Antenna equipment

Abstract

To provide an antenna apparatus capable of reducing a leak current that flows toward a cable without increasing cost or weight.SOLUTION: An antenna apparatus 10 includes: antenna elements 11A, 11B; a printed board 12 with the antenna elements 11A, 11B mounted on one surface; and a ground board 13 arranged on the other surface of the printed board 12 and receiving a ground potential applied thereto. A high-frequency ground point is formed in a range from a feeding point Pa of the antenna element 11A on the printed board 12 to λ / 8-λ / 32. On the printed board 12, formed is a pattern of a conductive layer extending from a region including the ground point to a region excluding a wiring pattern of the printed board 12. The ground point is electrically connected to the pattern of the conductive layer.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to an antenna device including an antenna element mounted on a printed circuit board, and more particularly to a technology effective when applied to, for example, an antenna device for vehicle mounting.

Background Art

[0002] Since an antenna device mounted on a vehicle for transmitting and receiving a wireless communication signal in a predetermined frequency band is desired to be small, a device in which an antenna element (antenna element) is mounted on a printed circuit board or a floor board on which electronic components such as an amplifier and a filter are mounted has been put into practical use. When such a device is mounted on a vehicle as a product and a coaxial cable is connected, it is known that the current flowing through the outer conductor of the cable has an adverse effect, the cable becomes an antenna, causing unnecessary resonance, and the reception sensitivity of the antenna decreases.

[0003] To solve the above problems, conventionally, a method of loading a ferrite core on a cable to block the leaking current is often used, but there is a problem that trade-off matters such as an increase in cost and weight due to the ferrite occur when it is made into a product. There is also an invention related to an in-vehicle integrated antenna in which a leakage current blocking portion formed of a strip line is formed in the vicinity of the cable end on the substrate (Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The antenna device described in Patent Document 1 is a type of antenna device in which the end of the cable is fixed to the ground plate, and a leakage current blocking section composed of a stripline is formed near the cable end on the ground plate. Therefore, there is a problem in that it is difficult to apply to antenna devices of the type in which a connector for connecting the cable end is provided on a printed circuit board.

[0006] This invention was made in response to the above-mentioned problems, and its purpose is to provide an antenna device that can reduce leakage current flowing towards the cable without increasing costs or weight. Another object of the present invention is to provide an antenna device that can improve receiving sensitivity. [Means for solving the problem]

[0007] To achieve the above objective, the present invention An antenna device comprising an antenna element and a printed circuit board on which the antenna element is mounted on one side, The aforementioned printed circuit board, On the side opposite to the aforementioned one side, From the feed point of the aforementioned antenna element , with the receiving wavelength of the antenna element being λ High-frequency grounding points are provided in the range of λ / 8 to λ / 32. The printed circuit board has a conductive layer pattern formed on it that extends from the region including the ground point to the region excluding the linear wiring pattern of the printed circuit board, and the ground point is configured to be electrically connected to the conductive layer pattern.

[0008] In an antenna device having the above configuration, a high-frequency grounding point (spring contact) is provided in the range of λ / 8 to λ / 32 from the feed point of the antenna element. Therefore, by allowing a portion of the leakage current that would otherwise flow from the antenna element through the conductive layer of the printed circuit board to the cable to flow to the outside via the grounding point, the leakage current flowing toward the cable can be reduced, thereby improving the antenna's receiving sensitivity.

[0009] Furthermore, by reducing leakage current and suppressing the cable from acting as an antenna, unwanted resonance can be suppressed when measures are taken to intentionally create a resonance point on the cable side. Furthermore, since it is possible to reduce leakage current flowing towards the cable without using cables with ferrite cores as in conventional methods, it has the advantage of not leading to increased costs or weight. [Effects of the Invention]

[0010] The antenna device according to the present invention can reduce leakage current flowing towards the cable without increasing costs or weight. Furthermore, it has the effect of improving the antenna's receiving sensitivity. [Brief explanation of the drawing]

[0011] [Figure 1] This is a perspective view showing one embodiment of an antenna device to which the present invention is applied. [Figure 2] This is a cross-sectional view of the antenna device showing the cross-sectional structure along line II-II in Figure 1. [Figure 3] (A) and (B) are current distribution diagrams showing the results of simulation verification of the current distribution flowing on the surface of the antenna element, circuit board, and cable connected to the connector for antenna devices with a ground point on the circuit board and those without a ground point. [Figure 4] (A) is a graph showing the received level for each frequency calculated for an antenna device without a ground point and an antenna device with a ground point, and (B) is a graph showing the received level when the distance from the feed point of the antenna element to the ground point is changed. [Figure 5] This is a plan view showing an appropriate range for providing a grounding point in the antenna device of the embodiment. [Figure 6] This is a plan view showing an appropriate range for providing a grounding point considering two antenna elements in the antenna device of the embodiment. [Modes for carrying out the invention]

[0012] Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. Figure 1 shows a perspective view of one embodiment of the antenna device according to the present invention. In the following description, the lower left side of the antenna device 10 in Figure 1 will be referred to as the front end, and the upper right side as the rear end. Also, for convenience, the direction that is upward in the state shown in Figure 1 will be referred to as upward, and the direction that is downward will be referred to as downward.

[0013] As shown in Figure 1, the antenna device 10 of this embodiment comprises two antenna elements 11A and 11B made of conductive metal plates, a circuit board 12 on which these antenna elements 11A and 11B are mounted, and a flat plate-shaped bracket 13 made of conductive metal disposed below the circuit board 12 and bolted to the lower surface of the circuit board 12. The bracket 13 is supplied with a ground potential and functions as a ground board. The bracket 13 is rectangular in shape and slightly larger than the circuit board 12, and also functions as a housing that protects the lower surface of the circuit board 12.

[0014] Although not particularly limited, in the antenna device 10 of this embodiment, the two antenna elements 11A and 11B have a symmetrical shape and are formed to receive signals (radio waves) in the same frequency band. Furthermore, each antenna element 11A and 11B is composed of a horizontal portion 11a parallel to the circuit board 12, a vertical portion 11b hanging down toward the circuit board 12 from one side of the horizontal portion 11a, a folded portion 11c bent 90 degrees backward from the vertical portion 11b, and a leg portion 11d bent downward from the folded portion 11c, and is arranged at a predetermined interval.

[0015] Furthermore, a plurality (for example, two) of engaging protrusions 11e are provided at the lower ends of the leg portions 11d of the antenna elements 11A and 11B, and the antenna elements 11A and 11B are coupled to the circuit board 12 by engaging the engaging protrusions 11e with slit-shaped engaging holes formed in a predetermined portion of the circuit board 12. Also, the two engaging protrusions 11e are coupled to the circuit board 12 by soldering, and among the two engaging protrusions 11e, the engaging protrusion located on the side of the substrate is electrically connected to a feeding strip line formed so as to electrically connect the portion to the terminal of the connector, and is configured to be a feeding point to the antenna elements 11A and 11B.

[0016] The circuit board 12 is constituted by a printed board having a wiring pattern made of a conductive layer, and although not shown, electronic components such as a distributor, an amplifier, a filter, an attenuator, etc. are mounted. And at a position near the vertical portions of the antenna elements 11A and 11B on the lower surface of the circuit board 12, a spring contact 14 made of a leaf spring of a conductive material that forms a Z shape when viewed from the rear is fixed so as to protrude downward. Specifically, the spring contact 14 has an upper horizontal piece, an inclined piece that protrudes obliquely downward from an end of the upper horizontal piece, and a lower horizontal piece that is folded back in the horizontal direction from the inclined piece, and the upper horizontal piece is connected to the lower surface of the circuit board 12. Note that the shape of the spring contact 14 is not limited to a Z shape.

[0017] Also, at an edge portion on the antenna element coupling side of the lower surface of the circuit board 12, a connector 15 is provided into which an end portion of a coaxial cable (hereinafter abbreviated as a cable) connected to a device called a head unit having a tuner or the like is inserted and connected from below. The connector 15 is formed with a plurality of locking pieces 15a that protrude upward and have claws at both side portions of the upper surface thereof, and the connector 15 is coupled to the circuit board 12 by inserting the locking pieces 15a into engaging holes formed in a predetermined portion of the circuit board 12. And on the circuit board 12, a linear wiring pattern (strip line) that connects between a terminal to which the inner conductor of the cable of the connector 15 is connected and the feeding points (Pa, Pb in FIG. 6) of the antenna elements 11A and 11B is formed.

[0018] Furthermore, on the circuit board 12, a conductive layer is formed over most of the area including the installation position of the spring contact 14, excluding the wiring pattern (strip line) that electrically connects between the above electronic components and between the electronic components and the connector. Then, the spring contact 14 is connected to the circuit board 12 while being electrically connected to this conductive layer, and the height is set such that the lower horizontal piece at the lower end of the inclined piece of the spring contact 14 is coupled to the bracket 13 as shown in FIG. 4.

[0019] As described above, when the spring contact 14 contacts the upper surface of the bracket 13 at the ground potential, the ground potential is applied to the conductive layer of the circuit board 12. That is, the spring contact 14 becomes the ground point of the circuit board 12. The way of determining the installation position of this spring contact 14 is the point of the present invention, and this will be described in detail later.

[0020] On the other hand, an opening 13a is formed in a part of the bracket 13 corresponding to the connector 15, and the connector 15 is inserted inside this opening 13a. Further, pedestal portions 13b are formed at a plurality of locations (four locations in the figure) of the bracket 13 by raising a part of the bracket 13 and bending it into a "U" shape in a front view. Then, the lower surface of the circuit board 12 is joined to the upper surfaces of these pedestal portions 13b, and the circuit board 12 and the bracket 13 are configured to be coupled by screws (not shown) inserted through screw insertion holes 12b formed at corresponding portions of the upper horizontal pieces of the pedestal portions 13b and the circuit board 12.

[0021] In the antenna device configured as shown in Figure 1, the distance between the antenna elements 11A and 11B and the circuit board 12 affects the antenna's receiving sensitivity, and a larger distance is preferable. However, the distance between the circuit board 12 and the bracket 13 does not affect the antenna's receiving sensitivity, so it is possible to eliminate the base portion 13b and configure the device so that the bottom surface of the circuit board 12 and the top surface of the bracket 13 are joined together. Nevertheless, the reason why the bracket 13 is provided with a base portion 13b, as described above, is that it is difficult to sufficiently reduce the height of the connector 15 used, while the amount of protrusion of the connector 15 from the bottom surface of the case housing the entire antenna device shown in Figure 1 is determined by the user's specifications. Therefore, depending on the conditions, the bracket 13 may be made without a base portion 13b.

[0022] Furthermore, the conductive layer within the circuit board 12 extends around the screw insertion holes 12b of the circuit board 12 that correspond to the two base portions 13b located to the left and right of the connector 15 among the four base portions 13b mentioned above. As a result, when conductive screws are inserted into the screw insertion holes 12b of the circuit board 12 that correspond to the screw insertion holes of the base portions and the bracket 13 are connected, the circuit board 12 and the bracket 13 are electrically connected via the screws.

[0023] On the other hand, the conductive layer does not extend around the screw insertion holes 12b of the circuit board 12 that correspond to the two base portions 13b located furthest from the connector 15. In other words, the application of the ground potential to the conductive layer of the circuit board 12 is limited to the two base portions 13b located to the left and right of the spring contact 14 and the connector 15. This is done because, in the antenna device of this embodiment, a portion of the antenna elements 11A and 11B is located above the two base portions that are farther from the connector 15. If the conductive layer of the circuit board 12 is extended to this portion, the distance between the antenna elements 11A and 11B and the conductive layer becomes small, resulting in a decrease in reception sensitivity.

[0024] In contrast, since there are no antenna elements 11A and 11B above the two base portions 13b located on the left and right sides of the connector 15, the reception sensitivity will not decrease even if the conductive layer of the circuit board 12 is connected to the bracket 13. Therefore, a connection to the ground potential can also be made at the two base portions located on the left and right sides of the connector 15. However, since the application of the ground potential is insufficient in this connection, in this embodiment, a separate spring contact 14 is provided to avoid a situation where the application of the ground potential is insufficient.

[0025] Furthermore, instead of the elastically deformable spring contact 14, a non-elastically deformable component such as a screw may be used to connect the conductive layer of the circuit board 12 to the bracket 13. Also, the spring contact 14 and screw are not limited to metal; they may be made of any conductive material other than metal, such as resin. In addition, the antenna device 10 of this embodiment is provided with two antenna elements 11A and 11B that receive signals (radio waves) in the same frequency band, but there may be one or more antenna elements, or the antenna elements 11A and 11B may be configured to receive signals (radio waves) in different frequency bands by changing their lengths.

[0026] A key feature of this invention is that the position of the grounding point on the circuit board on which the antenna element is mounted is set within a range of λ / 8 to λ / 32 from the feed point of the antenna element. The following describes the optimal placement of the grounding point (spring contact 14) in the antenna device 10 of this embodiment, which is effective in suppressing leakage current flowing from the antenna element 11A to the cable side via the connector 15. Prior to the present invention, the inventors simulated the distribution of current flowing on the surface of the cable connected to the antenna element 11A, the circuit board 12, and the connector 15 for an antenna device having the configuration shown in Figure 1 and equipped with a grounding point (spring contact 14), and for a similar configuration but without a grounding point (spring contact 14).

[0027] The verification results are shown in Figures 3(A) and 3(B). In Figures 3(A) and 3(B), the three lines in the lower right are magnified views of the three cables C1, C2, and C3 connected to the antenna device in the upper left. Figure 3(A) relates to an antenna device without a ground point, and Figure 3(B) relates to an antenna device with a ground point. In Figure 3, areas with high current are represented by lighter colors closer to white, and areas with low current are represented by darker colors closer to black.

[0028] Comparing the shading of cable C3 in the lower right of Figure 3(A) with that of cable C3 in the lower right of Figure 3(B), we can see that cable C3 in Figure 3(B) is generally darker, meaning the current is smaller. This means that the antenna device with a grounding point (spring contact 14) in Figure 3(A) has less leakage current flowing through the surface of the cable than the antenna device without a grounding point in Figure 3(B).

[0029] Next, the inventors calculated the reception level for an antenna device without a spring contact and an antenna device with a ground point, while varying the frequency in the telephone communication frequency band. The results are shown in Figure 4(A). In Figure 4(A), the dashed line shows the reception level for an antenna without a ground point at each frequency, while the solid line shows the reception level for an antenna with a ground point at each frequency. From Figure 4(A), it can be seen that the reception level of the antenna with a ground point (shown by the solid line) is higher than that of the antenna without a ground point (shown by the dashed line) in the lower frequency band (800-900 MHz).

[0030] Next, we investigated the optimal position for providing a grounding point on the circuit board 12. The results are shown in Figure 4(B). In Figure 4(B), A shows the reception level for each frequency when the grounding point is located at a position λ / 4 from the feed point of the antenna element, B shows the reception level when it is located at a position λ / 8 from the feed point, C shows the reception level when it is located at a position λ / 32 from the feed point, and D shows the reception level when it is located at a position λ / 64 from the feed point. Here, λ is the wavelength of the signal (radio wave) corresponding to the receiving frequency of the antenna element (800 MHz).

[0031] Figure 4(B) shows that, compared to the reception level when the grounding point is located in the range of λ / 8 to λ / 32 from the feed point of the antenna element, the characteristics deteriorate in the lower frequency band (800 to 900 MHz) when the grounding point is less than λ / 8 or greater than λ / 32. This indicates that the appropriate position for the contact is in the range of λ / 8 to λ / 32 from the feed point of the antenna element, and that setting the grounding point within this range effectively reduces the leakage current flowing into the cable.

[0032] Figure 5 shows the area suitable for establishing a grounding point using hatching. In the figure, the center of the circle is the feed point Pa of antenna element 11A. Figure 5 shows the appropriate setting range for the grounding point (spring contact 14) when there is one antenna element. When there are two antenna elements 11A and 11B, as in the antenna device of the embodiment in Figure 1, it is preferable to set the grounding point (spring contact 14) in the area where the mesh is drawn by overlapping circles representing the ranges centered on the respective feed points Pa and Pb of the two antenna elements 11A and 11B, as shown in Figure 6.

[0033] As described above, by setting the grounding point to a range of λ / 8 to λ / 32 from the feed point of the antenna element, the leakage current flowing into the cable can be reduced, improving the receiving sensitivity of the antenna element. Furthermore, by reducing the leakage current flowing into the cable, it is possible to prevent the cable from acting as an antenna and suppress unwanted resonance. Furthermore, since it is possible to reduce leakage current flowing into the cable without adding ferrite cores or other protective measures to the cable as in conventional methods, it has the advantage of reducing costs and weight.

[0034] Although the present inventors' inventions have been described in detail above based on embodiments, the present invention is not limited to the above embodiments. For example, in the above embodiments, the connection between the ground point of the circuit board 12 and the bracket 13 is made by a means of physical contact such as a spring contact, but the ground point does not need to be in physical contact as long as it is connected at high frequency by, for example, opposing electrodes or a structure in which metal layers face each other and behave like a capacitor. Furthermore, although the above embodiment shows two antenna elements 11A and 11B mounted on the circuit board 12, the number of antenna elements is not limited to two; it may be one or three or more. The shape of the antenna elements is also not limited to that shown in Figure 1; antenna devices with antenna elements of other shapes mounted on the circuit board can be applied. [Explanation of symbols]

[0035] 10…Antenna device, 11A,11B…Antenna elements, 12…Circuit board (printed circuit board), 12b…Screw insertion hole, 13…Bracket (ground board), 13b…Base, 14…Spring contact (grounding point), 15…Cable connector, Pa,Pb…Feed point

Claims

1. An antenna device comprising an antenna element and a printed circuit board on which the antenna element is mounted on one side, On the printed circuit board, on the side opposite to the one side, a high-frequency grounding point is provided in the range of λ / 8 to λ / 32, where λ is the receiving wavelength of the antenna element, from the feed point of the antenna element. The antenna device is characterized in that the printed circuit board has a conductive layer pattern formed thereon that extends from the region including the ground point to the region excluding the linear wiring pattern of the printed circuit board, and the ground point is electrically connected to the conductive layer pattern.

2. Multiple antenna elements are mounted on the aforementioned printed circuit board. The antenna device according to claim 1, characterized in that a high-frequency grounding point is provided on the printed circuit board in a region where the ranges from λ / 8 to λ / 32 from the feed point of the antenna element overlap.

3. The printed circuit board is provided with a ground board that is positioned opposite to one of the aforementioned surfaces and is spaced at a predetermined distance from the printed circuit board, to which a ground potential is applied. The antenna device according to claim 1 or 2, characterized in that one end of a spring contact made of a conductive leaf spring is connected to the grounding point on the surface of the printed circuit board facing the ground board, and the other end of the spring contact is connected to the opposite portion of the ground board.

4. The antenna device according to claim 3, characterized in that a plurality of base portions are formed on the ground board, the printed circuit board is bonded to the base portions by conductive screws, and the pattern of the conductive layer extends to the bonding region of the printed circuit board corresponding to at least some of the plurality of base portions.

5. The antenna device according to claim 4, characterized in that, among the plurality of base portions, the conductive layer pattern is not extended to the bonding region of the printed circuit board corresponding to the base portion in which the antenna element is located above.

6. The printed circuit board is provided with a connector to which the end of a coaxial cable having an inner conductor and an outer conductor can be connected. The antenna device according to claim 1, characterized in that the printed circuit board has a linear wiring pattern formed thereon that connects the terminal to which the inner conductor of the connector is connected to the feed point of the antenna element.

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