Antenna Device

Abstract

The antenna device includes a housing (10) in which an antenna (12) is provided, a control board (20) provided in the housing (10), a signal ground (22) that constitutes a reference ground for a circuit in the control board (20) and on which a wireless module (21) is mounted and that is connected to the antenna (12) by a coaxial cable (11), a frame ground (23) that constitutes a ground for the housing (10), a capacitor (24) that connects between the signal ground (22) and the frame ground (23), a housing-side grounding part 13 that grounds the coaxial cable 11, and a board-side grounding part (26) that grounds the coaxial cable (11). The loop length of a closed loop (30) that passes through the housing-side grounding part (13), the board-side grounding part (26), the capacitor (24), and the connection part between the housing (10) and the frame ground (23) is less than a wavelength corresponding to the maximum transmission and reception frequency of the wireless module (21).

Description

[Technical field]

[0001] The present disclosure relates to an antenna device. [Background technology]

[0002] In some antenna devices, a coaxial cable is used to connect a wireless module mounted on a control board to an antenna. In this case, the antenna device can obtain stable antenna characteristics by securing a ground. An example of such an antenna device is disclosed in Patent Document 1. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2007-158462 A Summary of the Invention [Problem to be solved by the invention]

[0004] The antenna device disclosed in Patent Document 1 includes a conductive sheet. One end of the conductive sheet is connected to the outer sheath of the coaxial cable, while the other end of the conductive sheet is connected to a conductor that serves as a ground for the antenna. Therefore, the antenna device disclosed in Patent Document 1 can ensure grounding with a simple configuration.

[0005] Here, for example, some antenna devices have one ground separated into a ground on the control board side and a ground on the housing side, and these grounds are connected to each other by a capacitor. In such an antenna device with two grounds, when the outer sheath of the coaxial cable is connected to the ground of the housing, a large closed loop of the ground is formed across the outer sheath of the coaxial cable, the ground of the control board, the ground of the housing, and the capacitor. Such a closed loop formed in the ground becomes an antenna for external noise, and causes the external noise to be superimposed on the coaxial cable. This may result in a decrease in reception sensitivity.

[0006] The present disclosure has been made to solve the above-mentioned problems, and aims to provide an antenna device that can suppress the superposition of external noise on a coaxial cable even when it is equipped with two grounds. [Means for solving the problem]

[0007] The antenna device according to the present disclosure comprises a housing formed of a metal material and in which an antenna is provided, a control board provided in the housing, a signal ground provided on the control board and constituting a reference ground for a circuit in the control board, and on which a wireless module is mounted which is connected to the antenna by a coaxial cable, a frame ground provided on the control board, electrically connected to the housing and constituting a ground for the housing, a capacitor electrically connecting between the signal ground and the frame ground, a housing-side grounding portion provided on the housing for fixing and grounding the coaxial cable, and a board-side grounding portion provided on the signal ground for fixing and grounding the coaxial cable, wherein the loop length of a closed loop passing through the housing-side grounding portion, the board-side grounding portion, the capacitor, and the connection portion between the housing and the frame ground is less than a wavelength corresponding to the maximum transmission and reception frequency of the wireless module. Effect of the Invention

[0008] According to the present disclosure, even when two grounds are provided, it is possible to suppress the superposition of external noise on the coaxial cable, and therefore, the present disclosure can suppress a decrease in reception sensitivity. [Brief description of the drawings]

[0009] [Figure 1] 1 is a schematic configuration diagram of an electronic device to which an antenna device according to a first embodiment is applied. [Diagram 2] 1 is a perspective view of an electronic device to which an antenna device according to a first embodiment is applied. [Diagram 3] 4 is a perspective view showing a configuration of a housing-side grounding portion. FIG. [Figure 4] FIG. 4 is a perspective view showing a configuration of a substrate-side ground portion. [Diagram 5] 11 is a perspective view showing a configuration of a board-side ground part in an electronic device to which an antenna device according to a second embodiment is applied. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] In order to describe the present disclosure in more detail, embodiments of the present disclosure will be described below with reference to the accompanying drawings. Note that the following embodiments will describe an example in which an antenna device according to the present disclosure is applied to an electronic device 100.

[0011] Embodiment 1 The antenna device according to the first embodiment will be described with reference to FIGS. 1 to 4. FIG.

[0012] As shown in FIGS. 1 and 2, an electronic device 100 to which the antenna device according to the first embodiment is applied includes, for example, a housing 10, a coaxial cable 11, an antenna 12, a control board 20, and a wireless module 21.

[0013] The housing 10 is made of a metal material. The housing 10 has an antenna 12 and a housing-side grounding portion 13. The antenna 12 and a wireless module 21, which will be described later, are electrically connected by a coaxial cable 11. The housing-side grounding portion 13 is a portion of the housing 10 where the coaxial cable 11 is grounded. The housing-side grounding portion 13 will be described later in detail.

[0014] The control board 20 is a circuit board. The control board 20 is attached to the housing 10. Specifically, the control board 20 is fixed to the same surface of the housing 10 as the surface on which the housing side ground portion 13 is provided. The control board 20 also has a wireless module 21, a signal ground 22, a frame ground 23, a capacitor 24, a metal stud 25, and a board side ground portion 26.

[0015] The wireless module 21 is a module for transmitting and receiving signals. The wireless module 21 is mounted on the control board 20 via a signal ground 22.

[0016] The signal ground 22 serves as a reference ground for the circuits in the control board 20 including the wireless module 21. The frame ground 23 serves as a ground for the housing 10. The signal ground 22 and the frame ground 23 are electrically connected to each other via a capacitor 24. The signal ground 22 and the frame ground 23 are provided on the same mounting surface of the control board 20. The size of the signal ground 22 is larger than the size of the frame ground 23, and occupies most of the mounting surface of the control board 20.

[0017] The frame ground 23 is electrically connected to the housing 10 via a metal stud 25. The metal stud 25 constitutes a connection between the housing 10 and the frame ground 23. The metal stud 25 is formed in a cylindrical shape. One end of the metal stud 25 is electrically connected to the frame ground 23 by penetrating the control board 20 and the frame ground 23 in that order. The other end of the metal stud 25 is electrically connected to the housing 10 by directly contacting the surface of the housing 10.

[0018] The connection point between frame ground 23 and one end of metal stud 25 is located as close as possible to the installation position of capacitor 24. Also, the connection point between housing 10 and one end of metal stud 25 is located as close as possible to the installation position of housing-side ground part 13.

[0019] Although the control board 20 is fixed to the housing 10 at multiple points, electrical connection between the housing 10 and the control board 20 is made only by the metal studs 25. Here, fixing points other than the metal studs 25 that are not electrical connections are omitted.

[0020] The board-side grounding portion 26 is a portion of the control board 20 where the coaxial cable 11 is grounded. The board-side grounding portion 26 is provided on the surface of the signal ground 22. Specifically, the board-side grounding portion 26 is fixed to the same surface of the signal ground 22 on which the wireless module 21 is provided. Details of the board-side grounding portion 26 will be described later.

[0021] Here, for example, the coaxial cable 11 has a structure in which a core wire (internal conductor) serving as a signal line made of copper or the like is surrounded by an insulating layer, a shield conductor layer (external conductor) 11a, and an insulating protective coating 11b made of an insulating material, in that order (see FIG. 5). In this way, by covering the core wire with the shield conductor layer 11a, the coaxial cable 11 prevents the electrical signal flowing through the core wire from leaking to the outside and prevents interference due to external noise (electromagnetic waves) from the outside. Therefore, the coaxial cable 11 can suppress attenuation of the electrical signal and disturbance due to external noise.

[0022] The coaxial cable 11 is fixed to the housing-side grounding portion 13 of the housing 10. In detail, the coaxial cable 11 is fixed in a state where the insulating protective coating 11b is in contact with the housing-side grounding portion 13 without exposing the shielding conductor layer 11a. The shielding conductor layer 11a is not in contact with the housing 10 and the housing-side grounding portion 13. Therefore, the coaxial cable 11 is grounded at high frequency by the electrostatic capacitance generated between the shielding conductor layer 11a and the housing 10.

[0023] Specifically, as shown in Fig. 3, the housing 10 has a cut-and-raised piece 13a as the housing-side grounding part 13. This cut-and-raised piece 13a is formed by cutting and raising the housing 10. The coaxial cable 11 is sandwiched between the surface of the housing 10 and the cut-and-raised piece 13a, and is thereby grounded at high frequencies. In other words, the cut-and-raised piece 13a constitutes a grounding conductor.

[0024] Furthermore, the coaxial cable 11 is fixed to the board-side ground portion 26 of the control board 20. In detail, the coaxial cable 11 is fixed to the board-side ground portion 26 with the insulating protective coating 11b in contact with the board-side ground portion 26 without exposing the shielding conductor layer 11a. The shielding conductor layer 11a is not in contact with the signal ground 22 and the board-side ground portion 26. Therefore, the coaxial cable 11 is grounded at high frequencies by the electrostatic capacitance generated between the shielding conductor layer 11a and the signal ground 22.

[0025] Specifically, as shown in Fig. 4, the signal ground 22 has a pad 26a and a clamp 26b as the board-side ground portion 26. The pad 26a is made of a conductive material. The pad 26a is provided on the surface of the signal ground 22. The clamp 26b is made of a metallic material. The clamp 26b is mounted on the surface of the pad 26a. The coaxial cable 11 is sandwiched between the clamp 26b and is thus grounded at high frequencies. That is, the pad 26a and the clamp 26b form a ground conductor.

[0026] Although the cut-out piece 13a and the clamp 26b are used as the structure of each grounding portion for the coaxial cable 11, the structure is not limited to this. The structure may have a capacitance that provides a sufficiently low impedance in the operating frequency band of the wireless module 21. For example, the electronic device 100 may be configured such that the coaxial cable 11 is fixed to the housing 10 and the signal ground 22 using conductive tape.

[0027] 2, in the electronic device 100, the installation positions of the case-side ground part 13, the board-side ground part 26, the capacitor 24, and the metal stud 25 are set so that the loop length of the closed loop 30 passing through all of these parts is less than the wavelength corresponding to the maximum transmission and reception frequency of the wireless module 21. Specifically, the electronic device 100 can set the loop length of the closed loop 30, which is formed by the creepage distance between each of the components, to a length less than the wavelength corresponding to the maximum transmission and reception frequency of the wireless module 21, by bringing the case-side ground part 13, the board-side ground part 26, the capacitor 24, and the metal stud 25 close to each other. Note that the maximum transmission and reception frequency of the wireless module 21 refers to the frequency that is maximum when the wireless module 21 transmits and receives wireless signals.

[0028] Therefore, a radio signal output from the radio module 21 is transmitted through the coaxial cable 11 and transmitted from the antenna 12. Moreover, a radio signal arriving from the outside is received by the antenna 12, then transmitted through the coaxial cable 11 and input to the radio module 21. The radio module 21 processes the input radio signal as a received signal.

[0029] Here, when exogenous noise of the same frequency band as that of the transmitted or received wireless signal occurs near the electronic device 100, the closed loop 30 passing through the case-side grounding part 13, the board-side grounding part 26, the capacitor 24, and the metal stud 25 becomes an antenna to receive the exogenous noise. At this time, the received exogenous noise is superimposed on the shielding conductor layer 11a of the coaxial cable 11. In this way, the exogenous noise superimposed on the shielding conductor layer 11a of the coaxial cable 11 becomes a noise component for the normal wireless signal, degrading the quality of the wireless signal. As a result, the receiving sensitivity of the wireless module 21 may decrease.

[0030] In contrast, in the electronic device 100 according to the first embodiment, the housing-side grounding part 13, the board-side grounding part 26, the capacitor 24, and the metal stud 25 are arranged so that the loop length of the closed loop 30 is less than the wavelength corresponding to the maximum transmission / reception frequency of the wireless module 21. In general, the resonant frequency of a loop antenna is an integer multiple of the frequency where the loop length is one wavelength.

[0031] In this way, the closed loop 30 becomes a loop antenna including the shield conductor layer 11a of the coaxial cable 11, but the loop length is shorter than the wavelength corresponding to the maximum transmission / reception frequency of the wireless module 21. Therefore, the resonant frequency of the loop antenna formed by the closed loop 30 is set to the higher frequency side than the operating frequency band of the wireless module 21. As a result, even if exogenous noise of the same frequency band as the frequency band of the transmitted wireless signal or the received wireless signal is generated near the electronic device 100, the sensitivity of the loop antenna formed by the closed loop 30 to the exogenous noise is low. Therefore, the superposition of the exogenous noise on the shield conductor layer 11a is suppressed.

[0032] As described above, the antenna device according to the first embodiment includes a housing 10 formed of a metal material and provided with an antenna 12, a control board 20 provided in the housing 10, a signal ground 22 provided in the control board 20, constituting a reference ground for a circuit in the control board 20, and mounting a wireless module 21 connected to the antenna 12 by a coaxial cable 11, a frame ground 23 provided in the control board 20, electrically connected to the housing 10, and constituting a ground for the housing 10, a capacitor 24 electrically connecting between the signal ground 22 and the frame ground 23, a housing-side grounding section 13 provided in the housing 10 for fixing and grounding the coaxial cable 11, and a board-side grounding section 26 provided in the signal ground 22 for fixing and grounding the coaxial cable 11. In this case, the antenna device sets the loop length of a closed loop 30 passing through the housing-side grounding section 13, the board-side grounding section 26, the capacitor 24, and the connection section between the housing 10 and the frame ground 23 to be less than a wavelength corresponding to the maximum transmission / reception frequency of the wireless module 21. Therefore, even when the antenna device includes the two grounds 22 and 23, it is possible to suppress superposition of external noise on the coaxial cable 11. As a result, the antenna device can suppress a decrease in the receiving sensitivity of the antenna 12.

[0033] In the antenna device according to the first embodiment, the coaxial cable 11 has a shield conductor layer 11a provided on the outer periphery of a core wire through which a radio signal passes, and an insulating protective coating 11b provided on the outer periphery of the shield conductor layer 11a. In this case, the housing-side grounding portion 13 and the board-side grounding portion 26 ground the insulating protective coating 11b. Therefore, the antenna device can suppress superposition of external noise on the coaxial cable 11 with a simple configuration.

[0034] The antenna device according to the first embodiment includes a metal stud 25 that electrically connects the housing 10 and the frame ground 23. Therefore, the antenna device can easily electrically connect the housing 10 and the frame ground 23.

[0035] In the antenna device according to the first embodiment, the housing-side grounding portion 13 is a cut-and-raised piece 13a that is provided in the housing 10 and sandwiches the coaxial cable 11. Therefore, the antenna device can easily ground the insulating protective coating 11b of the coaxial cable 11. As a result, the antenna device can ground the shield conductor layer 11a of the coaxial cable 11 at high frequencies to the cut-and-raised piece 13a that serves as a ground conductor.

[0036] In the antenna device according to the first embodiment, the board-side grounding section 26 has a pad 26a mounted on the surface of the control board 20 and a clamp 26b mounted on the surface of the pad 26a and clamping the coaxial cable 11. Therefore, the antenna device can easily ground the insulating protective coating 11b of the coaxial cable 11. As a result, the antenna device can ground the shield conductor layer 11a of the coaxial cable 11 at high frequency to the clamp 26b, which serves as a ground conductor.

[0037] Embodiment 2 An antenna device according to the second embodiment will be described with reference to Fig. 5. Note that components having the same functions as those described in the first embodiment above are given the same reference numerals, and the description thereof will be omitted.

[0038] 5, the coaxial cable 11 is fixed to the board-side ground part 26 with the shield conductor layer 11a in direct contact with the board-side ground part 26. Specifically, the insulating protective coating 11b of the coaxial cable 11 is removed from a portion corresponding to the board-side ground part 26, and the shield conductor layer 11a is exposed from the portion from which the insulating protective coating 11b has been removed. The exposed portion of the shield conductor layer 11a is sandwiched by a clamp 26b mounted on a pad 26a, and is thereby electrically grounded.

[0039] Therefore, the shield conductor layer 11a exposed from the coaxial cable 11 and the board-side ground portion 26 are electrically conductive with each other. As a result, the exposed shield conductor layer 11a is grounded with low impedance to the board-side ground portion 26 in all bands including the low-frequency band.

[0040] In order to protect the exposed shield conductor layer 11a, a metal member may be provided so as to be in contact with and cover the surface of the exposed shield conductor layer 11a, and this metal member may be sandwiched between the clamp 26b. For example, the electronic device 100 protects the exposed shield conductor layer 11a by providing a metal sleeve as the metal member on the coaxial cable 11. Then, the electronic device 100 sandwiches the sleeve between the clamp 26b while the sleeve and the clamp 26b are electrically connected to each other.

[0041] Here, in addition to the wireless module 21, the control board 20 is equipped with electronic components such as a CPU (Central Processing Unit) and a power supply IC (Integrated Circuit). Therefore, the operation of each electronic component may generate noise in a frequency band lower than the operating frequency of the wireless module 21. In this case, when the noise propagates to the board-side grounding part 26, the noise is radiated to the outside using the coaxial cable 11 as an antenna. Therefore, the electronic device 100 may cause EMI (Electromagnetic Interference).

[0042] In contrast, in the electronic device 100 according to the second embodiment, the shield conductor layer 11a of the coaxial cable 11 is electrically connected to the board-side ground portion 26, so that the noise propagated from the board-side ground portion 26 to the shield conductor layer 11a of the coaxial cable 11 can be returned to the board-side ground portion 26. Therefore, the electronic device 100 can suppress the propagation of noise generated in the control board 20 to the coaxial cable 11.

[0043] As described above, in the antenna device according to the second embodiment, the coaxial cable 11 has the shield conductor layer 11a provided on the outer periphery of the core wire through which the wireless signal passes, and the insulating protective coating 11b provided on the outer periphery of the shield conductor layer 11a. In this case, the housing-side grounding section 13 grounds the insulating protective coating 11b, and the board-side grounding section 26 grounds the shield conductor layer 11a exposed from the insulating protective coating 11b. Therefore, the antenna device can suppress the propagation of noise generated in the control board 20 to the coaxial cable 11 with a simple configuration.

[0044] In the antenna device according to the second embodiment, the board-side grounding section 26 has a pad 26a mounted on the surface of the control board 20 and a clamp 26b mounted on the surface of the pad 26a and clamping the coaxial cable 11. Therefore, the antenna device can easily ground the shield conductor layer 11a of the coaxial cable 11. As a result, the antenna device can electrically connect the shield conductor layer 11a of the coaxial cable 11 to the clamp 26b, which serves as a ground conductor.

[0045] In addition, within the scope of the present disclosure, the embodiments may be freely combined, or any of the components in each embodiment may be modified, or any of the components in each embodiment may be omitted. [Industrial Applicability]

[0046] The antenna device according to the present disclosure has a closed loop length that is less than the wavelength corresponding to the maximum transmission and reception frequency of the wireless module, so that even when the antenna device has two grounds, it is able to suppress external noise and is suitable for use in antenna devices, etc. [Explanation of symbols]

[0047] 10 housing, 11 coaxial cable, 11a shield conductor layer, 11b insulating protective coating, 12 antenna, 13 housing side grounding portion, 13a cut-out piece, 20 control board, 21 wireless module, 22 signal ground, 23 frame ground, 24 capacitor, 25 metal stud, 26 board side grounding portion, 26a pad, 26b clamp, 30 closed loop, 100 electronic device.

Claims

1. A housing formed of a metal material, provided with an antenna; A control board provided on the housing; A signal ground provided on the control board, configuring a reference ground for a circuit within the control board, and having a wireless module mounted thereon, which is connected to the antenna by a coaxial cable; A frame ground provided on the control board, electrically connected to the housing, and configuring a ground for the housing; A capacitor electrically connecting the signal ground and the frame ground; A housing-side grounding portion provided on the housing, fixing and grounding the coaxial cable; A board-side grounding portion provided on the signal ground, fixing and grounding the coaxial cable; The loop length of a closed loop passing through the housing-side grounding portion, the board-side grounding portion, the capacitor, and the connection portion between the housing and the frame ground is less than the wavelength corresponding to the maximum transmission and reception frequency in the wireless module. An antenna device characterized by the above.

2. The coaxial cable has a shield conductor layer provided on the outer periphery of a core wire through which a wireless signal passes, and an insulating protective film provided on the outer periphery of the shield conductor layer. The housing-side grounding portion and the board-side grounding portion ground the insulating protective film. The antenna device according to Claim 1, characterized by the above.

3. The coaxial cable has a shield conductor layer provided on the outer periphery of a core wire through which a wireless signal passes, and an insulating protective film provided on the outer periphery of the shield conductor layer. The housing-side grounding portion grounds the insulating protective film. The board-side grounding portion grounds the shield conductor layer exposed from the insulating protective film. The antenna device according to Claim 1, characterized by the above.

4. Comprising a metal stud for electrically connecting the housing and the frame ground. The antenna device according to Claim 1, characterized by the above.

5. The housing-side grounding portion is A raised piece provided on the housing for sandwiching the coaxial cable. The antenna device according to Claim 1, characterized by the above.

6. The board-side grounding portion is A pad mounted on the surface of the control board, and A clamp mounted on the surface of the pad for sandwiching the coaxial cable. The antenna device according to any one of Claims 1 to 5, characterized by the above.

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