Antenna device

Abstract

This invention relates to an antenna device. The antenna device comprises a rectangular ground plane (10) and an antenna element (2). The short side of the ground plane (10) is set to be shorter than half the wavelength (λ) of the radio wave to be transmitted or received. The antenna element (2) is positioned near one end of the ground plane (10) along its long side. In the ground plane (10), a connection point (11) at an odd multiple of λ / 4 from the far end of the antenna is connected to a grounding cable (51), which is the end of the ground plane (10) that is farthest from the antenna element (2) along its long side.

Description

[0001] Cross-reference to related applications

[0002] This application is based on Japanese Patent Application No. 2020-110670 filed on June 26, 2020, and the contents of the base application are incorporated herein by reference in their entirety. Technical Field

[0003] This disclosure relates to an antenna device used for cable connection to an external device. Background Technology

[0004] As antenna devices, various antenna devices such as monopole antennas and patch antennas have been proposed and developed (e.g., Patent Document 1). These antenna devices have a conductor plate, i.e., a ground plane, that provides ground potential, separate from the radiating element.

[0005] In these antenna devices, if the area of ​​the ground plane is insufficient relative to the wavelength of the radio wave being transmitted or received, the current leaking from the ground plane into the cable (hereinafter referred to as leakage current) may increase, resulting in a decrease in gain or instability in directivity.

[0006] As a technology related to such a subject, Patent Document 1 discloses a method that suppresses leakage current to a cable by filtering high-frequency current using a circuit element that functions as a low-pass filter, i.e., a filter element.

[0007] Patent Document 1: Japanese Patent Application Publication No. 2005-27134

[0008] In the structure disclosed in Patent Document 1, since a filter element is required, there is a problem of increased cost corresponding to the filter element. Summary of the Invention

[0009] This disclosure is made in light of this situation, and its purpose is to provide an antenna device that can suppress leakage current to the cable while suppressing the increase in cost.

[0010] The antenna device for achieving this purpose includes a rectangular flat conductor component, i.e., a ground plane, and a conductor component, i.e., an antenna element, which is provided with a power supply point electrically connected to a power supply line. The length of the ground plane in a predetermined direction is set to be shorter than the wavelength of the radio wave to be transmitted or received, i.e., the target wavelength. In the ground plane, a grounding cable is connected at a position at a distance from the edge of the ground plane that is an odd multiple of 1 / 4 of the target wavelength.

[0011] Developers, through simulations and other verifications, reduced the ground plane area of ​​antenna devices, gaining the insight that positions at odd multiples of 1 / 4 of the target wavelength from the edge of the ground plane act as nodes in the potential distribution. A node is the position of minimum potential. The structure described above is based on this insight. By connecting a grounding cable at an odd multiple of 1 / 4 of the target wavelength from the edge of the ground plane, leakage current is suppressed because it is difficult to generate a potential difference between the grounding cable and the ground plane. Furthermore, according to this structure, filter elements for suppressing leakage current to the cable are unnecessary. In other words, leakage current to the cable can be suppressed while minimizing increased costs.

[0012] Furthermore, the reference numerals in parentheses in the claims indicate the correspondence between specific units described in the embodiments described later as an example, and do not limit the technical scope of this disclosure. Attached Figure Description

[0013] Figure 1 This is a perspective view of the antenna device 1.

[0014] Figure 2 It is a general expression Figure 1 A cross-sectional view at line II-II shown.

[0015] Figure 3 This is a top view of antenna device 1.

[0016] Figure 4 This is a diagram showing the potential distribution on the ground plane 10.

[0017] Figure 5 This is a diagram showing the simulation results of the directionality when a cable connection point 11 is set at a distance of λ / 2 from the edge of the ground plane 10.

[0018] Figure 6 This is a diagram showing the simulation results of the directionality when a cable connection point 11 is set at a distance of λ / 4 from the edge of the ground plane 10.

[0019] Figure 7 This is a diagram showing an example of antenna device 1 being mounted on a vehicle.

[0020] Figure 8 This is a diagram showing an example of the connection posture between the grounding cable 51 and the grounding plate 10.

[0021] Figure 9 This is a diagram showing an example of the connection posture between the grounding cable 51 and the grounding plate 10.

[0022] Figure 10This is a diagram showing an example of the structure of the grounding plate 10.

[0023] Figure 11 This is a diagram showing a modified example of the position of antenna element 2 relative to ground plane 10.

[0024] Figure 12 This is a diagram showing a modified example of the position of antenna element 2 relative to ground plane 10.

[0025] Figure 13 This is a diagram showing a modified example of the position of antenna element 2 relative to ground plane 10.

[0026] Figure 14 This is a diagram showing a structural example of the antenna device 1 with a housing 60. Detailed Implementation

[0027] Hereinafter, embodiments of the present disclosure will be described using figures. Furthermore, components having the same function will henceforth be referred to by the same reference numerals, and their descriptions will be omitted. Additionally, where only a portion of the structure is mentioned, the structure of the previously described embodiments can be applied to other parts.

[0028] Figure 1 This is a perspective view showing an example of the general structure of the antenna device 1 according to this embodiment. Figure 2 yes Figure 1 The image shows a cross-sectional view of the antenna device 1 at line II-II. The antenna device 1 is used, for example, mounted on a moving body such as a vehicle.

[0029] The antenna device 1 is configured to transmit and receive radio waves at a specified target frequency. Of course, as another method, the antenna device 1 can also be used only for either transmission or reception. Since the transmission and reception of radio waves are reversible, a structure capable of transmitting radio waves of a certain frequency is also capable of receiving radio waves of that frequency.

[0030] Here, as an example, the target frequency is set to 2.45 GHz. Of course, the target frequency can be designed appropriately; other methods include setting it to 300 MHz, 760 MHz, 850 MHz, 900 MHz, 1.17 GHz, 1.28 GHz, 1.55 GHz, 5.9 GHz, etc. The antenna device 1 can transmit and receive not only the target frequency but also radio waves within a specified range based on the target frequency. For example, the antenna device 1 can be configured to transmit and receive frequencies belonging to the 2400 MHz to 2500 MHz band, i.e., the 2.4 GHz band.

[0031] In other words, antenna device 1 is configured to transmit and receive radio waves in the frequency bands used by short-range wireless communications such as Bluetooth Low Energy (Bluetooth is a registered trademark), Wi-Fi (a registered trademark), and ZigBee (a registered trademark). In other words, antenna device 1 is configured to transmit and receive radio waves in the frequency bands (so-called ISM bands) allocated by the International Telecommunication Union for general use in industrial, scientific, and medical fields.

[0032] The "λ" that follows indicates the wavelength of the object. The wavelength of the object refers to the wavelength of the radio wave at the object's frequency. For example, "λ / 2" and "0.5λ" refer to half the length of the object's wavelength, while "λ / 4" and "0.25λ" refer to one-quarter the length of the object's wavelength. Furthermore, the wavelength (i.e., λ) of 2.4 GHz radio waves in a vacuum and in air is 125 mm.

[0033] Antenna device 1 is connected, for example, to a communication ECU (Electronic Control Unit) mounted in the vehicle via a cable. Signals received by antenna device 1 are sequentially output to the communication ECU. Additionally, antenna device 1 converts electrical signals input from the communication ECU into radio waves and radiates them into space. The communication ECU utilizes the signals received by antenna device 1 and supplies it with high-frequency power corresponding to the transmitted signals.

[0034] As an example, this explanation assumes that antenna device 1 is connected to the communication ECU via an AV cable. The AV cable is an automotive low-voltage wire, typically made by covering soft copper stranded wire with an insulating material such as vinyl chloride. In AV cable, "A" stands for automotive low-voltage wire, and "V" stands for vinyl resin. The AV cable connected to antenna device 1 can be either a grounding cable (providing ground potential) or a signal cable (for signal transmission). Furthermore, the connecting cable between antenna device 1 and the communication ECU can also be automotive thin-walled low-voltage wire (AVSS cable) or automotive compressed conductor ultra-thin-walled vinyl chloride insulated low-voltage wire (CIVUS cable). In AVSS, "SS" stands for ultra-thin-wall type. In CIVUS, "C" stands for compressed conductor type, "I" stands for ISO standard, "V" stands for vinyl resin, and "US" stands for ultra-thin-wall type. Additionally, other communication cables such as coaxial cables or feeder cables can also be used to connect antenna device 1 and the communication ECU. Impedance matching circuits can also be installed at the connection point between antenna device 1 and the cable.

[0035] The specific structure of antenna device 1 will be described below. Figure 1As shown, the antenna device 1 includes a ground plane 10, a support plate 20, a counter conductor plate 30, and a short-circuit section 40. For ease of explanation, the side of the ground plane 10 where the counter conductor plate 30 is disposed will be described below as the upper side of the antenna device 1. In other words, the direction from the ground plane 10 toward the counter conductor plate 30 corresponds to the upper direction of the antenna device 1. Furthermore, the direction from the counter conductor plate 30 toward the ground plane 10 corresponds to the lower direction of the antenna device 1.

[0036] The ground plane 10 is a plate-shaped conductor component made of a conductor such as copper. The ground plane 10 is disposed along the lower side of the support plate 20. The plate shape here can also include a thin film such as metal foil. In other words, the ground plane 10 can also be a plate with a pattern formed on the surface of a resin board such as a printed wiring board by electroplating or the like. Alternatively, the ground plane 10 can be implemented using a conductor layer disposed inside a multilayer substrate containing multiple conductor layers and an insulating layer. This ground plane 10 is electrically connected to the grounding cable 51, providing the ground potential (in other words, the grounding potential) in the antenna device 1. The ground plane 10 is equivalent to a conductor plate directly or indirectly connected to the grounding cable 51. The grounding cable 51 can also be referred to as a grounding wire. The grounding cable 51 can also be the outer conductor of a coaxial cable. The location of the connection point between the ground plane 10 and the grounding cable 51, i.e., the cable connection point 11, will be described below.

[0037] Ground plane 10 is formed in a rectangular shape. The length of the short side of ground plane 10 is, for example, electrically equivalent to 0.4λ. The length of the long side of ground plane 10 is electrically set to 1.2λ. Here, "electrical length" refers to the effective length taking into account edge electric fields, wavelength shortening effects based on the dielectric, etc. This structure is equivalent to a rectangular ground plane 10 whose short side length is shorter than the target wavelength and whose long side length is set to be more than twice the length of the short side. Furthermore, the length of the short side of ground plane 10 can also be 0.6λ, 0.8λ, etc. The short side of ground plane 10 only needs to be longer than λ / 4. The length of the long side of ground plane 10 only needs to be longer than the short side, and can also be 1.0λ, 1.5λ, etc. The ratio of the short side to the long side length of ground plane 10 can be approximately set to 1:2, 1:3, 1:4, 2:3, 2:5, etc. Furthermore, when the support plate 20 is formed using a dielectric with a relative permittivity of 4.3, the wavelength of the ground plane 10 surface is theoretically around 60 mm due to the wavelength shortening effect of the dielectric material serving as the support plate 20. Therefore, the electrically equivalent length of 1.2λ becomes 72 mm.

[0038] Figure 1In the various diagrams shown, the X-axis represents the direction of the long side of the ground plane 10, the Y-axis represents the direction of the short side of the ground plane 10, and the Z-axis represents the vertical direction. The Y-axis direction corresponds to a defined direction. This three-dimensional coordinate system with X, Y, and Z axes is a concept used to illustrate the structure of the antenna device 1. Furthermore, as another method, when the ground plane 10 is square, the direction along any side can be set as the X-axis.

[0039] Furthermore, the ground plane 10 only needs to be at least larger than the opposing conductor plate 30. The dimensions of the ground plane 10 can be appropriately varied. The length of one side of the ground plane 10 can also be set to a value that is electrically smaller than a wavelength, such as 1 / 3 of the target wavelength. In addition, the shape of the ground plane 10, i.e., its planar shape, viewed from above, can be appropriately varied. Here, as an example, the planar shape of the ground plane 10 is set to be rectangular, but in other cases, the planar shape of the ground plane 10 can also be square. Alternatively, it can be other polygons. For example, the ground plane 10 can also be a square with one side set to be electrically equivalent to a wavelength. Rectangles include both rectangles and squares.

[0040] The support plate 20 is a plate-shaped component used to arrange the ground plane 10 and the opposing conductor plate 30 opposite each other at a predetermined interval. The support plate 20 is a rectangular flat plate, and when viewed from above, its size is approximately the same as that of the ground plane 10. The support plate 20 is implemented, for example, using a dielectric material with a specified relative permittivity, such as glass epoxy resin. As an example, the support plate 20 is implemented using a glass epoxy resin of FR4 (Flame Retardant Type 4) with a relative permittivity of 4.3.

[0041] In this embodiment, as an example, the thickness H1 of the support plate 20 is, for example, 1.5 mm. The thickness H1 of the support plate 20 corresponds to the spacing between the ground plane 10 and the opposing conductor plate 30. By adjusting the thickness H1 of the support plate 20, the spacing between the opposing conductor plate 30 and the ground plane 10 can be adjusted. The specific value of the thickness H1 of the support plate 20 can be appropriately determined through simulation or experimentation. Of course, the thickness H1 of the support plate 20 can also be 2.0 mm, or 3.0 mm, etc. Furthermore, the wavelength of the support plate 20 is approximately 60 mm due to the wavelength shortening effect of the dielectric. Therefore, a thickness of 1.5 mm is electrically equivalent to 1 / 40 of the target wavelength (i.e., λ / 40).

[0042] Furthermore, the support plate 20 only needs to achieve the above-described functions, and its shape can be appropriately modified. The structure used to arrange the opposing conductor plate 30 and the ground plane 10 opposite each other can also be multiple columns. Although this embodiment uses a structure where the ground plane 10 and the opposing conductor plate 30 are filled with resin as the support plate 20, it is not limited to this. The ground plane 10 and the opposing conductor plate 30 can also be hollow or vacuum-sealed. A honeycomb structure or the like can also be used as the support plate 20. Furthermore, the structures illustrated above can also be combined. When using a printed wiring board to implement the antenna device 1, the multiple conductor layers of the printed wiring board can be used as the ground plane 10 and the opposing conductor plate 30, and the resin layer separating the conductor layers can be used as the support plate 20.

[0043] The thickness H1 of the support plate 20, as described later, also functions as a parameter for adjusting the length of the short-circuit section 40. In other words, the thickness H1 of the support plate 20 functions as a parameter for adjusting the inductance provided by the short-circuit section 40. In addition, the thickness H1 also functions as a parameter for adjusting the electrostatic capacitance formed by the ground plane 10 and the opposing conductor plate 30.

[0044] Alternatively, a transceiver circuit 70 can be formed on one side of the opposing conductor plate 30, i.e., the upper side 20a of the support plate, within the support plate 20. The transceiver circuit 70 is a circuit module that performs at least one of modulation, demodulation, frequency conversion, amplification, digital-to-analog conversion, and detection. The transceiver circuit 70 is an electrical assembly of various components such as ICs, analog circuit elements, and connectors. The transceiver circuit 70 is electrically connected to the opposing conductor plate 30 via a microstrip line, which serves as a power supply line 71. Furthermore, the transceiver circuit 70 is also connected to the ground plane 10 via vias or shorting pins. The transceiver circuit 70 is also electrically connected to an AV line, which serves as a signal cable. In other words, the transceiver circuit 70 is connected to the communication ECU via a signal cable. Moreover, the connection position of the signal cable in the antenna device 1 can be arbitrary.

[0045] The opposing conductor plate 30 is a plate-shaped conductor component made of a conductor such as copper. As described above, the plate shape here also includes a thin film such as copper foil. The opposing conductor plate 30 is configured to be opposed to the ground plane 10 via the support plate 20. The opposing conductor plate 30 may also be a plate with a pattern formed on the surface of a resin board such as a printed wiring board, similar to the ground plane 10. In addition, "parallel" here is not limited to a completely parallel state. It may also be tilted from a few degrees to about 30 degrees. In other words, it can include a roughly parallel state (the so-called approximately parallel state). The expression "perpendicular" in this disclosure is also not limited to a completely perpendicular state, but also includes a tilted state from a few degrees to about 30 degrees.

[0046] By arranging the opposing conductor plate 30 and the ground plane 10 opposite each other, an electrostatic capacitance corresponding to the area of ​​the opposing conductor plate 30 and the spacing between the opposing conductor plate 30 and the ground plane 10 is formed. The opposing conductor plate 30 is configured to form an electrostatic capacitance that resonates in parallel with the inductor of the short-circuit section 40 at the target frequency. The area of ​​the opposing conductor plate 30 only needs to be appropriately designed to provide the desired electrostatic capacitance. The desired electrostatic capacitance refers to an electrostatic capacitance that operates at the target frequency through cooperation with the inductor of the short-circuit section 40. Furthermore, if the operating frequency is set as f, the inductance of the short-circuit section 40 is set as L, and the electrostatic capacitance formed between the opposing conductor plate 30 and the ground plane 10 is set as C, then the relationship f = 1 / {2π√(LC)} holds. Those skilled in the art can determine the appropriate area of ​​the opposing conductor plate 30 based on this relationship.

[0047] For example, the opposing conductor plate 30 is formed as a square with one side electrically 12 mm. Due to the wavelength shortening effect of the support plate 20, the wavelength of the surface of the opposing conductor plate 30 becomes approximately 60 mm, so the value of 12 mm is electrically equivalent to 0.2λ. Of course, the length of one side of the opposing conductor plate 30 can be appropriately changed, and can be 14 mm, 15 mm, 20 mm, 25 mm, etc. Furthermore, the planar shape of the opposing conductor plate 30 can also be circular, regular octagonal, regular hexagonal, etc. Additionally, the opposing conductor plate 30 can also be rectangular, elongated elliptical, etc.

[0048] A power supply point 31 is formed on the opposing conductor plate 30. The power supply point 31 is the part that electrically connects the circuit 71 to the opposing conductor plate 30. In this structure, the power supply point 31 can be configured in any position, as long as it is positioned to achieve impedance matching with the power supply circuit 71. In other words, the power supply point 31 only needs to be positioned where the return loss is within the specified allowable level. For example, the power supply point 31 can be configured in any position, such as the edge or central region of the opposing conductor plate 30. Here, as an example, the power supply point 31 is formed on a straight line passing through the center of the opposing conductor plate 30 and parallel to the X-axis.

[0049] Furthermore, various methods can be used to supply power to the opposing conductor plate 30, including direct connection and electromagnetic coupling. Direct connection refers to directly connecting the power supply line 71 to the opposing conductor plate 30. Electromagnetic coupling refers to a power supply method that utilizes microstrip lines or similar devices for power supply to electromagnetically couple with the opposing conductor plate 30.

[0050] The short-circuit section 40 is a conductive component that electrically connects the ground plane 10 to the opposing conductor plate 30. The short-circuit section 40 can be implemented using a conductive pin, i.e., a short-circuit pin. By adjusting the diameter and length of the short-circuit pin, the inductance of the short-circuit section 40 can be adjusted.

[0051] Furthermore, the short-circuit section 40 can be any linear component that is electrically connected at one end to the ground plane 10 and at the other end to the opposing conductor plate 30. When using a printed wiring board as the substrate to implement the antenna device 1, the short-circuit section 40 can be used as a via provided in the printed wiring board.

[0052] The short-circuit section 40 is, for example, located at the center of the conductor plate. Here, the center of the conductor plate refers to the center of the opposing conductor plate 30. The center of the conductor plate corresponds to the centroid of the opposing conductor plate 30. In this embodiment, since the opposing conductor plate 30 is square, the center of the conductor plate corresponds to the intersection of the two diagonals of the opposing conductor plate 30. Furthermore, the concentric arrangement of the ground plane 10 and the opposing conductor plate 30 corresponds to a configuration where the center of the opposing conductor plate 30 overlaps with the center of the ground plane 10 when viewed from above.

[0053] Furthermore, the location of the short-circuit portion 40 does not need to be strictly aligned with the center of the conductor plate. The short-circuit portion 40 can also be offset from the center of the conductor plate by approximately a few millimeters. The short-circuit portion 40 only needs to be formed in the central region of the opposing conductor plate 30. The central region of the opposing conductor plate 30 refers to the area further inward than the line connecting the points that divide the conductor plate from its center to its edge in a 1:5 ratio. According to other viewpoints, the central region corresponds to the area where concentric patterns of the opposing conductor plate 30 are similarly reduced to approximately 1 / 6 of their original size and overlap.

[0054] <Position of the opposing conductor plate 30 relative to the ground plane 10>

[0055] like Figure 3 As shown, the opposing conductor plate 30 is positioned opposite the ground plane 10 with one set of opposite sides parallel to the X-axis and the other set of opposite sides parallel to the Y-axis. For example, the opposing conductor plate 30 is positioned at a position where its center is offset from the center of the ground plane 10 in the negative X-axis direction by a predetermined offset amount ΔX. The offset amount ΔX can be set to, for example, 0.125λ, 0.25λ, 0.5λ, etc. The opposing conductor plate 30 can also be positioned at the end of the ground plane 10 in the negative X-axis direction. The offset amount ΔX can be appropriately varied within a range where the opposing conductor plate 30 does not protrude beyond the outside of the ground plane 10 when viewed from above. The opposing conductor plate 30 is positioned opposite the ground plane 10 at least over its entire area (in other words, its entire surface). The offset amount ΔX corresponds to the offset between the center of the ground plane 10 and the center of the opposing conductor plate 30.

[0056] In addition, Figure 3 To clearly show the positional relationship between the ground plane 10 and the opposing conductor plate 30, the support plate 20 and the transceiver circuit 70 are shown through. In other words, the diagram is omitted. Figure 3The dashed line Lx1 represents a straight line passing through the center of ground plane 10 and parallel to the X-axis, and the dashed line Ly1 represents a straight line passing through the center of ground plane 10 and parallel to the Y-axis. The double-dash line Ly2 represents a straight line passing through the center of the opposing conductor plate 30 and parallel to the Y-axis. According to other viewpoints, line Lx1 corresponds to the axis of symmetry with respect to ground plane 10 and opposing conductor plate 30. Line Ly1 corresponds to the axis of symmetry with respect to ground plane 10. Line Ly2 corresponds to the axis of symmetry with respect to opposing conductor plate 30. The dashed line Lx1 also passes through the center of opposing conductor plate 30. In other words, the dashed line Lx1 corresponds to a straight line parallel to the X-axis and passing through the centers of ground plane 10 and opposing conductor plate 30. The intersection of lines Lx1 and Ly1 corresponds to the center of the ground plane, and the intersection of lines Lx1 and Ly2 corresponds to the center of the conductor plate.

[0057] <Operating Principle of Antenna Device 1>

[0058] The operation of the antenna device 1 will be explained here. The antenna device 1 is short-circuited with the ground plane 10 through the short-circuit portion 40 provided in the central region of the opposing conductor plate 30, and the area of ​​the opposing conductor plate 30 is the area of ​​the electrostatic capacitor that forms a parallel resonance with the inductance of the short-circuit portion 40 at the target frequency.

[0059] Therefore, if a high-frequency signal is input from the transceiver circuit 70, an LC parallel resonance is generated through energy exchange between the inductor and the capacitor, producing an electric field perpendicular to both the ground plane 10 and the opposing conductor plate 30. This perpendicular electric field propagates from the short-circuit portion 40 toward the edge of the opposing conductor plate 30. At the edge of the opposing conductor plate 30, the perpendicular electric field becomes a linearly polarized wave with a polarization plane perpendicular to the ground plane 10, i.e., a ground plane vertically polarized wave, and propagates in space. In other words, the structure including the short-circuit portion 40 and the opposing conductor plate 30 functions as a radiating element, or in other words, as an antenna element 2. Furthermore, the ground plane vertically polarized wave here refers to an electric wave whose vibration direction is perpendicular to the ground plane 10 and the opposing conductor plate 30.

[0060] Furthermore, the antenna device 1 is directional in the horizontal direction at the target frequency. Therefore, when the ground plane 10 is configured to be horizontal, the antenna device 1 functions as an antenna with a main beam in the horizontal direction. Here, the horizontal direction of the antenna refers to the direction from the center of the opposing conductor plate 30 toward its edge. According to other views, the horizontal direction of the antenna refers to the direction orthogonal to the perpendicular line from the center of the opposing conductor plate 30 to the ground plane 10. In other words, the horizontal direction of the antenna is equivalent to the lateral direction (or sideways direction) for the antenna device 1.

[0061] Furthermore, the operation of antenna device 1 when transmitting (radiating) radio waves is reversible with its operation when receiving radio waves. That is, according to the above-described antenna device 1, it is possible to receive vertically polarized waves from the ground plane arriving from the horizontal direction of the antenna.

[0062] <Location of cable connection point 11 in ground plane 10>

[0063] In this disclosure, the connection point 11 between the grounding cable 51 and the grounding plate 10 is located at a distance α of λ / 4 from the end of the grounding plate 10 in the positive X-axis direction (the right end in the attached figure). Specifically, it is located at a distance λ / 4 from the far end 12 of the antenna on a straight line Lx1 passing through the center of the grounding plate 10 and parallel to the X-axis. The far end 12 of the antenna refers to the end where the opposing conductor plate 30, which serves as the antenna element 2, is not disposed. For ease of explanation, the portion of the grounding plate 10 at a distance λ / 4 from the far end 12 of the antenna will also be referred to as the λ / 4 location.

[0064] Alternatively, it can be positioned at a distance of three or five times λ / 4 from the end of the ground plane 10 in the positive X-axis direction. The cable connection point 11 only needs to be positioned at a distance α from the end of the ground plane 10 that is λ / 4 × N (N is an odd number). Furthermore, the cable connection point 11 only needs to be positioned at an odd multiple of λ / 4 from the far end 12 of the antenna; its position in the Y direction is not limited to the straight line Lx1. It can also be positioned from... Figure 3 The position shown is offset in the positive or negative direction of the Y-axis.

[0065] Preferably, the grounding cable 51 is routed from the cable connection point 11 in a position parallel to the Y-axis, or routed at a distance of λ / 20 or more from the grounding plate 10. With this structure, electrical or electromagnetic coupling between the grounding cable 51 and the grounding plate 10 outside the cable connection point 11 can be suppressed.

[0066] <Effects>

[0067] The simulation results confirm that the current flowing through the ground plane 10 via the LC parallel resonance mainly flows from the short-circuit portion 40 to the edge of the ground plane 10. Additionally, the current flowing from the opposing conductor plate 30 through the short-circuit portion 40 into the ground plane 10 flows from the short-circuit portion 40 to both sides along the long side of the ground plane 10. In other words, the current flowing through the ground plane 10 flows from the short-circuit portion 40 to the far end 12 of the antenna.

[0068] Here, since the current is zero at the far end 12 of the antenna, therefore... Figure 4As shown, the potential is highest at the far end 12 of the antenna and lowest at a position λ / 4 × N from the far end 12. At the point of lowest potential, the potential of the ground plane 10 does not change even if a conductor approaches. Therefore, at the point of lowest potential, no change in current occurs even if a conductor approaches. Therefore, by setting the cable connection point 11 at an odd multiple of λ / 4 from the far end 12 of the antenna, leakage current from the ground plane 10 to the grounding cable 51 can be suppressed.

[0069] Figure 5 as well as Figure 6 The results are derived from analyzing the changes in directivity caused by the presence or absence of the grounding cable 51 when the cable connection point 11 is located at a distance of λ / 2 from the far end 12 of the antenna and when it is located at a distance of λ / 4. Figure 5 This illustrates the case where the cable connection point 11 is positioned at a distance of λ / 2 from the distal end 12 of the antenna. Figure 6 This illustrates the case where the cable connection point 11 is positioned at a distance of λ / 4 from the far end 12 of the antenna. Figure 5 , Figure 6 The dashed lines represent the simulation results of directional orientation without the grounding cable 51, while the solid lines represent the simulation results of directional orientation with the grounding cable 51. In other words, Figure 5 as well as Figure 6 The gap between the dashed and solid lines in the diagram represents the degree to which the grounding cable 51 affects the directivity. If... Figure 5 as well as Figure 6 A comparison clearly shows that by setting the cable connection point 11 at a distance of λ / 4, the directional disturbance caused by the grounding cable 51 can be suppressed. Furthermore, the directional disturbance originates from the leakage current to the grounding cable 51. In other words, Figure 5 as well as Figure 6 This indirectly shows that by setting the position of the cable connection point 11 at a distance of λ / 4, leakage current to the grounding cable 51 can be suppressed.

[0070] As described above, according to the above structure, even when the size of the ground plane 10 is insufficient relative to the target wavelength, the leakage of current to the grounding cable 51 can be reduced. In structures where the length of the short side of the ground plane 10 is less than 0.75λ, the above-described cable connection method relative to the ground plane 10 works particularly well. Furthermore, a structure in which the ground plane 10 is rectangular with a long side and an antenna element 2 is disposed at one end of the long side is particularly preferred. This is because in a structure where the antenna element 2 is disposed at one end of the long side, current flows to the opposite end, i.e., the far end 12 of the antenna, making it easier to form antinodes and nodes in the voltage distribution.

[0071] The antenna device 1 described above achieves LC parallel resonance through antenna element 2, which includes opposing conductor plate 30 and short-circuit portion 40, enabling it to transmit and receive ground-ground vertically polarized waves in the horizontal direction of the antenna. Furthermore, as another structure capable of transmitting and receiving ground-ground vertically polarized waves, a monopole antenna can also be used as antenna element 2. However, in a structure where antenna element 2 is a monopole antenna, a height of λ / 4 is required. In contrast, the antenna device 1 described above can achieve a height (in other words, thickness) of approximately λ / 100. That is, according to the disclosed structure, the height of the antenna device 1 can be suppressed.

[0072] In addition, by positioning the cable connection point 11 at an odd multiple of λ / 4, leakage current to the grounding cable 51 can be suppressed without the need for circuit components such as low-pass filters. In other words, it is possible to achieve both cost reduction in manufacturing and stabilization of antenna characteristics.

[0073] <How to use antenna device 1>

[0074] For example, Figure 7 As shown, the antenna device 1 described above can be installed on the outer side of the vehicle's B-pillar 91, with the floor 10 facing the surface of the B-pillar 91 and the X-axis direction along the long side of the B-pillar 91 (i.e., the vehicle height direction). Alternatively, it can be installed in the same orientation on the part of the door panel that overlaps with the B-pillar 91.

[0075] Based on the above mounting posture, the upward direction of antenna device 1, i.e., the positive Z-axis direction, is approximately consistent with the vehicle width direction, and the horizontal direction of the antenna is along the side of the vehicle (in other words, parallel). With this mounting posture, a communication area can be formed along the side of the vehicle.

[0076] Furthermore, the mounting location and posture of the antenna device 1 are not limited to the examples described above. The antenna device 1 can be mounted at any location on the exterior of the vehicle, such as the outer surface of the A-pillar or C-pillar, the lower side beam (in other words, the door sill) 94, or the interior / near the exterior door handle 95. For example, the antenna device 1 can also be housed inside the exterior door handle 95 with the X-axis along the long side of the handle and the Y-axis along the vehicle height. Alternatively, the antenna device 1 can also be mounted on the roof 93 of the vehicle.

[0077] The embodiments of this disclosure have been described above, but this disclosure is not limited to the first embodiment described above. Various supplements and modifications described below are also included within the technical scope of this disclosure. Furthermore, in addition to the following, various modifications can be made without departing from the spirit of the text. For example, the various modifications described below can be appropriately combined and implemented without causing technical contradictions.

[0078] <Antenna Element 2>

[0079] In the above embodiments, the antenna device 1 is disclosed to have a structure including a counter conductor plate 30 and a short-circuit portion 40 as the antenna element 2. In other words, a structure using a zero-order resonant antenna as the antenna element 2 is disclosed, but it is not limited to this. The antenna element 2 can also be a monopole antenna or a patch antenna. The antenna element 2 can also be an inverted-F antenna or a loop antenna. Various antenna structures can be used as the antenna element 2 of the antenna device 1.

[0080] <Connection method of grounding cable 51 relative to grounding plate 10>

[0081] At cable connection point 11, grounding cable 51 can also be used as follows: Figure 8 The connector 52 is shown to be vertically connected to the grounding plate 10. This configuration reduces the possibility of external or electromagnetic coupling between the grounding cable 51 and the grounding plate 10 at the cable connection point 11.

[0082] In addition, as other methods, such as Figure 9 As shown, a slit 13 of width W can also be provided from the far end 12 of the antenna toward a location λ / 4, and a grounding cable 51 can be routed through the centerline of this slit 13. The grounding cable 51 is connected to the grounding plate 10 at the inner end of the slit 13. Here, "inner" refers to the direction from the far end 12 of the antenna toward the opposite end in the direction of the slit 13's extension configuration. Figure 8 In the connection structure shown, connector 52 is connected to ground plane 10 in a vertical position, so the overall height of antenna device 1 is increased to a corresponding height of connector 52. In contrast, according to... Figure 9 In the structure shown, the connector 52 is connected parallel to the ground plane 10, thus suppressing the height of the antenna device 1. In other words, it improves mounting capability in locations with less mounting space, such as the B-pillar 91. Furthermore, the width W only needs to be sufficient to prevent electromagnetic coupling between the grounding cable 51 passing through the center of the slit 13 and the ground plane 10; for example, the width W can be set to λ / 10 or more. According to this structure, the Y-axis spacing between the grounding cable 51 and the ground plane 10 is approximately λ / 20 or more, which suppresses electromagnetic coupling.

[0083] Alternatively, an insulating layer equivalent to the support plate 20 can be formed on the underside of the ground plane 10. That is, the ground plane 10 can also be implemented using an inner layer of a printed circuit board. In a structure where the ground plane 10 is implemented using an inner layer of a printed multilayer board, it is difficult to mount the connector 52 at the inner end of the slit 13. Therefore, as... Figure 10As shown, a conductive line, i.e., a lead-out line 14, can also be formed from the λ / 4 point 11a to the far end 12 of the antenna, passing through the center of the slit 13, and a grounding cable 51 can be connected to the end of the lead-out line 14. The lead-out line 14 is, for example, equivalent to patterned wiring. The lead-out line 14 can also be formed as a microstrip or stripline. With such a structure, a connector 52 can be arranged at the far end 12 of the antenna, and the actual connection point can also be set at the λ / 4 point. This structure is equivalent to a structure in which the grounding cable 51 is electrically connected to the grounding plate 10 via the lead-out line 14 by connecting the grounding cable 51 in series with the lead-out line 14. The lead-out line 14 only needs to be attached to the insulating layer of the support plate 20 formed on at least one of the upper and lower sides of the ground plate 10. When the antenna device 1 is constructed using a multilayer substrate containing multiple conductor layers and insulating layers, the communication cable can be electrically connected at any position of a conductor layer different from the conductor layer of the ground plate 10.

[0084] <Supplement to the shape and positional relationship of the ground plane 10 and the opposing conductor plate 30>

[0085] The ground plane 10 only needs to be approximately rectangular, and the corners can be rounded. Additionally, the edges of the ground plane 10 can be partially or entirely curved. A rectangle also includes shapes with minute irregularities on its edges. As long as the irregularities on the edges of the ground plane 10 and the slits formed at locations away from the edges of the ground plane 10 do not affect antenna operation, they can be ignored in defining the appearance of the ground plane 10. These minute irregularities are approximately in the range of millimeters.

[0086] A slit can also be provided in the opposing conductor plate 30, or the corners can be rounded. For example, a cutout as a degeneracy separation element can also be provided in the diagonal portion of a pair. The edges of the opposing conductor plate 30 can also be partially or entirely set into a curved shape. Unevennesses or depressions on the edges of the opposing conductor plate 30 that do not affect operation can be ignored.

[0087] Furthermore, the shape of the ground plane 10 and the arrangement of the opposing conductor plate 30 relative to the ground plane 10 are not limited to the structure disclosed in the embodiment. As for the arrangement of the opposing conductor plate 30 relative to the ground plane 10, the following can be adopted: Figures 11-13 The example illustrates various configuration methods. For example, such as... Figure 11 As shown, the opposing conductor plate 30 can also be configured such that the end of the negative X-axis direction coincides with the end of the negative X-axis direction of the ground plane 10. Figures 11-13 In order to clearly show the positional relationship between the ground plane 10 and the opposing conductor plate 30, the diagrams of the support plate 20 and the transceiver circuit 70 are omitted. The dimensions of each diagram are for illustrative purposes and can be changed as appropriate.

[0088] also, Figure 12 The Lx2 shown represents a straight line passing through the center of the opposing conductor plate 30 and parallel to the X-axis. Additionally, Figure 12 ΔX represents the offset of the opposing conductor plate 30 relative to the ground plane 10 in the X-axis direction, and ΔY represents the offset in the Y-axis direction. ΔX and ΔY can be the same value or different values. Figure 12 The disclosed structure is equivalent to configuring the opposing conductor plate 30 to be offset by a predetermined amount in the X-axis and Y-axis directions from a position concentric with the ground plane 10.

[0089] Furthermore, the end of the ground plane 10, which serves as the reference for setting the cable connection point 11, is not limited to the end in the long side direction. For example... Figure 13 The position shown can also be set at an odd multiple of λ / 4 away from the end of the short-circuit section 40, which is relatively far away from the end in the short-side direction.

[0090] <Supplement to the overall structure of antenna device 1>

[0091] like Figure 14 As shown, the antenna device 1 may also include a housing 60 that houses the support plate 20 forming the opposing conductor plate 30 and the short-circuit portion 40. Furthermore, Figure 14 This is a conceptual diagram illustrating the internal structure of the housing 60. To ensure visual clarity, shading lines indicating material types are omitted. For example, the housing 60 is constructed by combining an upper housing and a lower housing that can be separated in the upward and downward directions. For example, polycarbonate (PC) resin is used to construct the housing 60. Furthermore, various resins can be used as materials for the housing 60, such as synthetic resins that are PC resin mixed with acrylonitrile-butadiene-styrene copolymer (ABS), and polypropylene (PP). The housing 60 includes a housing bottom 61, sidewall portions 62, and a housing top plate portion 63. The housing bottom 61 provides the bottom of the housing 60. The housing bottom 61 is formed into a flat plate shape. Inside the housing 60, a circuit board including a ground plane 10, an opposing conductor plate 30, and a transceiver circuit 70 is arranged such that the ground plane 10 is opposite to the housing bottom 61.

[0092] The side wall portion 62 is a structure that provides the side surface of the housing 60, and is erected vertically upward from the edge of the bottom 61 of the housing. The height of the side wall portion 62 is designed, for example, such that the separation between the inner surface of the top plate portion 63 of the housing and the opposing conductor plate 30 is less than λ / 25. The top plate portion 63 of the housing is a structure that provides the upper part of the housing 60. In this embodiment, the top plate portion 63 of the housing is formed into a flat plate shape. In addition, the top plate portion 63 of the housing can also adopt various shapes such as a dome shape. The top plate portion 63 of the housing is configured such that its inner surface faces the upper surface 20a of the support plate. A hole, i.e., a cable lead-out portion 64, is provided in the side wall portion 62 for leading out the grounding cable 51, etc. According to the structure of providing the cable lead-out portion 64 in the side wall portion 62, the mounting capability to the B-pillar 91, etc. can be improved.

[0093] When the top plate portion 63 of the housing is located near the opposing conductor plate 30, as described above, it is possible to suppress the vertical electric field radiated through the LC resonant mode from the edge of the opposing conductor plate 30 to the upper side, thereby improving the radiation gain in the horizontal direction of the antenna. Here, "near the opposing conductor plate 30" refers, for example, to a region where the distance from the opposing conductor plate 30 is electrically less than 1 / 25 of the target wavelength.

[0094] In addition, such as Figure 14 As shown, an upper rib 631 that abuts against the edge of the opposing conductor plate 30 may also be formed on the top plate portion 63 of the housing. The upper rib 631 is a convex structure formed on the inner side of the top plate portion 63 of the housing facing downward. The upper rib 631 is configured to abut against the edge of the opposing conductor plate 30. The upper rib 631 serves to fix the position of the support plate 20 inside the housing 60 and to suppress the vertical polarization wave of the ground plane from the end of the opposing conductor plate 30 to the upper side, thereby improving the radiation gain in the horizontal direction of the antenna. A metal pattern such as copper foil may also be applied to the vertical surface (i.e., the outer side) of the upper rib 631 that connects to the edge of the opposing conductor plate 30.

[0095] In addition, it is preferable to fill the interior of the housing 60 with a sealing material 65 such as silicon. As the sealing material 65, polyurethane resin such as polyurethane prepolymer can be used. Of course, other materials such as epoxy resin and silicone resin can also be used as the sealing material 65. With the structure of filling the housing 60 with the sealing material 65, the sealing material 65 located above the opposing conductor plate 30 effectively suppresses vertically polarized waves from the ground plane from the end of the opposing conductor plate 30 to the upper side, thereby improving the radiation gain in the horizontal direction of the antenna. At least the side and upper parts of the housing 60 can be formed of resin or ceramic having a specified relative permittivity. Furthermore, the structure of filling the housing 60 with the sealing material 65 also improves water resistance, dust resistance, and vibration resistance.

[0096] Of course, the filling of the sealing material 65 inside the housing 60 is arbitrary. The upper rib 631 is also arbitrary. Furthermore, the housing top plate 63, the upper rib 631, and the sealing material 65 are equivalent to a structure responsible for suppressing the vertical electric field radiated through the LC resonant mode from the edge of the opposing conductor plate 30 to the upper side, i.e., a radio wave shielding body. The above structure is equivalent to a structure in which a radio wave shielding body made of a conductor or dielectric is disposed on the upper side of the opposing conductor plate 30.

[0097] Either the housing bottom 61 or the housing top plate 63 of the housing 60 may be omitted. When either the housing bottom 61 or the housing top plate 63 is omitted, it is preferable to use a resin that maintains its solidity within a specified operating temperature range assuming the environment in which the antenna device 1 is used. The operating temperature range can be, for example, set to -30°C or higher and 100°C or lower. Furthermore, a structure that omits either the housing bottom 61 or the housing top plate 63 results in a housing with either the top or bottom surface as an opening.

Claims

1. An antenna device comprising: A ground plane is a conductor component formed into a rectangular flat plate; and An antenna element is a conductor component that has a power supply point that is electrically connected to a power supply line. The length of the aforementioned ground plane in the specified direction is set to be shorter than the target wavelength, wherein, The wavelength of the object mentioned above refers to the wavelength of the radio waves being transmitted and received. In the aforementioned grounding plate, a grounding cable is connected at a position that is an odd multiple of 1 / 4 of the wavelength of the target object, at a distance from the edge of the grounding plate. In the aforementioned ground plane, a slit with a length that is an odd multiple of 1 / 4 of the wavelength of the target object is formed along the long side from the aforementioned edge. The grounding cable is electrically connected to the inner end of the slit.

2. The antenna device according to claim 1, wherein, The aforementioned ground plane is a rectangle whose shorter side is shorter than the wavelength of the object, and the length of the longer side is set to be more than twice that of the shorter side. The antenna element is positioned offset from the center of the ground plane towards its long side. The grounding cable is connected at a position that is an odd multiple of 1 / 4 of the wavelength of the object at a distance from the far end of the antenna, and the far end of the antenna is the end of the long side of the ground plane that is far away from the antenna element.

3. An antenna device comprising: A ground plane is a conductor component formed into a rectangular flat plate; and An antenna element is a conductor component that has a power supply point that is electrically connected to a power supply line. The aforementioned ground plane is a rectangle whose shorter side is shorter than the target wavelength, and the longer side is set to be more than twice the length of the shorter side. The wavelength of the object mentioned above refers to the wavelength of the radio waves being transmitted and received. The antenna element is positioned offset from the center of the ground plane towards its long side. In the aforementioned grounding plate, a grounding cable is connected at a position that is an odd multiple of 1 / 4 of the wavelength of the target antenna at a distance from the far end of the antenna. The far end of the antenna is the end of the grounding plate that is furthest from the antenna element along its long side.

4. An antenna device comprising: A ground plane is a conductor component formed into a rectangular flat plate; and An antenna element is a conductor component that has a power supply point that is electrically connected to a power supply line. The aforementioned ground plane is a rectangle whose shorter side is shorter than the target wavelength, and the longer side is set to be more than twice the length of the shorter side. The wavelength of the object mentioned above refers to the wavelength of the radio waves being transmitted and received. The antenna element is positioned offset from the center of the ground plane towards its long side. A slit with a length that is an odd multiple of 1 / 4 of the target wavelength is formed at the end of the ground plane that is furthest from the antenna element, i.e., the end facing the opposite side from the far end of the antenna. A conductive line passing through the center of the aforementioned slit is formed along the center line of the slit. A grounding cable is connected to the aforementioned grounding plate via the aforementioned conductive lines. One end of the aforementioned conductive line is connected to the inner end of the aforementioned slit, and the other end of the aforementioned conductive line is connected to the aforementioned grounding cable.

5. The antenna device according to claim 3 or 4, wherein, The antenna element is disposed at one end of the long side of the ground plane.

6. An antenna device comprising: A ground plane is a conductor component formed into a rectangular flat plate; and An antenna element is a conductor component that has a power supply point that is electrically connected to a power supply line. The length of the aforementioned ground plane in the specified direction is set to be shorter than the target wavelength, wherein, The wavelength of the object mentioned above refers to the wavelength of the radio waves being transmitted and received. In the aforementioned grounding plate, a grounding cable is connected at a position that is an odd multiple of 1 / 4 of the wavelength of the target object, at a distance from the edge of the grounding plate. The antenna element is disposed at one end of the long side of the ground plane.

7. The antenna device according to claim 6, wherein, The above-mentioned antenna element is constructed using the following components: The opposing conductor plate is a flat conductor component disposed at a predetermined interval from the aforementioned ground plane, and is provided with the aforementioned power supply point; and A short-circuit section is provided in the central region of the aforementioned opposing conductor plate, and electrically connects the aforementioned opposing conductor plate to the aforementioned ground plane. The antenna element is configured to resonate in parallel at a predetermined target frequency using the inductance of the short-circuit portion and the electrostatic capacitance formed by the ground plane and the opposing conductor plate.

8. An antenna device comprising: A ground plane is a conductor component formed into a rectangular flat plate; and An antenna element is a conductor component that has a power supply point that is electrically connected to a power supply line. The length of the aforementioned ground plane in the specified direction is set to be shorter than the target wavelength, wherein, The wavelength of the object mentioned above refers to the wavelength of the radio waves being transmitted and received. In the aforementioned grounding plate, a grounding cable is connected at a position that is an odd multiple of 1 / 4 of the wavelength of the target object, at a distance from the edge of the grounding plate. The above-mentioned antenna element is constructed using the following components: The opposing conductor plate is a flat conductor component disposed at a predetermined interval from the aforementioned ground plane, and is provided with the aforementioned power supply point; and A short-circuit section is provided in the central region of the aforementioned opposing conductor plate, and electrically connects the aforementioned opposing conductor plate to the aforementioned ground plane. The antenna element is configured to resonate in parallel at a predetermined target frequency using the inductance of the short-circuit portion and the electrostatic capacitance formed by the ground plane and the opposing conductor plate.

9. The antenna device according to claim 8, wherein, The aforementioned antenna element is any one of a monopole antenna, patch antenna, inverted-F antenna, and loop antenna.

10. The antenna device according to claim 8 or 9, wherein, The aforementioned grounding cable is connected perpendicularly to the aforementioned grounding plate.

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