JPWO2020065715A1 - Radar device - Google Patents

Abstract

The radar device (100) includes an antenna (1) that emits radio waves and a radome (2) for the antenna (1), and the radome (2) is made of a plurality of first fibers (6). It has a fiber reinforced plastic layer (3) including a first fiber bundle (4) and a plurality of second fiber bundles (5) composed of a plurality of second fibers (7), and has a fiber reinforced plastic layer (3). 3) is provided so that the longitudinal direction of each first fiber bundle (4) is along the direction orthogonal to the polarization direction of the antenna (1), and the longitudinal direction of each second fiber bundle (5) is long. The direction is provided so as to be parallel to the polarization direction, and the electric conductivity of the individual first fiber (6) is higher than that of the individual second fiber (7).

Description

The present invention relates to a radar device.

Conventionally, radomes for antennas have been developed in radar devices. For example, Patent Document 1 discloses a radome having a so-called "sandwich structure". More specifically, the radome (10) described in Patent Document 1 has a structure in which one core layer (C) is provided between two skin layers (S1 and S2) (Patent Document 1). 1).

JP-A-2017-79448

Conventionally, in-vehicle radar devices using so-called "millimeter wave" have been developed (hereinafter referred to as "in-vehicle millimeter wave radar"). In the radome of an in-vehicle millimeter-wave radar, it is required to improve the transparency to millimeter waves, reduce the weight, and improve the rigidity.

Here, in the invention described in Patent Document 1, in a redome having a sandwich structure, the wall thickness of each skin layer is set based on a predetermined mathematical formula (see the formula (1) of Patent Document 1 and the like), and the meat of the core layer is formed. By setting the thickness based on another predetermined mathematical formula (see the formula (2) of Patent Document 1 and the like), the transparency to radio waves such as millimeter waves is improved. That is, the invention described in Patent Document 1 is not intended to reduce the weight and improve the rigidity. Therefore, the invention described in Patent Document 1 remains a problem from the viewpoint of achieving both improvement in transparency to radio waves such as millimeter waves, reduction in weight, and improvement in rigidity.

For example, if the radome described in Patent Document 1 is used for an in-vehicle millimeter-wave radar, the formula (2) of Patent Document 1 is obtained because the millimeter-wave frequency is 30 GHz (hereinafter referred to as “GHz”) or higher. ), The wall thickness of the core layer may be set to 2.5 mm (hereinafter referred to as “mm”) or less. Since the core layer is thin in this way, when each skin layer is thinned (that is, when the value of n in the formula (1) of Patent Document 1 is reduced), the weight of the radome can be easily reduced. It becomes difficult to improve the rigidity of the radome. On the other hand, when each skin layer is made thicker (that is, when the value of n in the formula (1) of Patent Document 1 is increased), the rigidity of the radome can be easily improved, but it is difficult to reduce the weight of the radome. Become.

The present invention has been made to solve the above-mentioned problems, and in a radome of an in-vehicle radar device, the present invention is to improve the transparency to radio waves such as millimeter waves, reduce the weight, and improve the rigidity. The purpose is to achieve both.

The radar device of the present invention includes an antenna that emits radio waves and a radome for the antenna, and the radome includes a plurality of first fiber bundles made of a plurality of first fibers and a plurality of radomes made of a plurality of second fibers. It has a fiber reinforced plastic layer including a second fiber bundle of a book, and the fiber reinforced plastic layer is provided so that the longitudinal direction of each first fiber bundle is along the direction orthogonal to the polarization direction of the antenna. Moreover, the longitudinal direction of each second fiber bundle is provided so as to be parallel to the polarization direction, and the electric conductivity of each first fiber is higher than that of each second fiber. It is a thing.

According to the present invention, since the radome is configured as described above, it is possible to improve the transparency of radio waves such as millimeter waves, reduce the weight, and improve the rigidity of the radome of a radar device for vehicles. ..

It is a front view which shows the main part of the antenna for the radar apparatus which concerns on Embodiment 1. FIG. It is a front view which shows the main part of the fiber reinforced plastic layer which the radome for the radar apparatus which concerns on Embodiment 1 has. It is sectional drawing which follows the AA' line shown in FIG. 2A. It is a front view which shows the main part of the radar apparatus which concerns on Embodiment 1. FIG. It is sectional drawing which follows the AA' line shown in FIG. 3A. It is a characteristic diagram which shows the millimeter wave transmittance by the radome for the radar apparatus which concerns on Embodiment 1. FIG. It is a front view which shows the main part of another radar apparatus which concerns on Embodiment 1. FIG. It is a front view which shows the main part of the fiber reinforced plastic layer of one of the two fiber reinforced plastic layers which the radome for the radar apparatus which concerns on Embodiment 2 has. It is sectional drawing which follows the AA' line shown in FIG. 6A. It is a front view which shows the main part of the other fiber reinforced plastic layer of the two fiber reinforced plastic layers which the radome for the radar apparatus which concerns on Embodiment 2 has. It is sectional drawing which follows the AA' line shown in FIG. 7A. It is a front view which shows the main part of the radar apparatus which concerns on Embodiment 2. FIG. It is sectional drawing which follows the AA' line shown in FIG. 8A. It is a characteristic diagram which shows the millimeter wave transmittance by the radome for the radar apparatus which concerns on Embodiment 2. FIG.

Hereinafter, in order to explain the present invention in more detail, a mode for carrying out the present invention will be described with reference to the accompanying drawings.

Embodiment 1.
FIG. 1 is a front view showing a main part of an antenna for a radar device according to the first embodiment. FIG. 2A is a front view showing a main part of the fiber reinforced plastic layer included in the radome for the radar device according to the first embodiment. FIG. 2B is a cross-sectional view taken along the line AA'shown in FIG. 2A. FIG. 3A is a front view showing a main part of the radar device according to the first embodiment. FIG. 3B is a cross-sectional view taken along the line AA'shown in FIG. 3A. With reference to FIGS. 1 to 3, the radar device 100 of the first embodiment will be described focusing on an example used for an in-vehicle millimeter-wave radar. That is, the radar device 100 is mounted on a vehicle (not shown).

In the figure, 1 is an antenna. The antenna 1 emits a radio wave having a predetermined frequency f (for example, 77 GHz), that is, a millimeter wave. The antenna 1 receives the reflected radio wave when the radiated radio wave is reflected by an obstacle (not shown) outside the vehicle. The control unit (not shown) measures the distance between the vehicle and an obstacle based on the difference value Δf between the frequency f of the radio wave radiated by the antenna 1 and the frequency f'of the radio wave received by the antenna 1. is there. The control unit is composed of, for example, an ECU (Electronic Control Unit).

Hereinafter, the radio waves radiated by the antenna 1 and the radio waves radiated by the antenna 1 are collectively referred to as "radiated waves". Further, the frequency f of the radio wave radiated by the antenna 1, that is, the frequency f of the radiated wave may be referred to as a "carrier frequency".

The antenna 1 is composed of, for example, a so-called "planar array antenna". In the examples shown in FIGS. 1 and 3, a plurality of antenna elements 12 are arranged in a plane, that is, in a two-dimensional array on the surface of the substrate 11.

The radiation direction (so-called "main beam direction") of the main radio wave (so-called "main beam") of the radiated waves is, for example, a direction orthogonal to or substantially orthogonal to the plate surface of the substrate 11, that is, the Z axis in the drawing. It is set in the direction along. In the figure, MB indicates a region corresponding to the main beam, that is, a region to which the main beam passes.

Further, the antenna 1 is a so-called "linearly polarized antenna". The polarization direction of the antenna 1 is set to be parallel to or substantially parallel to the plate surface of the substrate 11, and more specifically, to be along the Y axis in the drawing.

The radar device 100 has a radome 2 for the antenna 1. The radome 2 is arranged so as to face the surface portion of the substrate 11. That is, the radome 2 is arranged to face the plurality of antenna elements 12. The radome 2 will be described below.

As shown in FIGS. 2 and 3, the radome 2 has a fiber reinforced plastic layer 3. The fiber reinforced plastic layer 3 is provided, for example, in parallel with or substantially parallel to the plate surface of the substrate 11.

The fiber-reinforced plastic layer 3 includes a plurality of fiber bundles (hereinafter, may be referred to as "first fiber bundles") 4. Further, the fiber reinforced plastic layer 3 includes another plurality of fiber bundles (hereinafter, may be referred to as “second fiber bundle”) 5. Each of the plurality of first fiber bundles 4 is formed by bundling a plurality of fibers (hereinafter, may be referred to as "first fibers") 6 in a thread shape. Further, each of the plurality of second fiber bundles 5 is formed by bundling other plurality of fibers (hereinafter, sometimes referred to as "second fibers") 7 in a thread shape.

The fiber-reinforced plastic layer 3 is produced, for example, by applying a liquid plastic to a woven fabric made of these fiber bundles 4 and 5 and then curing the plastic. That is, the plurality of first fiber bundles 4 correspond to either one of the warp threads or the weft threads in the woven fabric, and the plurality of second fiber bundles 5 correspond to either the warp threads or the weft threads in the woven fabric. It corresponds to either one or the other. The longitudinal direction of each of the plurality of first fiber bundles 4 (hereinafter referred to as "first longitudinal direction") and the longitudinal direction of each of the plurality of second fiber bundles 5 (hereinafter referred to as "second longitudinal direction"). Are orthogonal or substantially orthogonal to each other.

Hereinafter, in the fiber reinforced plastic layer 3, a direction orthogonal to or substantially orthogonal to the polarization direction of the antenna 1 is referred to as an “orthogonal direction”. Further, in the fiber reinforced plastic layer 3, a direction parallel to or substantially parallel to the polarization direction of the antenna 1 is referred to as a "parallel direction". The fiber reinforced plastic layer 3 is provided so that the first longitudinal direction is along the orthogonal direction and the second longitudinal direction is along the parallel direction. More specifically, the angle θ between the first longitudinal direction and the direction orthogonal to the polarization direction, that is, the angle θ between the second longitudinal direction and the direction parallel to the polarization direction. Is set to a value that satisfies the condition shown in the following equation (1). In the examples shown in FIGS. 2 and 3, θ = 0 ° is set.

-13 ° ≤ θ ≤ + 13 ° (1)

Each of the plurality of first fibers 6 is composed of, for example, carbon fibers, metal fibers, boron fibers, or fine metal wires having a thickness of 100 micrometers (hereinafter referred to as “μm”) or less. The thickness of each of the plurality of first fibers 6 is set to a value of 1/10 or less of the wavelength of the radiated wave in vacuum. On the other hand, each of the plurality of second fibers 7 is composed of, for example, glass fibers or quartz fibers.

That is, the electric conductivity of each of the plurality of first fibers 6 is higher than that of each of the plurality of second fibers 7, and the electric conductivity of each of the plurality of first fibers 6 is sufficient. The dielectric loss is larger than the dielectric loss due to each of the plurality of second fibers 7. The relative permittivity ε of the portion of the fiber-reinforced plastic layer 3 excluding the first fiber 6 (that is, the portion composed of the second fiber 7 and the plastic) is about 2.0 to 6.0.

The wall thickness t of the fiber reinforced plastic layer 3 is set to a value corresponding to, for example, an integral multiple of a half wavelength of the radiated wave at a portion of the fiber reinforced plastic layer 3 excluding the first fiber 6. More specifically, the wall thickness t is set to a value based on the following equation (2).

t = (n × λ ₀ ) / (2 × √ε) (2)

λ ₀ is the wavelength of the radiated wave in vacuum. n is any integer greater than or equal to 1.

In this way, the main part of the radar device 100 is configured.

Next, the effect of using the radome 2 in the radar device 100 will be described.

Generally, the transmittance T when a structure having a finite impedance transmits a radio wave is divided into a component T _⊥ perpendicular to the polarization direction of the radio wave and a component T _‖ parallel to the polarization direction of the radio wave. To. For example, the transmittances T _⊥ and T _‖ when a structure having a predetermined wavelength order size transmits a radio wave having the wavelength are represented by the following equations (3) and (4), respectively.

T _⊥ = (4 × Z _⊥ ² ) / (1 + 4 × Z _⊥ ² ) (3)
T _‖ = (4 × Z _‖ ² ) / (1 + 4 × Z _‖ ² ) (4)

Z _⊥ is the equivalent impedance of the structure in the direction perpendicular to the polarization direction of the radio wave. Z _‖ is the equivalent impedance of the structure in the direction parallel to the polarization direction of the radio wave. The equations (3) and (4) are based on the description of Reference 1 below.

[Reference 1]
JP Auton, Appl. Opt., Vol.6, 1023 (1967)

Here, as described above, the thickness of each of the plurality of first fibers 6 is set to a value of 1/10 or less of the wavelength of the radiated wave in vacuum. As a result, the current flowing through the first fiber 6 (that is, the current flowing along the first longitudinal direction in the fiber reinforced plastic layer 3) is not generated, so that the equivalent impedance Z _⊥ of the first fiber 6 becomes Z _⊥ ≫1. .. Therefore, the transmittance T _⊥ in the first fiber 6 is T _⊥ ≈ 1. On the other hand, the equivalent impedance Z _‖ of the second fiber 7 is 1 / √ε times the impedance in vacuum. Therefore, the transmittance T _‖ in the second fiber 7 is a value equivalent to the value calculated using the so-called “Fresnel equations”.

According to the above principle, a material having high electrical conductivity and a large dielectric loss, more specifically, a material such as carbon fiber or metal fiber is used for the first fiber 6, but the Frenel loss due to the fiber reinforced plastic layer 3 The increase can be avoided. That is, even though these materials are contained in the fiber reinforced plastic layer 3, it is possible to avoid a decrease in transparency to radio waves such as millimeter waves (in other words, transparency to radio waves such as millimeter waves). Can be improved.)

Further, the first fiber 6 using these materials can improve the rigidity and reduce the weight of the fiber reinforced plastic layer 3 as compared with the conventional fiber reinforced plastic layer. As a result, the rigidity of the radome 2 can be improved and the weight can be reduced as compared with the conventional radome having the conventional fiber reinforced plastic layer. Here, the conventional fiber reinforced plastic layer is made of glass fiber reinforced plastic, quartz fiber reinforced plastic, or the like. That is, the conventional fiber reinforced plastic layer does not contain the material (carbon fiber, metal fiber, boron fiber, metal fine wire, etc.) used for the first fiber 6 in the fiber reinforced plastic layer 3.

Further, since the transmittance T _⊥ in the first fiber 6 is T _⊥ ≈ 1, the wall thickness t is set to a value based on the equation (2), so that a predetermined value including the carrier frequency f (for example, 77 GHz) is included. Millimeter wave transmittance in the frequency range can be improved.

The characteristic line I in FIG. 4 shows the millimeter wave transmittance by the radome 2. This millimeter wave transmittance is calculated using Fresnel's equation. In the calculation of the millimeter wave transmittance, the dielectric loss is ignored and the Fresnel loss is included in the calculation. This is because the dielectric loss is smaller than the Fresnel loss.

In the radome 2 according to the characteristic line I, the first fiber 6 is made of carbon fiber and the second fiber 7 is made of glass fiber. In the radome 2 related to the characteristic line I, θ = 0 °. In the radome 2 according to the characteristic line I, the relative permittivity with respect to the polarization direction of the antenna 1 at the portion of the fiber reinforced plastic layer 3 excluding the first fiber 6 is 4.0 (that is, ε = 4.0). It is.). In the radome 2 related to the characteristic line I, the wall thickness t is set to 1.95 mm (that is, where f = 77 GHz and ε = 4.0, n = 2). Hereinafter, a configuration example of the radome 2 according to the characteristic line I will be referred to as a “first configuration example”.

As shown in FIG. 4, by using the radome 2 of the first configuration example, the Fresnel loss in the frequency range of 74 to 80 GHz can be reduced to 5% or less.

As described above, the angle θ is not limited to 0 °. As long as the condition shown in the equation (1) is satisfied, θ ≠ 0 ° may be set as shown in FIG.

However, the equivalent impedance Z _⊥'of the first fiber 6 when θ ≠ 0 ° is expressed by the following equation (5) with respect to the equivalent impedance Z _⊥ of the first fiber 6 when θ = 0 °. To. Further, the equivalent impedance Z _‖ of the second fiber 7 when θ ≠ 0 ° is expressed by the following equation (6) with respect to the equivalent impedance Z _‖ of the second fiber 7 when θ = 0 °. To.

Z _⊥ '＝ Z _⊥ × cosθ (5)
Z _‖ '＝ Z _‖ × sinθ (6)

Such Z _⊥ ', Z _‖' loss of radio waves based on becomes one represented by a function of sin ² theta. Therefore, from the viewpoint of reducing the loss to 5% or less, it is preferable to set the angle θ to a value within the range of ± 13 °, that is, a value within the range satisfying the condition shown in the equation (1).

Further, each of the plurality of first fibers 6 may be coated.

Further, the radiated wave is not limited to millimeter waves, and the carrier frequency f is not limited to 77 GHz. The antenna 1 may radiate a radio wave having any frequency f as long as it has a frequency f used in the radar device 100. For example, the antenna 1 may radiate a so-called "microwave" or "submillimeter wave".

Further, the radar device 100 is not limited to in-vehicle use, and the application of the radar device 100 is not limited to the measurement of the distance between the vehicle and the obstacle. The radar device 100 may be used for radar for any purpose.

As described above, the radar device 100 of the first embodiment includes an antenna 1 that emits radio waves and a radome 2 for the antenna 1, and the radome 2 is composed of a plurality of first fibers 6 and a plurality of first fibers. It has a fiber reinforced plastic layer 3 including one fiber bundle 4 and a plurality of second fiber bundles 5 composed of a plurality of second fibers 7, and the fiber reinforced plastic layer 3 is an individual first fiber bundle 4. The longitudinal direction (that is, the first longitudinal direction) is provided so as to be perpendicular to the polarization direction of the antenna 1, and the longitudinal direction (that is, the second longitudinal direction) of each second fiber bundle 5 is polarized. It is provided so as to be parallel to the direction, and the electric conductivity of each first fiber 6 is higher than that of each second fiber 7. As a result, it is possible to avoid an increase in Fresnel loss due to the fiber reinforced plastic layer 3 while using a material such as carbon fiber or metal fiber for the first fiber 6. As a result, it is possible to improve the transparency of radio waves such as millimeter waves, reduce the weight, and improve the rigidity.

Further, the wall thickness t of the fiber reinforced plastic layer 3 is set to a value corresponding to an integral multiple of a half wavelength of the radio wave. By setting the wall thickness t to a value based on the equation (2), Fresnel loss in a predetermined frequency range including the carrier frequency f can be reduced.

Further, the individual first fiber 6 is composed of carbon fiber, metal fiber, boron fiber or metal fine wire, and the individual second fiber 7 is composed of glass fiber or quartz fiber. As described above, the material of the first fiber 6 is not limited to carbon fiber or metal fiber, and boron fiber, metal fine wire, or the like can also be used.

Further, the thickness of each first fiber 6 is set to a value of 1/10 or less with respect to the wavelength of the radio wave. By setting the thickness of each of the first fibers 6 to a sufficiently small value in this way, it is possible to more reliably prevent the generation of the current flowing through the first fibers 6.

Embodiment 2.
FIG. 6A is a front view showing a main part of one of the two fiber reinforced plastic layers included in the radome for the radar device according to the second embodiment. FIG. 6B is a cross-sectional view taken along the line AA'shown in FIG. 6A. FIG. 7A is a front view showing a main part of the fiber reinforced plastic layer of the other of the two fiber reinforced plastic layers included in the radome for the radar device according to the second embodiment. FIG. 7B is a cross-sectional view taken along the line AA'shown in FIG. 7A. FIG. 8A is a front view showing a main part of the radar device according to the second embodiment. FIG. 8B is a cross-sectional view taken along the line AA'shown in FIG. 8A. The radar device 100a of the second embodiment will be described with reference to FIGS. 6 to 8. In FIGS. 6 to 8, the same components as those shown in FIGS. 2 to 3 are designated by the same reference numerals, and the description thereof will be omitted.

The radar device 100a has a radome 2a for the antenna 1. The radome 2a has two fiber reinforced plastic layers 3 arranged so as to face each other. Further, the radome 2a has a gap layer 8 formed between the two fiber reinforced plastic layers 3. Each of the two fiber-reinforced plastic layers 3 is provided, for example, parallel to or substantially parallel to the plate surface of the substrate 11. Each of the two fiber-reinforced plastic layers 3 has a structure similar to that described in the first embodiment.

That is, fiber-reinforced plastic layer 3 ₁ One of the two fiber-reinforced plastic layer 3 are those containing a second fiber bundle 5 ₁ of a plurality of first fiber bundles 4 ₁ and a plurality of. First each of the fiber bundles 4 ₁ a plurality of is made by bundling a first fiber 6 ₁ a plurality of filamentous. Second, each of the fiber bundle 5 ₁ a plurality of is made by bundling a second fiber 7 ₁ a plurality of filamentous.

Fiber-reinforced plastic layer 3 _1, the first fiber bundle 4 ₁ of each of the longitudinal direction of the plurality of (that is, the first longitudinal direction) is provided along the perpendicular direction, and a second fiber bundle of a plurality of 5 ₁ of each of the longitudinal (i.e. second longitudinal direction) is provided along the parallel direction. More specifically, the angle θ ₁ between the first longitudinal direction and the direction orthogonal to the polarization direction of the antenna ₁ , that is, parallel to the second longitudinal direction and the polarization direction of the antenna 1. The angle θ ₁ with respect to the direction is set to a value satisfying the condition shown in the following equation (7). In the examples shown in FIGS. 6 and 8, θ ₁ = 0 ° is set.

-13 ° ≤ θ ₁ ≤ + 13 ° (7)

First each of the fibers ₆₁ a plurality of, for example, carbon fibers, metal fibers, is constituted by boron fibers or thin metal wires having the following thickness 100 [mu] m. First fiber 6 ₁ of each of the thickness of the plurality of is set to less than one-tenth with respect to the wavelength in vacuum of the radiation wave. In contrast, the second respective fibers ₇₁ a plurality of, for example, is constituted by glass fibers or quartz fibers.

That is, those first fibers ₆₁ of each of the electrical conductivity of the plurality of higher than the second fiber 7 ₁ of each of the electrical conductivity of the plurality of, and the first fiber 6 a plurality of ₁ each dielectric loss due to the is larger than the dielectric loss of the second fiber 7 ₁ of each of the plurality of lines. The dielectric constant epsilon ₁ site (i.e. site being constituted by the second fiber ₇₁ and plastic), except the first fiber _{6 1} of the fiber-reinforced plastic layer _{3 1} is in the order of 2.0 to 6.0 is there.

Thickness t ₁ of the fiber-reinforced plastic layer 3 ₁ is, for example, is set to a value corresponding to a half wavelength of the radiation waves at a site other than the first fiber 6 ₁ of the fiber-reinforced plastic layer 3 ₁ .. More specifically, the wall thickness t ₁ is set to a value based on the following equation (8).

t ₁ = λ ₀ / (2 × √ε ₁ ) (8)

The other fiber-reinforced plastic layer 3 ₂ of the two fiber-reinforced plastic layer 3, is intended to include a plurality of first fiber bundles 4 ₂ and a plurality second fiber bundle of the 5 _2. First each of the fiber bundles 4 ₂ a plurality of is made by bundling a first fiber 6 ₂ a plurality of filamentous. Second, each fiber bundle 5 _second plurality of is made by bundling a second fiber 7 ₂ a plurality of filamentous.

The fiber reinforced plastic layer 3 ₂ is provided so that the longitudinal direction (that is, the first longitudinal direction) of each of the plurality of first fiber bundles 4 ₂ is along the orthogonal direction, and the plurality of second fiber bundles 3 2 are provided. 5 ₂ of each of the longitudinal direction (i.e. second longitudinal direction) is provided along the parallel direction. More specifically, the angle θ ₂ between the first longitudinal direction and the direction orthogonal to the polarization direction of the antenna 1, that is, parallel to the second longitudinal direction and the polarization direction of the antenna 1. The angle θ ₂ with respect to the direction is set to a value satisfying the condition shown in the following equation (9). In the examples shown in FIGS. 7 and 8, θ ₂ = 0 ° is set.

-13 ° ≤ θ ₂ ≤ + 13 ° (9)

First respective fibers 6 ₂ a plurality of, for example, carbon fibers, metal fibers, is constituted by boron fibers or thin metal wires having the following thickness 100 [mu] m. The first fiber 6 ₂ each thickness of the plurality of is set to less than one-tenth with respect to the wavelength in vacuum of the radiation wave. In contrast, the second respective fiber 7 ₂ a plurality of, for example, is constituted by glass fibers or quartz fibers.

That is, those first fibers 6 ₂ of each of the electrical conductivity of the plurality of higher than the second fiber 7 ₂ of each of the electrical conductivity of the plurality of, and the first fiber 6 a plurality of ₂ each dielectric loss due to the is larger than the dielectric loss of the second fiber 7 ₂ of each of the plurality of lines. The dielectric constant epsilon ₂ of the site (i.e., site configured by the second fiber _{7 2} and plastic), except the first fiber _{6 2} of the fiber-reinforced plastic layer _{3 2} of about 2.0 to 6.0 is there.

Thickness t ₂ of the fiber-reinforced plastic layer 3 ₂ is, for example, is set to a value corresponding to a half wavelength of the radiation waves at a site other than the first fiber 6 ₂ of the fiber-reinforced plastic layer 3 ₂ .. More specifically, the wall thickness t ₂ is set to a value based on the following equation (10).

t ₂ = λ ₀ / (2 × √ε ₂ ) (10)

Air is contained in the gap layer 8. Normally, the relative permittivity of air is about 1.0. That is, the dielectric constant of the gap layer 8 (about 1.0) fiber-reinforced plastic layer ₃ 1, ₃ first fiber ₆ 1 of _2, the dielectric constant of the portion except the _{6 2} (2.0 to 6. It is smaller than (about 0).

Here, fiber-reinforced plastic layer 3 _1, 3 distance between ₂ d, the distance d with respect to more specific fiber-reinforced plastic layer 3 ₁ to _{3, 2} in the thickness direction (i.e. the direction along the Z axis in the figure), The value is set to an integral multiple of the half wavelength of the radiated wave in the interstitial layer 8. More specifically, the interval d is set to a value based on the following equation (11).

d = α × (m × λ 0/2) (11)

m is any integer greater than or equal to 1. α is a coefficient that satisfies the condition shown in the following equation (12).

0.8 ≤ α ≤ 1.2 (12)

In this way, the main part of the radar device 100a is configured.

Next, the effect of using the radome 2a in the radar device 100a will be described.

As described above, the first fibers ₆₁ of each of the thickness of the plurality of is set to less than one-tenth with respect to the wavelength in vacuum of the radiation wave. Thus, since the current flowing through the first fiber 6 ₁ (that is, the current flowing along the first longitudinal direction in the fiber-reinforced plastic layer 3 ₁₎ is not generated, the first fiber 6 ₁ equivalent impedance Z _⊥1 the Z _{⊥ 1} >> ₁ . Therefore, the transmittance T _{⊥ 1} in the first fiber ₆₁ is T _⊥ 1 ≈ 1. On the other hand, the equivalent impedance Z _{‖ 1} of the second fiber ₇₁ is 1 / √ε ₁ times the impedance in vacuum. Therefore, the transmittance T _{‖ 1} in the second fiber ₇₁ is a value equivalent to the value calculated using Fresnel's equation.

The first fiber 6 ₂ each thickness of the plurality of is set to less than one-tenth with respect to the wavelength in vacuum of the radiation wave. Thus, since the current flowing through the first fiber 6 ₂ (that is, the current flowing as in the fiber-reinforced plastic layer 3 ₂ along the first longitudinal direction) is not generated, the equivalent impedance Z _⊥2 the first fiber 6 ₂ Z _{⊥ 2} >> 1. Therefore, the transmittance T _{⊥ 2} in the first fiber ₆₂ is T _{⊥ 2} ≈ 1. In contrast, the second fiber 7 ₂ equivalent impedance Z _‖2 becomes 1 / √ε ₂ times the values for the impedance of the vacuum. Therefore, the transmittance T _‖2 the second fiber 7 ₂ becomes equivalent to the value of the value calculated using the Fresnel equations.

By the above principle, electrical conductivity is high dielectric loss material having a large, but more particularly used in the material ₁ is first fiber _6, 6 _2, such as carbon fiber or metal fiber, fiber-reinforced plastic layer 3 _1, 3 ₂ increase in Fresnel losses due can be avoided. In other words, despite these materials are contained in the fiber reinforced plastic layer 3 _1, 3 _2, it is possible to avoid a decrease in permeability to radio waves such as a millimeter-wave (in other words, such as a millimeter-wave It is possible to improve the transparency to radio waves.) Further, by fiber-reinforced plastic layer 3 _1, 3 low dielectric constant between ₂ layers (i.e. the gap layer 8) is provided, it is possible to further improve the permeability to radio waves such as a millimeter wave.

Further, the first fiber 6 _1, 6 ₂ using these materials, that compared to conventional fiber-reinforced plastic layer, improved and weight reduction of the stiffness of the fiber-reinforced plastic layer 3 _1, 3 ₂ it can. As a result, the rigidity of the radome 2a can be improved and the weight can be reduced as compared with the conventional radome having the conventional fiber reinforced plastic layer. Here, the conventional fiber reinforced plastic layer is made of glass fiber reinforced plastic, quartz fiber reinforced plastic, or the like. That is, the conventional fiber-reinforced plastic layer, fiber-reinforced plastic layer 3 _1, 3 first fiber 6 in _{2 1,} 6 ₂ in using its dependent material (carbon fiber, metal fiber, boron fiber or thin metal wires, etc.) It does not include.

Further, since the transmittance T _{⊥ 1} in the first fiber ₆₁ is T _⊥ 1 ≈ 1, and the transmittance T _{⊥ 2} in the first fiber ₆₂ is T _{⊥ 2} ≈ 1, the interval d is the equation ( By setting the value based on 11), the millimeter wave transmittance in a predetermined frequency range including the carrier frequency f (for example, 77 GHz) can be improved.

The characteristic line II in FIG. 9 shows the millimeter wave transmittance due to the radome 2a. This millimeter wave transmittance is calculated using Fresnel's equation. In the calculation of the millimeter wave transmittance, the dielectric loss is ignored and the Fresnel loss is included in the calculation. Further, the characteristic line I shown in FIG. 9 is the same as the characteristic line I shown in FIG. That is, the characteristic line I shows the millimeter wave transmittance by the radome 2.

In the radome 2a of the characteristic line II, the first fiber ₆ 1, _{6 2} are constituted by a carbon fiber, and a second fiber ₇ 1, _{7 2} is constituted by glass fibers. In the radome 2a related to the characteristic line II, θ ₁ = θ ₂ = 0 °. In the radome 2a of the characteristic line II, the dielectric constant with respect to the polarization direction of the antenna 1 at a site other than the first fiber ₆ 1, _{6 2} of the fiber-reinforced plastic layer ₃ 1, _{3 2} is a 4.0 (That is, ε ₁ = ε ₂ = 4.0.). In the radome 2a related to the characteristic line II, t ₁ = t ₂ = 0.97 mm is set. In the radome 2a related to the characteristic line II, d = 1.95 mm is set (that is, where f = 77 GHz, m = 1 and α = 1.0). Hereinafter, a configuration example of the radome 2a according to the characteristic line II will be referred to as a “second configuration example”.

As shown in FIG. 9, by using the radome 2 of the first configuration example, the Fresnel loss in the frequency range of 74 to 80 GHz can be reduced to 5% or less. On the other hand, by using the radome 2a of the second configuration example, the Fresnel loss in the frequency range of 73 to 81 GHz can be reduced to 5% or less.

It should be noted that, of course, when α = 1.0, as long as it is within the range satisfying the condition shown in the equation (12), even if α ≠ 1.0, it is in a predetermined frequency range including the carrier frequency f. The effect of improving the millimeter wave transmittance can be obtained. This is of course if it is set in the main beam direction is fiber-reinforced plastic layer 3 ₁ of the antenna _1, 3 ₂ in the direction along the thickness direction (i.e. the direction along the Z axis), is the main beam direction It is shown that the effect of improving the millimeter wave transmittance in the frequency range can be obtained even when the thickness is set to be slightly inclined with respect to the thickness direction.

Further, as described above, the angle θ ₁ is not limited to 0 °. As long as it is within the range satisfying the condition shown in the equation (7), θ ₁ ≠ 0 ° may be satisfied. Further, as described above, the angle θ ₂ is not limited to 0 °. Θ ₂ ≠ 0 ° may be satisfied as long as the condition shown in the equation (9) is satisfied.

The first of each of the fibers ₆₁ of the plurality of may be those coated is made. The first of each of the fibers 6 _second plurality book may be one coat was made.

In addition, by one or more support members (not shown) is provided between the fiber-reinforced plastic layer 3 _1, 3 _2, may be one gap layer 8 is formed. By using an appropriate material for these support members, the rigidity of the radome 2a can be further improved while reducing the weight of the radome 2a.

In addition, the radar device 100a can employ various modifications similar to those described in the first embodiment, that is, various modifications similar to the radar device 100. For example, radiated waves are not limited to millimeter waves. Further, the radar device 100a is not limited to the vehicle-mounted one.

As described above, in the radar device 100a of the second embodiment, the radome 2a has the gap layer 8 formed between the two fiber reinforced plastic layers 3 arranged to face each other and the two fiber reinforced plastic layers 3. The distance d between the two fiber reinforced plastic layers 3 is set to a value corresponding to an integral multiple of the half wavelength of the radio wave. By using the radome 2a, it is possible to achieve both improvement in transparency to radio waves such as millimeter waves, reduction in weight, and improvement in rigidity, as in the case of using the radome 2. Further, by fiber-reinforced plastic layer 3 _1, 3 low dielectric constant between ₂ layers (i.e. the gap layer 8) is provided, it is possible to further improve the permeability to radio waves such as a millimeter wave. Further, since the interval d is set to a value based on the equation (11), the Fresnel loss in a predetermined frequency range including the carrier frequency f can be reduced.

Further, the interval d is an interval with respect to the radiation direction (more specifically, the main beam direction) of the radio wave by the antenna 1. As a result, the radiated wave (more specifically, the main beam) can pass through the radome 2a with the high transmittance as described above.

It should be noted that, within the scope of the invention, the present invention can be freely combined with each embodiment, modified from any component of each embodiment, or omitted from any component in each embodiment. ..

The radar device of the present invention can be used, for example, in an in-vehicle millimeter-wave radar.

1 antenna, 2, 2a radome, 3 fiber reinforced plastic layer, 4 fiber bundle (1st fiber bundle), 5 fiber bundle (2nd fiber bundle), 6 fiber (1st fiber), 7 fiber (2nd fiber), 8 gap layer, 11 substrate, 12 antenna element, 100, 100a radar device.

Claims (8)

It is equipped with an antenna that radiates radio waves and a radome for the antenna.
The radome has a fiber reinforced plastic layer including a plurality of first fiber bundles made of a plurality of first fibers and a plurality of second fiber bundles made of a plurality of second fibers.
The fiber-reinforced plastic layer is provided so that the longitudinal direction of each of the first fiber bundles is along the direction perpendicular to the polarization direction of the antenna, and the longitudinal direction of each of the second fiber bundles is the said. It is provided along the direction parallel to the polarization direction, and is provided.
A radar device characterized in that the electric conductivity of each of the first fibers is higher than the electric conductivity of each of the second fibers. The radar device according to claim 1, wherein the radio wave is a millimeter wave. The radar device according to claim 1, wherein the radar device is for in-vehicle use. The radome has two fiber-reinforced plastic layers arranged so as to face each other and a gap layer formed between two fiber-reinforced plastic layers.
Any one of claims 1 to 3, wherein the distance between the two fiber-reinforced plastic layers is set to a value corresponding to an integral multiple of the half wavelength of the radio wave. The radar device described in the section. The radar device according to claim 4, wherein the interval is the interval with respect to the radiation direction of the radio wave by the antenna. The method according to any one of claims 1 to 3, wherein the wall thickness of the fiber reinforced plastic layer is set to a value corresponding to an integral multiple of the half wavelength of the radio wave. Radar device. The individual first fibers are composed of carbon fibers, metal fibers, boron fibers or fine metal wires.
The radar device according to any one of claims 1 to 3, wherein each of the second fibers is made of glass fiber or quartz fiber. The radar device according to any one of claims 1 to 3, wherein the thickness of each of the first fibers is set to a value of 1/10 or less with respect to the wavelength of the radio wave. ..

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