Antenna device

Abstract

To provide an antenna device that is small and can operate at multiple frequencies.SOLUTION: An antenna device 1 includes a ground plate 11, a power supply antenna 20 for high frequency (first frequency), and a non-power supply antenna 30 for low frequency (second frequency). The power supply antenna 20 is formed as a plate-shaped monopole antenna that is bent into an L-shape, and includes a power supply side counter part 21 and an extension part 22. The power supply side counter part 21 is a flat plate part that is opposed to the ground plate 11. The extension part 22 is configured to extend toward the ground plate 11 from the edge of the power supply side counter part 21. A power supply point is arranged at the root of the extension part 22. The non-power supply antenna 30 is formed as a metamaterial antenna and includes a non-power supply side counter part 31 and a short circuit part 32. The non-power supply side counter part 31 is arranged in close proximity to the power supply side counter part 21 so that a signal of the second frequency can propagate.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an antenna device equipped with an antenna that utilizes zero-order resonance, which is an applied technology of metamaterials. [Background technology]

[0002] Patent Document 1 discloses an antenna having a structure including a ground plate that is a flat metal conductor and functions as a ground, an opposing conductor plate that is a flat metal conductor and is arranged opposite the ground plate, and a short-circuit portion that electrically connects the center of the opposing conductor plate to the ground plate. This structure is a so-called mushroom structure, which is the same as the basic structure of a metamaterial. This type of antenna device can be considered, in one aspect, as an antenna that applies metamaterial technology, and is therefore sometimes referred to as a metamaterial antenna.

[0003] In a metamaterial antenna, the capacitance formed between the ground plane and the patch section and the inductance of the short-circuit section cause parallel resonance at a frequency corresponding to the capacitance and inductance. Among the dispersion characteristics of metamaterials, the phenomenon of resonance at a frequency where the phase constant β is zero (0) is called zeroth-order resonance. The phase constant β is the imaginary part of the propagation coefficient γ of the wave propagating through the transmission line. In one aspect, the above antenna can be considered an antenna designed to operate in the zeroth-order resonance mode at the desired operating frequency. Therefore, metamaterial antennas are sometimes called zeroth-order resonance antennas.

[0004] Patent Document 2 discloses a configuration in which an opposing conductor plate constituting a metamaterial antenna is virtually divided into a plurality of sub-patch sections by a plurality of slits, and a short circuit section is provided for each sub-patch section. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-5663 [Patent Document 2] Japanese Patent Application Publication No. 2019-129439 Summary of the Invention [Problem to be solved by the invention]

[0006] Some communication methods use multiple frequencies that are 500 MHz or more apart. For example, Wi-Fi (registered trademark) can use multiple frequencies, such as the 2.4 GHz band (2400 to 2497 MHz) and the 5 GHz band (5150 to 5730 MHz). As such, antenna devices are sometimes required to be configured to operate at multiple frequencies that are 500 MHz or more apart. In addition, antenna devices are also required to be compact (low profile).

[0007] The present disclosure has been made based on the above considerations or points of view, and one of its objectives is to provide an antenna device that is small and can operate at multiple frequencies. [Means for solving the problem]

[0008] The antenna device disclosed herein comprises a ground plate (11), a powered antenna (20) which is a conductive member for transmitting or receiving radio waves of a predetermined first frequency and has a feed point, and a parasitic antenna (30) which is a conductive member for transmitting or receiving radio waves of a second frequency lower than the first frequency and has no feed point, the powered antenna comprising a powered-side facing portion (21) which is a plate-like member arranged parallel to the ground plate at a predetermined distance, and an extension portion (22) which extends from the edge of the powered-side facing portion towards the ground plate and has a feed point at its lower end, the parasitic antenna comprising a parasitic-side facing portion (31) arranged adjacent to the powered-side facing portion so as to face the ground plate, and a parasitic-side short-circuit portion (32) which connects the center of the parasitic-side facing portion to the ground plate, and the antenna spacing which is the distance between the parasitic-side facing portion and the powered-side facing portion is set to a value which causes electromagnetic field coupling between the powered-side facing portion and the parasitic-side facing portion at the second frequency.

[0009] In the above antenna device, the powered antenna operates at the first frequency. The parasitic antenna included in the above antenna device has a configuration in which the opposing portion on the parasitic side is short-circuited at the center, allowing it to operate as a metamaterial antenna. The antenna spacing between the powered antenna and the parasitic antenna is set to a value that allows a signal at the second frequency to propagate from the powered antenna to the parasitic antenna by electromagnetic coupling. Therefore, at the second frequency, the parasitic antenna operates as a metamaterial antenna using the power propagated from the powered antenna. Unlike a monopole, a metamaterial antenna does not require a quarter-wavelength length. Therefore, with the above configuration, a compact antenna for the second frequency can be realized. In other words, with the above configuration, the antenna is compact and can operate in multiple frequency bands.

[0010] Note that the symbols in parentheses in the claims indicate a correspondence with the specific means described in the embodiments described below as one aspect, and do not limit the technical scope of the present disclosure. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 2 is an external perspective view of the antenna device. [Figure 2] FIG. 2 is a top view of the antenna device. [Figure 3] FIG. 2 is a cross-sectional view taken along line III-III shown in FIG. [Figure 4] FIG. 2 is a view of the antenna device as seen from the positive direction of the X-axis. [Figure 5] FIG. 2 is a side view of an antenna device provided with a support and a circuit. [Figure 6] FIG. 10 is a diagram showing an example of a metal plate that is the base of the power supply antenna. [Figure 7] 1A and 1B are diagrams illustrating the basic configuration of a metamaterial antenna. [Figure 8] 10 is a graph showing the VSWR for each frequency of the antenna device. [Figure 9] FIG. 10 is a diagram showing the directivity of the antenna device on the XY plane at 5.2 GHz. [Figure 10] FIG. 10 is a diagram showing the directivity of the antenna device in the XZ plane at 5.2 GHz. [Figure 11] 10 is a diagram showing the directivity of the antenna device in the XY plane at 2.4 GHz. FIG. [Figure 12] 10 is a diagram showing the directivity of the antenna device in the XZ plane at 2.4 GHz. FIG. [Figure 13] 10 is a graph showing VSWR for each frequency when the antenna spacing is changed. [Figure 14] 10 is a graph showing the relationship between the minimum VSWR and the antenna spacing in each frequency band. [Figure 15] FIG. 1 is a diagram showing an antenna device including a plurality of parasitic antennas. [Figure 16] 16 is a graph showing the relationship between VSWR and frequency of the antenna device shown in FIG. 15. [Figure 17] FIG. 10 is a diagram illustrating another example of a configuration in which a plurality of parasitic antennas are provided. [Figure 18] FIG. 10 is a diagram illustrating another example of a configuration in which a plurality of parasitic antennas are provided. [Figure 19] 10A and 10B are diagrams for explaining a configuration in which a short-circuit portion is provided in a power supply antenna. [Figure 20] 1 is a side view of an antenna device including a power feeding antenna provided with a short-circuit portion. [Figure 21] 10A and 10B are diagrams illustrating other configuration examples of the extension portion. [Figure 22] 10A and 10B are diagrams illustrating other configuration examples of the extension portion. [Figure 23] 10A and 10B are diagrams illustrating other configuration examples of the extension portion. [Figure 24] 24 is a graph showing the relationship between VSWR and frequency of an antenna device using an extension portion having the shape shown in FIG. 23. [Figure 25] FIG. 10 is a diagram illustrating another configuration example of the antenna device. [Figure 26] FIG. 26 is a top view of the antenna device shown in FIG. [Figure 27] FIG. 26 is a side view of the antenna device shown in FIG. [Figure 28] FIG. 26 is a view of the antenna device shown in FIG. 25 as viewed from the positive direction of the X-axis. [Figure 29] FIG. 26 is a diagram showing horizontal plane average gain for each frequency of the antenna device shown in FIG. [Figure 30] 10A and 10B are diagrams illustrating an example of the configuration of an antenna device provided with a resin case. [Figure 31] 10A and 10B are diagrams illustrating an example of a configuration in which a resin case has a protrusion. [Figure 32] 10A and 10B are diagrams illustrating an example of the positions where protrusions are formed. [Figure 33] 10A and 10B are diagrams showing other examples of forming protrusions. [Figure 34] 10 is a graph showing the change in VSWR depending on the amount of protrusions. [Figure 35] 10A and 10B are diagrams showing other examples of forming protrusions. [Figure 36] FIG. 36 is a cross-sectional view taken along line XXXVI-XXXVI shown in FIG. 35. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the following embodiments, and various modifications described below are also included within the technical scope of the present disclosure. Furthermore, various modifications other than those described below can be implemented without departing from the gist of the present disclosure. Various supplements and modifications can be implemented in appropriate combinations as long as no technical contradictions arise. Components having the same function are given the same reference numerals, and their description may be omitted. Furthermore, when only a portion of a configuration is mentioned, the description given elsewhere can be applied to the other portions.

[0013] In the present disclosure, "parallel" is not limited to a completely parallel state. The "parallel" state also includes a state inclined by several degrees to approximately 15 degrees. In other words, the expression "parallel" can include a state in which the two are roughly parallel (a so-called substantially parallel state). The expression "perpendicular" in the present disclosure is also not limited to a completely perpendicular state, but also includes a state inclined by several degrees to approximately 15 degrees. In the present disclosure, "opposed" refers to a state in which the two components face each other with a predetermined distance between them. The opposed state also includes a state in which the two components face each other roughly, such as a state in which the two components face each other at an angle of approximately 15 degrees.

[0014] The antenna device 1 of the present disclosure is used by being attached to a moving object such as a vehicle. The antenna device 1 may be attached to the roof of the vehicle, the upper edge of the windshield, the dashboard, a pillar, a door panel, a bumper, or the like. The antenna device 1 can be used by being connected to a communication ECU (Electronic Control Unit) mounted on the vehicle. The ECU can use signals received by the antenna device 1 and can also input transmission signals to the antenna device 1.

[0015] The antenna device 1 and the communication ECU can be connected by a coaxial cable, a feeder line, or the like. The antenna device 1 and the communication ECU may also be connected by one or more AV lines. The AV line is a low-voltage wire for automobiles, and is realized by covering a soft copper stranded wire with an insulating material such as vinyl chloride. The "A" in the AV line stands for low-voltage wire for automobiles, and the "V" stands for vinyl.

[0016] The antenna device 1 is configured to operate in two frequency bands, i.e., a first frequency band and a second frequency band, which are separated by 500 MHz or more. The first frequency band is a higher frequency band than the second frequency band. Both the first frequency band and the second frequency band may be frequency bands used by Wi-Fi (registered trademark). The antenna device 1 may be used for only either transmission or reception. Since radio wave transmission and reception are reversible, a configuration capable of transmitting radio waves of a certain frequency is also a configuration capable of receiving radio waves of that frequency. In the following description, the term "transmission and reception" refers to at least one of transmission and reception.

[0017] In the following, as an example, the antenna device 1 is configured to support the 2.4 GHz band of Wi-Fi and 5 GHz. In this embodiment, the first frequency band refers to the 5 GHz band from 5150 MHz to 5730 MHz, and the second frequency band refers to the 2.4 GHz band from 2400 MHz to 2497 MHz. The first frequency band has a larger bandwidth than the second frequency band. Specifically, the first frequency band has a bandwidth of 500 MHz or more.

[0018] Of course, the specific values ​​of the first frequency band and the second frequency band may be changed as appropriate depending on the application. The first frequency band and the second frequency band may be frequency bands used for different types of communication. The first frequency band may be a frequency band corresponding to channel 3, channel 5, channel 7, or channel 9 of UWB (Ultra Wide Band) defined in IEEE802.15.4z. Channel 3 is a channel with a center frequency of 4492 MHz, and channel 5 is a channel with a center frequency of 6489.6 MHz. Channel 9 is a channel with a center frequency of 7987.2 MHz. The bandwidth of each channel is 500 MHz.

[0019] The second frequency band may be the 2.4 GHz band (2402 MHz to 2480 MHz) used by Bluetooth (registered trademark). Alternatively, the second frequency band may be the 700 MHz band, 800 MHz band, 900 MHz band, 1.5 GHz band, 1.7 GHz band, 2 GHz band, 2.5 GHz band, 3.4 GHz band, 3.7 GHz band, 4.5 GHz band, etc. used in cellular communications (4G / 5G). The second frequency band may also correspond to frequency bands used in GNSS (Global Navigation Satellite System) and road-to-vehicle communications.

[0020] Any frequency belonging to a first frequency band corresponds to the first frequency. For example, the center frequency of the first frequency band corresponds to the first frequency. Note that the first frequency may be the lowest frequency, the highest frequency, or another frequency in the first frequency band. The first frequency band may be interpreted as a frequency range determined based on the targeted first frequency. Similarly, any frequency belonging to a second frequency band corresponds to the second frequency. For example, the center frequency of the second frequency band corresponds to the second frequency. The second frequency may be the lowest frequency, the highest frequency, or another frequency in the second frequency band. The second frequency band may be interpreted as a frequency range determined based on the targeted second frequency. Since the frequency bands are separated by 500 MHz or more, the second frequency can be a frequency that is 500 MHz or more lower than the first frequency.

[0021] Hereafter, "λ 1L " represents the first minimum wavelength, which is the wavelength of the radio wave with the lowest frequency in the first frequency band. 1L / 2" and "0.5λ 1L " refers to half the length of the first minimum wavelength, and "λ 1L / 4" and "0.25λ 1L " refers to a quarter of the first minimum wavelength. In this embodiment, the minimum frequency of the first frequency band is 5150 MHz. The wavelength of a 5150 MHz radio wave in a vacuum and in air (i.e., λ 1L ) is 58.2 mm. Therefore, λ 1L / 4 is approximately 14.6mm.

[0022] In the following, the first central wavelength, which is the wavelength of the radio wave at the central frequency of the first frequency band, will be referred to as "λ 1M " will also be written as ". 1M / 2" and "0.5λ 1M " refers to half the length of the first central wavelength, and "λ 1M / 4" and "0.25λ 1M " refers to a quarter of the first central wavelength.

[0023] Furthermore, from now on, the second central wavelength, which is the wavelength of the radio wave at the center frequency of the second frequency band, will be referred to as "λ 2M " will also be written as ". 2M / 2" and "0.5λ 2M " refers to half the length of the second central wavelength, and "λ 2M / 4" and "0.25λ 2M " refers to a quarter of the second center wavelength. In this embodiment, the center frequency of the second frequency band is approximately 2450 MHz. The wavelength of a 2450 MHz radio wave in a vacuum and in air (i.e., λ 2M ) is 122.4 mm. Therefore, λ 2M / 4 is approximately 30.6mm.

[0024] In this disclosure, "λ 1L " and "λ 1M ", "λ 2M Expressions using wavelength (λ), such as ", " are used to explain the dimensions of various components. The wavelength (λ) used to explain the dimensions of the components that make up the antenna device 1 can be understood as the electrical length. The electrical length here is the effective length that takes into account factors such as fringing electric fields and the wavelength shortening effect caused by dielectrics. The electrical length is also sometimes called the effective length.

[0025] <Specific Configuration of Antenna Device 1> 1 to 4, the antenna device 1 includes a ground plane 11, a power-fed antenna 20, and a parasitic antenna 30. The power-fed antenna 20 and the parasitic antenna 30 are arranged above the ground plane 11 at a predetermined interval along a predetermined parallel direction. In this embodiment, the Y-axis direction corresponds to the parallel direction.

[0026] The ground plane 11 is a plate-shaped conductive member made of a conductive material such as copper. Here, the plate-shaped member includes a thin film such as a metal foil. In other words, the ground plane 11 may be a conductive layer laminated (applied) by electroplating or the like on the surface of a resin plate such as a printed wiring board. The ground plane 11 may also be realized using a conductive layer disposed inside a multilayer substrate including multiple conductive layers and insulating layers. The ground plane 11 is electrically connected to a grounding cable via, for example, a power supply circuit, and provides a ground potential (in other words, a ground potential) for the antenna device 1.

[0027] The ground plate 11 has a first surface and a second surface. The first surface is the surface on which the parasitic antenna 30 is attached. The first surface may be referred to as the top surface. The second surface is the surface opposite to the first surface. The second surface may be referred to as the back surface or bottom surface. The direction perpendicular to the ground plate 11 is the up-down direction for the antenna device 1. The up-down direction is the direction from the second surface to the first surface of the two surfaces of the ground plate 11.

[0028] The ground plate 11 is formed in a rectangular shape. The configuration of the antenna device 1 will be described below by introducing the concept of a right-handed three-dimensional coordinate system having an X-axis, a Y-axis, and a Z-axis that are orthogonal to each other. The X-axis shown in various drawings such as FIG. 1 is parallel to the longitudinal direction of the ground plate 11, and the Y-axis is parallel to the lateral direction of the ground plate 11. The Z-axis is parallel to the up-down direction. In another embodiment, if the ground plate 11 is square, the direction along any one side can be set as the X-axis.

[0029] As shown in Fig. 2, the ground plate 11 has a size that can accommodate the power-fed antenna 20 and the parasitic antenna 30 when viewed from above. The length of the short side of the ground plate 11 is set to a value of 40 mm or less, such as 25 mm or 30 mm. The length of the long side of the ground plate 11 is set to a value of 60 mm or less, such as 35 mm, 40 mm, or 50 mm. The lengths of the short and long sides of the ground plate 11 are λ 2M The length of the short side of the base plate 11 may be 0.3λ. 2MThe length of the long side of the base plate 11 may be set to a value corresponding to 0.6λ. 2M The length of the ground plane 11 in the short direction may be set to a value corresponding to the second center wavelength (λ 2M ) and the length in the longitudinal direction may be set to be at least twice the length in the lateral direction. 2M Or, 0.8λ 2M The length of the base plate 11 in the longitudinal direction may be 0.8λ. 2M Or, 1.2λ 2M etc. may also be used.

[0030] As described above, the dimensions of the main plate 11 can be changed as appropriate. The shape of the main plate 11 as viewed from above can also be changed as appropriate. The main plate 11 may be circular or square. It may also be other polygonal shapes such as a hexagon or an octagon. The main plate 11 may have a line-symmetric shape such as a square or a regular hexagon, or a shape with rotational symmetry such as a parallelogram. The term "rectangular" includes a rectangle and a square. The term "circular" can include not only a perfect circle but also an ellipse.

[0031] As shown in FIG. 5, a support portion 12 may be formed on the upper side of the base plate 11. The support portion 12 is a plate-shaped insulator attached to the upper surface of the base plate 11. The support portion 12 is realized using any insulating material, such as prepreg, which is made by impregnating fibers such as glass or carbon with resin and then curing them, or solder resist. As mentioned above, the plate-shaped support portion 12 also includes a thin film (sheet-shaped support portion). A transceiver circuit 13 and a feeder line 14 may be formed on the support portion 12. The transceiver circuit 13 is a circuit module for performing signal processing on transmission signals and reception signals. The transceiver circuit 13 may include a connector to which a cable is connected, an IC chip (Integrated Circuit), a memory, and the like. The transceiver circuit 13 performs, for example, modulation, demodulation, frequency conversion, amplification, and the like. The feeder line 14 is a microstrip line / wiring pattern that electrically connects the transceiver circuit 13 and the power supply antenna 20. In this disclosure, the configuration including the base plate 11 and the support portion 12 is also referred to as a substrate 10.

[0032] The power supply antenna 20 is a conductive member for transmitting and receiving radio waves in the first frequency band. 1L The power supply antenna 20 is configured as a three-dimensional planar monopole antenna having a length of 1 / 4. The power supply antenna 20 can also be called a first antenna. The power supply antenna 20 includes a power supply side facing portion 21 and an extension portion 22.

[0033] The power feed side facing portion 21 is a plate-shaped conductive member made of a conductor such as copper. The power feed side facing portion 21 has a rectangular shape that is long in the Y-axis direction. The power feed side facing portion includes a power feed side first edge E11, a power feed side second edge E12, a power feed side third edge E13, and a power feed side fourth edge. The power feed side first edge E11 and the power feed side second edge E12 are each edges parallel to the Y-axis (i.e., long sides), and the power feed side third edge E13 and the power feed side fourth edge are each edges parallel to the X-axis (i.e., short sides). The power feed side first edge E11 is an edge located in the negative direction of the X-axis relative to the power feed side second edge E12. The power feed side third edge E13 is an edge located in the negative direction of the Y-axis relative to the power feed side fourth edge.

[0034] The power supply side facing portion 21 is disposed to face the ground plate 11 at a predetermined first distance (D1). The power supply side facing portion 21 is supported by the extension portion 22. The power supply side facing portion 21 may be supported by a resin block added onto the ground plate 11 or the support portion 12. D1 shown in FIG. 3 indicates the first distance, which is the distance between the power supply side facing portion 21 and the ground plate 11. The first distance (D1) is set to 5 mm, for example. Of course, the first distance (D1) may also be set to 3 mm, 4 mm, 6 mm, etc.

[0035] 2, L1x represents the length of the power supply side facing portion 21 in the X-axis direction, and L1y represents the length of the power supply side facing portion 21 in the Y-axis direction. The length of the power supply side facing portion 21 in the X-axis direction (L1x) may be set to various values, such as 2 mm, 3 mm, 5 mm, or 10 mm. The length of the power supply side facing portion 21 in the Y-axis direction (L1y) may be set to 15 mm, 17 mm, or 20 mm.

[0036] The extension portion 22 is a conductive member that extends from an edge of the power supply side facing portion 21 toward the ground plate 11. The extension portion 22 is oriented perpendicular to the ground plate 11, and its upper end is connected to a first edge of the power supply side facing portion 21. The extension portion 22 and the power supply side facing portion 21 may be at a right angle. A feed point is formed at the lower end of the extension portion 22. The feed point is the portion where the transceiver circuit 13 and the power supply antenna 20 are electrically connected via the feed line 14.

[0037] The extension portion 22 is also plate-shaped. The length of the extension portion 22 in the Y-axis direction is set to be the same as the length of the power supply side facing portion 21 in the Y-axis direction. The height (L1z) of the extension portion 22 may be approximately equal to the first distance (D1). Note that the length of the extension portion 22 in the Y-axis direction may be shorter than the length of the power supply side facing portion 21 in the Y-axis direction.

[0038] The sum of the length (L1x) of the power supply side facing portion 21 in the X-axis direction and the height (L1z) of the extension portion 22 is designed based on simulations or the like so that the power supply antenna 20 can transmit and receive radio waves in the first frequency band. For example, the sum of L1x and L1z is λ 1L That is, the distance from the feed point to the feed-side second edge E12 is set to a length equivalent to λ 1L The dimensions of each part are designed to be / 4.

[0039] 4, the extension portion 22 may be virtually divided into an upper portion 221 and a leg portion 222. The upper portion 221 is located above the leg portion 222 and refers to a region having the same width as the length of the power supply side opposing portion 21 in the Y-axis direction.

[0040] Leg portion 222 refers to a portion located below upper portion 221 and having a narrower width than upper portion 221. The width of leg portion 222 may be set to 1 mm, 3 mm, or the like. The height of leg portion 222 may be set to 2 mm, 3 mm, or the like. The length of upper portion 221 in the height direction may be 3 mm or 4 mm. A power feed point is provided at the lower end of leg portion 222. Leg portion 222 may be pin-shaped, rod-shaped, or wire-shaped and sufficiently thin compared to the length (L1y) of power feed side opposing portion 21 in the Y-axis direction.

[0041] The leg portion 222 is configured to prevent the entire lower end of the extension portion 22 from electromagnetically coupling with the ground plate 11. If the leg portion 222 were not provided, the extension portion 22 and the ground plate 11 would be closer to each other in a larger area, making it difficult for the extension portion 22 to function as a monopole antenna. The width and height of the leg portion 222 may be designed so that current supplied from the feed point flows toward the power supply side facing portion 21. The length of the upper portion 221 in the height direction may be adjusted so that the power supply side facing portion 21 and the ground plate 11 are separated by a first distance. The upper portion 221 and the power supply side facing portion 21 are plate-shaped members connected to the leg portion 222. Here, the term "plate-shaped" means that the upper portion 221 is not linear and has a width sufficiently larger than that of the leg portion 222, e.g., a shape having a width three or five times or more than that of the leg portion 222. Specifically, a shape having a width of 5 mm or more or 10 mm or more corresponds to a plate-shaped member as viewed from the leg portion 222. Such a power feeding antenna 20 corresponds to a plate-shaped monopole antenna, in which the portion of the radiating element that is at least a predetermined distance (for example, 3 mm) away from the power feeding point is formed in a plate shape.

[0042] As mentioned above, the wavelength of radio waves is subject to the shortening effect of the dielectric. Furthermore, since the power supply antenna 20 is plate-shaped, various current paths can be taken. Therefore, even if the combined value of L1x and L1z is approximately 7 mm to 10 mm, the power supply antenna 20 can operate as a monopole antenna for the first frequency band. The extension part 22 is fixed onto the support part 12 by soldering or the like so as not to be electrically connected to the base plate 11. The power supply antenna 20 may be supported by a three-dimensional object (e.g., a block) made of resin attached onto the base plate 11.

[0043] The feeding antenna 20 may be realized by, for example, bending the metal plate 20B shown in FIG. 6 at a right angle along the dashed line. The feeding antenna 20 may be realized by a thin metal film applied by plating or the like to the surface of a resin block having a thickness of a first distance. The extension portion 22 may be referred to as a hanging portion or a bent portion. The extension portion 22 may also be understood as a configuration that is erected relative to the substrate 10. Therefore, the extension portion 22 may be referred to as an erect portion. The feeding-side facing portion 21 may also be understood as a configuration that is extended from the upper end of the erect portion. The feeding antenna 20 may be referred to as a first antenna, a feeding element, or the like. The feeding-side facing portion 21 may also be referred to as a first facing portion, or the like.

[0044] The parasitic antenna 30 is a conductive structure for transmitting and receiving radio waves in the second frequency band. The parasitic antenna 30 is disposed adjacent to the powered antenna 20 on the positive side of the X-axis. The parasitic antenna 30 itself does not have a feed point. The parasitic antenna 30 is electromagnetically coupled to the powered antenna 20 in the second frequency band, and operates using power supplied from the powered antenna 20.

[0045] The parasitic antenna 30 comprises a parasitic side facing portion 31 and a short-circuit portion 32. As will be explained below, the parasitic side facing portion 31 is electrically connected to the ground plate 11 by the short-circuit portion 32 provided in its center. This structure corresponds to a mushroom structure, which is a basic structure of metamaterials. The parasitic antenna 30 is designed to have a size that allows it to function as a metamaterial antenna in cooperation with the ground plate 11 in the second frequency band. The parasitic antenna 30 can also be called a second antenna or a resonant structure. The parasitic side facing portion 31 can also be called a second facing portion.

[0046] The parasitic side facing portion 31 is a plate-shaped conductive member made of a conductive material such as copper. Similar to the powered side facing portion 21, the parasitic side facing portion 31 is arranged to face the ground plate 11 at a first distance. By being arranged to face the ground plate 11, the parasitic side facing portion 31 forms a capacitance according to the area of ​​the parasitic side facing portion 31 and the distance between the parasitic side facing portion 31 and the ground plate 11 (i.e., the first distance).

[0047] The parasitic-side facing portion 31 has a size that forms a capacitance that resonates in parallel with the inductance of the short-circuit portion 32 in the second frequency band. The area of ​​the parasitic-side facing portion 31 may be appropriately designed to provide a desired capacitance. The desired capacitance is a capacitance that operates in the second frequency band in cooperation with the inductance of the short-circuit portion 32. Note that if the operating frequency is f, the inductance of the short-circuit portion 32 is Ls, and the capacitance formed between the parasitic-side facing portion 31 and the ground plane 11 is C, then the relationship f≈1 / {2π√(Ls·C)} holds. The operating frequency (f) may be the center frequency of the second frequency band. A person skilled in the art would be able to determine an appropriate area for the parasitic-side facing portion 31 based on this relationship.

[0048] For example, the parasitic side facing portion 31 is formed in a square shape with a side length equal to the length (L1y) of the powered side facing portion 21 in the Y-axis direction. Of course, the parasitic side facing portion 31 may also be a square shape with a side length shorter or longer than L1y. The length (L2x) of the parasitic side facing portion 31 in the X-axis direction and the length (L2y) of the parasitic side facing portion 31 in the Y-axis direction may be set to 15 mm, 17 mm, 20 mm, or the like. The length of one side of the parasitic side facing portion 31 can be changed as appropriate and may be 20 mm, 25 mm, or the like. The larger the parasitic side facing portion 31, the greater the capacitance formed, and the lower the operating frequency of the parasitic antenna 30 may be. The dimensions of the parasitic side facing portion 31 can be determined taking into account the value of the second frequency, the wavelength shortening effect of surrounding components, and the like.

[0049] The length of the passive side facing portion 31 in the X-axis direction is 0.02λ 2M or 0.15λ 2MThe length in the Y-axis direction may be expressed in terms of wavelength, for example. The same applies to the length in the Y-axis direction. The parasitic side facing portion 31 may be circular, hexagonal, polygonal, or the like. The parasitic side facing portion 31 may have a line-symmetric shape such as a square or a regular hexagon, or may have a rotationally symmetric shape such as a parallelogram.

[0050] The length of each side of the passive side facing portion 31 is 0.25λ. 2M Rectangular shape set shorter than 0.25λ or diameter 2M The size of the parasitic antenna 30 may be set to fit within the circle. Because the parasitic antenna 30 is an antenna that utilizes zero-order resonance, the parasitic side facing portion 31 can be set to be sufficiently small compared to a patch antenna, which requires a size of half the wavelength.

[0051] The parasitic side facing part 31 is disposed at the same height (plane) as the fed side facing part 21, with the base plate 11 as the reference. The parasitic side facing part 31 can be supported by the short-circuit part 32. The parasitic side facing part 31 may be supported by a resin block (step) or pillar added on top of the base plate 11 or the support part 12.

[0052] The rectangular parasitic side facing portion 31 has four edges (sides). The parasitic side facing portion 31 is disposed with one side parallel to the X-axis. The four edges of the parasitic side facing portion 31 are hereinafter also referred to as a parasitic side first edge E21, a parasitic side second edge E22, a parasitic side third edge E23, and a parasitic side fourth edge E24. The parasitic side first edge E21 and the parasitic side second edge E22 correspond to a pair of opposite sides parallel to the Y-axis, and the parasitic side third edge E23 and the parasitic side fourth edge E24 correspond to a pair of opposite sides parallel to the X-axis.

[0053] The parasitic side facing portion 31 and the power-feeding side facing portion 21 are arranged side by side in the X-axis direction with a predetermined gap between them. Specifically, the parasitic side first edge E21 is arranged to face and be close to the power-feeding side second edge E12. The gap between the parasitic side facing portion 31 and the power-feeding side facing portion 21 corresponds to the antenna gap between the parasitic antenna 30 and the power-feeding antenna 20. In the present disclosure, the edge of the parasitic side facing portion 31 that is close to the power-feeding side facing portion 21 is also referred to as the close edge.

[0054] Here, "close proximity" refers to a state in which there is a distance sufficient to allow propagation of a high-frequency signal in the second frequency band, in other words, a distance sufficient to allow electromagnetic field coupling. The coupling limit, which is the upper limit of the distance for electromagnetic field coupling in the second frequency band, is, for example, 2.75 mm. The coupling limit may vary depending on the size of each part and the presence or absence of protrusions, which will be described later. The coupling limit may also vary depending on the required performance for radio waves in the second frequency band.

[0055] The coupling limit value may be determined based on simulations and required performance. If a voltage standing wave ratio (VSWR) in the second frequency band is allowed up to about 4, the coupling limit value may be set to 3.0 mm. The coupling limit value is 0.025 λ. 2M or 0.02λ 2M The coupling limit value may be expressed using wavelength, such as L2x. The coupling limit value may be defined based on L2x. For example, the coupling limit value may be one-sixth of L2x.

[0056] D2 in the figure indicates the antenna spacing. The antenna spacing (D2) may be set to a value smaller than the coupling limit value. The antenna spacing (D2) may be set to any value equal to or smaller than 3.0 mm. For example, the antenna spacing (D2) is set to 1.0 mm. The antenna spacing (D2) may also be set to 0.5 mm, 0.75 mm, 1.5 mm, etc. The antenna spacing (D2) may be set to a value smaller than 1 / 6 of L2x and greater than 1 / 50 of L2x.

[0057] The short-circuiting portion 32 is a conductive member that electrically connects the ground plane 11 and the parasitic side facing portion 31. The short-circuiting portion 32 may be a conductive pin (hereinafter referred to as a short pin) or a member made by processing a metal plate. The inductance of the short-circuiting portion 32 can be adjusted by adjusting the diameter and length of the short-circuiting portion 32. The length of the short-circuiting portion 32 is a first distance (D1). The diameter of the short-circuiting portion 32 is set to 2 mm, for example. Of course, the diameter of the short-circuiting portion 32 may also be 1.0 mm, 1.5 mm, or 3.0 mm. The cross section of the short-circuiting portion 32 may be configured as a polygonal prism such as a rectangle or a hexagon. For example, the cross section of the short-circuiting portion 32 may be a rectangle with a length of 1.5 mm in the X-axis direction and a length of 0.5 mm in the Y-axis direction.

[0058] The short-circuiting portion 32 may be a conductive member having one end electrically connected to the ground plane 11 and the other end electrically connected to the passive side facing portion 31. If the antenna device 1 is realized using a printed wiring board as the base material, a via provided in the printed wiring board can be used as the short-circuiting portion 32.

[0059] The short-circuit portion 32 is provided at the center of the opposing plate, which is the center of the parasitic side opposing portion 31. If the parasitic side opposing portion 31 is square or rectangular, the center of the parasitic side opposing portion 31 corresponds to the intersection of the diagonals. If the parasitic side opposing portion 31 is triangular, the inner center can be used as the center. The center of the triangular parasitic side opposing portion 31 may also be the orthocenter or circumcenter. The center of the parasitic side opposing portion 31 is determined geometrically.

[0060] The position where the short-circuit portion 32 is formed does not need to coincide strictly with the center of the opposing plate. The short-circuit portion 32 may be shifted from the center of the opposing plate by several millimeters. The short-circuit portion 32 only needs to be formed in the center of the parasitic side opposing portion 31. The center of the parasitic side opposing portion 31 refers to the area inside the line connecting the points that divide the opposing plate in a 1:5 ratio from the center to the edge. From another perspective, the center corresponds to the area where concentric figures obtained by reducing the parasitic side opposing portion 31 to about one-sixth of their original size overlap.

[0061] <Basic structure and operation of metamaterial antennas> Before explaining the operation of the antenna device 1, a basic configuration 200 of a metamaterial antenna and its operating principle will be explained using Fig. 7. Fig. 7 shows basic configuration 200 of a metamaterial antenna, which includes a ground plane 11x, a facing portion 31x, and a short-circuit portion 32x.

[0062] The feed point is positioned at the facing portion 31x at a location that allows impedance matching. Here, impedance matching refers to making the impedance value of the signal sending side and the impedance value of the signal receiving side approximately the same. Note that if the impedances are not matched, gain may decrease due to reflections, etc., and ultimately the practicality of the antenna may decrease.

[0063] A metamaterial antenna is an antenna that utilizes zero-order resonance, a phenomenon in which a metamaterial resonates at a frequency where the phase constant β becomes zero, among the dispersion characteristics of the metamaterial. A metamaterial antenna is characterized by its operation through LC parallel resonance between the capacitance (C) formed between the ground plate 11x and the opposing portion 31x and the inductance (L) of the short-circuit portion 32x. The resonant frequency corresponds to the operating frequency of the antenna.

[0064] In a metamaterial antenna, when power at an operating frequency is supplied from a feed point to the facing portion 31x, parallel resonance occurs due to energy exchange between the inductor and the capacitor, generating an electric field between the ground plate 11x and the facing portion 31x that is perpendicular to the ground plate 11x. That is, an electric field is generated in the Z-axis direction. This perpendicular electric field propagates from the short-circuit portion 32x toward the edge of the facing portion 31x. The perpendicular electric field becomes vertically polarized at the edge of the facing portion 31x and is radiated into space. Note that, in this disclosure, vertical polarization refers to radio waves whose electric field vibration direction is perpendicular to the ground plate 11x and the facing portion 31x, and may also be referred to as ground-vertically polarized waves or simply vertically polarized waves.

[0065] The propagation direction of the vertical electric field generated by the above-described LC parallel resonance (in other words, zero-order resonance) is symmetrical with respect to the short-circuit portion 32x, and therefore has approximately the same gain in all directions in the antenna horizontal plane. In other words, one metamaterial antenna has directivity in all directions (360°) from the center of the facing portion 31x toward its edge. In this disclosure, the antenna horizontal plane refers to a plane parallel to the ground plane 11x and the facing portion 31x. In this disclosure, the direction from the center of the facing portion 31x toward its edge is also referred to as the antenna horizontal direction. From another perspective, the antenna horizontal direction is a direction perpendicular to the Z-axis direction and includes the X-axis direction and the Y-axis direction. Simply put, the antenna horizontal direction corresponds to the lateral direction (in other words, the side) of the antenna device 1.

[0066] Furthermore, the operation of the antenna when it transmits (radiates) radio waves and the operation when it receives radio waves are reversible. Although the above explanation has been given using the example of radiating radio waves, the above configuration allows the antenna to receive vertically polarized waves arriving from the horizontal direction.

[0067] The above-described ground plane 11x, opposing portion 31x, and short-circuit portion 32 correspond, in this order, to the ground plane 11, the parasitic-side opposing portion 31, and the short-circuit portion 32 of the antenna device 1. The explanation of the operation of the basic configuration 200 above may be used as an explanation of the parasitic antenna 30. Note that, in the antenna device 1, the adjacent edge may be considered as the feeding point for the parasitic antenna 30.

[0068] In addition to metamaterial antennas, there are patch antennas, which use a metal plate facing a ground plane. Patch antennas utilize the resonance phenomenon that occurs when the path length of a current is λ / 2, and their operating principle differs from that of metamaterial antennas. Furthermore, while patch antennas require the radiating element to have a dimension that is λ / 2, metamaterial antennas do not require the opposing portion 31x to be λ / 2 in length. Furthermore, metamaterial antennas differ from patch antennas in terms of directivity. That is, patch antennas and planar inverted-F antennas form beams perpendicular to the ground plane (i.e., upward), whereas metamaterial antennas generally form beams horizontally rather than upward. Furthermore, patch antennas do not require a short-circuit, while metamaterial antennas require a short-circuit. Thus, metamaterial antennas differ from patch antennas in terms of their operating principle, directivity, and configuration.

[0069] <Operation of antenna device 1> Here, the operation of the antenna device 1 will be described. First, the feed antenna 20 has a feed point. The feed antenna 20 is electrically 1L The antenna device 1 is configured as a monopole antenna having a length of 1 / 4 and an open end formed in a plate shape. Therefore, in the antenna device 1, the power supply antenna 20 operates in the first frequency band. The open end refers to the end of the monopole antenna where no power supply point is provided.

[0070] Furthermore, the parasitic antenna 30 is disposed at a distance that allows electromagnetic field coupling with the powered antenna 20 in the second frequency band, and has a mushroom structure that operates as a metamaterial antenna in the second frequency band. Therefore, in the antenna device 1, the parasitic antenna 30 operates in the second frequency band. The operating principle as a metamaterial antenna is as explained using the basic configuration 200.

[0071] As described above, the antenna device 1 has two operation modes: a first mode in which the power-fed antenna 20 mainly operates, and a second mode in which the parasitic antenna 30 mainly operates due to electromagnetic coupling with the power-fed antenna 20.

[0072] Fig. 8 is a graph showing the measurement results of the VSWR for each frequency of the antenna device 1 with the antenna spacing (D2) set to 1.0 mm. The horizontal axis of the graph shown in Fig. 8 represents frequency, and the vertical axis represents VSWR. As shown in Fig. 8, it has been confirmed that the antenna device 1 has a VSWR of 3.5 or less in the range of 5.07 GHz to 6.88 GHz, which includes the first frequency band, and in the range of 2.37 GHz to 2.53 GHz, which includes the second frequency band. Furthermore, the VSWR is generally 3.0 or less in both the first and second frequency bands.

[0073] VSWR is an index that represents the degree of impedance matching, and the closer it is to 1, the better the impedance of the transmission line is matched. In the technical field of communication antennas, a range where the VSWR is 3.0 or 3.5 or less is generally considered to be a practical frequency range. Even when compared with such standards commonly used in this technical field, it can be seen that the antenna device 1 of the present disclosure can operate in two frequency bands.

[0074] Furthermore, with the antenna device 1 of this embodiment, the VSWR is 3.5 or less in the band from 5.07 GHz to 6.88 GHz on the high frequency side. In other words, an operating band exceeding 1.5 GHz (close to 1.8 Hz) can be realized. The operating band here refers to a frequency band that can be used for transmitting and receiving signals. In this disclosure, this refers to the frequency range in which the VSWR is 3.5 or less, but depending on the required performance and application, a frequency range in which the VSWR is 3 or less may be considered the operating band. Even when the frequency range in which the VSWR is 3 or less is considered the operating band, it is clear from FIG. 8 that the configuration of this disclosure can have an operating band of 1 GHz in the vicinity of 6 GHz.

[0075] The practical upper limit of VSWR may vary depending on the antenna's intended use. The lower the transmission power, the more relaxed the VSWR requirements are, and a relatively large value may be tolerated. A relatively large VSWR may also be tolerated when the antenna is used exclusively for reception. Therefore, depending on the intended use, a frequency range with a VSWR of 3.5 or 4 may also be considered the antenna's operating band.

[0076] Furthermore, in the configuration of the present disclosure, the feed antenna 20 targeted for the first frequency band is formed as a planar monopole antenna, enabling a wider bandwidth than an orthodox (linear) monopole antenna. If the feed antenna 20 were configured as a linear monopole antenna, the operating bandwidth on the high frequency side would be narrow, making it difficult to achieve an operating bandwidth of, for example, approximately 1 GHz. In other words, it is difficult to achieve a wide first frequency band with a linear monopole antenna. In response to this issue, the antenna device 1 has the advantage of being able to widen the operating frequency on the high frequency side with a relatively simple configuration.

[0077] 9 and 10 are diagrams showing the directivity of the antenna device 1 in the first frequency band (specifically, 5.2 GHz). FIG. 9 shows the directivity in the XY plane, in other words, the horizontal direction of the antenna. FIG. 10 shows the directivity in the XZ plane. As shown in FIGS. 9 and 10, the feed antenna 20 has directivity in both the horizontal direction of the antenna and the upward direction. This is because the feed antenna 20 is L-shaped in side view, that is, has an extension portion 22 that stands upright on the ground plate 11 and a feed-side facing portion 21 that is parallel to the ground plate 11. Simulations have confirmed that the antenna device 1 has similar directivity not only at 5.2 GHz but also at 6 GHz and 7 GHz.

[0078] 11 and 12 are diagrams showing the directivity of the antenna device 1 in the second frequency band (specifically, 2.4 GHz). FIG. 11 shows the directivity in the XY plane, in other words, the horizontal direction of the antenna. FIG. 12 shows the directivity in the XZ plane. As shown in FIG. 11, the power-fed antenna 20 has directivity in all directions in the horizontal direction of the antenna. This directivity coincides with the characteristics of a metamaterial antenna. This also shows that the parasitic antenna 30 is operating in the second frequency band.

[0079] Fig. 13 is a graph showing the results of measuring the VSWR for each frequency when the antenna spacing (D2) is changed while keeping the configuration (e.g., dimensions) of the powered antenna 20 and the parasitic antenna 30 constant. In Fig. 13, the dashed line shows the VSWR when D2 = 0.6 mm, the solid line shows the VSWR for each frequency when D2 = 1.0 mm, and the dashed-dotted line shows the VSWR for each frequency when D2 = 1.4 mm.

[0080] As shown in Figure 13, in the three test patterns described above, the first and second frequency bands may shift to lower frequencies as the antenna spacing (D2) decreases. However, in all patterns, two operating bands separated by 500 MHz or more are realized. With the antenna device 1, the desired two operating frequencies can be obtained by adjusting the antenna spacing (D2).

[0081] FIG. 14 is a graph showing simulation results of the minimum VSWR for each frequency band when the antenna spacing is changed. The solid line in FIG. 14 represents the transition of the minimum VSWR for each frequency band from 2 GHz to 2.7 GHz, and the dashed line in FIG. 14 represents the transition of the minimum VSWR for each frequency band from 5 GHz to 7.2 GHz. The high-frequency operating band indicated by the dashed line in FIG. 14 is derived from the powered antenna 20 and is therefore not significantly affected by the antenna spacing. On the other hand, the low-frequency operating band indicated by the solid line in FIG. 14 varies greatly depending on the antenna spacing. This is because the ease of electromagnetic coupling, in other words, the degree of impedance matching between the transmission path and the parasitic antenna 30, changes depending on the antenna spacing. As shown in FIG. 14, to ensure gain in the second frequency band, the antenna spacing is preferably set to a value between 0.35 mm and 2.74 mm. More preferably, the antenna spacing may be set to a value between 0.4 mm and 2.5 mm.

[0082] The antenna device 1 of this embodiment corresponds to a configuration in which a planar monopole antenna operating over a wide band near a first frequency is provided as a feeding element, and a metamaterial antenna for a second frequency is arranged adjacent to it. Generally, metamaterial antennas have the advantage of being able to be realized with dimensions of λ / 4 or less (i.e., small size), but have the disadvantage of a narrow operating band. For this reason, in this embodiment, the parasitic antenna 30 serving as a metamaterial antenna supports a relatively narrow frequency band, while the feeding antenna 20 supports a wider frequency band. This configuration of this embodiment makes it easier to support communication systems that use multiple frequency bands, such as Wi-Fi, 4G, and 5G, where each frequency band has a different bandwidth. Furthermore, the antenna device 1 of the present disclosure is capable of multiple resonances, has a low profile, and can transmit vertically polarized waves in all directions in the horizontal direction. Furthermore, the antenna device 1 of the present disclosure requires only one feeding point, simplifying the circuitry. The antenna device 1 of the present disclosure is suitable for a communication system that requires that the lower frequency side of two target frequency bands be a relatively narrow band and the higher frequency side be a wide band.

[0083] <Variation (1)> The antenna device 1 may include a plurality of parasitic antennas 30. For example, the antenna device 1 may have a configuration in which a second parasitic antenna 40 is arranged next to a first parasitic antenna 30 as the parasitic antenna 30, as shown in Fig. 15. In the configuration shown in Fig. 15, the powered antenna 20, the first parasitic antenna 30, and the second parasitic antenna 40 are arranged in this order in the positive direction of the X-axis. The second parasitic antenna 40 has a mushroom structure, similar to the first parasitic antenna 30. In other words, the second parasitic antenna 40 includes an opposing conductor plate 41 and a short-circuit portion 42.

[0084] The opposing conductor plate 41 is disposed adjacent to the parasitic side opposing portion 31 on the same plane as the parasitic side opposing portion 31, at a distance that allows electromagnetic field coupling with the parasitic side opposing portion 31 at the third frequency. The third distance (D3), which is the separation between the opposing conductor plate 41 and the parasitic side opposing portion 31, may also be set to 0.5 mm, 1.0 mm, 1.5 mm, or the like. The opposing conductor plate 41 has an area that forms a capacitance that resonates in parallel with the inductance of the short-circuit portion 42 at the third frequency. The opposing conductor plate 41 may be referred to as the third opposing portion, and the short-circuit portion 42 may be referred to as the third short-circuit portion.

[0085] The third frequency may be any frequency, for example, 3 GHz. Since the operating frequency decreases as the opposing conductor plate 41 becomes larger, when the third frequency is higher than the second frequency, the opposing conductor plate 41 may be smaller than the parasitic side opposing part 31. For example, the opposing conductor plate 41 may be a square with one side measuring approximately 12 mm to 14 mm.

[0086] Fig. 16 is a graph showing the results of a simulation of the VSWR for each frequency of the entire antenna device 1 when the opposing conductor plate 41 is a square with sides of 13 mm. As is clear from a comparison of Fig. 16 with Fig. 8, the addition of the second parasitic antenna 40 enables the antenna device 1 to operate at 2.9 GHz. As mentioned above, the operating frequency added by the addition of the second parasitic antenna 40 can be adjusted by the size of the second parasitic antenna 40, etc.

[0087] The installation position of the second parasitic antenna 40 is not limited to the opposite side of the fed antenna 20 as viewed from the first parasitic antenna 30. As shown in Fig. 17, the second parasitic antenna 40 may be placed on the opposite side of the fed antenna 20 as viewed from the first parasitic antenna 30. In other words, the second parasitic antenna 40 may be placed in the negative direction of the X-axis from the fed antenna 20. The distance between the opposing conductor plate 41 and the fed-side opposing portion 21 may be set to a value that allows electromagnetic coupling at the third frequency.

[0088] 18, the second parasitic antenna 40 may be disposed on the negative Y-axis side of the first parasitic antenna 30. The second parasitic antenna 40 may be disposed in a position shifted in the negative X-axis direction from the position illustrated in FIG. 18, for example, in a position facing both the feed side third edge E13 and the parasitic side third edge E23. The second parasitic antenna 40 may be disposed close to (adjacent to) the feed side third edge E13 or the feed side fourth edge. By providing multiple parasitic elements, further multiple resonances can be achieved.

[0089] <Variation (2)> As shown in Figures 19 and 20, the feed antenna 20 may include a feed-side short-circuiting portion 23, which is a conductive member that electrically connects the feed-side opposing portion 21 and the ground plane 11. The feed-side short-circuiting portion 23 may be a conductive pin (hereinafter referred to as a short pin) or a processed sheet metal member. The length of the feed-side short-circuiting portion 23 is the first distance (D1). The diameter of the feed-side short-circuiting portion 23 is set to 1 mm, for example. Of course, the diameter of the feed-side short-circuiting portion 23 may also be 0.5 mm or 1.5 mm. Like the non-feed-side short-circuiting portion 32, the feed-side short-circuiting portion 23 may be configured as a polygonal prism with a rectangular or hexagonal cross section.

[0090] The feed-side short-circuit portion 23 is disposed, for example, at a corner where the feed-side second edge E12 and the feed-side third edge E13 are connected. Of course, the position of the feed-side short-circuit portion 23 may be changed as appropriate. For example, the feed-side short-circuit portion 23 may be disposed at a corner where the feed-side second edge E12 and the feed-side fourth edge E13 are connected, or may be disposed at a position a predetermined distance away from the center or corner of the feed-side second edge E12. The feed-side short-circuit portion 23 may be provided at a position a predetermined distance (for example, 5 mm) away from the extension portion 22 on the feed-side third edge E13.

[0091] In a configuration including the power supply side short-circuit portion 23, impedance adjustment becomes easy. As a result, the gain of the antenna device 1 can be increased. The power supply antenna 20 including the power supply side short-circuit portion 23 corresponds to a planar inverted-F antenna. Paradoxically, the power supply antenna 20 of the embodiment can also be understood as a planar inverted-F antenna with the short-circuit portion removed. The power supply antenna 20 may be a planar monopole antenna or a planar inverted-F antenna.

[0092] Hereinafter, the short-circuit portion 32 provided in the parasitic antenna 30 will also be referred to as the parasitic-side short-circuit portion 32 in order to distinguish it from the power-fed side short-circuit portion 23 .

[0093] <Variation (3)> The leg portion 222 of the extension portion 22 may be configured in multiple stages as shown in FIG. 21 . That is, the leg portion 222 may include a primary leg 222a and a secondary leg 222b having different lengths (i.e., widths) in the Y-axis direction. The primary leg 222a is located below the secondary leg 222b and is formed thinner than the secondary leg 222b. The primary leg 222a is also electrically connected to the power feed line 14. The secondary leg 222b is located between the primary leg 222a and the upper portion 221 and is formed thicker than the primary leg 222a. The width of the secondary leg 222b may be a value between the width of the primary leg 222a and the width of the upper portion 221. In this way, the extension portion 22 may have a shape whose width increases stepwise from bottom to top. This configuration further reduces the risk of the extension portion 22 and the base plate 11 bonding together.

[0094] For the same reason, the extension portion 22 (mainly the upper portion 221) may have the shape of a downward-facing isosceles triangle as shown in Fig. 22. Alternatively, the extension portion 22 may have a pentagonal shape with a rectangle connected to the top of a downward-facing isosceles triangle, i.e., a downward-facing home plate shape, as shown in Fig. 23. The home plate shape is a pentagon in which two consecutive angles are right angles, and is a type of right-angled pentagon.

[0095] 23, the current in the feed antenna 20 can easily flow along the edge of the extension 22 to the feed-side opposing portion 21. As a result, the operating band on the high frequency side can be further widened.

[0096] Fig. 24 is a graph showing the results of a simulation of the relationship between frequency and VSWR in a configuration in which the extension portion 22 of the embodiment is configured in the downward-facing home plate shape shown in Fig. 23. As can be seen by comparing Fig. 18 with Fig. 24, by changing the shape of the extension portion 22, an even wider bandwidth can be achieved. Specifically, the operating band on the high frequency side can be expanded from 1.8 GHz to 3.14 GHz. It is also clear from the above simulation results that changing the shape of the extension portion 22 does not affect the operation of the parasitic antenna 30.

[0097] <Variation (4)> The parasitic side facing portion 31 may have a slit 33 extending from the edge toward the center of the facing plate. For example, the parasitic side facing portion 31 may have a slit 33 extending from the center of the parasitic side third edge E23 toward the center of the facing plate, as shown in FIG. 25. The antenna device 1a shown in FIG. 25 is a combination of the configurations disclosed as modified examples (2) and (3), with a slit 33 further provided in the parasitic side facing portion 31. That is, in the antenna device 1 shown in FIG. 25, the feed antenna 20 includes a feed side short-circuit portion 23, and the extension portion 22 is formed in a downward home plate shape, as shown in FIGS. 27 and 28. Furthermore, the parasitic side facing portion 31 has a slit 33 as shown in FIG. 26. The antenna device 1a shown in FIGS. 25 to 28 corresponds to an improved version of the antenna device 1 disclosed as an embodiment.

[0098] The slit 33 is parallel to the Y-axis. The width (Ws) of the slit 33 may be, for example, 3 mm or 5 mm. The length (Ls) of the slit 33 may be set to, for example, 40% or 45% of the length (L2y) of the parasitic side facing portion 31 in the Y-axis direction. Specifically, if L2y = 18 mm, Ls may be set to, for example, 8 mm. The slit 33 may be formed so as to terminate at the center of the facing plate or 1 mm before that. The slit 33 may be formed up to just before the short-circuit portion 32.

[0099] According to the above configuration, when the parasitic antenna 30 is realized using a metal plate, the portion cut out as the slit 33 can be used to realize the parasitic-side short-circuit portion 32. That is, a three-dimensional module serving as the parasitic antenna 30 can be manufactured by performing a process including a cutting step and a bending step on a single metal plate. The cutting step is a step of cutting out the portion corresponding to the slit 33 except for the portion to be used as the parasitic-side short-circuit portion 32, and the bending step is a step of bending the remaining portion corresponding to the parasitic-side short-circuit portion 32 at a right angle. According to the configuration in which the slit 33 is formed in the parasitic-side facing portion 31, part of the portion removed as the slit 33 can be used as the parasitic-side short-circuit portion 32, thereby reducing the manufacturing cost of the antenna device 1.

[0100] Furthermore, the developers of this disclosure verified the operation of an antenna device 1 without the slit 33 and found that, near 6 GHz, part of the current flows from the powered antenna 20 into the unpowered-side facing portion 31, causing the unpowered-side facing portion 31 to function as a patch antenna. Analysis of the current distribution also revealed that the current path when operating as a patch antenna is parallel to the X-axis. This is presumably because the length (L2x) of the unpowered-side facing portion 31 in the X-axis direction is unintentionally half the wavelength of the 6 GHz radio wave. If radiation in the upward direction of the antenna is not required, the above-described operation is unnecessary.

[0101] To address this issue, according to the antenna device 1 of this modified example, the slit 33 is formed in the parasitic side facing portion 31 so as to obstruct the current path when the device operates as a patch antenna. Therefore, according to this modified example, it is expected that the parasitic side facing portion 31 will be prevented from malfunctioning as a patch antenna.

[0102] Fig. 29 is a graph showing the change in horizontal plane average gain for each frequency depending on whether or not the slit 33 is present. The horizontal plane average gain is the average value of the gain for each azimuth in the horizontal direction of the antenna. The solid line in Fig. 29 shows the relationship between frequency and horizontal plane average gain for the antenna device 1a. The dotted line shows the relationship between frequency and horizontal plane average gain for a configuration in which the slit 33 is removed from the antenna device 1a.

[0103] As shown in Fig. 29, when the parasitic side facing portion 31 has the slit 33, the horizontal average gain at around 6 GHz is improved by about 4 dB compared to when the parasitic side facing portion 31 does not have the slit 33. This indicates that the provision of the slit 33 makes it difficult for the parasitic side facing portion 31 to function as a patch antenna, and the power that previously contributed to radiation in the upward direction of the antenna now contributes to radiation in the horizontal direction. In other words, the configuration shown in Fig. 25 has the effect of suppressing the parasitic side facing portion 31 from functioning as a patch antenna.

[0104] The frequency at which the parasitic side facing portion 31 operates as a patch antenna can vary depending on the length (L2x) of the parasitic side facing portion 31 in the X-axis direction and the surrounding dielectric. Because a patch antenna requires a current path of half the wavelength, it is predicted that the frequency at which the parasitic side facing portion 31 operates as a patch antenna will increase as L2x becomes shorter.

[0105] The position and extension direction of the slit 33 may be changed as appropriate. As another configuration, the slit 33 may be formed in a direction in which the parasitic-side short-circuit portion 32 is not present. The slit 33 may be formed in a position shifted a predetermined amount in the X-axis direction from the position shown in FIG. 26. Furthermore, the extension direction of the slit 33 does not necessarily have to be parallel to the Y-axis. The slit 33 may be formed parallel to the X-axis from any position on the parasitic-side first edge E21 or the parasitic-side second edge E22.

[0106] <Variation (5)> 30, the antenna device 1 may include a resin case 90 for protecting the feeding antenna 20 and the like. The resin case 90 is realized using, for example, polycarbonate (PC) resin. Note that various resins can be used as the material for the resin case 90, such as a synthetic resin obtained by mixing PC resin with acrylonitrile butadiene styrene copolymer (so-called ABS), or polypropylene (PP).

[0107] The resin case 90 can be handled by dividing it into a side wall portion 91 and a top plate portion 92, either physically or virtually. The side wall portion 91 is configured to provide the side surface of the resin case 90 and stands upward from the edge of the base plate 11. The top plate portion 92 is configured to provide the upper surface of the resin case 90. The top plate portion 92 may be formed, for example, in a flat plate shape. The outer surface of the top plate portion 92 may have any shape, such as a dome shape. The inner surface (back surface) of the top plate portion 92, which is the internal ceiling surface 92a, may be formed flat so as to face the base plate 11 / unpowered side facing portion 31, etc.

[0108] The resin case 90 may be configured such that the inner ceiling surface 92a abuts against the powered side facing portion 21 and the parasitic side facing portion 31. This configuration can be achieved by adjusting the height of the side wall portion 91. When the inner ceiling surface 92a abuts against the powered side facing portion 21 and the parasitic side facing portion 31, the wavelength shortening effect of the resin case 90 allows the powered side facing portion 21 and the parasitic side facing portion 31 to be further reduced in size.

[0109] Furthermore, the power-fed side facing portion 21 and the parasitic side facing portion 31 may be fixed to the interior ceiling surface 92a. For example, the antenna device 1 may be manufactured by assembling a resin case 90 to which the power-fed antenna 20 and the parasitic antenna 30 are fixed to the base plate 11. With this configuration, it is possible to omit members (such as resin blocks) for supporting the power-fed antenna 20 and the parasitic antenna 30, which have three-dimensional structures.

[0110] The side wall portions 91 may be fixed to the base plate 11 using screws, adhesive, or the like, so that the resin case 90 is fixed integrally with the base plate 11. In another embodiment, the antenna device 1 may be provided with a lower case. The lower case is a case that houses the base plate 11 and the like from below. The resin case 90 may be formed, for example, by combining an upper case and a lower case that are configured to be separable in the vertical direction.

[0111] Furthermore, if the distance between the power-supply side facing part 21 and the non-power-supply side facing part 31 (i.e., the antenna spacing) deviates from the design value, the antenna performance may change. Even if the amount of variation in the antenna spacing is the same, when the antenna spacing is smaller than the design value, the amount of variation in the frequency characteristics is larger than when the antenna spacing is larger than the design value.

[0112] For this reason, a protrusion 93 may be formed on the interior ceiling surface 92a as shown in FIG. 31. The protrusion 93 is configured to prevent the power-fed antenna 20 and the parasitic antenna 30 from getting too close to each other. The protrusion 93 protrudes downward from the portion of the interior ceiling surface 92a between the power-fed antenna 20 and the parasitic antenna 30. The protrusion 93 only needs to fulfill the role of regulating the positions of the power-fed antenna 20 and the parasitic antenna 30, and its length in the Z-axis direction may be on the order of a few millimeters. The protrusion 93 may be called a partition portion or a position regulating portion, etc.

[0113] The protrusions 93 may be provided on both ends of the gap, for example, as shown in Fig. 32. The gap here refers to the area located on the inner ceiling surface 92a between the power supply side facing portion 21 and the non-power supply side facing portion 31. Alternatively, the protrusions 93 may be provided in the center of the gap, as shown in Fig. 33. Furthermore, the protrusions 93 may be formed over the entire gap.

[0114] However, the protrusions 93 are made of resin and have a configuration that has a wavelength shortening effect. As the proportion of the protrusions 93 present in the gap increases, the effective antenna spacing for the second frequency signal may become longer. This may also change the impedance of the parasitic antenna 30 as seen from the powered antenna 20. Of course, performance degradation due to the protrusions 93 can be reduced by designing the dimensions, etc., taking into account the effect of the protrusions 93, but this may result in an increase in design man-hours. For these reasons, it is preferable to provide as few protrusions 93 as possible in the gap.

[0115] Fig. 34 is a graph showing the results of a test on the effect on frequency characteristics of the amount of protrusions placed in the gaps. The solid line in the figure represents the case where no protrusions 93 are placed in the gaps, and the dashed line represents the case where protrusions 93 are placed only on both ends of the gaps (pattern A) as shown in Fig. 32. The dashed-dotted line represents the case where protrusions 93 are placed over the entire gap (pattern B). It can also be seen from Fig. 34 that the more protrusions 93 occupying the gaps, the more difficult it becomes for parasitic antenna 30 to operate.

[0116] Note that the protrusions 93 only need to fulfill the role of regulating the position of each antenna, and their position and shape can be modified as appropriate. For example, as shown in FIGS. 35 and 36 , multiple protrusions 93 may be formed to fit into holes 34 formed in the parasitic side facing portion 31. Similarly, the protrusions 93 may be formed to fit into holes 24 formed in the powered side facing portion 21. The diameters of the holes 24 and 34 may be approximately several millimeters. The diameter of the protrusions 93 may be set to a value corresponding to the diameters of the holes 24 and 34. While FIG. 35 illustrates an example in which holes 34 are formed in the four corners of the parasitic side facing portion 31, the positions and number of the holes 34 may be modified as appropriate. The holes 34 for engaging the parasitic side facing portion 31 may be formed in only one pair of diagonal corners. The number of engaging locations may be three, five, or more.

[0117] The transmission / reception circuit 13 is an optional element and may be omitted. The antenna device 1 including the transmission / reception circuit 13 can be considered as a communication device in one aspect. The antenna device 1 of the present disclosure may be implemented in the form of a communication device or a communication system. [Explanation of symbols]

[0118] 1·1a antenna device, 10 substrate, 11 base plate, 12 support portion, 20 power-supply antenna, 21 power-supply side facing portion, 22 extension portion, 23 power-supply side short-circuit portion, 30 parasitic antenna, 31 parasitic side facing portion, 32 short-circuit portion (parasitic side short-circuit portion), 33 slit, 40 second parasitic antenna, 90 resin case, 91 side wall portion, 92 case top plate portion, 92a inner ceiling surface, 93 protrusion portion

Claims

1. A main plate (11), a feeding antenna (20) that is a conductor member for transmitting or receiving radio waves of a predetermined first frequency and has a feeding point; a parasitic antenna (30) that is a conductor member for transmitting or receiving radio waves at a second frequency that is lower than the first frequency and that does not have a feeding point; The feeding antenna is a power supply side facing portion (21) which is a plate-like member arranged parallel to the base plate at a predetermined interval; an extension portion (22) extending from an edge portion of the power supply side facing portion toward the base plate, the power supply point being provided at a lower end thereof; The parasitic antenna is a non-power-fed side facing portion (31) disposed adjacent to the power-fed side facing portion so as to face the ground plane; a parasitic side short-circuit portion (32) connecting a center portion of the parasitic side facing portion and the ground plane, an antenna device in which the antenna spacing, which is the distance between the unpowered side opposing portion and the powered side opposing portion, is set to a value at which the powered side opposing portion and the unpowered side opposing portion are electromagnetically coupled at the second frequency;

2. 2. The antenna device according to claim 1, wherein the passive side facing portion has a slit (33) of a predetermined width extending from an edge portion thereof toward a center portion thereof.

3. 3. The antenna device according to claim 2, wherein the slit is formed parallel to a gap between the passive side facing portion and the powered side facing portion.

4. 2. The antenna device according to claim 1, wherein the feeding antenna is configured as a plate-shaped monopole antenna in which a portion of the feeding antenna that is a predetermined distance or more away from the feeding point is formed in a plate shape.

5. The antenna device according to claim 1, further comprising a power supply side short-circuiting portion (23) that short-circuits the power supply side opposing portion.

6. The antenna device according to claim 1 , wherein the feed antenna is configured as a planar inverted-F antenna.

7. 2. The antenna device according to claim 1, wherein the passive side facing portion has a rectangular shape, and the length of each side is set to be shorter than one-fourth of the wavelength of the second frequency.

8. 2. The antenna device according to claim 1, wherein the passive side facing portion is sized to fit within a circle whose diameter is one-fourth the wavelength of the second frequency.

9. 2. The antenna device according to claim 1, wherein the power-supply-side facing portion and the non-power-supply-side facing portion are each formed as a metal foil on a surface of or inside a resin plate provided parallel to the ground plane.

10. a resin case (90) for accommodating the powered antenna and the parasitic antenna; 2. The antenna device according to claim 1, wherein the resin case is provided with a protrusion (93) that abuts against each of the powered antenna and the parasitic antenna to restrict a change in position of the parasitic antenna relative to the powered antenna.

11. The power supply side facing portion has a rectangular shape, The antenna device according to claim 1 , wherein the passive side facing portion is disposed adjacent to the powered side facing portion in the lateral direction.

12. The antenna device according to claim 1 , wherein the extension portion has a width that decreases as it approaches the base plate.

13. The antenna device according to claim 1 , wherein the extension portion has a shape of a downward-facing isosceles triangle or a pentagon formed by connecting a rectangle to a downward-facing isosceles triangle.

14. 2. The antenna device according to claim 1, wherein the antenna spacing is set to 0.35 mm to 2.74 mm.

15. The antenna device according to claim 1 , wherein a plurality of the parasitic antennas operating in different bands are arranged around the powered antenna.

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