Monopole antenna

Abstract

To provide a small-sized monopole antenna capable of obtaining a stable characteristic in regardless of an installation environment.SOLUTION: A length of a long direction of a metal antenna element 2 is an element length in a substantially rectangular shape. This element length is set to 1 / 2 of a use wavelength. The metal antenna element 2 is folded to two at a substantially center part of a long direction, and a first antenna element part 21 and a second antenna element part 22 are formed. A power supply part 3 is provided to a free end edge 2a on the first antenna element part 21 side in the long direction of the antenna element 2. The free end edge 2a is formed so as to be inclined toward the power supply part 3, and the other one free end edge 2b is contacted to a ground plate.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a monopole antenna for use in wireless communication. [Background technology]

[0002] Conventionally, an inverted-F antenna has been known as a small-sized plate-type antenna system (see, for example, Patent Document 1, etc.). This inverted-F antenna utilizes the image effect of the ground plate, making the element length 1 / 4λ (λ: wavelength) and compact, and also facilitating impedance adjustment by a short-circuit element.

[0003] However, in an inverted-F antenna, the ground plate also functions as a part of the antenna, and current also flows through the ground plate, so it is susceptible to the surrounding and installation environment of the ground plate (for example, a metal case). For this reason, as shown in Figures 5 and 6, a monopole antenna 501 is known in which the element length is 1 / 2λ by folding (folding back) a metal plate in two (see, for example, Non-Patent Document 1, etc.).

[0004] This monopole antenna 501 is capable of reducing the current flowing through the ground plate G by shorting the tip of the antenna element to the ground plate G. Electric power is supplied to the monopole antenna 501 from a power supply section (power supply point) 502 of the monopole antenna 501. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2012-147263 A [Non-Patent Document 1] "Basic Study of L-Shaped Folded Monopole Antenna for Mobile Terminals" by Kim Yo-Hiro, Morishita Hisashi, and Koyanagi Yoshio, IEICE General Conference, March 7, 2007, p.128 Summary of the Invention [Problem to be solved by the invention]

[0006] Incidentally, in the above-mentioned conventional monopole antenna 501, it has been confirmed that impedance mismatch between the power supply section 502 and the antenna element (monopole antenna 501) causes a portion of the current to flow through the ground plate G. Under these circumstances, there has been a demand for a small-sized antenna for wireless communication that is less affected by the installation environment and has stable characteristics.

[0007] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide a small monopole antenna that is capable of obtaining stable characteristics regardless of the installation environment. [Means for solving the problem]

[0008] In order to achieve the above-mentioned object, the invention described in claim 1 is a monopole antenna, characterized in that the element length is the longitudinal length of an approximately rectangular metallic antenna element, which is set to 1 / 2 of the wavelength used, the antenna element is folded in half approximately at the longitudinal center to form a first antenna element portion and a second antenna element portion, a power supply portion is provided on a free end edge of the antenna element on the first antenna element portion side or the second antenna element portion side in the longitudinal direction, the free end edge is formed so as to be inclined toward the power supply portion side, and the other free end edge of the antenna element is in contact with a ground plate.

[0009] The invention as recited in claim 2 is the monopole antenna as recited in claim 1, characterized in that the power feeding portion is provided approximately in the center of the free edge. Effect of the Invention

[0010] According to the invention described in claim 1, the other free edge of the antenna element (the side opposite the power feeder) comes into contact with the ground plate and shorts out, making it possible to reduce the current flowing through the ground plate. Moreover, one free edge of the antenna element (the side facing the power feeder) is formed so as to be inclined toward the power feeder, so that the impedance mismatch between the power feeder and the antenna element is reduced, making it possible to suppress the current flowing through the ground plate, etc. As a result, it is possible to obtain stable characteristics regardless of the installation environment.

[0011] Furthermore, even if the length of the antenna element is 1 / 2 (1 / 2λ) of the wavelength used, since the antenna element is folded in half, the area it occupies on a plane is small (approximately 1 / 4λ in length), making it possible to reduce the size.

[0012] According to the invention described in claim 2, the power supply part is provided approximately at the center of the free edge of the antenna element, and both sides are inclined from approximately the center of the free edge. This makes it possible to reduce the impedance mismatch between the power supply part and the antenna element and to further suppress the current flowing through the ground plate, etc. [Brief description of the drawings]

[0013] [Figure 1] 1 is a perspective view showing a monopole antenna according to an embodiment of the present invention; [Diagram 2] FIG. 2 is a schematic perspective view showing an installation state of the monopole antenna in FIG. [Diagram 3] FIG. 2 is a diagram showing the reflection characteristics of the monopole antenna of FIG. [Figure 4] 2 is a diagram showing current distribution on the ground plate and metal side wall in the monopole antenna of FIG. 1. [Diagram 5] FIG. 1 is a perspective view showing a conventional monopole antenna. [Figure 6] FIG. 6 is a schematic perspective view showing an installation state of the monopole antenna in FIG. 5. [Figure 7] FIG. 6 is a diagram showing the reflection characteristics of the monopole antenna of FIG. [Figure 8]6 is a diagram showing current distribution on the ground plate and metal side wall in the monopole antenna of FIG. 5. [Figure 9] FIG. 1 is a perspective view showing a conventional inverted-F antenna. [Figure 10] FIG. 10 is a schematic perspective view showing an installation state of the inverted-F antenna of FIG. [Figure 11] FIG. 10 is a diagram showing the reflection characteristics of the inverted-F antenna of FIG. [Figure 12] 10 is a diagram showing current distribution on the ground plate and metal side wall in the inverted-F antenna of FIG. 9. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, the present invention will be described based on the illustrated embodiment.

[0015] Fig. 1 is a perspective view showing a monopole antenna 1 according to an embodiment of the present invention, and Fig. 2 is a schematic perspective view showing a state in which the monopole antenna 1 is installed on a ground plate G. The monopole antenna 1 is an antenna that is built into a mobile terminal, a personal computer, or the like and is used for wireless communication, and is made of a metal plate.

[0016] That is, the antenna element 2, which is substantially rectangular and horizontally long (strip-shaped), is folded in two at substantially the center in the longitudinal direction to form a first antenna element portion 21 and a second antenna element portion 22. At this time, a separation portion 23 having a predetermined width and thickness is provided between the first antenna element portion 21 and the second antenna element portion 22, so that the first antenna element portion 21 and the second antenna element portion 22 are arranged in parallel, separated by a predetermined interval and distance. Here, when installed on the ground plate G, the first antenna element portion 21 is located at the upper position, and the second antenna element portion 22 is located below the first antenna element portion 21.

[0017] The first antenna element portion 21 has a free end bent substantially vertically to have a horizontal surface portion 211 substantially parallel to the ground plate G and a vertical surface portion 212 substantially perpendicular to the ground plate G. Similarly, the second antenna element portion 22 has a free end bent substantially vertically to have a horizontal surface portion 221 substantially parallel to the ground plate G and a vertical surface portion 222 substantially perpendicular to the ground plate G.

[0018] The length of the antenna element 2 in the longitudinal direction, that is, the linear length from one free edge 2a to the other free edge 2b when the antenna element 2 is deployed in a straight line, is defined as the element length, and this element length is set to 1 / 2 (1 / 2λ) of the wavelength λ used. The length of the antenna element 2 in the short direction, that is, the width dimension, is set so as to be compatible with a predetermined wide frequency band. Furthermore, the dimensions of the horizontal planes 211, 221, the vertical planes 212, 222, and the separation portion 23 are set so as to obtain predetermined antenna characteristics.

[0019] In addition, in this embodiment, a power supply section 3 for supplying power to the monopole antenna 1 is provided at a free edge 2a on the first antenna element section 21 side in the longitudinal direction of the antenna element 2, that is, approximately at the center of one of the free edges 2a of the antenna element 2 (the center in the width direction of the antenna element 2).

[0020] The antenna element 2 is formed so that the other free end edge 2b of the antenna element 2 is in contact with (shorted to) the ground plate G over its entire length.

[0021] Furthermore, one free edge 2a of the antenna element 2 is formed so as to incline toward the power feeder 3 side (approximately V-shaped with the power feeder 3 as the center). That is, one free edge 2a is formed so as to incline linearly (bifurcated) at the same angle from the power feeder 3 side toward the other free edge 2b side, and the width of the free edge 2a side of the vertical surface portion 212 of the first antenna element portion 21 is formed so as to gradually increase from the power feeder 3. This prevents both sides of the one free edge 2a in the width direction from contacting the ground plate G.

[0022] Here, the inclination of one free edge 2a is set to reduce the impedance mismatch between the antenna element 2 and the power feeder 3, and to reduce the current flowing through the ground plate G and the like.

[0023] With the monopole antenna 1 configured as described above, the other free edge 2b (on the side opposite the power feeder 3) of the antenna element 2 comes into contact with the ground plate G and shorts out, making it possible to reduce the current flowing through the ground plate G, etc. Furthermore, one free edge 2a (on the power feeder 3 side) of the antenna element 2 is formed so as to be inclined toward the power feeder 3, so that the impedance mismatch between the power feeder 3 and the antenna element 2 is reduced, making it possible to suppress the current flowing through the ground plate G, etc.

[0024] That is, since the width of the free edge 2a side of the vertical surface portion 212 of the first antenna element portion 21 gradually increases from the power supply portion 3, the current from the power supply portion 3 gradually flows to the vertical surface portion 212 of the first antenna element portion 21. This makes it possible to suppress the current flowing to the ground plate G and the metal members around the monopole antenna 1. As a result, it becomes possible to obtain stable characteristics regardless of the installation environment.

[0025] Moreover, since the power supply portion 3 is provided approximately in the center of one of the free edges 2a of the antenna element 2 and both sides are inclined from approximately the center of the free edge 2a, it is possible to reduce the impedance mismatch between the power supply portion 3 and the antenna element 2 and further suppress the current flowing to the ground plate G, etc.

[0026] Furthermore, even if the element length of the antenna element 2 is 1 / 2 (1 / 2λ) of the wavelength used, since the antenna element 2 is folded in half, the area it occupies on a plane is small (approximately 1 / 4λ in length), making it possible to reduce the size.

[0027] Next, the results of verifying such effects will be described below. Here, a conventional monopole antenna 501 as shown in Figures 5 and 6 is compared with a conventional inverted-F antenna 601 as shown in Figures 9 and 10. Note that reference numerals 602 and 603 in Figures 9 and 10 indicate a power feed section and a short section.

[0028] In this verification, the reflection characteristics and current distribution to the ground plate G and metal side wall H were confirmed when metal side wall H was provided around each of the antennas 1, 501, and 601 and when metal side wall H was not provided. The reflection characteristics of this monopole antenna 1 are shown in Fig. 3 and the current distribution in Fig. 4, the reflection characteristics of the conventional monopole antenna 501 in Fig. 7 and the current distribution in Fig. 8, and the reflection characteristics of the conventional inverted-F antenna 601 in Fig. 11 and the current distribution in Fig. 12.

[0029] From the verification results, it was confirmed that the monopole antenna 1 has smaller reflection loss and return loss than the conventional monopole antenna 501 and the inverted-F antenna 601, and is also less affected by the metal side wall H. It was also confirmed that the monopole antenna 1 has reduced current flowing through the ground plate G and the metal side wall H compared to the conventional monopole antenna 501 and the inverted-F antenna 601, and is less affected by the installation environment.

[0030] Although the embodiment of the present invention has been described above, the specific configuration is not limited to the above embodiment, and the present invention includes design changes and the like that do not deviate from the gist of the present invention. For example, in the above embodiment, the power supply unit 3 is provided at approximately the center of one free edge 2a of the antenna element 2, but the power supply unit 3 may be provided at one end of the free edge 2a depending on the circuit configuration, etc., as long as desired characteristics are obtained. In this case, the free edge 2a has a shape that is inclined from the other end toward the one end. [Explanation of symbols]

[0031] 1 Monopole Antenna 2 Antenna elements 21 First antenna element section 22 Second antenna element section 2a One free edge 2b The other free edge 3 Power supply unit G Ground plate H Metal side wall

Claims

1. a length in a longitudinal direction of a substantially rectangular antenna element made of metal is defined as an element length, and the element length is set to 1 / 2 of a wavelength to be used, and the antenna element is folded in half at a substantially central portion in the longitudinal direction to form a first antenna element portion and a second antenna element portion; a power supply portion is provided on a free end edge of the antenna element on the first antenna element portion side or the second antenna element portion side in a longitudinal direction of the antenna element, and the free end edge is formed so as to be inclined toward the power supply portion side; The other free edge of the antenna element is in contact with a ground plate. A monopole antenna characterized by

2. The power supply portion is provided at approximately the center of the free edge.

2. The monopole antenna according to claim 1 .

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