conditions as antenna device 1. The element width W31 of antenna device 3 was set to 1 [mm]. In antenna device 3, if the antenna width Ly is set to 20 [mm], the same as antenna device 1, the antenna length Lx needs to be 40 [mm] to achieve a resonant frequency of 907 [MHz]. In other words, when the resonant frequency is the same, the size of antenna device 3 is larger than the size of antenna device 1.

[0026] As described above, according to this embodiment, the antenna device 1 includes an antenna element 10. The antenna element 10 extends with a width. The antenna element 10 has element sections 11 and 12. Element section 12 is narrower than element section 11. The ratio of the element length of element section 12 to the element length of antenna element 10 is less than or equal to a predetermined threshold corresponding to a gain of 0.2 dB. Therefore, the resonant frequency can be changed in the antenna device 1 by adding element section 12. Furthermore, since the element length of antenna element 10 is not changed, the antenna device 1 can be miniaturized. In addition, by keeping the ratio of the element length of element section 12 to the element length of antenna element 10 below a predetermined threshold, the antenna characteristics such as gain and radiation efficiency of the antenna device 1 can be improved.

[0027] Furthermore, the element section 12 has a feed point P1 connected to its central position in the extending direction. The element section 11 is connected to the end of the element section 12 along the extending direction from the feed point P1. Similar to a dipole antenna, the antenna element 10 forms a maximum current distribution (a standing wave peak) near the feed point P1. Therefore, by positioning the element section 12 near the feed point P1, the current distribution can be easily adjusted, and the resonant frequency can be easily changed.

[0028] Furthermore, the antenna element 10 is a pattern of conductors. The antenna device 1 includes a substrate 20 on which the antenna element 10 is mounted. Therefore, the antenna device 1 can be applied to electronic devices such as RFID tags that can accommodate the substrate 20.

[0029] Furthermore, the antenna element 10 has a meander structure. The predetermined threshold for the ratio [%] of the element length of the element section 12 to the total element length of the antenna element 10 is 30%. Therefore, the resonant frequency of the antenna device 1 can be changed, improving the antenna characteristics and allowing the antenna device 1 to be made more compact.

[0030] (modified version) Modified examples of the above embodiment will be described with reference to Figures 5 and 6. Figure 5 is a schematic diagram showing antenna device 4. Figure 6 is a schematic diagram showing antenna device 5 as an example of antenna device 4.

[0031] In the above embodiment, the antenna device 1 was configured to include an antenna element 10 with a meander line structure. The antenna device 4 of this modified example is configured to include an antenna element 40 of a dipole antenna.

[0032] As shown in Figure 5, the antenna device 4 is a small antenna device used for applications such as RFID tags and mobile communication equipment. The antenna device 4 comprises an antenna element 40. The antenna element 40 is a rod-shaped dipole antenna made of a conductor such as copper, positioned in space and extending in the Z-axis direction. In Figure 5, the support part of the antenna element 40 is not shown. The antenna element 40 has element sections 41, 42 and a feed point P1.

[0033] The element sections 41 and 42 have a structure that is symmetrical in the Z-axis direction with respect to the axis of symmetry in the XY plane passing through the feed point P1. Element section 41 is a cylindrical conductor portion with a normal element diameter D41, located at both the +Z and -Z ends of the antenna element 10. Element section 42 is a cylindrical conductor portion with an element diameter D42, located between the feed point P1 and either the +Z-side element section 41 or the -Z-side element section 41. Element diameter D42 is smaller than element diameter D41. Thus, the antenna element 40 has a structure in which some element sections 42 have a smaller element diameter than the normal element sections 41. The feed point P1 is connected to an impedance-matched path, coaxial cable, etc., and is connected to a signal transmission and reception circuit via this path, etc. The feed point P1 is used for both antenna current supply and grounding. In three-dimensional space, the length of the antenna element 40 in the Z-axis direction is denoted as the total length Lz.

[0034] Referring to Figure 6, a conventional antenna device 5 will be described as a comparative example of antenna device 4. Antenna device 5 is also a dipole antenna. However, in antenna device 5, the same parts as in antenna device 4 are given the same numbers and their descriptions are omitted. Antenna device 5 includes an antenna element 50. The antenna element 50 is also a rod-shaped dipole antenna made of a conductor such as copper, arranged in space and extending in the Z-axis direction. The antenna element 50 has an element section 51 and a feed point P1.

[0035] The element section 51 has a structure that is symmetrical with respect to the Z-axis with respect to the feed point P1. The element section 51 is connected to the feed point P1 and is a cylindrical conductive portion with a normal element diameter D51, positioned at both the +Z and -Z ends of the antenna element 50. Thus, all element sections 51 of the antenna element 50 have the same element diameter D51 structure. In three-dimensional space, the length of the antenna element 50 in the Z-axis direction is denoted as the total length Lz. The length of the element section 42 in the Z-axis direction is denoted as the element length L42.

[0036] Next, the antenna characteristics of antenna device 4 will be explained. In antenna device 4, as an example, the element length L42 was designed to be 36 [mm], the total length Lz to be 154 [mm], the element diameter D41 to be 1 [mm], and the element diameter D42 to be 0.5 [mm]. The antenna element 40 was made of copper. Under these conditions, the antenna characteristics of antenna device 4 were simulated and confirmed using HFSS simulation. The antenna characteristics of antenna device 5 were also simulated under similar conditions. The element diameter D51 of antenna device 5 was set to 1 [mm].

[0037] The resonant frequency of antenna device 5 was 918 MHz. When the total length Lz was the same as that of antenna device 5, and the element diameter D42 of some element sections 42 was made thinner than the element diameter D42 to form antenna device 4, its resonant frequency changed to 898 MHz. From this, it can be concluded that antenna device 4 can achieve the same effect as antenna device 1 in the embodiment. In other words, in order to obtain a gain of antenna device 4 above a predetermined threshold, it can be concluded that by appropriately adjusting the ratio [%] of the element length L42 of element sections 42 to the total length Lz, a high radiation efficiency of antenna device 4 can also be obtained.

[0038] As described above, according to this modified example, the antenna element 40 of the antenna device 4 has the shape of a rod-shaped dipole antenna. Therefore, the antenna device 4 also achieves the same effects as the antenna device 1 of the embodiment, and the antenna device 4 can be applied to electronic devices such as RFID tags that implement a dipole antenna.

[0039] The above-described embodiments and modifications are merely examples of antenna devices according to the present invention and are not limited thereto.

[0040] Furthermore, the detailed configuration and operation of the antenna devices 1 and 4 in the above embodiments and modified examples can also be modified as appropriate without departing from the spirit of the present invention. [Explanation of Symbols]

[0041] 1,3,4,5 Antenna equipment 10, 30, 40, 50 Antenna Elements 11,12,31,41,42,51 Element section P1 Power supply point 20 circuit boards

Claims

1. It has an antenna element that extends with width, The aforementioned antenna element is The first element section, It has a second element portion that is narrower than the first element portion, An antenna device in which the ratio of the element length of the second element to the element length of the antenna element is less than or equal to a predetermined threshold corresponding to a gain of 0.2 dB.

2. The second element section is connected to a power supply point, The antenna device according to claim 1, wherein the first element portion is connected to the end portion of the second element portion that extends in the direction from the feed point.

3. The aforementioned antenna element is a pattern of conductors, The antenna device according to claim 1, comprising a substrate on which the antenna element is mounted.

4. The aforementioned antenna element has a meander structure, The antenna device according to any one of claims 1 to 3, wherein the predetermined threshold is 30%.

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