Wireless communication device

Abstract

The wireless communication device includes a rectangular base plate (10), a square opposing conductor plate (30), and a short-circuit section (40), configured as a zero-order resonant antenna that uses the electrostatic capacitance formed by the opposing conductor plate (30) and the base plate (10) and the inductance of the short-circuit section (40) to achieve LC parallel resonance. A power supply point (31) is formed at the edge of the opposing conductor plate (30). The opposing conductor plate (30) is positioned at a position offset by a predetermined end offset (De) from the end of the base plate (10) in the long side direction. The length of the base plate (10) in the long side direction is set to λ / 4×N+α. N is a natural number, and α is a predetermined value of 0.025λ or more and less than 0.225λ.

Description

[0001] Cross-reference to related applications

[0002] This application is based on Japanese Patent Application No. 2020-213995, filed on December 23, 2020, and the contents of the base application are incorporated herein by reference in their entirety. Technical Field

[0003] This invention relates to a wireless communication device that uses a zero-order resonant antenna. Background Technology

[0004] Patent Document 1 discloses an antenna device comprising: a base plate, which is a flat metal conductor for providing a ground potential; a counter conductor plate, which is a flat metal conductor disposed opposite to the base plate and provided with a power supply point; and a short-circuit section for electrically connecting the base plate and the counter conductor plate.

[0005] In this type of antenna, parallel resonance occurs at a frequency corresponding to the electrostatic capacitance formed between the base plate and the opposing conductor plate, as well as the inductance of the short-circuit section. The electrostatic capacitance formed between the base plate and the opposing conductor plate is determined based on the area of ​​the opposing conductor plate.

[0006] The antenna device with the above structure can set the frequency (hereinafter referred to as the target frequency) that is the object of transmission and reception in the antenna device to a desired value by adjusting the area of ​​the opposing conductor plate or adjusting the distance between the base plate and the opposing conductor plate.

[0007] In this invention, for convenience, the antenna device that utilizes the LC resonance generated by the electrostatic capacitance formed between the base plate and the opposing conductor plate and the inductance of the short-circuit section is also referred to as a zero-order resonant antenna or a metamaterial antenna.

[0008] Patent Document 1: Japanese Patent Application Publication No. 2018-61137

[0009] Patent document 1 only discloses the structure of the zero-order resonant antenna, and does not study the specific structure of the wireless communication device that integrates circuit modules such as transceiver circuits and power supply circuits as a whole with an antenna module.

[0010] The developers of this invention, considering vehicle mounting and other factors, have researched a structure for a wireless communication device as follows: a conductor pattern serving as a base plate is formed into a rectangular shape, and an antenna element including opposing conductor plates and a circuit module are arranged along the long side of the base plate. This structure is equivalent to extending the base plate of the antenna element to the underside of the circuit module in a manner that allows it to be used as a circuit ground.

[0011] Generally, the larger the base plate, the more stable the antenna operation. Therefore, based on the above-mentioned research structure, it is expected to maintain the stability of the antenna operation. However, the developers verified the operation of the above-mentioned research structure and obtained the following insights: under certain conditions, when the size of the base plate and the position of the opposing conductor plate relative to the base plate meet certain conditions, the base plate itself resonates at a frequency near the target frequency, increasing the leakage current to the communication cable. Summary of the Invention

[0012] The present invention was made based on this situation, and its purpose is to provide a wireless communication device that can suppress leakage current to communication cables in a structure using a zero-order resonant antenna.

[0013] The first wireless communication device for achieving this purpose is a wireless communication device for transmitting and receiving radio waves at a predetermined target frequency, comprising: a base plate, which is a rectangular conductor plate configured such that the length of its short side is less than λ / 2 and the length of its long side is greater than λ / 2; a zero-order resonant antenna element disposed at a position offset by a predetermined amount from the center of the base plate in the long side direction; and a circuit module for performing signal processing for transmitting and receiving using the zero-order resonant antenna element. The zero-order resonant antenna element and the circuit module are configured to be arranged in the long side direction of the base plate. The zero-order resonant antenna element includes: an opposing conductor plate spaced from the base plate by a predetermined distance. The device includes spaced-apart flat conductor components and power supply points that are electrically connected to the power supply line; and a short-circuit section located in the central region of the opposing conductor plate, electrically connecting the opposing conductor plate and the base plate. The wireless communication device is configured to use the inductance of the short-circuit section and the electrostatic capacitance formed by the base plate and the opposing conductor plate to resonate in parallel at the target frequency. The wireless communication device is configured such that the length (Lg) of the long side of the base plate satisfies Lg=λ / 4×N+α (N is a natural number, λ is the wavelength of the target frequency, α is a specified value of 0.025λ or more and 0.225λ or less, and Lg is the length of the long side of the base plate).

[0014] The above structure was developed based on the observation that a significant trend in leakage current was observed when the length of the base plate was an integer multiple of λ / 4. According to the structure described above, when the length of the base plate deviates from the specified amount (i.e., an integer multiple of λ / 4, which is the condition for operation as a monopole antenna), the base plate does not resonate. Therefore, it is also possible to suppress the current excited on the base plate and suppress leakage current to the communication cable.

[0015] Furthermore, the second wireless communication device for achieving the above-mentioned objective is a wireless communication device for transmitting and receiving radio waves at a predetermined target frequency, comprising: a base plate, which is a rectangular conductor plate configured such that the length of its short side is less than λ / 2 and the length of its long side is greater than λ / 2; a zero-order resonant antenna element disposed at a position offset by a predetermined amount from the center of the base plate in the long side direction; and a circuit module for performing signal processing for transmitting and receiving using the zero-order resonant antenna element. The zero-order resonant antenna element and the circuit module are configured to be arranged in the long side direction of the base plate. The zero-order resonant antenna element includes: an opposing conductor plate, which is connected to the base plate... The plate has flat conductors spaced at predetermined intervals and has power supply points that are electrically connected to the power supply line; and a short circuit is provided in the central area of ​​the opposing conductor plate, which electrically connects the opposing conductor plate and the base plate. The wireless communication device is configured to use the inductance of the short circuit and the electrostatic capacitance formed by the base plate and the opposing conductor plate to resonate in parallel at the target frequency. The opposing conductor plate is set to have an end offset of 0.075λ (λ is the wavelength of the target frequency) or more. The end offset is the distance from the end of the base plate near the opposing conductor plate, i.e., the end near the antenna, to the opposing conductor plate.

[0016] The above structure is based on the insight that, in a structure where a zero-order resonant antenna is positioned offset from the center of a rectangular base plate, the end offset is set to be 0.075λ or greater, which suppresses the current excited on the base plate. According to the above structure, it is also possible to suppress the current excited on the base plate and suppress leakage current to the communication cable.

[0017] Furthermore, the reference numerals within 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 the present invention. Attached Figure Description

[0018] Figure 1 This is a three-dimensional view of the appearance of a wireless communication device.

[0019] Figure 2 It is a conceptual representation Figure 1 A cross-sectional view at line II-II shown.

[0020] Figure 3 This is a top view of a wireless communication device.

[0021] Figure 4 This diagram illustrates the conditions for excitation of the base plate.

[0022] Figure 5 This diagram is used to illustrate the current distribution when the base plate resonates.

[0023] Figure 6This is a graph showing the results of simulating the current distribution when LC parallel resonance occurs in the comparison structure.

[0024] Figure 7 This is a graph showing the results of simulating the current distribution when the LC parallel resonates in the proposed structure.

[0025] Figure 8 This is a graph showing the reflection characteristics of the comparison structure and the proposed structure at each frequency.

[0026] Figure 9 This is a diagram showing an example of mounting on a vehicle.

[0027] Figure 10 This is a diagram showing a variation of the connector's placement.

[0028] Figure 11 This is a diagram showing a variation of the connector's placement.

[0029] Figure 12 This is a diagram showing a variation of the shape of the opposing conductor plate.

[0030] Figure 13 This is a diagram showing a variation of the location where a power supply point is formed.

[0031] Figure 14 This diagram shows a structure in which an additional conductor is placed near the opposing conductor plate.

[0032] Figure 15 This diagram shows a structure in which an internal additional conductor is placed near the opposing conductor plate.

[0033] Figure 16 This diagram shows a structure with a fold-back section located near the antenna end.

[0034] Figure 17 This diagram shows a structure with a foldback section at the far end of the antenna.

[0035] Figure 18 This is a diagram showing a structure with a folded-back section formed inside the support section.

[0036] Figure 19 This is a diagram illustrating an example of the overall structure of a wireless communication device with a housing. Detailed Implementation

[0037] <First Implementation>

[0038] Hereinafter, a first embodiment of the present invention will be described using figures. Furthermore, components having the same function will be labeled with the same reference numerals, and their descriptions will be omitted. Additionally, where only a part of the structure is mentioned, the structure of the previously described embodiment can be applied to other parts.

[0039] Figure 1 This is a perspective view showing an example of the schematic structure of the wireless communication device 1 according to this embodiment. Figure 2 yes Figure 1 The wireless communication device 1 shown at line II-II is a cross-sectional view. The wireless communication device 1 is used, for example, mounted on a mobile body such as a vehicle.

[0040] The wireless communication device 1 is configured to transmit and receive radio waves at a predetermined target frequency Ft. Of course, as another method, the wireless communication device 1 can also be used solely 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.

[0041] Here, as an example, the target frequency Ft is set to 2.45 GHz. Of course, the target frequency Ft can be appropriately designed, and in other ways, it can be set to, for example, 300 MHz, 760 MHz, 850 MHz, 900 MHz, 1.17 GHz, 1.28 GHz, 1.55 GHz, 5.9 GHz, etc. The wireless communication device 1 can not only transmit and receive the target frequency Ft, but also transmit and receive radio waves within a specified frequency range determined based on the target frequency Ft. For example, the wireless communication device 1 is configured to be able to transmit and receive frequencies belonging to the frequency band from 2400 MHz to 2500 MHz (hereinafter, the 2.4 GHz band).

[0042] That is, the wireless communication device 1 is configured to transmit and receive radio waves in frequency bands used in short-range wireless communication such as Bluetooth Low Energy, Wi-Fi, and ZigBee. In other words, the wireless communication device 1 is configured to transmit and receive radio waves in frequency bands (so-called ISM bands) allocated by the International Telecommunication Union for general use in the industrial, scientific, and medical fields.

[0043] The "λ" hereafter refers to the wavelength of the radio wave at the target frequency Ft (hereinafter also referred to as the target wavelength). For example, "λ / 2" and "0.5λ" refer to half the length of the target wavelength, and "λ / 4" and "0.25λ" refer to one-quarter the length of the target wavelength. Furthermore, the wavelength (i.e., λ) of a 2.4 GHz radio wave in a vacuum and air is 125 mm. In the examples of the dimensions of the components constituting the wireless communication device 1, the expression using λ can be understood as electrical length. Here, electrical length refers to the effective length taking into account edge electric fields, wavelength shortening effects caused by the dielectric, etc. Electrical length is sometimes also called effective length. Of course, for parts without wavelength shortening effects, λ can be understood as the length in a vacuum or air.

[0044] The wireless communication device 1 is connected, for example, to a communication ECU (Electronic Control Unit) mounted in the vehicle via a communication cable 61. Signals received by the wireless communication device 1 are sequentially output to the communication ECU. Furthermore, the wireless communication 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 the wireless communication device 1 and inputs baseband signals corresponding to the transmitted signals to the wireless communication device 1. The communication ECU connected to the wireless communication device 1 can, for example, be a smart ECU providing a smart access system. A smart ECU is an ECU that performs controls such as locking and unlocking the vehicle based on the reception status of signals emitted from a smartphone.

[0045] Here, as an example, we will assume that an AV cable is used as the communication cable 61 connecting the wireless communication device 1 and the communication ECU. An AV cable is an automotive low-voltage wire, implemented by covering soft copper wire with an insulating material such as vinyl chloride. In AV cable, "A" stands for automotive low-voltage wire, and "V" stands for vinyl chloride. As the AV cable connecting the wireless communication device 1, there are AV cables for providing grounding potential (grounding cable) and AV cables for signal flow (signal cable). Furthermore, as the connection cable between the wireless communication device 1 and the communication ECU, automotive thin-walled low-voltage wire (AVSS cable) and automotive compressed conductor ultra-thin-walled vinyl chloride insulated low-voltage wire (CIVUS cable) can also be used. 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 chloride, and "US" stands for ultra-thin-wall type. Of course, as the communication cable 61 connecting the wireless communication device 1 and the communication ECU, coaxial cables, feeder cables, etc., can also be used.

[0046] The specific structure of the wireless communication device 1 will be described below. Figure 1 As shown, the wireless communication device 1 includes a base plate 10, a support portion 20, a counter conductor plate 30, a short-circuit portion 40, a control circuit 50, and a connector 60. The support portion 20, as described later, is a plate-shaped component, with the base plate 10 formed on one side. The counter conductor plate 30 and the control circuit 50 are disposed on the other side of the support portion 20.

[0047] For convenience, the side where the opposing conductor plate 30 is located relative to the base plate 10 will be described from the perspective of the upper side of the wireless communication device 1. That is, the direction from the base plate 10 toward the opposing conductor plate 30 corresponds to the upper direction from the perspective of the wireless communication device 1. In addition, the direction from the opposing conductor plate 30 toward the base plate 10 corresponds to the lower direction from the perspective of the wireless communication device 1. From now on, the side of the support portion 20 where the opposing conductor plate 30 is located will also be described as the antenna forming surface 20A.

[0048] The base plate 10 is a plate-shaped conductor component made of a conductor such as copper. The base plate 10 is disposed along the lower side of the support portion 20. The plate shape can also include a thin film such as metal foil. That is, the base plate 10 can also be patterned on the surface of a resin board such as a printed wiring board by electroplating. Alternatively, the base plate 10 can be implemented using a conductor layer (so-called inner layer) disposed inside a multilayer substrate including multiple conductor layers and insulating layers. The base plate 10 is electrically connected to the communication cable 61, providing a ground potential in the wireless communication device 1. The base plate 10 provides a ground potential for the control circuit 50 described later. Therefore, the base plate 10 can also be referred to as a circuit grounding portion. The base plate 10 is equivalent to a grounding portion.

[0049] The base plate 10 is rectangular. The length of the shorter side of the base plate 10 is, for example, set to a value electrically equivalent to 0.2λ. Furthermore, the length of the longer side of the base plate 10 is set to 0.75λ. This structure is equivalent to a rectangular base plate 10 where the length of the shorter side is shorter than 0.5λ (specifically 0.25λ) and the length of the longer side is more than twice the length of the shorter side. Moreover, the length of the longer side of the base plate 10 can be 0.6λ, 0.8λ, 1.0λ, 1.5λ, etc., as long as it is longer than the shorter side. The ratio of the length of the shorter side to the longer side of the base plate 10 can be approximately set to 1:2, 1:3, 1:4, 2:3, 2:5, etc.

[0050] Figure 1 In the various diagrams shown, the X-axis represents the direction of the long side of the base plate 10, the Y-axis represents the direction of the short side of the base plate 10, and the Z-axis represents the vertical direction. The Y-axis direction is equivalent to a defined direction. This three-dimensional coordinate system with X, Y, and Z axes is a concept used to explain the structure of the wireless communication device 1.

[0051] Furthermore, the base plate 10 only needs to be at least larger than the opposing conductor plate 30. The dimensions of the base plate 10 can be appropriately changed. Additionally, the shape of the base plate 10 viewed from above, i.e., its planar shape, can be appropriately changed. The planar shape can also be referred to as the top view shape. In the accompanying drawings, as an example, the four corners of the base plate 10 are shown as right angles, but the corners of the base plate 10 can also be rounded. Furthermore, the edges of the base plate 10 can be partially or entirely formed into a zigzag shape. A rectangular shape also includes a shape with minute irregularities on its edges. Additionally, slits can be provided in the base plate 10. The irregularities on the edges of the base plate 10 and the slits formed at positions away from the edges of the base plate 10 can be ignored in defining the appearance of the base plate 10 as long as they do not affect antenna operation. Here, minute irregularities refer to irregularities of about a few millimeters.

[0052] The support portion 20 is a plate-shaped component used to arrange the base plate 10 and the opposing conductor plate 30 opposite each other at a predetermined interval. The support portion 20 is rectangular flat, and its size, when viewed from above, is approximately the same as that of the base plate 10. The support portion 20 is implemented using a dielectric material having a predetermined relative permittivity. Here, as an example, the support portion 20 is implemented using polytetrafluoroethylene (PTFE) with a relative permittivity of 2.3. Furthermore, when the support portion 20 is formed using a dielectric material with a relative permittivity of 2.3, the wavelength λ inside the support portion 20 becomes approximately 82 mm due to the wavelength shortening effect of the dielectric material. Of course, various resin materials or ceramics can be used as the material for the support portion 20. For example, the material for the support portion 20 can also be glass epoxy resin (in other words, FR4: Flame Retardant Type 4) with a relative permittivity of about 4.3 to 4.9. In addition, the support portion 20 can also have a structure composed of various resin components.

[0053] In this embodiment, as an example, the thickness H of the support portion 20 is, for example, 1.5 mm. The thickness H of the support portion 20 corresponds to the distance between the base plate 10 and the opposing conductor plate 30. By adjusting the thickness H of the support portion 20, the distance between the opposing conductor plate 30 and the base plate 10 can be adjusted. The specific value of the thickness H of the support portion 20 can be appropriately determined through simulation and experimentation. Of course, the thickness H of the support portion 20 can also be 1.0 mm, 2.0 mm, 3.0 mm, etc.

[0054] Furthermore, the support portion 20 only needs to achieve the above-described functions, and its shape can be appropriately modified. The structure for aligning the opposing conductor plate 30 and the base plate 10 can also be multiple pillars. In this embodiment, a structure is used where the space between the base plate 10 and the opposing conductor plate 30 is filled with resin, serving as the support portion 20, but this is not a limitation. The space between the base plate 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 portion 20. Furthermore, the structures illustrated above can be combined. When using a printed wiring board to implement the wireless communication device 1, the multiple conductor layers of the printed wiring board can be used as the base plate 10 and the opposing conductor plate 30, and the resin layer separating the conductor layers can be used as the support portion 20.

[0055] The thickness H of the support portion 20 corresponds to the length of the short-circuit portion 40, as described later. In other words, the thickness H of the support portion 20 functions as a parameter for adjusting the inductance provided by the short-circuit portion 40. Furthermore, the thickness H also functions as a parameter for adjusting the electrostatic capacitance formed by the base plate 10 and the opposing conductor plate 30.

[0056] In addition to the opposing conductor plate 30, a control circuit 50 is also formed on the antenna forming surface 20A. The control circuit 50 is located in the region along the positive X-axis when viewed from the opposing conductor plate 30. The control circuit 50 includes, for example, a transceiver circuit and a power supply circuit. The transceiver circuit is a circuit module that performs signal processing, including at least one of signal transmission and signal reception. The transceiver circuit performs at least one of modulation, demodulation, frequency conversion, amplification, digital-to-analog conversion, and detection. The control circuit 50 is an electrical assembly of various components such as ICs, analog circuit elements, and connectors. The control circuit 50 is equivalent to a circuit module.

[0057] The control circuit 50 is connected to the opposing conductor plate 30 via a microstrip line serving as a power supply line 51. Additionally, the control circuit 50 is also connected to the base plate 10 via a through-hole or shorting pin. The control circuit 50 is also electrically connected to an AV line, which serves as a signal cable, via a connector 60. That is, the control circuit 50 is connected to the communication ECU via a signal cable. The connector 60 is a structure used to electrically connect the signal cable, the grounding cable, and the wireless communication device 1. The connector 60 is, for example, positioned at the end of the base plate 10 in the positive X-axis direction. Furthermore, the position of the connector 60 can be appropriately changed; it can be along the short side or the long side of the base plate 10.

[0058] The opposing conductor plate 30 is a plate-shaped conductor component made of a conductor such as copper. As described above, the plate shape also includes a thin film such as copper foil. The opposing conductor plate 30 is configured to face the base plate 10 across the support portion 20. The opposing conductor plate 30 may also have a pattern formed on the surface of a resin board such as a printed wiring board, just like the base plate 10. In addition, "parallel" here is not limited to a completely parallel state. It may also be inclined from a few degrees to about 30 degrees. That is, it may include a generally parallel state (the so-called generally parallel state). Regarding the expression "perpendicular" in this invention, it is not limited to a completely perpendicular state, but also includes a state inclined from a few degrees to about 30 degrees.

[0059] By arranging the opposing conductor plate 30 and the base plate 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 base plate 10 is formed. The opposing conductor plate 30 is configured to form an electrostatic capacitance that resonates in parallel with the inductance of the short-circuit section 40 at the target frequency Ft. 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 Ft through cooperation with the inductance of the short-circuit section 40. Furthermore, if the inductance of the short-circuit section 40 is set to L, and the electrostatic capacitance formed between the opposing conductor plate 30 and the base plate 10 is set to C, then the relationship Ft = 1 / {2π√(LC)} holds. Those skilled in the art can determine the appropriate area of ​​the opposing conductor plate 30 based on this relationship.

[0060] For example, the opposing conductor plate 30 is formed as a square with one side electrically 12 mm. Of course, the length of one side of the opposing conductor plate 30 can be appropriately varied, and can be 14 mm, 15 mm, 20 mm, 25 mm, etc. The planar shape of the opposing conductor plate 30 can also be circular, regular octagonal, regular hexagonal, etc. Furthermore, the opposing conductor plate 30 can also be rectangular, elongated elliptical, etc. Moreover, due to the wavelength shortening effect of the support portion 20, the wavelength (λ) inside the support portion 20 and on the surface of the opposing conductor plate 30 is approximately 82 mm. Therefore, for the electric field propagating within the support portion 20, a value of 12 mm is electrically equivalent to 0.13λ.

[0061] 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 power supply line 51 to the opposing conductor plate 30. Here, as an example, the power supply point 31 is formed in the center of the edge portion of the opposing conductor plate 30 where the control circuit 50 is located. This structure is equivalent to setting the power supply point 31 at a position closest to the edge portion of the control circuit 50, on a straight line passing through the center of the opposing conductor plate 30 and parallel to the X-axis. Furthermore, the power supply point 31 can be arranged in any position. It can be set at a position that achieves impedance matching with the power supply line 51. In other words, the power supply point 31 can be set at a position where the return loss is at a specified allowable level. For example, the power supply point 31 can also be arranged at any position such as the edge portion or the central region of the opposing conductor plate 30. In addition, the power supply point 31 can also be set at the edge portion parallel to the X-axis.

[0062] 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 51 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.

[0063] The short-circuit section 40 is a conductive component that electrically connects the base plate 10 and the opposing conductor plate 30. The short-circuit section 40 can be implemented using only a conductive pin (hereinafter referred to as 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. Preferably, to suppress the antenna height, the length of the short-circuit section 40, or in other words, the thickness H of the support section 20, is set to 0.05λ or less. Here, as an example, the length of the short-circuit section 40 is set to 0.01λ.

[0064] Furthermore, the short-circuit section 40 can be any linear component that is electrically connected at one end to the base plate 10 and at the other end to the opposing conductor plate 30. When the wireless communication device 1 is implemented using a printed wiring board as a substrate, the through-holes provided on the printed wiring board can be used as the short-circuit section 40.

[0065] The short-circuit portion 40 is, for example, positioned at the center of the opposing conductor plate 30 (hereinafter, the center of the conductor plate). Therefore, when the length of one side of the opposing conductor plate 30 is set to Lp, the distance La from the connection point of the short-circuit portion 40 in the opposing conductor plate 30 to the power supply point 31 is Lp / 2. Furthermore, the formation position 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 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 region inside the line connecting the points divided into 1:5 ratios from the center of the conductor plate to the edge. According to other views, the central region corresponds to the overlapping area of ​​concentric patterns obtained by similarly reducing the opposing conductor plate 30 to about one-sixth of its original size.

[0066] <Position of the opposing conductor plate 30 relative to the base plate 10>

[0067] like Figure 3 As shown, the opposing conductor plate 30 is positioned opposite the base plate 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 base plate 10 in the negative X-axis direction by a predetermined center offset Dc. The center offset Dc can be set to, for example, 0.125λ, 0.25λ, 0.5λ, etc.

[0068] Figure 3 Lp represents the length of one side of the opposing conductor plate 30, in other words, the length in the X-axis direction. De represents the distance from the end 11 near the antenna to the end of the opposing conductor plate 30 in the negative X-axis direction when viewed from above, i.e., the end offset.

[0069] The center offset Dc can be appropriately varied within a range where the opposing conductor plate 30 does not extend beyond the outer side of the base plate 10 when viewed from above. The opposing conductor plate 30 is configured to oppose the base plate 10 at least over its entire area (i.e., its entire surface). The center offset Dc corresponds to the offset between the center of the base plate 10 and the center of the opposing conductor plate 30. The center offset Dc is preferably set such that the end offset De is 0.075λ or more, as described later. Alternatively, the opposing conductor plate 30 may also be configured with its end along the negative X-axis direction (left end of the paper) of the base plate 10.

[0070] For convenience, the end of the base plate 10 in the negative X-axis direction along its long side will be referred to as the antenna proximity end 11. The antenna proximity end 11 corresponds to the end of the base plate 10 in the long side direction that is relatively close to the opposing conductor plate 30. Conversely, the end of the base plate 10 in the opposite direction to the antenna proximity end 11 will be referred to as the antenna distance end 12. The antenna distance end 12 corresponds to the end of the base plate 10 in the long side direction that is relatively far from the opposing conductor plate 30.

[0071] In addition, Figure 3 To clearly show the positional relationship between the base plate 10 and the opposing conductor plate 30, the support portion 20 and control circuit 50 are used, etc. That is, the figures are omitted. Figure 3 The single-dash line Lx1 represents a straight line passing through the center of the base plate 10 and parallel to the X-axis, and the single-dash line Ly1 represents a straight line passing through the center of the base plate 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 the base plate 10 and the opposing conductor plate 30. Line Ly1 corresponds to the axis of symmetry with respect to the base plate 10. Line Ly2 corresponds to the axis of symmetry with respect to the opposing conductor plate 30. The single-dash line Lx1 also passes through the center of the opposing conductor plate 30. That is, the single-dash line Lx1 corresponds to a straight line parallel to the X-axis and passing through the centers of the base plate 10 and the opposing conductor plate 30. The intersection of line Lx1 and line Ly1 corresponds to the center of the base plate, and the intersection of line Lx1 and line Ly2 corresponds to the center of the opposing conductor plate 30 (hereinafter, the center of the conductor plate). 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 is equivalent to the intersection of the two diagonals of the opposing conductor plate 30. Furthermore, the concentric arrangement of the base plate 10 and the opposing conductor plate 30 is equivalent to a configuration in which the center of the opposing conductor plate 30 overlaps with the center of the base plate 10 when viewed from above.

[0072] <Regarding the operating principle of wireless communication device 1>

[0073] Here, the operation of the wireless communication device 1 will be explained. In the wireless communication device 1, the opposing conductor plate 30 is short-circuited with the base plate 10 through the short-circuit portion 40 provided in the central region, and the area of ​​the opposing conductor plate 30 is the area of ​​the electrostatic capacitance that forms a parallel resonance with the inductance of the short-circuit portion 40 at the target frequency Ft.

[0074] Therefore, if a high-frequency signal is input from the control circuit 50, LC parallel resonance is generated through energy exchange between the inductor and the capacitor, producing an electric field perpendicular to both the base plate 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 surface perpendicular to the base plate 10 (hereinafter, the base plate vertically polarized wave) and propagates in space. That is, the structure including the short-circuit portion 40 and the opposing conductor plate 30 functions as a zero-order resonant antenna element ANT. Furthermore, the base plate vertically polarized wave here refers to an electric wave whose vibration direction is perpendicular to both the base plate 10 and the opposing conductor plate 30.

[0075] Such a wireless communication device 1 is directional in the horizontal direction of the antenna at the target frequency Ft. 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 short-circuit portion 40. The horizontal direction of the antenna is equivalent to the lateral direction (in other words, sideways) for the wireless communication device 1. When the base plate 10 is configured horizontally, the wireless communication device 1 functions as an antenna with a main beam in the horizontal direction.

[0076] Furthermore, the operation of the wireless communication device 1 when transmitting (emitting) radio waves is reversible with its operation when receiving radio waves. That is, according to the wireless communication device 1 described above, it is possible to receive vertically polarized waves from the base plate arriving from the horizontal direction of the antenna.

[0077] <Conditions for the 10th order resonance of the base plate>

[0078] Here, regarding the conditions for the 10th-order resonance of the substrate accompanied by the excitation of the zero-order resonant antenna element ANT, for... Figure 4 , Figure 5 Please provide an explanation. Figures 4-5 It is a conceptual representation of crossing Figure 3 A diagram showing the positional relationship of the base plate 10, the opposing conductor plate 30, and the short-circuit section 40 in a cross-section parallel to the XZ plane of the straight line Lx1. Figure 4 The La shown represents the distance from the power supply point 31 to the short-circuit section 40, and H represents the height, or in other words, the thickness, of the support section 20. The base plate length Lg and the end offset De are as described above. Furthermore, La in this invention corresponds to Lp / 2. Additionally, the relationship De = Lg / 2 - Dc - Lp / 2 exists. Figures 4-5 In this text, the thickness H of the support portion 20 is exaggeratedly large. H is a sufficiently small value that can be ignored compared to Lg.

[0079] As described above, the structure including the opposing conductor plate 30 and the short-circuit section 40 of this invention operates as a zero-order resonant antenna by means of a high-frequency signal input from the power supply point 31. At this time, as... Figure 5 As shown, the current input from the power supply point 31 flows through the short-circuit section 40 in the base plate 10. Simulations confirmed that the current flowing in the base plate 10 due to LC parallel resonance flows from the short-circuit section 40 towards the edges of the base plate 10 in all directions. Furthermore, the current flowing from the opposing conductor plate 30 through the short-circuit section 40 into the base plate 10 mainly flows from the short-circuit section 40 towards both sides in the long side direction of the base plate 10. That is, the current flowing in the base plate 10 flows from the short-circuit section 40 towards the antenna-proximity end 11 and the antenna-far end 12, respectively.

[0080] Here, assuming the base plate length Lg is λ / 4×N (N: an integer), the base plate 10 is excited, radiating unnecessary electromagnetic waves or increasing leakage current. For convenience, the resonance originating from the current flowing in the base plate 10 is also called base plate resonance. That is, base plate resonance occurs when the relationship Lg=λ / 4×N is satisfied.

[0081] Conversely, if the base plate length Lg is set such that the relationship Lg = λ / 4 × N is not satisfied, leakage current caused by base plate resonance can be suppressed. For example, by setting the base plate length Lg to a value that satisfies the non-resonance condition expressed by the following relationship, leakage current to the communication cable 61 can be suppressed.

[0082] Lg=λ / 4×N+α(0.025λ≤α≤0.225λ)

[0083] Furthermore, the range of α is a parameter used to disrupt the current distribution from the power supply point 31 to the far end of the antenna from the resonant distribution. If α is too small, the resonance cannot be disrupted. The specific range of values ​​for α is determined through simulation. For example, α can be 0.05λ, 0.1λ, 0.125λ, 0.15λ, or 0.2λ. α can be a preset value. N can be set based on the base plate length Lg, satisfying λ / 4×(N-1)≤Lg≤λ / 4×N. Based on the above, the base plate length Lg of the present invention is set to satisfy the value λ / 4×N+α.

[0084] <Regarding the effects of the present invention>

[0085] Here, a comparative structure is used to explain the effects of the structure of the present invention, i.e., the proposed structure. Furthermore, the details of the comparative structure and the proposed structure are as follows. The comparative structure includes a square opposing conductor plate 30, and the base plate length Lg is set to 82 mm. Since λ on various conductor surfaces becomes 82 mm due to the wavelength shortening effect at the support portion 20, the base plate length Lg of the comparative structure is approximately the same as λ / 4×4=1λ. That is, the comparative structure corresponds to a structure that satisfies the base plate resonance condition. Furthermore, the case where the base plate length Lg differs from the length satisfying λ / 4×N by approximately 0.02λ is also included in the case of satisfying the base plate resonance condition. In other words, the aforementioned α corresponds to the likelihood used in the design to avoid base plate resonance.

[0086] On the other hand, the base plate length Lg of the proposed structure is set to 90mm. That is, the base plate length Lg in the proposed structure is set to a value that deviates by approximately 8mm from the 82mm required to satisfy the resonance condition. Furthermore, the end offset De is set to 8mm. The proposed structure is equivalent to a structure with a base plate length Lg set to satisfy the non-resonance condition.

[0087] Figure 6 as well as Figure 7 This is a graph showing the results of analyzing the distribution of current flowing in the base plate 10 based on whether the non-resonance condition is met. Specifically, Figure 6 This indicates the current distribution in the comparison structure. Figure 7 This indicates the current distribution within the proposal structure.

[0088] like Figure 6 As shown, in the comparative structure, it can be seen that currents are distributed alternately at antinodes and nodes every λ / 4 up to the far end 12 of the antenna, resulting in resonance. Furthermore, the resonant current can be distributed so that the far end 12 of the antenna becomes a node of the resonant current. On the other hand, in the proposed structure, as... Figure 7 As shown, the current flow in the base plate 10 is roughly limited to the region involved in the zeroth resonance, i.e., the portion opposite to the opposing conductor plate 30, and base plate resonance does not occur. Furthermore, the average surface current of the base plate 10 in the comparative structure is 22.0 dBA / m, while the average surface current of the base plate 10 in the proposed structure is -1.8 dBA / m. That is, according to the proposed structure, the average surface current of the base plate 10 can be reduced by approximately 23.8 dB.

[0089] in addition, Figure 8 This represents the simulation results of the S-parameters (reflection characteristics) in the comparison structure and the proposal structure. Like... Figure 8As shown in the simulation results of the reflection characteristics, it can be seen that in the comparison structure, in addition to the LC resonance (in other words, the 0th order resonance) around the target frequency, i.e., 2.4 GHz, a resonance occurs around 2.7 GHz. The resonance around 2.7 GHz corresponds to the substrate resonance. In contrast, in the proposed structure, no reflection characteristics indicating the generation of substrate resonance were observed in the region near the target frequency. According to the proposed structure, concerns about substrate resonance occurring in the region near the target frequency can be reduced. Furthermore, as a result, leakage current to the communication cable 61 can be suppressed. In addition, the region near the target frequency here refers to, for example, the range within ±0.4 GHz of the target frequency.

[0090] Furthermore, as another structure for suppressing leakage current to the communication cable 61, a structure in which circuit elements such as low-pass filters and high-pass filters are provided at the connection point with the communication cable 61 is also considered. However, in this assumed structure, the cost increases corresponding to the provision of elements or patterns that function as filtering circuits. To address this issue, the structure according to the present invention has the advantage of suppressing the increase in cost and suppressing leakage current to the communication cable 61.

[0091] <Example of installation of wireless communication device 1 in a vehicle>

[0092] For example, Figure 9 As shown, the aforementioned wireless communication device 1 can be installed on the exterior side of the B-pillar 91 of the vehicle with its upward direction relative to the vehicle exterior. Specifically, the base plate 10 is installed facing the outer side of the B-pillar 91, and the X-axis direction is along the long side of the B-pillar 91 (in other words, the vehicle height direction). Alternatively, the wireless communication device 1 can also be installed inside the door panel, in the portion overlapping the B-pillar 91, in the aforementioned manner.

[0093] Based on the above installation posture, the upward direction of the wireless communication device 1, i.e., the positive Z-axis direction, is roughly consistent with the vehicle width direction, and the horizontal direction of the antenna is along (in other words, parallel to) the side of the vehicle. With this installation posture, a communication area can be formed along the side of the vehicle.

[0094] Furthermore, the installation location and posture of the wireless communication device 1 are not limited to the examples described above. The wireless communication device 1 can be installed at any location on the exterior surface of the vehicle, such as the A-pillar 92, the exterior surface of the C-pillar, the rocker arm (in other words, the lower longitudinal beam) 94, or the interior / near the exterior door handle 95. For example, the wireless communication device 1 can also be housed inside the exterior door handle 95 with the X-axis along the long side of the steering wheel and the Y-axis along the vehicle height. Alternatively, the wireless communication device 1 can also be mounted on the roof 93 of the vehicle.

[0095] The embodiments of the present invention have been described above, but the present invention is not limited to the embodiments described above, and various supplements and modifications described thereafter are also included within the technical scope of the present invention. Furthermore, in addition to the following, various modifications can be made without departing from the spirit of the invention. For example, the various modifications described below can be appropriately combined and implemented without causing technical contradictions.

[0096] <Supplementary information regarding the mounting location of connector 60>

[0097] The above describes an example of arranging connector 60 along the distal end 12 of the antenna, but is not limited thereto. For example, as... Figure 10 As shown, the connector 60 can also be positioned and oriented along the edge of the support portion 20 in the positive or negative Y-axis direction.

[0098] In addition, such as Figure 11 As shown, connector 60 can also be positioned at a distance M times (M: odd number) from the distal end 12 of the antenna, offset from λ / 4. Furthermore, Figure 11 The 50A shown represents, for example, a transceiver circuit for modulation and demodulation, while 50B represents a power supply circuit. Of course, the contents of the circuits referred to by 50A and 50B can be appropriately changed. For example... Figure 11 As shown, the control circuit 50 can also be formed by dividing it into multiple blocks.

[0099] Furthermore, when the base plate 10 is formed using the inner layer of a multilayer substrate, a portion of the control circuit 50 can also be formed on the substrate surface located further below the base plate 10 (hereinafter, the back side of the substrate). Additionally, when the wireless communication device 1 is implemented using a multilayer substrate including multiple conductor layers, the antenna forming surface 20A corresponds to the front side of the multilayer substrate. For example, the transceiver circuit 50A may be formed on the front side of the substrate, which serves as the antenna forming surface 20A, while the power supply circuit 50B is formed on the back side of the substrate. The control circuit 50 can also be distributed across the front and back sides of the substrate. Furthermore, if the circuit is formed not only on the front side of the substrate but also on the back side, electronic components such as capacitors and IC chips will have a certain height, thus potentially increasing the height of the wireless communication device 1. To address this issue, by providing a structure in which most or all of the control circuit 50 is provided on the antenna forming surface 20A, the height of the wireless communication device 1 can be further suppressed. Furthermore, the structure prior to the installation of the control circuit 50 in the above structure, in other words, the structure from which the control circuit 50 is removed, corresponds to an antenna module.

[0100] <Supplement to the shape and positional relationship of the base plate 10 and the opposing conductor plate 30>

[0101] A slit can also be provided in the opposing conductor plate 30, or the corners of the opposing conductor plate 30 can be rounded. For example, cutouts as retraction separation elements can also be provided in a pair of diagonal portions. The edges of the opposing conductor plate 30 can also be partially or entirely designed as a zigzag shape. Unevennesses and concavities on the edges of the opposing conductor plate 30 that do not affect operation can be treated to be negligible. In addition, the opposing conductor plate 30 can also be... Figure 12 As shown, it is a circle, etc.

[0102] Furthermore, the location of the power supply point 31 is not necessarily limited to the edge of the opposing conductor plate 30. For example, Figure 13 As shown, the power supply point 31 can also be formed at a position away from the edge of the opposing conductor plate 30. Additionally, in Figure 13 The present invention discloses a method in which a power supply point 31 is provided on the long axis Lx of the base plate 10, but is not limited thereto. The power supply point 31 may also be provided at a position offset from the long axis Lx of the base plate 10.

[0103] <Variation Example (1)>

[0104] Circuit elements can also be arranged in the space created by configuring the zero-order resonant antenna element ANT, including the opposing conductor plate 30 and the short-circuit portion 40, away from the long side end of the base plate 10. Additionally, such as Figure 14 As shown, an additional conductor 71, electrically connected to the base plate 10 via a shorting pin 72, can also be arranged in this space. The additional conductor 71 is a plate-shaped conductor component, positioned opposite the opposing conductor plate 30 at a predetermined interval Gp on the antenna forming surface 20A on the negative X-axis side compared to the opposing conductor plate 30. For example, a through-hole formed on the circuit board can be used as the shorting pin 72. The additional conductor 71 can also be patterned or implemented using pads.

[0105] According to this structure, the electrostatic capacitance component that contributes to LC parallel resonance increases based on the electrostatic capacitance corresponding to the distance Gp between the additional conductor 71 and the opposing conductor plate 30. As a result, the size of the opposing conductor plate 30 can be further reduced. Furthermore, the distance Gp between the opposing conductor plate 30 and the additional conductor 71 is set to a value that minimizes electromagnetic coupling between them. For example, the distance Gp is ​​preferably set to λ / 100 or more.

[0106] In addition, such as Figure 15As shown, an internal additional conductor 71A can also be formed between the opposing conductor plate 30 and the base plate 10, parallel to them. The internal additional conductor 71A is electrically connected to the base plate 10 using a shorting pin 72A. When the wireless communication device 1 is implemented using a multilayer substrate, the internal additional conductor 71A can be implemented using an internal conductor layer of the multilayer substrate. The shorting pin 72A can also be implemented using a through-hole structure. The concept of a through-hole here includes not only through-holes that penetrate the entire substrate layer, but also gap (internal) through-holes connecting a portion of the layers, blind holes, buried holes connecting inner layers, etc.

[0107] according to Figure 15 The structure shown, based on the spacing GpA between the internal additional conductor 71A and the opposing conductor plate 30, and the area of ​​the overlapping portion of the internal additional conductor 71A and the opposing conductor plate 30 when viewed from above, helps to increase the electrostatic capacitance component of LC parallel resonance. Therefore, with the above structure, the area of ​​the opposing conductor plate 30 can also be reduced.

[0108] <Variation Example (2)>

[0109] The base plate length Lg is a value appropriately determined considering both vehicle mounting comfort and the necessary space for the control circuit 50. Therefore, it is sometimes difficult to set the base plate length Lg to a suitable length that satisfies the non-resonance condition of the base plate. Furthermore, if the base plate length Lg is lengthened in one direction, i.e., within the same plane, the volume of the wireless communication device 1 increases, worsening its mounting comfort in the vehicle. Conversely, if the base plate length Lg is shortened, it may be impossible to ensure the area required for mounting the control circuit 50.

[0110] Based on such circumstances, for example... Figure 16 As shown, a folded-back portion 73 can also be formed at the end 11 near the antenna to extend the length Lg of the base plate.

[0111] The foldback portion 73 includes a base plate extension portion 731 and a bridge portion 732. The base plate extension portion 731 is a flat plate conductor formed on the antenna forming surface 20A on the antenna near end 11 side. The bridge portion 732 connects the base plate extension portion 731 and the base plate 10 near the antenna near end 11.

[0112] According to this structure, the current reaching the distal end of the antenna of the base plate 10 flows via the bridge portion 732 toward the end of the base plate extension portion 731 in the positive X-axis direction. That is, the path length of the current flowing from the short-circuit portion 40 into the base plate 10 can be substantially lengthened. Therefore, the length of the base plate 10 in the X-axis direction can be suppressed. For example, even if it is difficult to ensure the desired base plate length Lg due to factors such as mounting space in a vehicle, it is possible to configure the base plate to satisfy the non-resonance condition by providing the foldback portion 73. That is, the generation of base plate resonance near the target frequency can be suppressed without changing the base plate length Lg when viewed from above. Furthermore, in the above structure, the end of the base plate extension portion 731 in the positive X-axis direction corresponds to the actual long side end of the base plate 10. In one viewpoint, the base plate extension portion 731 and the bridge portion 732 can also be understood as part of the base plate 10.

[0113] And, as Figure 17 As shown, the foldback portion 73, which extends the base plate length Lg, can also be formed on the antenna distal end 12 side. In this case, the bridge portion 732 corresponds to a structure that connects the base plate extension portion 731 and the base plate 10 near the antenna distal end 12. In the above structure, the end of the base plate extension portion 731 in the negative X-axis direction corresponds to the actual long side end of the base plate 10. For convenience, the length of the foldback portion 73, in other words, the path length of the current extended through the foldback portion 73, will also be referred to as the foldback length. Assuming that the base plate length Lg is set to an integer multiple of λ / 4, it is preferable that the foldback length is set to 0.025λ or more.

[0114] However, the closer to the short-circuit section 40, the higher the current density flowing in the base plate 10. Furthermore, the current density is sparse at the far end 12 of the antenna. That is, the current density is higher at the near end 11 of the antenna compared to the far end 12. Therefore, when the foldback length is constant, the structure with the foldback section 73 at the near end 11 tends to have a higher resonance suppression effect compared to the structure with the foldback section 73 at the far end 12. In other words, when the length of the base plate 10 is an integer multiple of λ / 4, the necessary foldback length at the near end 11 is smaller compared to the case where the foldback section 73 is located at the far end 12. This is because the current attenuation per unit length is different.

[0115] exist Figure 16 as well as Figure 17 The text discloses a method in which the base plate extension 731 is formed on the antenna forming surface 20A, in other words, on the same layer as the opposing conductor plate 30, but is not limited to this. For example, ... Figure 18As shown, the base plate extension 731 can also be formed on the underside of the opposing conductor plate 30, in other words, inside the support portion 20. For example, the base plate extension 731 can be implemented using the internal conductor layer of a multilayer substrate. The bridge portion 732 can be implemented using a through-hole structure. According to this structure, a connector 60 can be provided at the end of the antenna forming surface 20A on the positive X-axis direction side.

[0116] <Second Implementation>

[0117] In the above embodiment, the structure corresponds to the insight that the base plate 10 is prone to resonance when the base plate length Lg is an integer multiple of λ / 4. On the other hand, the structure that can avoid / suppress resonance of the base plate 10 is not limited to the above structure. The developer has conducted research and found that even when the base plate length Lg is an integer multiple of λ / 4, the base plate 10 does not resonate when the end offset De is 0.075λ or more, or the leakage current from the base plate 10 can converge to an acceptable level. The wireless communication device 1 as the second embodiment corresponds to this new insight. In the wireless communication device 1 of the second embodiment, Figure 4 The end offset De shown is set to 0.075λ or higher.

[0118] Furthermore, since the zero-order resonant antenna element ANT is positioned offset from the center of the base plate 10 along its long side, the upper limit of the end offset De is Lg / 2 - Lp / 2. That is, the end offset De is set to be greater than or equal to 0.075λ and less than Lg / 2 - Lp / 2.

[0119] According to this structure, assuming the base plate length Lg is an integer multiple of λ / 4, it is possible to suppress the increase in leakage current to the communication cable 61 caused by the excitation of the base plate 10. Furthermore, as described above, the effective length of λ in the base plate 10 is shortened due to the resin material that abuts against the base plate 10. Assuming that multiple resin components are provided around the base plate 10, the wavelength shortening effects of the multiple resin materials act in combination, making it difficult to determine the correct effective length. That is, when multiple resin components with different relative permittivity exist around the base plate 10, it is difficult to accurately determine λ / 4. As a result, it is difficult to adjust the dimensions of the base plate 10 based on λ / 4 as described in the first embodiment above.

[0120] To address this issue, according to the structure of the second embodiment, the end offset De can be 0.075λ or more, more preferably 0.1λ or more, so even if the estimated value of the effective length of λ includes a slight error, it is not likely to become a problem. For example, by setting the end offset De to be larger than the estimated value of 0.075λ, the non-resonance condition can be satisfied. That is, according to the structure of the second embodiment, the generation of base plate resonance can be suppressed based on the estimated value of λ. Thus, according to the second embodiment, compared with the first embodiment, the manufacturing difficulty can be reduced, and the leakage current to the communication cable 61 can be suppressed. Furthermore, the structure described above, which serves as various supplementary descriptions and modifications (1) and (2) to the first embodiment, can also be applied to this second embodiment.

[0121] <Supplement to the overall structure of wireless communication device 1>

[0122] The wireless communication device 1 includes a housing 80 that houses a circuit board on which a zero-order resonant antenna element ANT, control circuitry 50, etc., are mounted. Furthermore, Figure 19 This is a conceptual diagram showing the internal structure of the housing 80. To ensure visual clarity, shading indicating material types is sometimes omitted for certain parts. Additionally, diagrams of structures such as the power supply point 31 are omitted.

[0123] The housing 80 is constructed, for example, by combining an upper housing and a lower housing that are separable in the vertical direction. The housing 80 is constructed, for example, using polycarbonate (PC) resin. Furthermore, various resins can be used as the material for the housing 80, such as synthetic resins made by mixing acrylonitrile-butadiene-styrene copolymer (so-called ABS) into PC resin, and polypropylene (PP). The housing 80 includes a housing bottom 81, a side wall portion 82, and a housing top plate portion 83. The housing bottom 81 is a structure that provides the base of the housing 80. The housing bottom 81 is formed into a flat plate shape. Inside the housing 80, a circuit board is configured such that a base plate 10 faces the housing bottom 81.

[0124] The side wall portion 82 is a structure that provides the side surface of the housing 80, and is erected vertically upward from the edge of the bottom 81 of the housing. The height of the side wall portion 82 is designed, for example, such that the separation between the inner surface of the top plate portion 83 of the housing and the opposing conductor plate 30 is λ / 25 or less. The top plate portion 83 of the housing is a structure that provides the upper surface portion of the housing 80. In this embodiment, the top plate portion 83 of the housing is formed into a flat plate shape. In addition, the top plate portion 83 of the housing can also adopt various shapes such as a dome shape. The top plate portion 83 of the housing is configured such that its inner surface faces the antenna forming surface 20A. A hole, i.e., a cable lead-out portion 84, for leading out communication cables 61, etc. is provided in the side wall portion 82. According to the structure of providing the cable lead-out portion 84 in the side wall portion 82, the mounting capability on the B-pillar 91, etc., can be improved.

[0125] When the top plate portion 83 of the housing is located near the opposing conductor plate 30, as in the structure described above, it is possible to suppress the upward propagation of the vertical electric field emitted through the LC resonance mode from the edge of the opposing conductor plate 30, thereby improving the radiation gain in the horizontal direction of the antenna. Here, "near the opposing conductor plate 30" refers to, for example, a region where the distance from the opposing conductor plate 30 is electrically less than 1 / 25 of the target wavelength.

[0126] In addition, such as Figure 19 As shown, an upper rib 831 that abuts against the edge of the opposing conductor plate 30 may also be formed on the top plate portion 83 of the housing. The upper rib 831 is a convex structure formed on the inner side of the top plate portion 83 of the housing facing downward. The upper rib 831 is configured to abut against the edge of the opposing conductor plate 30. The upper rib 831 achieves the following effects: it fixes the position of the support portion 20 inside the housing 80 and suppresses the spread of vertically polarized waves from the end of the opposing conductor plate 30 to the upper bottom plate, thereby improving the radiation gain in the horizontal direction of the antenna. A metallic pattern such as copper foil may also be applied to the vertical surface (i.e., the outer surface) of the upper rib 831 that connects to the edge of the opposing conductor plate 30.

[0127] Furthermore, it is preferable to fill the interior of the housing 80 with a sealing material such as silicone. As the sealing material, polyurethane resins such as polyurethane prepolymers can be used. Of course, in addition to this, epoxy resin, silicone resin, and many other materials can be used as the sealing material. Figure 19 To ensure visual clarity, illustrations of the sealing material are omitted. Based on the structure where the housing 80 is filled with sealing material, the sealing material located above the opposing conductor plate 30 achieves the following effects: suppressing the propagation of vertically polarized waves from the end of the opposing conductor plate 30 upwards to the bottom plate, and improving the radiation gain in the horizontal direction of the antenna. The housing 80 only needs to be formed of resin or ceramic having a specified relative permittivity at least for its side and top surfaces. Furthermore, the structure of filling the housing 80 with sealing material also improves water resistance, dust resistance, and vibration resistance.

[0128] Of course, the filling of the sealing material inside the housing 80 is arbitrary. The upper rib 831 is also arbitrary. Furthermore, the housing top plate 83, the upper rib 831, and the sealing material are equivalent to a structure that suppresses the spread of the vertical electric field emitted through the LC resonance mode from the edge of the opposing conductor plate 30 upwards (hereinafter, a wave shield). The above structure is equivalent to a structure in which a wave shield made of a conductor or dielectric is disposed on the upper side of the opposing conductor plate 30.

[0129] Either the housing bottom 81 or the housing top plate 83 of the housing 80 may be omitted. When either the housing bottom 81 or the housing top plate 83 is omitted, the sealing material is preferably a resin that maintains a solid state within the temperature range assumed to be the environment in which the wireless communication device 1 is used (hereinafter, the operating temperature range). The operating temperature range can be, for example, set to -30°C to 100°C. Furthermore, a structure that omits either the housing bottom 81 or the housing top plate 83 is a housing with either the upper or bottom surface of the housing as an opening.

[0130] <Postscript>

[0131] The present invention also includes the following structures.

[0132]

Structure (1)

[0133] An antenna module for transmitting and receiving radio waves at a specified target frequency, wherein the antenna module includes:

[0134] The base plate (10) is a rectangular conductor plate that is set to have a length of less than λ / 2 in the short side direction and a length of more than λ / 2 in the long side direction;

[0135] The opposing conductor plate (30) is a flat conductor component disposed at a predetermined interval from the base plate at a position offset from the center of the base plate in the long side direction, and is provided with a power supply point (31) electrically connected to the power supply line (51); and

[0136] A short-circuit section (40) is provided in the central area of ​​the opposing conductor plate, electrically connecting the opposing conductor plate and the base plate.

[0137] The antenna module is configured to use the inductance of the short-circuit section and the electrostatic capacitance formed by the base plate and the opposing conductor plate to resonate in parallel at the target frequency.

[0138] The antenna module is set such that the length (Lg) of the long side of the base plate satisfies the following formula: Lg=λ / 4×N+α (N is a natural number, λ is the wavelength of the target frequency, and α is a specified value above 0.025λ and below 0.225λ).

[0139]

Structure (2)

[0140] An antenna module for transmitting and receiving radio waves at a specified target frequency, wherein the antenna module includes:

[0141] The base plate (10) is a rectangular conductor plate that is set to have a length of less than λ / 2 in the short side direction and a length of more than λ / 2 in the long side direction;

[0142] The opposing conductor plate (30) is a flat conductor component disposed at a predetermined interval from the base plate at a position offset from the center of the base plate in the long side direction, and is provided with a power supply point (31) electrically connected to the power supply line (51); and

[0143] A short-circuit section (40) is provided in the central area of ​​the opposing conductor plate, electrically connecting the opposing conductor plate and the base plate.

[0144] The antenna module is configured to use the inductance of the short-circuit section and the electrostatic capacitance formed by the base plate and the opposing conductor plate to resonate in parallel at the target frequency.

[0145] The opposing conductor plate is set to have an end offset (De) of 0.075λ (λ is the wavelength of the target frequency) or more. The end offset is the distance from the end of the base plate near the opposing conductor plate, i.e. the end near the antenna (11), to the opposing conductor plate.

Claims

1. A wireless communication device for transmitting and receiving radio waves at a predetermined target frequency, wherein, The wireless communication device includes: The base plate is a rectangular conductor plate that is defined as having a shorter side length of less than λ / 2 and a longer side length of more than λ / 2. A zero-order resonant antenna element is positioned at a location offset by a predetermined amount from the center of the base plate along its longitudinal direction; and The circuit module performs signal processing for transmission and reception using the zero-order resonant antenna element. The zero-order resonant antenna element and the circuit module are configured to be arranged along the long side of the base plate. The zero-order resonant antenna element comprises: The opposing conductor plate is a flat conductor component spaced at predetermined intervals from the base plate, and is provided with a power supply point electrically connected to the power supply line; and A short-circuit section is provided in the central region of the opposing conductor plate, electrically connecting the opposing conductor plate and the base plate. The wireless communication device is configured to use the inductance of the short-circuit section and the electrostatic capacitance formed by the base plate and the opposing conductor plate to resonate in parallel at the target frequency. The wireless communication device is configured such that the length of the long side of the base plate satisfies Lg=λ / 4×N+α, where N is a natural number, λ is the wavelength of the target frequency, α is a specified value of 0.025λ or higher and 0.225λ or lower, and Lg is the length of the long side of the base plate.

2. A wireless communication device for transmitting and receiving radio waves at a predetermined target frequency, wherein, The wireless communication device includes: The base plate is a rectangular conductor plate that is defined as having a shorter side length of less than λ / 2 and a longer side length of more than λ / 2. A zero-order resonant antenna element is positioned at a location offset by a predetermined amount from the center of the base plate along its longitudinal direction; and The circuit module performs signal processing for transmission and reception using the zero-order resonant antenna element. The zero-order resonant antenna element and the circuit module are configured to be arranged along the long side of the base plate. The zero-order resonant antenna element comprises: The opposing conductor plate is a flat conductor component spaced at predetermined intervals from the base plate, and is provided with a power supply point electrically connected to the power supply line; and A short-circuit section is provided in the central region of the opposing conductor plate, electrically connecting the opposing conductor plate and the base plate. The wireless communication device is configured to use the inductance of the short-circuit section and the electrostatic capacitance formed by the base plate and the opposing conductor plate to resonate in parallel at the target frequency. The opposing conductor plate is set to have an end offset of 0.075λ or more, where λ is the wavelength of the target frequency, and the end offset is the distance from the end of the base plate near the opposing conductor plate (i.e., the end near the antenna) to the opposing conductor plate.

3. The wireless communication device according to claim 1 or 2, wherein, The opposing conductor plate is square or circular, and is positioned at a predetermined offset along its long side from a position concentric with the base plate. The power supply point is located on the edge of the opposing conductor plate in the direction of the center of the base plate.

4. The wireless communication device according to claim 1 or 2, wherein, A fold-back portion is provided at the end of the base plate in the long side direction, away from the opposing conductor plate, i.e., at the far end of the antenna. The fold-back portion is a conductor component extending toward the end of the base plate in the long side direction, near the opposing conductor plate, i.e., near the antenna.

5. The wireless communication device according to claim 1 or 2, wherein, A fold-back portion is provided at the end of the base plate near the opposing conductor plate, i.e., near the antenna, along the long side of the base plate. The fold-back portion is a conductor component extending toward the end of the base plate away from the opposing conductor plate, i.e., at the far end of the antenna.

6. The wireless communication device according to claim 1 or 2, wherein, On the side or under the opposing conductor plate, an additional conductor, serving as a plate-shaped conductor component, is positioned parallel to the base plate at a predetermined interval from the opposing conductor plate. The additional conductor is electrically connected to the base plate using a short-circuit pin, which is a conductive component.

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