JP6981592B2 - Antenna device - Google Patents

Description

The present invention relates to an antenna device.

Conventionally, there is an antenna device mounted on a radar device in which transmission antennas for transmitting radio waves are arranged on a substrate. In such an antenna device, the radio waves transmitted by the transmitting antenna may cause multiple reflections between the radome and the substrate, and the radio waves of the adjacent transmitting antennas may interfere with each other to cause radio wave interference.

Therefore, there is an absorbing member (for example, AMC; Artificial Magnetic Conductor) that absorbs radio waves on the substrate of the antenna device, and the absorbing member absorbs the radio waves reflected on the substrate side (see, for example, Patent Document 1). ).

Japanese Unexamined Patent Publication No. 2017-11369

However, in the prior art, there is room for further improvement in preventing radio wave interference that occurs between adjacent antennas. Specifically, the absorption member has different efficiencies in absorbing radio waves depending on the incident angle of the radio waves. For this reason, in the prior art, radio waves may not be sufficiently absorbed and radio wave interference may not be suppressed depending on the incident angle of the absorbing member.

The present invention has been made in view of the above, and an object of the present invention is to provide an antenna device capable of suppressing radio wave interference generated between adjacent antennas.

The present invention includes a substrate, a radome, and an absorption unit in the antenna device. The substrate is arranged in parallel so that the antennas in which a plurality of antenna elements are arranged along the microstrip line are substantially parallel to each other. The radome has a main surface substantially parallel to the substrate and covers the substrate from the side on which the antenna is arranged. The absorption unit is provided in a thin film between the antennas on the substrate, and a plurality of absorption members having different absorption characteristics of radio waves transmitted or received by the antenna are arranged. Further, the absorption unit sets the reflection loss of the radio wave to a predetermined value or less when the radio wave is incident in the incident angle range between the first incident angle and the second incident angle different from the first incident angle. The distance from the position on the substrate to the antenna when the absorption member having the absorption characteristic reflects the radio wave transmitted from the antenna on the upper surface of the redome and is incident at the first incident angle. Is the minimum value, and the distance from the position on the substrate to the antenna when the radio wave transmitted from the antenna is reflected by the lower surface of the radome and is incident at the second incident angle is the maximum value. It is provided so as to be arranged in a range.

According to the present invention, it is possible to suppress radio wave interference that occurs between adjacent antennas.

FIG. 1 is a schematic cross-sectional view of the antenna device. FIG. 2A is a diagram (No. 1) showing a specific example of the absorption characteristics with respect to the incident angle of the absorption member. FIG. 2B is a diagram (No. 2) showing a specific example of the absorption characteristics with respect to the incident angle of the absorption member. FIG. 2C is a diagram (No. 1) showing a specific example of the absorption characteristics in which the absorption members are combined. FIG. 3A is a diagram showing a method of determining the arrangement position of the absorbing member. FIG. 3B is a diagram showing an example of arrangement of the transmitting antenna and the absorbing unit. FIG. 4A is a diagram (No. 1) showing a specific example of the absorption characteristic with respect to the frequency of the absorption member. FIG. 4B is a diagram (No. 2) showing a specific example of the absorption characteristics with respect to the frequency of the absorption member. FIG. 4C is a diagram (No. 2) showing a specific example of the absorption characteristics in which the absorption members are combined. FIG. 5A is a schematic cross-sectional view of the radome. FIG. 5B is a diagram showing an example of absorption characteristics in which a radome having an uneven portion and an absorption member are combined.

Hereinafter, the antenna device according to the embodiment will be described in detail with reference to the accompanying drawings. The present invention is not limited to the embodiments shown below.

First, an outline of the antenna device according to the embodiment will be described with reference to FIG. FIG. 1 is a diagram showing an outline of an antenna device. In addition, in FIG. 1, in order to make the explanation easy to understand, three-dimensional Cartesian coordinates including the Z axis whose positive direction is vertically upward are also shown. The Cartesian coordinates may be shown in other drawings used in the following description.

As shown in FIG. 1, the antenna device 1 includes a substrate 2, a radome 5, and an absorption unit 30. A plurality of transmitting antennas 10 for transmitting radio waves W are arranged on the substrate 2. The transmitting antenna 10 is an example of an antenna. Further, the substrate 2 may be provided with a receiving antenna for receiving the radio wave W. Further, the substrate 2 may be provided with a transmission / reception antenna for transmitting and receiving radio waves W.

The transmitting antenna 10 is a so-called microstrip antenna. The radio wave W transmitted from the transmitting antenna 10 is irradiated to the outside of the antenna device 1 via the radome 5. By receiving the reflected wave reflected by the target by the receiving antenna (not shown), the position of the target, the relative speed, and the like can be detected.

However, as shown in FIG. 1, not all the radio waves W pass through the radome 5, and a part of the radio waves W may be reflected on the substrate 2 side by the radome 5. In this case, the radio wave W is reflected by the substrate 2, and multiple reflection of the radio wave W is generated between the substrate 2 and the radome 5.

Due to such multiple reflections, radio wave interference transmitted from the adjacent transmitting antenna 10 causes radio wave interference with each other, and the phase and amplitude of the radio wave W are disturbed. Further, due to such multiple reflections, the direct wave and the multiple reflection waves interfere with each other, which may cause a phenomenon in which the radiation directivity is distorted. There was room for further improvement in suppressing the distortion of the radial directivity of the antenna. Therefore, in the prior art, there is one provided with an absorbing member that absorbs the radio wave W in order to suppress multiple reflections.

As such an absorbing member, an AMC (Artificial Magnetic Conductor) is used. The AMC is printed so as to have a so-called periodic structure in which copper foil or the like is installed on the substrate at a predetermined cycle, and the radio wave is attenuated by resonating with the radio wave incident on the AMC.

Here, the AMC has different efficiency of absorbing radio waves (hereinafter referred to as absorption characteristics) depending on the incident angle and frequency of the radio waves. However, in the prior art, a single AMC was placed on the substrate. Therefore, in the prior art, only a part of the radio waves matching the absorption characteristics of the AMC could be absorbed.

Therefore, the antenna device 1 according to the embodiment is provided with an absorption unit 30 in which a plurality of absorption members 31 having different absorption characteristics are arranged. That is, the antenna device 1 can efficiently absorb the radio wave W by using the absorption members 31 having different absorption characteristics in combination.

For example, the antenna device 1 can widen the incident angle of the radio wave W that can be absorbed by using the absorbing member 31 having different absorption characteristics with respect to the incident angle of the radio wave W in combination. Details of this point will be described later with reference to FIGS. 2A to 2C, FIGS. 3A and 3B.

Further, the antenna device 1 can expand the frequency of the radio wave W that can be absorbed by using the absorbing member 31 having different absorption characteristics with respect to the frequency in combination. Details of this point will be described later with reference to FIGS. 4A to 4C.

As described above, the antenna device 1 according to the embodiment can efficiently absorb the radio wave W by providing the absorption unit 30 in which the absorption members 31 having different absorption characteristics are arranged. Therefore, in the antenna device 1 according to the embodiment, it is possible to suppress radio wave interference generated between adjacent transmitting antennas 10. In addition, it is possible to suppress the distortion of the radiation directivity of the antenna caused by the multiple reflections between the radome and the substrate.

In the antenna device 1 according to the embodiment, it is also possible to form fine irregularities on the radome 5 to improve the transmittance of the radio wave W in the radome 5. In other words, by suppressing the reflection of the radio wave W from the radome 5 to the substrate 2 side, it is possible to suppress the multiple reflection of the radio wave W. Details of this point will be described later with reference to FIGS. 5A and 5B.

Next, the details of the absorption characteristics of the absorption member 31 will be described with reference to FIGS. 2A to 2C. 2A and 2B are diagrams showing specific examples of absorption characteristics with respect to the incident angle of the absorption member 31, and FIG. 2C is a diagram showing specific examples of absorption characteristics in combination with the absorption member 31.

Note that FIG. 2A shows the absorption characteristics of the absorption member 31a with respect to the incident angle of the radio wave W, and FIG. 2B shows the absorption characteristics of the absorption member 31b with respect to the incident angle of the radio waves W. Further, in FIGS. 2A to 2C, the horizontal axis shows the incident angle of the radio wave W with respect to the absorbing member 31, and the vertical axis shows the reflection loss of the radio wave W at the incident angle.

Further, in FIGS. 2A to 2C, the vertical upward direction (Z axis) with respect to the absorbing member 31 is set to 0 deg, and the absorption characteristics when the radio wave W is incident on the absorbing member 31 from the negative direction side are shown. The absorption characteristics on the positive direction side are axisymmetric with the absorption characteristics on the negative direction side at 0 deg.

Here, it is assumed that the transmitting antenna 10 (see FIG. 1) transmits a radio wave W in the 76 GHz to 77 GHz band, and FIGS. 2A to 2C show absorption characteristics for an intermediate frequency of 76.5 GHz.

As shown in FIG. 2A, the absorbing member 31a can efficiently attenuate the radio wave W in the range r1 of the incident angles θ1 to θ2 in which the reflection loss is −10 dB or less, for example.

Further, as shown in FIG. 2B, since the absorption member 31b has a reflection loss of the radio wave W of −10 dB or less in the range r2 of the incident angle θ3 to θ4, the radio wave W can be efficiently attenuated in the range r2. Is.

Therefore, the antenna device 1 can absorb the radio wave W having a wider incident angle by using the absorbing member 31a and the absorbing member 31b in combination.

Specifically, as shown in FIG. 2C, when the absorbing member 31a and the absorbing member 31b are used in combination, the reflection loss is −10 dB or less in the range r3 of the incident angle θ2 to θ3.

That is, the range r3 is wider than the range r1 of the absorbing member 31a and the range r2 of the absorbing member 31b. That is, it becomes possible to absorb the radio wave W having a wider incident angle.

Next, the arrangement positions of the absorbing member 31a and the absorbing member 31b will be described with reference to FIGS. 3A and 3B. FIG. 3A is a diagram showing a method of determining the arrangement position of the absorbing member 31. FIG. 3B is a diagram showing an arrangement example of the transmitting antenna 10 and the absorbing unit 30.

Here, a method of determining the arrangement position will be described by taking the absorption member 31a shown in FIG. 2A as an example. As shown in FIG. 3A, the arrangement range R1 for arranging the absorbing members 31a is based on the height h1 from the transmitting antenna 10 to the upper surface 5a of the radome 5 and the height h2 from the transmitting antenna 10 to the lower surface 5b of the radome 5. It is determined.

That is, when the radio wave W transmitted from the transmitting antenna 10 is reflected by the radome 5, the position where the radio wave W is incident on the substrate 2 within the range r1 (incident angles θ1 to θ2; see FIG. 2A) is determined by the absorbing member 31a. The sequence range R1 is determined.

Specifically, when the radio wave W is reflected on the upper surface 5a and is incident on the substrate 2 at the incident angle θ1, the distance d1 from the position on the substrate 2 to the transmitting antenna 10 is the minimum value of the arrangement range R1.

Further, the distance d2 from the position on the substrate 2 to the transmitting antenna 10 when the radio wave W is reflected on the lower surface 5b and is incident on the substrate 2 at the incident angle θ2 is the maximum value of the arrangement range R1.

That is, by setting the arrangement range R1 to be a range obtained by subtracting the distance d1 from the distance d2, it is possible for the absorbing member 31a to efficiently absorb the radio wave W. Here, it can be obtained by the distance d1 = 2 × h1 × tan (θ1), and can be obtained by the distance d2 = 2 × h2 × tan (θ2).

Since the height h1 and the height h2 are known, the distance d1 and the distance d2 can be calculated based on the above equation. Further, it is possible to calculate the array range R1 from the distance d1 and the distance d2.

The arrangement range of the absorption member 31b having the absorption characteristics shown in FIG. 2B can be calculated in the same manner, and the arrangement range of the absorption member 31b is hereinafter referred to as the arrangement range R2.

Next, an actual arrangement example of the absorption member 31a and the absorption member 31b based on the above arrangement range will be described with reference to FIG. 3B. Note that FIG. 3B shows a view of a part of the substrate 2 when the radome 5 is removed as viewed from the positive direction of the Z axis.

As shown in FIG. 3B, the absorbing member 31a and the absorbing member 31b are arranged alternately with respect to the arrangement direction of the transmitting antenna 10. Further, the absorption members 31a are arranged and formed in the arrangement range R1, and the absorption members 31b are arranged and formed in the arrangement range R2.

As a result, even when the radio wave W transmitted from the adjacent transmitting antenna 10 is reflected by the radome 5 toward the substrate 2, the radio wave W can be efficiently absorbed by the absorbing member 31a and the absorbing member 31b. ..

Here, the AMC, which is the absorbing member 31, needs to have a repeating structure of a predetermined number of times or more in order to efficiently absorb the radio wave W. In other words, each absorbing member 31 needs to have a predetermined area. Therefore, the antenna device 1 repeatedly arranges the absorbing member 31 which is an AMC with respect to the arrangement direction of the transmitting antenna 10.

That is, by forming the absorbing members 31 by arranging them in the arrangement range, it is possible to efficiently absorb the radio wave W without impairing the original absorption characteristics of the absorbing member 31.

Although the case where two types of absorbing members 31 are used in combination is shown here, the absorbing member 31 is not limited to two types and may be three or more types. Further, the arrangement of the absorbing members 31 shown in FIG. 3B is an example, for example, different absorbing members 31 are arranged in a staggered pattern, or the absorbing members 31 are arranged in a direction opposite to the arrangement direction of the transmitting antenna 10. Etc. can be changed as appropriate.

By the way, in the antenna device 1, it is possible to transmit radio waves W having different frequencies from the transmitting antenna 10. That is, it is necessary to arrange the absorbing members 31 in consideration of the frequency in addition to the incident angle.

Therefore, it is also possible to use an absorption member 31 having different absorption characteristics for each frequency of the radio wave W. Here, the details of such a point will be described with reference to FIGS. 4A to 4C.

4A and 4B are diagrams showing specific examples of absorption characteristics with respect to the frequency of the absorption member 31, and FIG. 4C is a diagram showing specific examples of absorption characteristics in combination with the absorption member 31.

As described above, the transmitting antenna 10 transmits the radio wave W in the frequency band from 76 GHz to 77 GHz. Therefore, FIGS. 4A to 4C show absorption characteristics at a frequency of 76 GHz and absorption characteristics at a frequency of 77 GHz, respectively. Further, FIG. 4A shows the absorption characteristics of the absorption member 31c, and FIG. 4B shows the absorption characteristics of the absorption member 31d.

As shown in FIG. 4A, the absorbing member 31c exhibits good absorption characteristics at a predetermined incident angle with respect to the radio wave W having a frequency of 76 GHz, but is sufficient for any incident angle with respect to the radio wave W having a frequency of 77 GHz. Does not show good absorption characteristics.

On the other hand, as shown in FIG. 4B, the absorption member 31d does not exhibit sufficient absorption characteristics for a radio wave having a frequency of 76 GHz, but exhibits good absorption characteristics for a radio wave W having a frequency of 77 GHz.

That is, as shown in FIG. 4C, the absorbing member 31c absorbs the radio wave W having a frequency of 76 GHz, and the absorbing member 31d absorbs the radio wave W having a frequency of 77 GHz, so that the radio wave W having both frequencies is efficiently absorbed. Is possible.

That is, it is possible to suppress multiple reflections regardless of the radio wave W having any frequency. In other words, it is possible to suppress radio wave interference that occurs between adjacent transmission antennas 10 regardless of the radio wave W having any frequency.

For example, the absorption member 31c and the absorption member 31d may be arranged between the absorption member 31a and the absorption member 31b shown in FIG. 3B, respectively, or a part of the absorption member 31a and the absorption member 31b. May be replaced with the absorbing member 31c and the absorbing member 31d.

That is, regarding the arrangement of the absorption member 31a, the absorption member 31b, the absorption member 31c and the absorption member 31d in the absorption unit 30, it is possible to derive the optimum arrangement by experiments, simulations and the like.

Next, the surface structure of the radome 5 will be described with reference to FIG. FIG. 5 is a schematic cross-sectional view of the radome 5. In addition, FIG. 5 also shows an enlarged view of a part of the lower surface 5b of the radome 5.

As shown in FIG. 5, the upper surface 5a and the lower surface 5b of the radome 5 each have an uneven portion 51 having an uneven shape. By improving the transmittance of the radio wave W by the uneven portion 51, it is possible to suppress the reflection of the radio wave W on the radome 5 side.

Here, it is known that the radio wave W is reflected when the radio wave W passes between media having different dielectric constants. In other words, by reducing the difference in dielectric constant between the media, it is possible to suppress the reflection of the radio wave W and improve the transmittance.

In the present embodiment, paying attention to this point, the transmittance of the radome 5 with respect to the radio wave W is improved. Specifically, the dielectric constant of air is ε0, and the dielectric constant of the radome 5 is ε1 (ε0 <ε1).

In such a case, since air and the radome 5 coexist in the uneven portion 51, if the dielectric constant ε2 in the concave-convex portion 51, the magnitude of each dielectric constant is ε0 <ε2 <ε1.

That is, the dielectric constant ε2 in the uneven portion 51 is an intermediate value between the dielectric constant ε0 of air and the dielectric constant ε1 of the radome 5. That is, the uneven portion 51 functions as a cushioning material for efficiently passing the radio wave W from the air layer through the radome 5.

As a result, the difference in the dielectric constant between the air and the radome 5 is alleviated, so that the transmittance of the radio wave W can be improved. That is, it is possible to suppress the reflection of the radio wave W from the radome 5 to the substrate 2 side. As shown in FIG. 5A, the uneven portion 51 is similarly formed on the upper surface 5a of the radome 5. Therefore, the same effect can be obtained by the uneven portion 51 of the upper surface 5a.

That is, the antenna device 1 suppresses both the reflection of the radio wave W on the upper surface 5a and the reflection of the radio wave W on the lower surface 5b of the radome 5 by providing the uneven portions 51 on both the upper surface 5a and the lower surface 5b of the radome 5. Is possible.

By the way, the interval between adjacent irregularities in the concave-convex portion 51 is formed to be shorter than the wavelength of the radio wave W. If the interval between adjacent irregularities is longer than the wavelength of the radio wave W, the radio wave W may be reflected on the side surface of the irregularities, and the radio wave W may be diffusely reflected. That is, by making the interval between adjacent irregularities shorter than the wavelength of the radio wave W, it is possible to suppress the above-mentioned diffused reflection. In the above example, the antenna device 1 transmits the radio wave W in the band of 76 to 77 GHz. Since the wavelength of the transmitted wave in such a case is about 3.9 mm, the interval between adjacent irregularities is preferably 3.9 mm or less.

The unevenness may be formed uniformly, for example, along the depth direction (Y-axis) of the paper surface, or may be formed in another shape such as a grid pattern. Further, although the case where the uneven portion 51 is provided on both the upper surface 5a and the lower surface 5b of the radome 5 has been described here, the uneven portion 51 may be provided only on one surface.

By the way, the transmittance of the radio wave W can be changed depending on the shape (intervale-convex spacing, unevenness height, etc.) of the uneven portion 51. Therefore, in the antenna device 1, the radio wave W whose absorption characteristic of the radio wave W by the absorption member 31 is not sufficient is transmitted.

Here, the details of such a point will be described with reference to FIG. 5B. FIG. 5B is a diagram showing the absorption characteristics of the absorption member 31 and the uneven portion 51. The smaller the reflection loss of the uneven portion 51 shown in FIG. 5B, the larger the transmission amount of the radio wave W when the radio wave W is incident on the uneven portion 51.

As shown in FIG. 5B, the uneven portion 51 is designed to positively transmit the radio wave W having an incident angle with a low absorption characteristic of the absorbing member 31. That is, for the radio wave W having an incident angle in the range r4 shown in the figure, reflection is suppressed in advance on the radome 5 side.

That is, since the radio wave W is not reflected from the radome 5 to the substrate 2 side, it is not necessary for the absorbing member 31 to absorb the radio wave W, and multiple reflection by the radio wave W can be suppressed.

As described above, in the antenna device 1, the uneven portion 51 and the absorbing member 31 complement each other's absorption characteristics, so that the multiple reflection of the radio wave W can be efficiently suppressed.

As described above, the antenna device 1 according to the embodiment includes a substrate 2, a radome 5, and an absorption unit 30. A plurality of antennas (transmitting antenna 10) for transmitting or receiving radio waves W are arranged on the substrate 2. The radome 5 covers the substrate 2 from the exit surface side of the antenna. The absorption unit 30 is provided between the antennas on the substrate 2, and a plurality of absorption members 31 having different absorption characteristics of the radio wave W are arranged. Therefore, according to the antenna device 1 according to the embodiment, it is possible to suppress radio wave interference generated between adjacent antennas. Further, it is possible to suppress the distortion of the radiation directivity of the transmitting antenna 10 caused by the multiple reflections between the radome and the substrate.

By the way, in the above-described embodiment, the case where the absorbing member 31 is an AMC has been described, but the present invention is not limited to this. That is, the form of the absorption member 31 does not matter as long as it has different absorption characteristics. Further, the antenna device 1 can be applied to various antenna devices such as a radar device and a wireless LAN (Local Area Network).

Further, in the above-described embodiment, the case of the transmitting antenna for transmitting the radio wave W has been described, but the present invention is not limited to this. That is, it may be a receiving antenna that receives the radio wave W, or it may be a transmitting / receiving antenna that transmits and receives the radio wave W.

Further effects and variations can be easily derived by those skilled in the art. For this reason, the broader aspects of the invention are not limited to the particular details and representative embodiments described and described above. Thus, various changes are possible without departing from the spirit or scope of the overall concept of the invention as defined by the appended claims and their equivalents.

1 Antenna device 2 Board 5 Radome 5a Top 5b Bottom 10 Transmitting antenna 30 Absorbing part 31 Absorbing member 51 Concavo-convex part W radio wave

Claims (6)

A substrate in which antennas in which a plurality of antenna elements are arranged along a microstrip line are arranged in parallel so as to be substantially parallel, and a substrate.
A radome having a main surface substantially parallel to the substrate and covering the substrate from the side where the antenna is arranged,
It is provided with a thin film between the antennas on the substrate, and includes an absorption unit in which a plurality of absorption members having different absorption characteristics of radio waves transmitted or received by the antenna are arranged.
The absorption part is
It has the absorption characteristic that the reflection loss of the radio wave is set to a predetermined value or less when the radio wave is incident in the range of the incident angle between the first incident angle and the second incident angle different from the first incident angle. The absorption member minimizes the distance from the position on the substrate to the antenna when the radio wave transmitted from the antenna is reflected on the upper surface of the radome and is incident at the first incident angle. The radio waves transmitted from the antenna are reflected on the lower surface of the radome and are arranged in an arrangement range that maximizes the distance from the position on the substrate to the antenna when the antenna is incident at the second incident angle. An antenna device characterized by being installed in. The absorption part is
The antenna device according to claim 1, wherein the absorbing members having different absorption characteristics with respect to the incident angle of the radio wave are arranged. The absorption part is
The antenna device according to claim 1 or 2, wherein the absorption members having different absorption characteristics with respect to the frequency of the radio wave are arranged. The absorption part is
The antenna according to claim 1, 2 or 3, wherein a plurality of the absorbing members are arranged so that the absorbing members adjacent to each other in the direction in which the antennas are arranged in parallel have different absorption characteristics. Device. One of claims 1 to 4, further comprising an uneven portion provided on at least one of the main surfaces of the radome and formed so that the interval between adjacent irregularities is shorter than the wavelength of the radio wave. The antenna device described in one. The uneven portion is
The antenna device according to claim 5, wherein the radio wave having an incident angle at which the absorption characteristic is low for the absorption member is formed at a portion of the main surface where the radio wave is reflected before being incident on the absorption member.

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