Method for determining the setting position of antenna equipment and grounding point

Abstract

To provide an antenna apparatus capable of improving isolation performance between antenna elements and improving transmitting / receiving sensitivity, and provide a method for determining a position where a ground point is to be set.SOLUTION: An antenna apparatus includes a plurality of antenna elements (11A, 11B) and a printed board (12) with the antenna elements mounted on one surface, the printed board having a wiring pattern formed thereon for connecting an electronic component on the printed board to a terminal connected to an end of a cable. A high-frequency ground point is arranged in a portion close to a position at an equal distance from the antenna elements, in a region of the printed board where a relatively large current flows when electricity is supplied to one of the antenna elements and where the wiring pattern is not formed.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an antenna device provided with an antenna element mounted on a printed circuit board and a method for determining the setting position of a grounding point, and relates to a technique effective when applied to, for example, an antenna device for vehicle mounting.

Background Art

[0002] Since an antenna device mounted on a vehicle and 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. There is also a device in which a plurality of antenna elements are mounted on one substrate or in a housing. However, it is known that there is a problem that interference occurs when the distance between the antenna elements is short, and the transmission and reception sensitivity of the antenna decreases.

[0003] To prevent interference between a plurality of antenna elements, it is effective to increase the distance between the antenna elements, but it cannot be adopted for an antenna device that requires miniaturization such as an antenna device for vehicle mounting. In addition, in order to reduce interference with other antennas, there is an invention related to an in-vehicle integrated antenna that ensures isolation performance by giving each antenna directivities in opposite directions, namely, outside the vehicle and inside the vehicle (Patent Document 1). Patent Document 1 also describes that in an in-vehicle composite antenna, in order to improve isolation performance, the antenna for communication with the outside of the vehicle is offset by a predetermined distance in the forward or backward direction of the passenger compartment with respect to the center of the floor.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

[0005] When isolation performance is ensured by giving the antennas opposite directivity directions, as in the antenna device described in Patent Document 1, the transmission and reception sensitivity changes depending on the orientation of the antennas. Therefore, it is not appropriate to adopt this method except for limited applications such as improving the reception of radio waves from outside the vehicle, communication with the outside of the vehicle, and wireless communication inside the vehicle. Furthermore, for example, the dashboard of a car is densely packed with cables, tuners, and other components in addition to the antenna, so it is desirable for car-mounted antennas to be small, and increasing the distance between antennas would be counterproductive to miniaturization.

[0006] This invention was made in view of the above-mentioned problems, and its objective is to provide an antenna device and a method for determining the setting position of a ground point that can improve the isolation performance between antenna elements and improve the transmission and reception sensitivity, even when multiple antenna elements are mounted in close proximity on a substrate. Another object of the present invention is to provide an antenna device and a method for determining the setting position of a ground point that can be mounted in close proximity on a substrate without reducing the transmission and reception sensitivity, thereby enabling miniaturization of the housing. [Means for solving the problem]

[0007] To achieve the above objective, the present invention An antenna device comprising a plurality of antenna elements and a printed circuit board on which the plurality of antenna elements are mounted on one side, wherein a wiring pattern connecting an electronic component on the printed circuit board and a terminal to which the end of a cable is connected is formed on the printed circuit board, The aforementioned printed circuit board On the surface opposite to the aforementioned one surfaceThe configuration is such that a high-frequency grounding point is provided in a region where a relatively large current flows when power is supplied to any of the multiple antenna elements, and within a region where the wiring pattern is not formed, and at a location close to equidistant from the multiple antenna elements.

[0008] According to the antenna device having the above configuration, the current flowing through the circuit board and the antenna element on the side that is not powered can be concentrated near the ground point. This improves the isolation performance between multiple antenna elements and reduces the influence of other antenna elements, thereby improving the transmission and reception sensitivity. Furthermore, the improved isolation performance allows antenna elements to be placed closer together without physical contact, enabling a smaller enclosure for the antenna device. [Effects of the Invention]

[0009] According to the present invention, even when multiple antenna elements are mounted in close proximity on a substrate, the isolation performance between antenna elements can be improved, thereby enhancing the transmission and reception sensitivity. Furthermore, multiple antenna elements can be mounted in close proximity on a substrate without reducing the transmission and reception sensitivity, which has the effect of enabling miniaturization of the housing. [Brief explanation of the drawing]

[0010] [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] Figure 1 is a plan view of the antenna device, showing the area on the circuit board where the microstrip lines are provided. [Figure 4] (A) and (B) are current distribution diagrams showing the results of simulation verification of the current distribution flowing through the antenna element and the surface of the circuit board for antenna devices with a ground point on the circuit board and those without a ground point. [Figure 5] This graph shows the isolation characteristics in the telephone communication frequency band calculated for antenna devices with a grounding point on the circuit board and those without a grounding point. [Modes for carrying out the invention]

[0011] 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.

[0012] 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.

[0013] 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.

[0014] Furthermore, multiple (for example, two) engaging protrusions 11e are provided at the lower end of the leg portion 11d of the antenna elements 11A and 11B. These engaging protrusions 11e engage with slit-shaped engaging holes formed in predetermined parts of the circuit board 12, thereby connecting the antenna elements 11A and 11B to the circuit board 12. In addition, the two engaging protrusions 11e are connected to the circuit board 12 by soldering, and are electrically connected to a power supply stripline formed to electrically connect the engaging protrusion located on the side of the board to the terminals of the connector, thereby serving as a power supply point for the antenna elements 11A and 11B.

[0015] The circuit board 12 described above is made of a printed circuit board having a wiring pattern made of a conductive layer, and although not shown, electronic components such as a distributor, amplifier, filter, and attenuator are mounted on it. A spring contact 14 made of a conductive leaf spring that forms a Z shape when viewed from the rear is fixed to the lower surface of the circuit board 12 near the position between the vertical portions 11b of the antenna elements 11A and 11B, so as to protrude downward. Specifically, the spring contact 14 has an upper horizontal piece, an inclined piece that protrudes diagonally downward from the end of the upper horizontal piece, and a lower horizontal piece that folds back horizontally 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.

[0016] Furthermore, a connector 15 is provided on the lower edge of the circuit board 12 on the side where the antenna elements are coupled, into which the end of a coaxial cable (hereinafter referred to as "cable") connected to a device called a head unit, which has a tuner or the like, is inserted from below and connected. The connector 15 has a plurality of locking pieces 15a that protrude upward on both sides of its upper surface and have claws at their tips. These locking pieces 15a are inserted into engagement holes formed in predetermined parts of the circuit board 12, thereby coupling the connector 15 to the circuit board 12. The circuit board 12 has a linear wiring pattern (stripline) formed therein that connects the terminals to which the cable conductors of the connector 15 are connected to the feed points of the antenna elements 11A and 11B (Pa and Pb in Figure 5).

[0017] Furthermore, on the circuit board 12, a conductive layer is formed over most of the region including the set position of the spring contact 14, excluding the wiring pattern (stripline) that electrically connects between the above-mentioned electronic components and between the electronic component and the connector. The spring contact 14 is connected to the circuit board 12 in a state of being electrically connected to this conductive layer, and the height of the lower horizontal piece at the lower end of the inclined piece of the spring contact 14 is set so as to be coupled to the bracket 13 as shown in FIG. 4.

[0018] As described above, by connecting the spring contact 14 to 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 method of determining the set position of this spring contact 14 is the point of the present invention, which will be described in detail later.

[0019] On the other hand, an opening 13a is formed in a portion 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. 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 piece of the pedestal portion 13b and the circuit board 12.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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 three 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.

[0025] The key feature of this invention is that, on a circuit board on which antenna elements are mounted, the position of the grounding point is set to a region where a relatively large amount of current flows in the current distribution on the circuit board when power is being supplied to one of the antenna elements, where there are no microstrip lines and the distance from the two antenna elements is relatively equal, thereby concentrating the current at that location.

[0026] The following explains why the antenna device 10 of this embodiment is designed to improve the isolation performance between antenna elements and thus enhance transmission and reception sensitivity. Prior to the present invention, the inventors verified the distribution of current flowing on the surface of the circuit board 12 by simulation for an antenna device having the configuration shown in Figure 1 (with spring contacts) and a similar configuration but without spring contacts 14 (without spring contacts).

[0027] The verification results are shown in Figures 4(A) and 4(B). Figure 4(A) shows the current distribution for an antenna device without a ground point, and Figure 4(B) shows the current distribution for an antenna device with a ground point. In both cases, power is supplied only to antenna element 11A. The left and right L-shaped patterns represent antenna elements, and the power supply point to antenna element 11A is indicated by the symbol Pa. In Figure 4, 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] Focusing on the radio wave distribution in Figure 4(A), the antenna element 11B on the side that is not being fed is light-colored, indicating that a relatively large amount of current is flowing through antenna element 11B. This suggests that the antenna elements are interfering with each other and are not isolated. Furthermore, the central part of the circuit board 12, that is, the area closer to the center between the two antenna elements 11A and 11B, is also light-colored, indicating that a large amount of current is flowing through it.

[0029] Therefore, the inventors verified the current distribution by simulation when a grounding point was provided in a region near the center between antenna elements 11A and 11B, where a relatively large amount of current flows in the current distribution on the circuit board 12, in a region where there is no microstrip line and the distance from the two antenna elements is relatively the same. The results are shown in Figure 4(B).

[0030] In Figures 3 and 4(B), the location marked with the symbol G indicates the position where the grounding point is provided. The reason why the position G of the grounding point is shifted towards antenna element 11A rather than being in the center between antenna elements 11A and 11B is that, as shown in Figure 3, there is a region E in the center between antenna elements 11A and 11B where a microstrip line is provided to connect the elements (electronic components) that make up the circuit and the terminals of the connector 15. From Figure 4(B), it can be seen that the current is concentrated around the position G of the grounding point, and almost no current flows through antenna element 11B, meaning there is no interference between antenna elements 11A and 11B, and the isolation performance is improved.

[0031] Next, we calculated the isolation characteristics in the telephone communication frequency band for an antenna device with grounding points at the locations described above. Figure 5 shows the results. In Figure 5, the solid line A represents the isolation level with a ground contact point, and the dashed line B represents the isolation level without a ground contact point. Figure 5 shows that in the low frequency range (699-960MHz), the isolation level without a ground point is -10dB to -15dB, while the isolation level with a ground point is -20dB to -35dB, indicating a significant improvement in isolation characteristics.

[0032] As can be seen from Figure 5, in the high-frequency range, there is not much difference between the isolation level with and without a ground point, indicating that the above measures do not significantly improve isolation performance in the high-frequency range. Therefore, other measures are necessary to improve isolation performance in the high-frequency range. However, since the isolation level is -15dB or less in both cases (with and without a ground point), depending on the user's specifications, it may be possible to suffice with only the above measures without any additional measures.

[0033] In the antenna device of this embodiment, by providing a grounding point at the location described above, the current flowing to the circuit board and the antenna element on the unpowered side can be concentrated near the grounding point. This improves isolation performance and reduces the influence of the other antenna element, thereby improving transmission and reception sensitivity. Furthermore, because the isolation performance is improved, the antenna elements can be brought closer together to a point where they do not physically touch, which has the advantage of enabling miniaturization of the housing that houses the antenna device.

[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 it is sufficient if they are connected at high frequency by, for example, opposing electrodes or a structure in which metal layers face each other and behave like a capacitor, and physical contact is not required. Furthermore, the shape of the antenna element is not limited to that shown in Figure 1, and the antenna device can be applied to antenna devices that mount antenna elements of other shapes on a circuit board.

[0035] Furthermore, as in the embodiment described above, if the position G of the grounding point is set to a position that is off-center from the position equidistant from the antenna elements 11A and 11B, for reasons such as the provision of a microstrip line, a grounding point may also be provided at a symmetrical position to position G across the center line of the circuit board 12. If the isolation performance does not improve significantly even if two grounding points are provided, the decision of whether to provide two grounding points or one should be made from a cost-benefit perspective. [Explanation of Symbols]

[0036] 10…Antenna device, 11A,11B…Antenna element, 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, G…Grounding point setting position

Claims

1. An antenna device comprising a plurality of antenna elements and a printed circuit board on which the plurality of antenna elements are mounted on one side, wherein a wiring pattern connecting an electronic component on the printed circuit board and a terminal to which the end of a cable is connected is formed on the printed circuit board, An antenna device characterized in that a high-frequency grounding point is provided at a location close to equidistant from the plurality of antenna elements, in a region on the side of the printed circuit board opposite to the one side, in a region where a relatively large amount of current flows when power is supplied to any of the plurality of antenna elements, and in a region where the wiring pattern is not formed.

2. The antenna device according to claim 1, wherein 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 wiring pattern of the printed circuit board, and the ground point is electrically connected to the conductive layer pattern.

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 2, characterized in that one end of a spring contact made of a conductive leaf spring is connected to the position of 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 portion of the ground board facing the grounding point.

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. A method for determining the setting position of a high-frequency grounding point on a printed circuit board in an antenna device comprising a plurality of antenna elements and a printed circuit board on which the plurality of antenna elements are mounted on one side, The process involves obtaining the current distribution of the antenna device when power is supplied to any of the multiple antenna elements through simulation, A step of extracting a region on the side of the printed circuit board opposite to the one side, where a relatively large amount of current flows, based on the current distribution, A step of determining whether or not there is a portion in the extracted region where a wiring pattern is formed that connects an electronic component on the printed circuit board to a terminal to which the end of the cable is connected, If there is a portion in the extracted region where the wiring pattern is formed, the step of determining a location within the region excluding the portion, that is close to a position equidistant from the plurality of antenna elements, as the setting position for the high-frequency grounding point, A method for determining the setting position of a ground contact point, characterized by including [a specific feature].

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