Planar antenna for millimeter waves

Abstract

To suppress a decrease in gain in a planar antenna for millimeter wave.SOLUTION: A planar antenna 100 for millimeter wave includes: a substrate 10; a first patch part 20 disposed on the surface of the substrate; a via conductor 30 connected to the first patch part and extending in a plate thickness direction of the substrate; a transmission line 40 connected to the via conductor inside the substrate and extending in a second direction orthogonal to the plate thickness direction of the substrate and crossing the first direction; a first ground plate 50 which is disposed between the first patch part and the transmission line so as to face the first patch part inside the substrate and is provided with an open hole in which the via conductor inserts; a second ground plate 60 disposed on the surface opposite the surface where the first patch part is disposed; and a perturbation element 21 formed in the first patch part so as to generate a circular polarization of a phase that cancels circular polarization generated by the first direction and the second direction crossing.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a planar antenna for millimeter waves. [Background technology]

[0002] Conventionally, there is a radar device that is mounted on a vehicle or the like and detects obstacles by transmitting and receiving radio waves. The antenna device used in the radar device described in Patent Document 1 includes a resonant element, thereby suppressing multiple reflections of radio waves generated between the antenna device and a cover member, and suppressing deterioration of detection performance. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-7108 A Summary of the Invention [Problem to be solved by the invention]

[0004] The inventors discovered that in a planar antenna that transmits and receives millimeter-wave radio waves as linearly polarized waves, circular polarization occurs when power is fed from a direction intersecting the main polarization direction. In this case, there is a problem that the gain of the linearly polarized wave decreases and the detection performance decreases. [Means for solving the problem]

[0005] The present disclosure can be realized in the following forms.

[0006] According to one embodiment of the present disclosure, a millimeter wave planar antenna (100) is provided. This planar antenna is a millimeter wave planar antenna, and includes a substrate (10) including a dielectric, a first patch section (20) arranged on a surface of the substrate, a via conductor (30) that is connected to the first patch section at a position shifted a predetermined distance from the center of the first patch section in a first direction perpendicular to the thickness direction of the substrate and extends in the thickness direction of the substrate, and a via conductor (30) that is connected to the via conductor inside the substrate and extends in a second direction that is perpendicular to the thickness direction of the substrate and intersects with the first direction. The antenna includes a transmission line (40), a first ground plane (50) arranged between the first patch section and the transmission line so as to face the first patch section inside the substrate, the first ground plane (50) having a through hole through which the via conductor is inserted, a second ground plane (60) arranged on the surface of the substrate opposite the surface on which the first patch section is arranged, and a perturbation element (21) formed on the first patch section so as to generate a circularly polarized wave of a phase that cancels out a circularly polarized wave generated due to the intersection of the first direction and the second direction.

[0007] According to this form of planar antenna, a perturbation element is provided so as to generate a circularly polarized wave of a phase that cancels out the circularly polarized wave generated due to the intersection of the direction in which the connection position between the first patch portion and the via conductor is shifted from the center of the first patch portion and the extension direction of the transmission line. Therefore, the reduction in the linearly polarized wave component can be suppressed, and the reduction in the gain of the planar antenna as a linearly polarized wave can be suppressed. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a plan view illustrating a schematic configuration of a planar antenna according to a first embodiment. [Diagram 2] FIG. 2 is a cross-sectional view of FIG. [Diagram 3] FIG. 11 is a cross-sectional view illustrating a schematic configuration of a planar antenna according to a second embodiment. [Figure 4] FIG. 2 is a cross-sectional view taken along line II-II in FIG. [Diagram 5] FIG. 11 is a plan view illustrating a schematic configuration of a planar antenna according to a third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] A. First embodiment: A-1.Device configuration: The planar antenna 100 of this embodiment is mounted on, for example, a vehicle and is used to receive and / or transmit radio waves. In this embodiment, the planar antenna 100 is a millimeter wave planar antenna that transmits and receives millimeter wave band radio waves as linearly polarized waves. The planar antenna 100 may be mounted on a moving object such as an aircraft and used in addition to a vehicle. The planar antenna 100 may also be used as a component of a security system or a surveillance system.

[0010] 1 and 2, the planar antenna 100 includes a substrate 10, a patch unit 20, a via conductor 30, a transmission line 40, a first ground plane 50, and a second ground plane 60. The planar antenna 100 is configured as a printed circuit board, and the substrate 10 corresponds to an insulating base material of the printed circuit board. The patch unit 20, the via conductor 30, the transmission line 40, the first ground plane 50, and the second ground plane 60 correspond to conductor elements of the printed circuit board.

[0011] FIG. 1 shows arrows representing three mutually orthogonal coordinate axes, the X-axis, the Y-axis, and the Z-axis. The X-axis is parallel to the longitudinal direction of the substrate 10. The Y-axis is parallel to the lateral direction of the substrate 10. The Z-axis is parallel to the thickness direction of the substrate 10. In the following description, when specifying a direction, the positive direction indicated by the arrow is indicated by "+" and the negative direction opposite to the direction indicated by the arrow is indicated by "-", and both positive and negative signs are used to indicate the direction. The directions indicated by the arrows representing the X-axis, Y-axis, and Z-axis are the same in FIG. 1 and subsequent figures.

[0012] The substrate 10 is a plate-like member formed of a dielectric material such as resin. In this embodiment, the effective dielectric constant of the dielectric material forming the substrate 10 is 3.15. The substrate 10 is not limited to resin, and may be formed of a combination of resin and glass cloth or nonwoven fabric, or a material containing ceramic.

[0013] The patch unit 20 is a plate-like member having a square shape, formed of a conductor such as copper. The patch unit 20 includes a perturbation element 21 formed by cutting out a pair of opposing vertices of a square. The position and shape of the perturbation element 21 in the patch unit 20 will be described in detail later. The patch unit 20 is disposed on the surface of the substrate 10. The patch unit 20 corresponds to the "first patch unit" in this disclosure.

[0014] The via conductor 30 is a linear member formed of a conductor such as copper. The via conductor 30 is arranged to extend along the Z direction in a hole formed in the substrate 10. One end of the via conductor 30 is connected at a position shifted from the center PC of the patch unit 20 by a predetermined distance in the -Y direction. The center PC of the patch unit 20 in this embodiment corresponds to the center of gravity of the patch unit 20. In the following description, the connection point between the via conductor 30 and the patch unit 20 is also called the "feed point E". The offset of the feed point E from the center PC of the patch unit 20 is specified and set in advance by analysis or the like so as to obtain impedance matching. In addition, the polarization direction of the linearly polarized wave transmitted by the planar antenna 100 (hereinafter also called the "main polarization direction") is determined by the offset direction of the feed point E from the center PC of the patch unit 20, and in this embodiment, the main polarization direction is the Y direction. In the following description, the offset direction of the feed point E from the center PC of the patch unit 20 is also called the "offset direction". The offset direction corresponds to the "first direction" in this disclosure.

[0015] The transmission line 40 is a linear member formed of a conductor such as copper. The transmission line 40 is disposed inside the substrate 10 so as to extend along the X-direction. One end of the transmission line 40 is connected to one of the two ends of the via conductor 30 that is not the feeding point E of the patch unit 20. The other end of the transmission line 40 is connected to a power feeding circuit (not shown) and supplies high-frequency power to the patch unit 20 through the via conductor 30. In the following description, the extension direction of the transmission line 40 is also referred to as the "power feeding direction". In this embodiment, the offset direction and the power feeding direction are perpendicular to each other. The power feeding direction corresponds to the "second direction" in this disclosure.

[0016] The first ground plane 50 is a plate-like member made of a conductor such as copper. The first ground plane 50 is disposed inside the substrate 10 between the patch unit 20 and the transmission line 40 so as to face the patch unit 20. The first ground plane 50 has a through hole through which the via conductor 30 is inserted.

[0017] The second ground plane 60 is a plate-like member made of a conductor such as copper, similar to the first ground plane 50. The second ground plane 60 is disposed on the surface of the substrate 10 opposite to the surface on which the patch unit 20 is disposed. The first ground plane 50 and the second ground plane 60 are connected to a ground line of a power supply circuit (not shown) to provide a ground potential for the planar antenna 100.

[0018] In the planar antenna 100 that transmits and receives millimeter-wave radio waves as linearly polarized waves, the inventors have found that when the offset direction and the power supply direction intersect as described above, a potential difference occurs on the patch unit 20 due to the bias of the current in the via conductor 30, and a current flows in a direction different from the main polarization direction, generating a circularly polarized wave. For example, in the configuration shown in FIG. 1, a left-handed circularly polarized wave is generated. The perturbation element 21 is formed to generate a right-handed circularly polarized wave that cancels out the left-handed circularly polarized wave. More specifically, the perturbation element 21 is formed at two vertices of the patch unit 20 that are located in the second and fourth quadrants, when the center PC of the patch unit 20 is taken as the origin, an axis parallel to the offset direction is taken as the first axis, and an axis parallel to the power supply direction is taken as the second axis.

[0019] In this embodiment, the perturbation element 21 has a planar shape obtained by removing a region of the right-angled isosceles triangle, the length of which is in the range of more than 0.04 times and less than 0.05 times the long electrical wavelength of the radio wave of the operating frequency of the planar antenna 100, from the apex of the patch unit 20. The "long electrical wavelength" means a wavelength determined by the effective dielectric constant of the dielectric, and is obtained by dividing the operating frequency of the planar antenna 100 by the square root of the effective dielectric constant of the dielectric material forming the substrate 10. The shape of the perturbation element 21 in this embodiment is determined by performing a pre-analysis so as to widen the frequency band in which a gain exceeding a set threshold value can be obtained. The shape of the perturbation element 21 is not limited to the above-mentioned shape, and may be any shape.

[0020] According to the planar antenna 100 described above, since it is provided with the perturbation element 21 arranged to generate a circularly polarized wave of a phase that cancels out the circularly polarized wave generated due to the intersection of the offset direction and the power feeding direction, it is possible to suppress the decrease in the linearly polarized wave component and the decrease in the gain of the planar antenna 100 as a linearly polarized wave.

[0021] B. Second embodiment: 3 and 4, the planar antenna 100A of the second embodiment differs from the planar antenna 100 of the first embodiment in that it includes a plurality of short-circuit elements 31 arranged around the connection between the via conductor 30 and the transmission line 40 and electrically connecting the first ground plate 50 and the second ground plate 60. The other configurations of the planar antenna 100A are the same as those of the planar antenna 100 of the first embodiment, so the same configurations are denoted by the same reference numerals and detailed description thereof will be omitted.

[0022] The short element 31 is a linear member made of a conductor such as copper. The short element 31 is arranged inside the substrate 10 so as to extend along the Z-axis direction. The short element 31 is arranged on a circumference centered on the via conductor 30 at a certain interval from adjacent short elements 31, except for the portion overlapping with the transmission line 40. The interval between two adjacent short elements 31 is preferably equal to or less than ¼ of the wavelength of the radio wave at the operating frequency of the planar antenna 100A.

[0023] In a planar antenna having no short element 31, radio wave radiation occurs at the connection point between the via conductor 30 and the transmission line 40, resulting in a decrease in gain. According to the planar antenna 100A, the multiple short elements 31 arranged around the connection point between the via conductor 30 and the transmission line 40 provide a shielding effect, thereby suppressing radio wave radiation at the connection point between the via conductor 30 and the transmission line 40, thereby further suppressing a decrease in gain as linear polarization. The planar antenna 100A also provides the same effects as the planar antenna 100 of the first embodiment.

[0024] C. Third embodiment 5, the planar antenna 100B of the third embodiment differs from the planar antenna 100 of the first embodiment in that the planar antenna 100B includes a plurality of patch units 20 each including a perturbation element 21 and a plurality of patch units 20B each having a square shape and not including a perturbation element 21. The patch unit 20B corresponds to the "second patch unit" in the present disclosure.

[0025] The patch unit 20 and the patch unit 20B are respectively arranged on the front surface of the substrate 10B, and receive high-frequency power from a power supply circuit (not shown) through a phase shifter 70 arranged on the rear surface of the substrate 10B to control the phase of the transmission radio wave, a transmission line 40B, and a via conductor 30. In such a case, it is preferable that the transmission lines 40B connecting the patch unit 20 and the patch unit 20B to the phase shifter 70 are wired so that the distance between the transmission lines 40B is not close to each other and the wiring path is short. For this reason, since it is only necessary to arrange the patch unit 20 including the perturbation element 21 at the location where the offset direction and the power supply direction should intersect, it is not necessary to match the offset direction and the power supply direction, and this makes it possible to suppress a decrease in the degree of freedom of the wiring layout of the transmission line 40B.

[0026] Also, for example, a planar antenna mounted on a vehicle may have two planar antennas with different main polarization directions to prevent interference with radio waves transmitted from a radar device mounted on another vehicle. Although the main polarization direction can be changed by rotating the entire planar antenna, there are cases where the entire planar antenna cannot be rotated due to restrictions such as the arrangement with the power supply circuit. Even in such a case, in the planar antenna 100B, the main polarization direction can be changed only by the presence or absence of the perturbation element 21, the position where the perturbation element 21 is provided, and the wiring direction of the transmission line 40B, so that the reduction in the degree of freedom in designing the planar antenna 100B can be suppressed.

[0027] When the patch section has a square shape, the operating frequency of the patch is determined by the length of one side of the patch, but in the case of the patch section 20 having the perturbation element 21, the current flows around the part cut out as the perturbation element 21, so that the path of the current becomes longer. In this case, the operating frequency of the patch section 20 is lower than that of a form in which the perturbation element 21 is not provided. In a planar antenna in which a plurality of patch sections are arranged, if planar antennas with different operating frequencies are mixed, the gain as a linearly polarized wave decreases, so it is preferable that the patch section 20B is formed so that the operating frequency of the patch section 20 and the operating frequency of the patch section 20B match each other by lengthening the length of one side. By forming the patch section 20B in this way, the operating frequency of the patch section 20 and the operating frequency of the patch section 20B can be matched with each other, and the decrease in gain can be further suppressed.

[0028] The planar antenna 100B of the third embodiment described above provides the same effects as the planar antenna 100 of the first embodiment. In addition, in the case of arranging a plurality of patch units 20 and patch units 20B, the planar antenna 100B only requires arranging the patch units 20 equipped with the perturbation elements 21 at the locations where the offset direction and the power feeding direction should intersect. This eliminates the need to always match the offset direction and the power feeding direction, and thus makes it possible to suppress a decrease in the degree of freedom of the wiring layout of the transmission line 40B.

[0029] Furthermore, since the length of one side of patch section 20B is formed to be greater than the length of one side of patch section 20, the operating frequency of patch section 20, which becomes lower due to the presence of perturbation element 21, can be made to match the operating frequency of patch section 20B, thereby further suppressing the decrease in gain as a linearly polarized wave.

[0030] D. Other embodiments: (D1) In the above embodiment, the offset direction and the power supply direction are perpendicular to each other, but the present disclosure is not limited to this. The offset direction and the power supply direction may intersect at any angle other than a right angle.

[0031] The present disclosure is not limited to the above-mentioned embodiment, and can be realized in various configurations without departing from the spirit of the present disclosure. For example, the technical features in each embodiment corresponding to the technical features in the form described in the Summary of the Invention column can be appropriately replaced or combined in order to solve some or all of the above-mentioned problems or to achieve some or all of the above-mentioned effects. Furthermore, if the technical feature is not described as essential in this specification, it can be appropriately deleted. [Explanation of symbols]

[0032] REFERENCE SIGNS LIST 10...substrate, 20...patch portion, 21...perturbation element, 30...via conductor, 40...transmission line, 50...first ground plane, 60...second ground plane, 100...planar antenna

Claims

1. A planar antenna (100) for millimeter waves, A substrate (10) including a dielectric material; A first patch portion (20) disposed on a surface of the substrate; a via conductor (30) that is connected to the first patch portion at a position shifted from the center of the first patch portion by a predetermined distance in a first direction perpendicular to the thickness direction of the substrate and that extends in the thickness direction of the substrate; a transmission line (40) connected to the via conductor inside the substrate and extending in a second direction that is perpendicular to the thickness direction of the substrate and intersects with the first direction; a first ground plane (50) disposed between the first patch section and the transmission line inside the substrate so as to face the first patch section, the first ground plane having a through hole through which the via conductor is inserted; a second base plate (60) disposed on a surface of the substrate opposite to a surface on which the first patch portion is disposed; a perturbation element (21) formed on the first patch portion so as to generate a circularly polarized wave having a phase that cancels out a circularly polarized wave generated due to an intersection of the first direction and the second direction; Equipped with Flat antenna.

2. 2. A planar antenna as claimed in claim 1, The first and second ground planes are connected to each other by a plurality of short-circuit elements (31), the short-circuit elements (31) being arranged at intervals around a connection portion between the via conductor and the transmission line, and connecting the first and second ground planes. Flat antenna.

3. 3. The planar antenna according to claim 1, The first direction and the second direction are perpendicular to each other. Flat antenna.

4. 3. The planar antenna according to claim 1, the perturbation elements are formed at vertices of the first patch section that are located in a second quadrant and a fourth quadrant, when an axis parallel to the first direction is defined as a first axis and an axis parallel to the second direction is defined as a second axis, with the center of the first patch section as an origin. Flat antenna.

5. 3. The planar antenna according to claim 1, The first patch portion; A second patch portion (20B) disposed on the surface of the substrate and not including the perturbation element; Each has multiple The length of one side of the second patch portion is greater than the length of one side of the first patch portion. Flat antenna.

6. 3. The planar antenna according to claim 1, the perturbation element has a planar shape in which a right-angled isosceles triangle, the length of each of the equal sides of which is in a range greater than 0.04 times and less than 0.05 times the electrical long wavelength obtained by dividing the wavelength of the radio wave having the operating frequency of the planar antenna by the square root of the effective dielectric constant of the dielectric, is removed from the apex of the first patch section. Flat antenna.

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