Antenna device

Abstract

To provide an antenna device which can be miniaturized.SOLUTION: An antenna device (1) for microwaves includes a mono-pole antenna device (2) disposed on an upper surface of a substrate (3P), a first ground body (3) disposed on the upper surface of the substrate, a second ground body (4) having flexibility and having a flat-plate shape connected to the first ground body (3), and one housing (6) that houses the substrate and the second ground body, and the second ground body (4) is disposed in an extra space (7) formed on a side opposite to the mono-pole antenna device (2) with respect to the substrate (3P).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an antenna device for wireless communication between electronic devices, and more particularly to a small antenna device for transmitting and receiving microwaves. [Background technology]

[0002] Conventionally, an antenna device including a monopole antenna element and a ground conductor as a ground (GND) has been used for wireless communication of electronic devices, as disclosed in Patent Document 1. This antenna device can achieve a wide bandwidth and high gain by including a ground conductor with a length corresponding to, for example, ¼ of the wavelength of microwaves. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-130115 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the antenna device has limitations on miniaturization because it is necessary to ensure the length of the ground conductor. If the length of the ground conductor is set to a length corresponding to the wavelength, a housing of a corresponding length is required to house the antenna device, making it difficult to miniaturize the electronic device in which the antenna device is built.

[0005] The present invention has been made in view of the above background to achieve the following objects. An object of the present invention is to provide an antenna device that can be made smaller. [Means for solving the problem]

[0006] In order to solve the above-described problems, the present invention employs the following means. The microwave antenna device (1) comprises a monopole antenna element (2) arranged on the upper surface of a substrate (3P), a first ground conductor (3) arranged on the upper surface of the substrate, a flexible, flat-plate-shaped second ground conductor (4) connected to the first ground conductor (3), and a housing (6) for accommodating the substrate and the second ground conductor, wherein the second ground conductor (4) is arranged in a surplus space (7) formed on the opposite side of the substrate (3P) from the monopole antenna element (2). [Effects of the Invention]

[0007] In the antenna device of the present invention, the second ground conductor connected to the first ground conductor is positioned in the excess space on the opposite side of the substrate from the monopole antenna element, making it possible to ensure the length of the ground conductor by utilizing the excess space that does not interfere with the antenna device components, thereby making it possible to miniaturize the antenna device. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is an explanatory diagram showing a first embodiment of an antenna device. [Figure 2] FIG. 2 is an explanatory diagram showing a second embodiment and a third embodiment of the antenna device. [Figure 3] FIG. 3 is an explanatory diagram showing a fourth embodiment and a fifth embodiment of the antenna device. [Figure 4] FIG. 4 is an explanatory diagram showing a comparative example. [Figure 5] FIG. 5 is a graph showing antenna characteristics of the antenna device according to the first embodiment and a comparative example. [Figure 6] FIG. 6 is a current distribution diagram of the antenna device according to the first embodiment and the comparative example. [Figure 7] FIG. 7 is a graph showing antenna characteristics of the second to fifth embodiments of the antenna device and a comparative example. [Figure 8] FIG. 8 is an explanatory diagram showing a modified example of the antenna device according to the first and second embodiments. [Figure 9]FIG. 9 is a graph comparing the antenna characteristics of the first and second embodiments of the antenna device with those of the modified example. [Figure 10] FIG. 10 is a graph showing antenna characteristics of a modified example of the antenna device of the first embodiment and a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0009] (Antenna device 1(1)) An antenna device 1(1) of the present invention will be described below with reference to the drawings. The antenna device 1(1) is an antenna device for microwaves (300 MHz to 30 GHz) that is connected to an electronic device and used for wireless communication. As shown in Fig. 1, the antenna device 1(1) includes a monopole antenna element 2 disposed on the upper surface of a substrate 3P, a first ground conductor 3 disposed on the upper surface of the substrate 3P, a flexible, flat-plate-shaped second ground conductor 4 connected to the first ground conductor 3, and a housing 6 that houses the substrate 3P and the second ground conductor. In the drawings, the X-axis direction is the width direction of the substrate 3, the Y-axis direction is the front-rear direction of the substrate 3, and the Z-axis direction is the direction perpendicular to the XY plane.

[0010] The monopole antenna element 2 is configured so that the element has an electrical length corresponding to a predetermined frequency band (for example, an electrical length that is 1 / 4 of the wavelength of the microwave (300 MHz to 30 GHz) being transmitted and received), and for example, a monopole configuration of a meander element, an inverted L-type element, or an inverted F-type element is adopted.

[0011] The substrate 3P is a printed circuit board on which circuit components related to microwave transmission and reception are mounted, such as a matching circuit (not shown) for impedance matching, a filter circuit (not shown) corresponding to a predetermined frequency, etc. The substrate 3P is, for example, in the shape of a substantially rectangular flat plate made of a dielectric material, and is housed within the housing 6.

[0012] On the upper surface of the substrate 3P, there are arranged the monopole antenna element 2, a power feeder 3e having the function of feeding power to the monopole antenna element 2, a ground conductor 3, a matching circuit (not shown), etc. The monopole antenna element 2 is connected to the above-mentioned matching circuit (not shown) etc. via the power feeder 3e, and power is fed to the monopole antenna element 2 from the power feeder 3e. The matching circuit (not shown) etc. may be mounted on the substrate 3P via the first ground conductor 3 (on top of the ground conductor 3), or may be mounted directly on the substrate 3P without via the first ground conductor 3.

[0013] In addition, a first ground conductor 3 is disposed on the upper surface of the substrate 3P. The first ground conductor 3 is formed of a ground pattern made of a conductive material such as a conductor foil (copper foil, etc.), and serves as the ground potential of a matching circuit (not shown), etc. In Fig. 1, the length of the first ground conductor 3 is length L1 in the Y-axis direction perpendicular to the longitudinal direction of the monopole antenna element 2.

[0014] In this embodiment, the conductor is, for example, a conductive metal or a conductive polymer. The conductive metal is, for example, copper, aluminum, iron, gold, or silver, and the conductive polymer is, for example, polyacetylene or polythiophene.

[0015] The second ground conductor 4 has a generally rectangular, flat plate shape and is made of a flexible conductor. The second ground conductor 4 is not disposed on the top surface of the substrate 3P, but is connected to the first ground conductor 3 disposed on the top surface of the substrate 3P, thereby providing ground potential. The second ground conductor 4 may be referred to as a ground conductor extension of the first ground conductor 3, or as a ground extension that extends an area at ground potential. The monopole antenna element 2 is located on the positive side of the Y-axis relative to the first ground conductor 3, and the second ground conductor 4 is located on the negative side of the Y-axis relative to the first ground conductor 3. In other words, the second ground conductor 4 is not disposed on the top surface of the substrate 3P, but is located in the surplus space 7 on the opposite side of the first ground conductor 3 from the monopole antenna element 2, where it does not interfere with the antenna device components.

[0016] The second ground conductor 4 is connected to the side edge 3s of the substrate 3P via the first ground conductor 3. The second ground conductor 4 is connected to both ends of the first ground conductor 3 in the X-axis direction (the width direction of the substrate 3P and the first ground conductor 3) at two terminal portions 4e provided at both ends of the long side 4s in the X-axis direction. By bending the terminal portions 4e, the second ground conductor 4 can be formed so as to be inclined at an inclination angle θ with respect to the substrate 3, as shown in FIGS. 1(b) and 1(c).

[0017] Current is distributed from the substrate 3 to the second ground conductor 4 via two terminals 4e, and the first and second ground conductors 3 and 4 function as grounds. Connection at the terminals 4e is achieved, for example, by soldering, welding, screwing, or by conductive adhesive. The overall length of the ground conductors of the antenna device 1(1) is L1+L2, and the electrical length of L1+L2 is approximately 1 / 4 of the microwave wavelength λ. For example, when the microwave frequency is 920 MHz, the wavelength λ is 326 mm, so the electrical length of L1+L2 is preferably 81.5 mm.

[0018] The battery 5 is connected to the board 3P via a power supply unit 5e and serves as a power supply source for operating the terminal device. The battery 5 is preferably in the shape of a substantially rectangular parallelepiped so that it can be stored compactly together with the substantially rectangular board 3P.

[0019] The housing 6 houses the monopole antenna element 2, the substrate 3P (the monopole antenna element 2 and the first ground conductor 3, etc.), the second ground conductor 4, and the battery 5. For example, an electronic device is disposed outside the housing 6, and the antenna device 1(1) is connected to the outside of the electronic device as an external device for use. A surplus space 7 in which the second ground conductor 4 is disposed is formed within the housing 6. The surplus space 7 is a rectangular parallelepiped with a height HS and a width LS and rectangular sides. HS is equal to the thickness HE from the bottom surface of the battery 5 to the top surface of the substrate 3P (the first ground conductor 3). In other words, the surplus space 7 is formed by utilizing the thickness of the battery 5, etc. The second ground conductor 4 may be disposed along the diagonal of the surplus space 7 of the rectangular parallelepiped. The housing 6 is preferably made of a material that absorbs and transmits microwaves, such as polycarbonate resin or polyphenylene ether resin.

[0020] (Effect of Antenna Device 1(1)) In the antenna device 1(1), the second ground conductor 4 is disposed in the surplus space 7 on the opposite side of the first ground conductor 3 from the monopole antenna element 2, and is disposed in the surplus space 7 so as not to interfere with antenna device components such as the monopole antenna element 2. Therefore, the second ground conductor 4 can be disposed using the surplus space 7 in the housing 6, and the dimensions of the antenna device 1(1) can be minimized while extending the ground conductor (ground region).

[0021] 1(b) and 1(c), the antenna device 1(1) can shorten the length in the Y-axis direction while maintaining the length of the ground region by forming the second ground conductor 4 in the surplus space 7 at an inclination angle θ toward the substrate 3P with respect to the battery 5. Furthermore, by arranging the second ground conductor 4 at an inclination in the surplus space 7 within the housing 6, the length LB of the housing 6 in the Y-axis direction can be shortened, thereby miniaturizing the antenna device 1(1). Even if the total length of the first ground conductor 3 and the second ground conductor 4 is longer than the length of the housing 6, the entire ground conductors of the first ground conductor 3 and the second ground conductor 4 can be accommodated in the housing 6, while the electrical length of the entire ground conductors can be set to a length corresponding to the wavelength. In particular, since the entire ground conductor can be accommodated in the housing 60 with the second ground conductor 4 inclined at an angle θ greater than 45° with respect to the first ground conductor 3, the antenna device 1(1) can be accommodated in a housing 60 with a short length in the Y-axis direction.

[0022] Furthermore, since the second ground conductor 4 of the antenna device 1(1) is flexible, the LB can be shortened by bending the second ground conductor 4 as shown in FIG. 1(d), thereby making it possible to reduce the size of the entire antenna device 1(1).

[0023] Furthermore, the height HS of the surplus space 7 matches HE, and the thick battery 5 allows the surplus space 7 to be generated on the negative Y-axis side of the battery 5, allowing the second ground conductor 4 to be placed therein. Therefore, there is no need to expand the housing 6 in order to place the second ground conductor 4, and the dimensions of the housing 6 can be kept to a minimum.

[0024] Furthermore, when the second ground conductor 4 is arranged along the diagonal of the excess space 7 of the rectangular parallelepiped, the excess space 7 can be used to the maximum extent to arrange the second ground conductor 4 .

[0025] Furthermore, the antenna device 1(1) can be efficiently housed in the housing 6 having a rectangular parallelepiped shape, since the substrate 3P and the second ground conductor 4 have a substantially rectangular flat plate shape and the battery 5 has a substantially rectangular parallelepiped shape.

[0026] For example, when the microwave frequency is 800 to 1000 MHz, 1 / 4λ is 94 to 75 mm, so the electrical length of L1+L2 can be set to 94 to 75 mm. In this case, the electrical length LB of the rectangular parallelepiped housing 6 can be set to approximately 94 to 75 mm, and when built-in, a placement space with an electrical length of approximately 94 to 75 mm is sufficient.

[0027] Furthermore, since the ground conductor 4 is connected to the substrate 3 at two terminal portions 4e provided on the long side 4s, it is easy to form the ground conductor 4 at an inclination angle θ relative to the substrate 3, and the shapes of the substrate 3 and the ground conductor 4 can be maintained.

[0028] (Another embodiment of the antenna device) In the above embodiment, an example in which the first ground conductor 3 and the second ground conductor 4 are connected at two locations has been described, but this is not limiting and other connection configurations may be employed. For example, as shown in Fig. 2(a), the antenna device 1 (2) may be configured such that the long side 4s and the side 3s are connected at a single terminal 4e at the end of the long side 4s of the second ground conductor 4 in the negative X-axis direction. In this case, current is distributed from the first ground conductor 3 to the second ground conductor 4 via the single terminal 4e at the end in the negative X-axis direction, and the first ground conductor 3 and the second ground conductor 4 function as a ground region with a length of L1 + L2.

[0029] 2(b), the antenna device 1(3) may have a long side 4s and a side 3s connected at a single terminal 4e at the end of the long side 4s in the positive X-axis direction. In this case, current is distributed from the first ground conductor 3 to the second ground conductor 4 via the single terminal 4e at the end in the positive X-axis direction, and the first ground conductor 3 and the second ground conductor 4 function as a ground region with a length of L1 + L2.

[0030] Note that the present invention is not limited to an antenna device in which the first ground conductor 3 and the second ground conductor 4 are connected at the terminal portion 4e. For example, as shown in FIG. 3(a), an antenna device 1(4) may be used in which the first ground conductor 3 (substrate 3P) and the second ground conductor 4 are connected along the entire long side 4s of the second ground conductor 4. In this case, current is distributed from the first ground conductor 3 to the second ground conductor 4 along the entire long side 4s, and the first ground conductor 3 and the second ground conductor 4 function as a ground area with a length of L1 + L2. Alternatively, as shown in FIG. 3(b), an antenna device 1(5) may be used in which the first ground conductor 3 and the second ground conductor 4 are connected along the negative half of the long side 4s on the X-axis. In this case, current is distributed from the first ground conductor 3 to the second ground conductor 4 along half of the long side 4s, and the first ground conductor 3 and the second ground conductor 4 function as a ground area with a length of L1 + L2.

[0031] (Simulation results of antenna characteristics) The following describes the results of simulating the VSWR (Voltage Standing Wave Ratio), antenna radiation efficiency, and current distribution for the antenna devices 1(1) to 1(5) of this embodiment and the antenna devices of the comparative example. As a comparative example, FIG. 4(a) shows an antenna device 50(1) in which the second ground conductor 4 and the battery 5 are not provided and the length of the first ground conductor 3 is set to L1, and FIG. 4(b) shows an antenna device 50(2) in which the second ground conductor 4 is not provided and the battery 5 is provided and the length of the first ground conductor 3 is set to L1. The length of the first ground conductor 3 of the antenna device 50(1) and the length of the first ground conductor 3 of the antenna device 50(2) are L1, similar to the antenna devices 1(1) to 1(5).

[0032] The simulation was performed without the housing 6. The dimensions of the first ground conductor 3 and second ground conductor 4 used in the simulation were: length L1 of the first ground conductor 3 = 50 mm, width W1 of the first ground conductor 3 = 60 mm, length L2 of the second ground conductor 4 = 20 mm, width W2 of the second ground conductor 4 = 60 mm, and longitudinal length WA of the monopole antenna element 2 = 45 mm. L1 + L2 is 70 mm, which, taking into account the dielectric constant of the printed circuit board, approximately matches the electrical length of the antenna, which is 81.5 mm, which is ¼ of the wavelength λ of 920 MHz.

[0033] FIG. 5(a) is a graph comparing the VSWR of the antenna device 1(1) ("3" in the figure) with that of the antenna device 50(1) ("1" in the figure) and the antenna device 50(2) ("2" in the figure). According to FIG. 5(a), the antenna device 50(2) ("2") has a narrower bandwidth and a larger VSWR due to the influence of the battery compared to the antenna device 50(1) ("1"). On the other hand, the antenna device 1(1) ("3") has a bandwidth close to that of the antenna device 50(1) ("1") and a VSWR close to that of the antenna device 50(1) ("1").

[0034] FIG. 5(b) is a graph comparing the antenna radiation efficiency of the antenna device 1(1)("3") with that of the antenna device 50(1)("1") and the antenna device 50(2)("2"). According to FIG. 5(b), the efficiency of the antenna device 50(2)("2") is lower than that of the antenna device 1(1)("3") due to the influence of the battery. On the other hand, the efficiency of the antenna device 1(1)("3") is close to that of the antenna device 50(1)("1").

[0035] Fig. 6(a) shows a current distribution diagram for the antenna device 50(2), and Fig. 6(b) shows a current distribution diagram for the antenna device 1(1). According to Fig. 6, just as the current is evenly distributed over the entire first ground conductor 3 in the antenna device 50(2), the current is evenly distributed over the entire ground conductor area in the antenna device 1(1) by connecting the second ground conductor 4 to both ends of the first ground conductor 3.

[0036] FIG. 7(a) is a graph comparing the VSWR of antenna devices 1(1) ("3" in the figure), 1(2), 1(3), 1(4) and 1(5) with that of antenna device 50(2). The VSWR of the antenna device 1(2) (labeled "4" in the figure) is closer to 1 in the operating frequency band (920 MHz) than that of the antenna device 1(1) (labeled "3" in the figure). In addition to the operating frequency band (920 MHz), the VSWR also peaks at approximately 1.02 GHz outside the operating frequency band (920 MHz). The antenna device 1(3) ("6" in the figure) also has a VSWR closer to 1 than the antenna device 1(1) ("3") in the operating frequency band (920 MHz). In addition to the operating frequency band (920 MHz), the VSWR also peaks at approximately 1.075 GHz outside the operating frequency band (920 MHz).

[0037] FIG. 7(b) is a graph comparing the antenna radiation efficiency of the antenna devices 1(1) to 1(5) with that of the antenna device 50(2). The antenna device 1(2)("4") has a higher radiation efficiency in the operating frequency band (920 MHz) than the antenna device 1(1)("3"). In addition to the operating frequency band (920 MHz), the antenna device 1(2)("4") also has a high radiation efficiency in frequency bands outside the operating frequency band (920 MHz) (especially higher frequency bands). The antenna device 1(3)("6") also has a higher radiation efficiency than the antenna device 1(1)("3") in the operating frequency band (920 MHz). In addition to the operating frequency band (920 MHz), the antenna device 1(3)("6") also has a high radiation efficiency in frequency bands outside the operating frequency band (920 MHz) (especially higher frequency bands).

[0038] However, in the case of a configuration such as antenna device 1(2) or antenna device 1(3), the resonant frequency is divided into two, one due to the first ground conductor 3 and the other due to the second ground conductor 4. In particular, the tip of the second ground conductor 4 has high impedance and is easily electrically coupled to surrounding objects, causing changes in characteristics, which may lead to degradation of the antenna characteristics. Therefore, there are cases where it is not appropriate to adopt antenna device 1(2) or antenna device 1(3). In such cases, it is appropriate to adopt the configuration of antenna device 1(1), which can ensure stable characteristics only in the frequency band being used.

[0039] The results of a simulation of changes in antenna characteristics due to objects around the tip of the second ground conductor 4 are shown below. Figure 8(a) shows an antenna device 1(1) in which a resin body 4P is attached near the tip of the second ground conductor 4 in the positive direction of the X-axis, and Figure 8(b) shows an antenna device 1(2) in which a resin body 4P is attached near the tip of the second ground conductor 4 in the positive direction of the X-axis.

[0040] FIG. 9(a) is a graph comparing the VSWR of the antenna devices 1(1) and 1(2) without the resin body 4P attached with the antenna devices 1(1) and 1(2) with the resin body 4P attached. The antenna device 1(1) ("3" in the figure indicates the case without the resin body 4P, and "3'" indicates the case with the resin body 4P) has a stable VSWR that is approximately the same regardless of whether the resin body 4P is present or not. In contrast, the antenna device 1(2) has a significantly worse VSWR when the resin body 4P is present ("4'" in the figure) compared to when it is not present ("4" in the figure).

[0041] FIG. 9(b) is a graph comparing the antenna radiation efficiency of the antenna devices 1(1) and 1(2) without the resin body 4P attached with the antenna devices 1(1) and 1(2) with the resin body 4P attached. The antenna radiation efficiency of the antenna device 1(1) ("3", "3'") is approximately the same and stable regardless of whether or not the resin body 4P is present. In contrast, the antenna radiation efficiency of the antenna device 1(2) is significantly lower when the resin body 4P is present ("4'") than when it is not present ("4"), and problems occur in the characteristics near the frequency band used and in frequency bands above that.

[0042] Thus, compared to the antenna device 1(2), the antenna device 1(1) is not subject to degradation of antenna characteristics due to surrounding objects, and therefore it is appropriate to adopt the configuration of the antenna device 1(1).

[0043] Here, in the antenna devices 1(2) and (3) connected at one terminal 4e, it is easier to tilt the second ground conductor 4 relative to the first ground conductor 3 than in the antenna device 1(1) connected at two points. However, in the antenna devices 1(2) and (3), the tensile force due to the weight of the second ground conductor 4 is concentrated at one terminal 4e, and a bending moment due to the weight occurs at the terminal 4e. In contrast, the tensile force acting on the two terminal portions 4e of the antenna device 1(1) is half that of the antenna devices 1(2) and (3), and the bending moment acting on the terminal portions 4e is smaller than that of the antenna devices 1(2) and (3). For this reason, the antenna device 1(1) is more preferable from the viewpoint of mechanical durability.

[0044] Figure 10(a) is a graph comparing the VSWR when the inclination angle θ of the second ground conductor 4 of the antenna device 1(1) is 0° ("3" in the figure), 45° ("8" in the figure), and 60° ("9" in the figure) with that of the antenna device 50(2) ("2" in the figure). According to Fig. 10(a), the VSWR of the antenna device 1(1) when θ = 45° ("8") and when θ = 60° ("9") is similar to that when θ = 0° ("3") in the used frequency band (920 MHz). Also, the band is not so narrow compared to when θ = 0° ("3").

[0045] Figure 10(b) is a graph comparing the antenna radiation efficiency when the inclination angle θ of the second ground conductor 4 of the antenna device 1(1) is θ=0° ("3"), θ=45° ("8"), and θ=60° ("9") with that of the antenna device 50(2) ("2"). According to Figure 10(b), the antenna radiation efficiency of antenna device 1(1) when θ = 45° ("8") and when θ = 60° ("9") is lower than when θ = 0° ("3") in frequency bands higher than the operating frequency band (920 MHz), but it can be said that it is similar at least in the operating frequency band (920 MHz).

[0046] As described above, by increasing θ and reducing the length of the ground conductor 4 in the Y-axis direction, it is possible to reduce the size of the antenna device while maintaining the antenna function. [Explanation of symbols]

[0047] 1(1), 1(2), 1(3), 1(4), 1(5) Antenna device 2 monopole antenna elements 3 First ground conductor 3P board 3e Antenna power supply 3s side 4 Second earth conductor 4e Terminal section 4s long side 5 batteries 5e Power supply unit 6. Housing 7. Surplus Space HS: Height of excess space HE Thickness from the bottom of the battery to the top of the substrate L1 Board length L2 Length of earth conductor LB Housing length LS Width of surplus space

Claims

1. An antenna device for microwaves, a monopole antenna element disposed on an upper surface of the substrate; a first ground conductor disposed on an upper surface of the substrate; a second ground conductor having a flexible flat plate shape connected to the first ground conductor; a housing that houses the substrate and the second ground conductor, the second ground conductor is disposed in a surplus space formed on the opposite side of the first ground conductor from the monopole antenna element. Antenna device.

2. a battery disposed on the underside of the substrate; a total length of the first ground conductor and the second ground conductor is greater than a length of the housing; the second ground conductor is housed in the housing in a state inclined toward the battery with respect to the first ground conductor. The antenna device according to claim 1 .

3. the second ground conductor is connected to one end of the first ground conductor in the width direction; The antenna device according to claim 2 .

4. the second ground conductor is connected to both widthwise ends of the first ground conductor; The antenna device according to claim 2 .

5. the second ground conductor is housed in the housing in a state inclined downward at an angle greater than 45° with respect to the first ground conductor; The antenna device according to any one of claims 2 to 4.

6. the height of the excess space is equal to the thickness from the bottom surface of the battery to the top surface of the substrate; the second ground conductor is disposed along a diagonal line of the excess space. The antenna device according to any one of claims 2 to 4.

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