JP7628982B2 - Planar antenna for millimeter waves - Google Patents

Description

This disclosure relates to a planar antenna for millimeter waves.

Conventionally, there are radar devices that are mounted on vehicles and the like to detect obstacles by transmitting and receiving radio waves. The antenna device used in the radar device described in Patent Document 1 is provided with a resonant element, which suppresses multiple reflections of radio waves that occur between the antenna device and the cover member, thereby suppressing deterioration of detection performance.

JP 2018-7108 A

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, resulting in poor detection performance.

This disclosure can be realized in the following forms:

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) disposed on the 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 device comprises a transmission line (40), a first ground plane (50) disposed between the first patch section and the transmission line so as to face the first patch section inside the substrate and having a through hole through which the via conductor is inserted, a second ground plane (60) disposed on the surface of the substrate opposite the surface on which the first patch section is disposed, 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 the circularly polarized wave generated due to the intersection of the first direction and the second direction.

This type of planar antenna is provided with a perturbation element that generates a circularly polarized wave of a phase that cancels out the circularly polarized wave that occurs when the direction in which the connection position between the first patch section and the via conductor is shifted from the center of the first patch section crosses the extension direction of the transmission line, thereby suppressing the decrease in the linearly polarized wave component and the decrease in the gain of the planar antenna as a linearly polarized wave.

1 is a plan view illustrating a schematic configuration of a planar antenna according to a first embodiment. 2 is a cross-sectional view taken along line II in FIG. 1. FIG. 11 is a cross-sectional view showing a schematic configuration of a planar antenna according to a second embodiment. This is a cross-sectional view taken along line II-II in FIG. FIG. 11 is a plan view showing a schematic configuration of a planar antenna according to a third embodiment.

A. First embodiment:
A-1. Device configuration:
The planar antenna 100 of this embodiment is mounted on, for example, a vehicle and performs at least one of receiving and transmitting 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.

As shown in Figures 1 and 2, the planar antenna 100 includes a substrate 10, a patch section 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 the insulating base material of the printed circuit board. The patch section 20, the via conductor 30, the transmission line 40, the first ground plane 50, and the second ground plane 60 correspond to the conductor elements of the printed circuit board.

In FIG. 1, arrows are shown representing three mutually orthogonal coordinate axes, the X, Y, and Z axes. 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, positive and negative signs are used in combination to indicate the direction, with the positive direction indicated by the arrow being "+" and the negative direction opposite to the direction indicated by the arrow being "-". Note that the directions indicated by the arrows representing the X, Y, and Z axes are the same in FIG. 1 and subsequent figures.

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, nonwoven fabric, or the like, or may be formed of a material containing ceramic.

The patch unit 20 is a plate-like member having a square shape, formed from 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.

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 a predetermined distance in the -Y direction from the center PC of the patch unit 20. 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 amount of deviation 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 referred to as the "main polarization direction") is determined by the deviation 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 deviation direction of the feed point E from the center PC of the patch unit 20 is also referred to as the "offset direction". The offset direction corresponds to the "first direction" in this disclosure.

The transmission line 40 is a linear member formed of a conductor such as copper. The transmission line 40 is arranged 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 via 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.

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.

The second ground plane 60, like the first ground plane 50, is a plate-like member made of a conductor such as copper. The second ground plane 60 is disposed on the surface of the substrate 10 opposite 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.

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 section 20 due to the bias of the current in the via conductor 30, and a circular polarization occurs due to the current flowing in a direction different from the main polarization direction. 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 section 20 located in the second and fourth quadrants, when the center PC of the patch section 20 is taken as the origin, the axis parallel to the offset direction is taken as the first axis, and the axis parallel to the power supply direction is taken as the second axis.

In this embodiment, the perturbation element 21 has a planar shape obtained by removing from the apex of the patch section 20 a region of the right-angled isosceles triangle in which the length of the equilateral sides is in the range of more than 0.04 times and less than 0.05 times the electrical long wavelength of the radio wave at the operating frequency of the planar antenna 100. The "electrical long 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 that forms 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.

The planar antenna 100 described above is provided with a perturbation element 21 that is arranged to generate a circularly polarized wave with a phase that cancels out the circularly polarized wave generated due to the intersection of the offset direction and the power supply direction, so that the reduction in the linearly polarized wave component can be suppressed, and the reduction in the gain of the planar antenna 100 as a linearly polarized wave can be suppressed.

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 plane 50 and the second ground plane 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 components are denoted by the same reference numerals and detailed description thereof will be omitted.

The short-circuit element 31 is a linear member made of a conductor such as copper. The short-circuit element 31 is arranged inside the substrate 10 so as to extend along the Z-axis direction. The short-circuit elements 31 are arranged on a circumference centered on the via conductor 30 with a certain distance between adjacent short-circuit elements 31, except for the portion that overlaps with the transmission line 40. The distance between two adjacent short-circuit elements 31 is preferably 1/4 or less of the wavelength of the radio wave at the operating frequency of the planar antenna 100A.

In a planar antenna without a short element 31, radio wave radiation occurs at the connection point between the via conductor 30 and the transmission line 40, reducing the gain. With 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, suppressing radio wave radiation at the connection point between the via conductor 30 and the transmission line 40, and further reducing the reduction in gain as linear polarization. The planar antenna 100A also provides the same effect as the planar antenna 100 of the first embodiment.

C. Third embodiment As shown in Fig. 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 this disclosure.

The patch section 20 and the patch section 20B are 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 transmitted 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 section 20 and the patch section 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 shorter. For this reason, since it is sufficient to place the patch section 20 equipped with 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 the reduction in the degree of freedom of the wiring layout of the transmission line 40B can be suppressed.

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. The main polarization direction can be changed by rotating the entire planar antenna, but it may not be possible to rotate the entire planar antenna due to constraints such as the placement of the power supply circuit. Even in such cases, the planar antenna 100B can change the main polarization direction simply by changing the presence or absence of the perturbation element 21, the position at which the perturbation element 21 is provided, and the wiring direction of the transmission line 40B, thereby suppressing a decrease in the design freedom of the planar antenna 100B.

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 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 without the perturbation element 21. In a planar antenna in which multiple 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 to form the patch section 20B 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.

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, when multiple patch sections 20 and patch sections 20B are arranged in the planar antenna 100B, patch sections 20 equipped with perturbation elements 21 may be arranged at locations where the offset direction and the power feed direction should intersect. This eliminates the need to necessarily match the offset direction and the power feed direction, and reduces the reduction in the degree of freedom of the wiring layout of the transmission line 40B.

In addition, the length of one side of patch section 20B is formed to be greater than the length of one side of patch section 20, so that the operating frequency of patch section 20, which is lowered by providing perturbation element 21, can be matched with the operating frequency of patch section 20B, and the decrease in gain as a linearly polarized wave can be further suppressed.

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.

The present disclosure is not limited to the above-described embodiments, and can be realized in various configurations without departing from the spirit of the present disclosure. For example, the technical features in each embodiment that correspond to the technical features in the form described in the Summary of the Invention column can be replaced or combined as appropriate to solve some or all of the above-described problems or to achieve some or all of the above-described effects. Furthermore, if a technical feature is not described in this specification as essential, it can be deleted as appropriate.

10...substrate, 20...patch section, 21...perturbation element, 30...via conductor, 40...transmission line, 50...first ground plane, 60...second ground plane, 100...planar antenna

Claims (6)

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