JP2020060506A - Radome - Google Patents

Abstract

To improve performance of a radome which covers a radar and the like.SOLUTION: A radome 100 covering a radar 200 comprises a resin film 101 having a front surface and a rear surface, a front surface film 102 formed on the front surface side of the resin film 101, and a rear surface film 103 formed on the rear surface side of the resin film 101. Here, the resin film 101 is formed into a concavoconvex shape. A dielectric constant of a substance being present between the front surface film 102 and the resin film 101 and a dielectric constant of a substance being present between the rear surface film 103 and the resin film 101 are both lower than a dielectric constant of the resin film 101. These substances are, for example, air.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a radome, and particularly to a radome that covers a millimeter wave radar mounted on an automobile or the like.

  In vehicles such as automobiles, railroads, airplanes, and ships, Doppler sensors or radar sensors using radio waves are known as peripheral detection sensors for safe operation or safe operation. To simplify the description, an automobile will be mainly described below as an example of a vehicle.

  As radars for automobiles, a plurality of radars having different detection distances and detection angle ranges are used to detect the entire circumference of the automobile in order to support safe driving and realize autonomous driving. In particular, a radar for a front of a car and for a long distance has a maximum detection distance of 200 m so that the car can be safely stopped even when traveling on an autobahn or the like without a speed limit at a speed of 200 km / h. The above is desired. In such a radar antenna, a high-gain characteristic of the antenna can be obtained by applying a narrow-angle beam with a horizontal azimuth detection range of ± 8 deg or more and a vertical azimuth half-value width of ± 2 deg or less. ing.

  In addition, most of the time a car operates is spent traveling in urban areas. Therefore, even for long-distance radars that use high-gain antennas, it is desirable to detect obstacles around the vehicle according to the road conditions when turning right or left at an intersection or when passing a pedestrian crossing. It is rare. As such a demand, for example, wide-angle detection of ± 30 deg or more is desired.

  If the angle detection is within a range of about ± 8 deg, by designing the thickness of the radome, which is a resin film covering the radar, to be an integral multiple of λ / 2, and using standing waves, it is possible to use air with different dielectric constants. Even at the interface with the resin film, it is possible to minimize deterioration of the radio wave transmission characteristics.

  However, in order to realize angle detection in a range of ± 30 deg or more in a millimeter wave radar that handles radio waves in the millimeter wave band, it is necessary to design the radome thickness in the transmission direction to be an integral multiple of λ / 2. A curved radome centered on the radiation source of the antenna is required. In addition, a millimeter-wave radar having an antenna array composed of multiple antennas requires curved radomes that have the same distance from multiple radiation sources. It is very difficult to suppress the variation of.

  Further, when the radar is arranged on the back side of a bumper or the like, a design in which a curved radome is locally applied only to a portion of the bumper through which radio waves pass is not desired from the viewpoint of vehicle design. .

  For example, as shown in the following patent documents, various techniques have been studied in order to suppress the reflection effect at the boundary between air and a resin film having different dielectric constants.

  Patent Document 1 discloses a technique that uses a physical law. When a bumper made of a resin film is installed in the emission direction of a radio wave of a millimeter wave radar, the incident angle of the radio wave on the resin film is referred to as Brewster's angle. A matched bumper structure is disclosed.

  Patent Document 2 discloses a technique in which a radar is directly mounted on a bumper made of a resin film. The bumper and the millimeter wave radar are connected using a horn-shaped bracket, and the bumper and the millimeter-wave radar are connected according to the opening diameter of the horn antenna. A structure in which a hole is provided in a bumper is disclosed.

  Patent Document 3 discloses a technique for suppressing reflection by processing a part of a bumper made of a resin film as a mountain having an uneven shape.

JP, 2007-248167, A JP, 2005-37139, A JP, 2007-249678, A

  The bumper disclosed in Patent Document 1 can minimize the reflection intensity by matching only a part of the wide-angle radiation range of the antenna with the Brewster angle. However, most of the wide-angle detection angles have a problem that reflection cannot be suppressed.

  The bumper disclosed in Patent Document 2 can reduce unnecessary reflection in the propagation path of radio waves by making a hole in the bumper. However, since the wave front of the radio wave is flattened inside the tapered horn, the antenna gain in the wide-angle azimuth is low and it is not suitable for wide-angle detection. Further, since there is a hole in the bumper, there is a possibility that foreign matter such as dust or dirt may be mixed in while the vehicle is traveling, or water droplets may be mixed in during rain, and these problems deteriorate the antenna characteristics.

  In the bumper disclosed in Patent Document 3, a plurality of pyramid-shaped uneven portions (covering parts) are provided in an array on the surface of the bumper on the radar side, and the height of the base up to the uneven portion is an odd number of 1/4 of the wavelength. Doubled. By adopting the pyramid shape, the radio waves emitted from the radar device pass through the uneven portion and reach the inside of the bumper. However, the radio wave is specularly reflected at the critical angle caused by the difference between the dielectric constant of the bumper and the dielectric constant of air. If the range of angle detection of the radar device is within the range of the critical angle, the reflection intensity is small, but for example, in the case of a resin film having a dielectric constant of about 4 (refractive index of about 2), the critical angle becomes 45 degrees or more. In the angle azimuth direction, the transmitted power decreases, so the sensitivity of the radar device decreases.

  Also, if the bumper surface is provided with pyramid-shaped irregularities, mud, water, dirt, etc. will adhere to the bumper surface in an environment where automobiles are normally used, so that good millimeter wave transmission characteristics are maintained. Difficult to do. Furthermore, if the bumper surface is coated with the bumps and dips on the bumper surface being exposed, the paint is embedded in the bumps and depressions, so that the pyramid-shaped function cannot be maintained. Providing the uneven portion on the surface of the bumper is not practical in terms of the design of the vehicle.

  The present inventors considered reducing the dielectric constant of the resin film from the viewpoint of suppressing the reflection intensity on the surface of the bumper. 2. Description of the Related Art In recent years, vehicles such as automobiles, railroads, airplanes, and ships have been increasingly electrified and have reduced fuel consumption. For example, in automobiles, efforts have been made to reduce the weight of the vehicle body as part of the reduction in fuel consumption, and in order to reduce the weight, foaming of a resin film which is a material for a bumper is being studied. Further, by promoting foaming of the resin film, lowering of the dielectric constant of the resin film is also promoted.

  Further, from the viewpoint of coating, hardness and smoothness are required on the front surface side of the bumper, so that the foamed resin film has few bubbles. Then, many bubbles of the foamed resin film are contained inside the bumper. That is, the dielectric constant of the foamed resin film forming the bumper is large on the surface of the bumper and small inside the bumper. Further, since the bumper using the foamed resin film also pays attention to the mechanical strength, the foamed resin film has a foaming rate of about 50% and the foamed resin film has a dielectric constant of about 2.4. Such a value is not sufficiently small to suppress reflection on the bumper surface.

  As described above, since the antenna of the millimeter wave radar is easily affected by the environment outside the antenna, the antenna is mechanically and environmentally protected by the resin film radome or bumper that easily transmits radio waves. Then, even if the antenna used for the millimeter-wave radar for automobiles is a radar antenna for a long distance, wide-angle detection performance with a half value width in the horizontal direction of ± 30 deg to ± 60 deg is required. There is.

  Further, even if the antenna has a wide-angle radiation range, if the transmitted power is attenuated by reflection on the surface of the radome that protects the antenna, the wide-angle radiation characteristic of the antenna is sacrificed, and the sensitivity of the antenna decreases, The reflected power is re-input into the antenna as a multipath. As a result, interference noise occurs in radar detection.

  Therefore, in a radome or the like that covers the radar, it is necessary to reduce the difference in dielectric constant between the radome and the contact surface between the radome and the air outside the radome so that the reflection intensity is suppressed. Therefore, the radome is required to have a structure that achieves both low dielectric constant of the material forming the radome and mechanical strength capable of withstanding the usage environment. That is, it is required to improve the performance of a covering member such as a radome that covers a radar or the like.

  Other problems and novel features will be apparent from the description of the present specification and the accompanying drawings.

  The following is a brief description of the outline of a typical embodiment among the embodiments disclosed in the present application.

  The radome which is one embodiment has a resin film having a front surface and a back surface, a first film formed on the front surface side of the resin film, and a second film formed on the back surface side of the resin film. Here, the dielectric constant of the substance existing between the first film and the resin film and the dielectric constant of the substance existing between the second film and the resin film are lower than the dielectric constant of the resin film, respectively.

  According to the embodiments disclosed in the present application, it is possible to improve the performance of the radome that covers the radar and the like.

FIG. 3 is a cross-sectional view showing the radome of the first embodiment, and is a schematic view showing the relationship between the radome and the radar. FIG. 3 is a perspective view showing a resin film according to the first embodiment. FIG. 3 is a perspective view showing a resin film according to the first embodiment. FIG. 3 is a perspective view showing a resin film according to the first embodiment. FIG. 6 is a plan view showing a resin film according to a second embodiment. It is sectional drawing which shows the radome of Embodiment 2, and is a schematic diagram which shows the relationship between a radome and a radar. It is sectional drawing which shows the radome of the modification 1, and is a schematic diagram which shows the relationship between a radome and a radar. It is sectional drawing which shows the radome of the modification 2, and is a schematic diagram which shows the relationship between a radome and a radar. It is sectional drawing which shows the radome of Embodiment 3, and is a schematic diagram which shows the relationship between a radome and a radar. It is sectional drawing which shows the radome of Embodiment 4, and is a schematic diagram which shows the relationship between a radome and a radar. It is sectional drawing which shows the radome of Embodiment 5, and is a schematic diagram which shows the relationship between a radome and a radar. It is sectional drawing which shows the radome of the modification 3, and is a schematic diagram which shows the relationship between a radome and a radar. It is sectional drawing which shows the radome of Embodiment 6, and is a schematic diagram which shows the relationship between a radome and a radar. It is sectional drawing which shows the radome of Embodiment 7, and is a schematic diagram which shows the relationship between a radome and a radar.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In all the drawings for explaining the embodiments, members having the same function are designated by the same reference numerals, and the repeated description thereof will be omitted. In the following embodiments, the description of the same or similar parts will not be repeated in principle unless particularly necessary.

(Embodiment 1)
In the present embodiment, a radar 200 mounted on a vehicle that is a vehicle and a radome 100 that is a covering member that covers the radar 200 will be described. FIG. 1 is a cross-sectional view showing a radome 100 according to this embodiment, and is a schematic view showing a relationship between the radome 100 and a radar 200. In the present embodiment, the radome 100 constitutes the whole or a part of a bumper attached to the front of the automobile, and the radar 200 mounted inside the automobile is covered by the radome 100.

  The Z direction shown in the drawing is the thickness direction of the radome 100, and the direction from the back film 103 to the front film 102 is the front direction of the automobile. The X direction is the side direction of the automobile and the Y direction is the height direction of the automobile. These X direction, Y direction and Z direction are orthogonal to each other.

  As shown in FIG. 1, the radome 100 includes a resin film 101 having a front surface and a back surface, a surface film 102 formed on the front surface side of the resin film 101, and a back film 103 formed on the back surface side of the resin film 101. Have and. The front surface side of the resin film 101 is the outside of the automobile, and the back surface side of the resin film 101 is the inside of the automobile. A radar 200 is mounted inside the vehicle.

  The radar 200 is a millimeter wave radar and has a plurality of antennas 201 and an RF circuit (high frequency circuit) 202 electrically connected to the plurality of antennas 201. The plurality of antennas 201 are provided in an array and include transmitting and receiving antennas.

  The RF circuit 202 internally generates a millimeter wave signal, and the millimeter wave signal is radiated from the antenna 201 for transmission to the outside of the automobile through the radome 100. The radiated millimeter wave signal reaches the target, and the millimeter wave signal reflected (scattered) by the target is received by the receiving antenna 201 via the radome 100. In the millimeter wave signal handled by the radar 200 of the present embodiment, the wavelength is, for example, 3 mm, and the frequency is, for example, 77 GHz band or 79 GHz band.

  The structure of the radome 100 of this embodiment will be described in detail below.

  The resin film 101 is made of synthetic resin, for example, polypropylene or polystyrene, and has a thickness of, for example, 30 to 50 μm. The dielectric constant of the resin film 101 is 3.0, for example. Further, the resin film 101 of the present embodiment has a corrugated board structure and has an uneven shape. That is, the resin film 101 has a shape in which a concave portion projecting to the back surface side of the resin film 101 and a convex portion projecting to the front surface side of the resin film 101 are alternately repeated. Further, the resin film 101 is formed such that its surface is inclined with respect to the traveling direction of the radio wave transmitted through the inside of the radome 100.

  2 to 4 are perspective views each showing an example of the shape of the resin film 101.

  In FIG. 2, the resin film 101 has a structure forming a one-dimensional triangular waveform, and includes a triangle formed by the resin film 101 and the front surface film 102 and a triangle formed by the resin film 101 and the back surface film 103. However, it is a so-called truss structure, which is a structure that is continuously connected. That is, in cross-sectional view, the shape of the resin film 101 between the apex 105 of the concave portion and the apex 104 of the convex portion is linear.

  In FIG. 3, the resin film 101 has a structure forming a one-dimensional sine waveform. That is, in cross-sectional view, the shape of the resin film 101 between the apex 105 of the concave portion and the apex 104 of the convex portion is curved. The structure of FIG. 2 has high strength against pressure from a direction perpendicular to the surface of the radome 100 (the front surface of the automobile). The structure of FIG. 3 has high strength against pressure from a direction perpendicular to the surface of the radome 100, and is higher than the structure of FIG. 2 against pressure from a direction oblique to the surface of the radome 100. Have strength.

  In FIG. 4, as in FIG. 3, the resin film 101 between the apex 105 of the concave portion and the apex 104 of the convex portion has a curved shape in a cross-sectional view, but the resin film 101 has a two-dimensional shape. It has a structure that forms the waveform of a typical trigonometric function. Such a structure of FIG. 4 has higher strength than the structures of FIGS. 2 and 3 against pressure from directions perpendicular to the surface of the radome 100 and oblique directions.

  As described above, the resin film 101 having the concave portion and the convex portion preferably has the shape shown in FIGS. 2 to 4. However, the surface of the resin film 101 with respect to the traveling direction of the radio wave transmitted through the inside of the radome 100 is preferable. It only has to have an oblique shape. For example, the shapes of the concave portion and the convex portion may be pyramidal, conical, hemispherical, or semielliptic, respectively. Further, these shapes may be applied to all or a part of the plurality of concave portions and the plurality of convex portions.

  Further, in the above-mentioned concavo-convex shape, the period of the wave having the triangular waveform or the sine waveform is set to be less than the wavelength of the millimeter wave transmitted through the radome 100. That is, the cycle in which the pair of concave and convex portions is formed is less than the wavelength of the millimeter wave transmitted through the radome 100.

  The resin film 101 is adhered to the front surface film 102 and the back surface film 103. Specifically, the resin film 101 is adhered to the front surface film 102 at the apex 104 of the convex portion and adhered to the back surface film 103 at the apex 105 of the concave portion. Therefore, a desired substance can be present between the resin film 101 and the front surface film 102 and between the resin film 101 and the back surface film 103. In the present embodiment, air AIR is exemplified as such a substance.

  For each of the front surface film 102 and the rear surface film 103, it is preferable to use a resin film as a material having solvent resistance to a water-based or oil-based paint and environment resistance. In the present embodiment, each of the front surface film 102 and the back surface film 103 is made of a plate-shaped synthetic resin, for example, polyphenylene sulfide (PPS).

  Each of the front surface film 102 and the back surface film 103 is formed of a resin material having a higher dielectric constant and a higher hardness than the resin film 101 in order to improve mechanical strength.

  Further, the thickness of each of the front surface film 102 and the rear surface film 103 is sufficiently smaller than the wavelength used in the radar 200, and is a thickness that allows transmission of millimeter waves, and is, for example, 50 to 100 μm. Therefore, it is possible to ensure the transparency of the millimeter wave that passes through the radome 100. The thickness of the region where the uneven resin film 101 and the air AIR are present, that is, the distance between the front surface film 102 and the back surface film 103 is, for example, 3 to 5 mm.

<Main features of the present embodiment>
The main features of the radome 100 of this embodiment are described below.

  In radome 100 of the present embodiment, air AIR having a lower dielectric constant than resin film 101 exists between resin film 101 and front surface film 102 and between resin film 101 and rear surface film 103. There is. Air AIR has a dielectric constant of 1.0. Although the resin film 101 is also formed inside the radome 100, since the resin film 101 is thin and is made of a material having a low dielectric constant, the equivalent dielectric constant in the entire radome 100 can be kept low. In other words, since the dielectric constant averaged by the air AIR and the resin film 101 can be regarded as an equivalent dielectric constant, in the radome 100 of the present embodiment, the radome 100 is composed of the resin film 101. Also, the dielectric constant can be lowered.

  That is, the permittivity inside the radome 100 can be made closer to the permittivity outside the radome 100 (permittivity of air). Further, the thickness of each of the front surface film 102 and the back surface film 103 is such that millimeter waves can be transmitted. Therefore, when the millimeter wave reflected from the target outside the vehicle passes through the inside of the radome 100, the millimeter wave is received by the radar 200 without being substantially attenuated.

  Further, inside the radome 100, the resin film 101 is formed in a concavo-convex shape, and the surface of the resin film 101 is inclined with respect to the traveling direction of the radio wave transmitted through the inside of the radome 100. Further, in the concavo-convex shape, the cycle in which the pair of concave and convex portions is formed is less than the wavelength of the millimeter wave transmitted through the radome 100.

  Therefore, the millimeter wave passes through the resin film 101 and the air AIR inside the radome 100. In the traveling direction of millimeter waves, the dielectric constant inside the radome 100 is gently changed by the resin film 101 and the air AIR, so that reflection and refraction of millimeter waves can be suppressed. That is, inside the radome 100, it is difficult for mirror reflection of millimeter waves to occur. As a result, the characteristic impedance of the radome 100 can be changed stepwise from the surface film 102 side to the inside of the radome 100, so that the characteristics of the inside of the radome 100 and the air AIR outside the radome 100. The impedance ratio is minimized.

  The uneven resin film 101 may be formed of a foamed resin film. In this case, since the dielectric constant of the resin film 101 itself can be further reduced, the equivalent dielectric constant inside the radome 100 can be further reduced.

  If the radome 100 according to the present embodiment is provided so as to sufficiently cover the radiation range of the antenna 201, it is possible to suppress the reflection intensity of millimeter waves. As a result, multipath due to irregular reflection is reduced, erroneous detection of the radar 200 is suppressed, and the detection accuracy of the radar 200 can be improved.

  Further, in the radome 100 of the present embodiment, the uneven resin film 101 formed between the front surface film 102 and the rear surface film 103 serves as a pillar. Therefore, the mechanical strength of the radome 100 itself can be improved. That is, the radome 100 of the present embodiment can improve the mechanical strength of the radome 100 to such an extent that the radome 100 can withstand a use environment such as an automobile without lowering the detection accuracy of the radar 200.

  If the surface film 102 is not provided and the resin film 101 is exposed, foreign matter such as mud, water, and dirt may be accumulated in the concave portion of the resin film 101. When such a foreign substance adheres to the radome 100, problems such as reflection or attenuation of millimeter waves are likely to occur near the surface of the radome 100. In this embodiment, since the film 102 having a flat surface and a thickness capable of transmitting millimeter waves is formed on the surface side of the uneven resin film 101, such a problem is solved. can do.

  As described above, according to the present embodiment, the performance of the radome 100 that covers the radar 200 can be improved.

(Embodiment 2)
The radome 100 according to the second embodiment will be described below with reference to FIGS. 5 and 6. FIG. 5 is a plan view of the resin film 101 according to the second embodiment, which is a plan view parallel to the XY plane. In the following description, differences from the first embodiment will be mainly described.

  In the first embodiment, the entire resin film 101 has an uneven shape inside the radome 100, but in the second embodiment, a part of the resin film 101 has an uneven shape.

  As shown in FIGS. 5 and 6, the resin film 101 of the second embodiment includes a transmissive region 101A and a fixed region 101B integrated with the transmissive region 101A. The resin film 101 in the transmissive region 101A has an uneven shape as in the first embodiment. The resin film 101 in the fixed area 101B is formed thicker than the resin film 101 in the transmissive area 101A so as to fill the space between the front surface film 102 and the back surface film 103. Such a resin film 101 can be manufactured by changing the shape of the mold.

  The front surface film 102 adheres to the front surface of each resin film 101 in the transmissive area 101A and the fixed area 101B, and the back surface film 103 adheres to the rear surface of each resin film 101 in the transmissive area 101A and the fixed area 101B. There is. In other words, the front surface film 102 and the back surface film 103 are formed so as to sandwich the resin film 101 in each of the transmissive region 101A and the fixed region 101B.

  In the second embodiment, inside the radome 100, a transmission region 101A is provided only in a region where millimeter waves are desired to be transmitted, in accordance with the angle detection range of the radar 200. In other words, the radar 200 is arranged so as to overlap the transmission area 101A and to be included in the transmission area 101A in a plan view (front view of the vehicle). Also in this case, similarly to the first embodiment, the detection accuracy of the radar 200 can be improved. Further, in the fixed region 101B that does not transmit millimeter waves, the mechanical strength of the radome 100 as a whole can be further improved by increasing the thickness of the resin film 101.

(Modification 1)
Below, the radome 100 of the modification 1 of Embodiment 2 is demonstrated using FIG. In the following description, differences from the second embodiment will be mainly described.

  As shown in FIG. 7, in the modified example 1, the front surface film 102 and the rear surface film 103 are formed only in the transmissive area 101A and not in the fixed area 101B. That is, the front surface and the back surface of the resin film 101 in the fixed region 101B are exposed from the front film 102 and the back film 103, respectively.

  As described above, in Modification 1, since the front surface film 102 and the back surface film 103 are selectively formed only in the transmissive region 101A having the uneven shape, the manufacturing cost can be suppressed as compared with the second embodiment. You can Further, when the radome 100 is used as the entire bumper, it is difficult to bond the front surface film 102 and the rear surface film 103 to the entire bumper with high accuracy, and there is a problem that a portion having a weak adhesive force is likely to exist locally. On the other hand, in the second modification, only the transmissive region 101A is partially heated to bond the front surface film 102 and the rear surface film 103 to the radome 100, so that the bonding accuracy can be improved and the heating time can be shortened. Can be achieved.

(Modification 2)
Below, the radome 100 of the modification 2 of Embodiment 2 is demonstrated using FIG. In the following description, differences from the second embodiment will be mainly described.

  As shown in FIG. 8, in Modified Example 2, the radome 100 does not constitute the entire bumper of the automobile, but is a member attached to the base material 106 which is the bumper, and constitutes a part of the bumper. There is. The radome 100 can be mounted on the base material 106 by providing, for example, an adhesive in the gap between the radome 100 and the base material 106.

  For example, in the case where the main part of the bumper is composed of the base material 106 that is a structure different from the radome 100, considering the manufacturing cost of the entire bumper, mechanical strength, or appearance, etc., the radar 200 is The radome 100 can be selectively attached to the place where it is arranged. Therefore, the degree of freedom in designing the bumper can be increased. Further, since the radome 100 of the modified example 2 is a structure having a size corresponding to the above-mentioned transmission area 101A, the detection accuracy of the radar 200 does not deteriorate as compared with the other embodiments.

  Further, the radome 100 and the base material 106 can be manufactured separately. Therefore, for example, the bumper, which is the base material 106, is manufactured on a manufacturing line of a predetermined factory, the radome 100 is manufactured on another manufacturing line or another factory, and they are finally combined to complete the bumper. You can also

  In Modification 2, as in Modification 1, only the portion corresponding to the transmissive region 101A is partially heated to bond the front surface film 102 and the back surface film 103 to the radome 100, thus improving the bonding accuracy. Therefore, it is possible to suppress the manufacturing cost associated with the film itself and the film adhesion.

(Embodiment 3)
The radome 100 according to the third embodiment will be described below with reference to FIG. In the following description, differences from the first embodiment will be mainly described.

  As shown in FIG. 9, in the third embodiment, a coating film 107 made of a material different from that of the surface film 102 is formed on the surface of the surface film 102 having solvent resistance. To form the coating film 107, a liquid obtained by diluting a base coat, which is a mixture of an aqueous or oily coating material and a curing agent, with thinner is used, and the coating film 107 is obtained by drying the liquid. Further, the coating film 107 may be formed by a printing technique. Further, even when a material such as a paint contains a metal such as indium, the thickness of the coating film 107 is set to 1/10 or less of the skin effect thickness (the conductor resistivity is 1Ω or more). To do.

  The thickness of the coating film 107 is sufficiently smaller than the wavelength used in the radar 200 and is a thickness that allows millimeter waves to pass through, and is, for example, 50 μm. The total thickness of the coating film 107 and the surface film 102 is also a thickness that allows millimeter waves to pass therethrough.

  By forming such a coating film 107, the radome 100 can be protected from the external environment (mud, rainwater, etc.) of the radome 100, and the appearance design can be improved.

  The technique disclosed in the third embodiment can also be applied to the radome 100 of the second embodiment.

(Embodiment 4)
The radome 100 according to the fourth embodiment will be described below with reference to FIG. In the following description, differences from the first embodiment will be mainly described.

  As shown in FIG. 10, in the fourth embodiment, the foamed resin film FP1 is filled between the resin film 101 and the surface film 102. The foamed resin film FP1 has a higher foaming rate than the resin film 101, and has a foaming rate of about 50 to 800%. The dielectric constant of the foamed resin film FP1 is lower than the dielectric constant of the resin film 101, and is 1.05 to 2.4, for example. That is, the dielectric constant of the foamed resin film FP1 is about 2.4 when the foaming rate is 50%, and about 1.05 when the foaming rate is 800%.

  In the first embodiment, the substance existing between the resin film 101 and the surface film 102 is air AIR having a dielectric constant of 1.0. However, in the fourth embodiment, the foamed resin film FP1 is used instead of the air AIR. Has been applied. Therefore, the equivalent dielectric constant inside the radome 100 of the fourth embodiment is slightly higher than that of the first embodiment.

  However, in the fourth embodiment, the mechanical strength of the radome 100 can be improved by applying the foamed resin film FP1 having a hardness higher than that of the air AIR and adhering the foamed resin film FP1 to the surface film 102. .

  That is, when pressure is applied from the outside of the radome 100, the surface film 102 may bend, the shape formed by the resin film 101 and the surface film 102 may change, and the equivalent dielectric constant may change. In particular, when the radome 100 is applied to a bumper of an automobile, a strong pressure is applied to the surface film 102 due to the wind pressure received by the automobile while the automobile is running.

  Therefore, the characteristic impedance inside the radome 100 may change, and the wavelength received by the radar 200 may shift. Therefore, by filling the space between the resin film 101 and the surface film 102 with a substance having higher mechanical strength than the air AIR, such as the foamed resin film FP1, the possibility that the surface film 102 will bend is reduced, and Such a fear can be suppressed.

  The technique disclosed in the fourth embodiment can also be applied to the radome 100 of the second and third embodiments.

(Embodiment 5)
The radome 100 of the fifth embodiment will be described below with reference to FIG. In the following description, differences from the first embodiment will be mainly described.

  As shown in FIG. 11, in the fifth embodiment, a hole 108 penetrating the back film 103 is formed in a part of the back film 103, and a hole 109 penetrating the resin film 101 is formed in a part of the resin film 101. Are formed.

  Although the air AIR exists inside the radome 100 of the fifth embodiment, the air AIR inside the radome 100 expands or expands or contracts when the temperature changes due to, for example, changes in the weather. For example, when the temperature decreases, the air contracts and the pressure inside the radome 100 decreases. Further, when the temperature rises, the air expands and the pressure inside the radome 100 increases. Then, inside the radome 100, a deviation may occur with respect to the thickness of the air AIR, the equivalent dielectric constant may change, and the characteristic impedance may change.

  Therefore, by providing the holes 108 and 109 in the radome 100, the pressure outside the radome 100 and the pressure inside the radome 100 can be made substantially the same. Therefore, the above fear can be suppressed.

The size (caliber) of each of the holes 108 and 109 may be such that air can enter, and is larger than, for example, nitrogen molecules (N ₂ ) and oxygen molecules (O ₂ ). Further, it is desirable that these sizes are such that a liquid cannot penetrate, and it is desirable that they are smaller than water molecules (H ₂ O), for example.

  Further, in the fifth embodiment, the case where one hole 108 and one hole 109 are provided is illustrated, but a plurality of holes 108 may be provided in the back film 103 and a plurality of holes 109 may be provided in the resin film 101. Further, in the region where the millimeter wave is transmitted, it is desirable that the equivalence of the millimeter wave is as uniform as possible at each place. Therefore, it is preferable that the holes 108 and 109 are provided at the places where the millimeter wave is not transmitted. .

  The technique disclosed in the fifth embodiment can also be applied to the radome 100 of the second to fourth embodiments.

(Modification 3)
Hereinafter, a radome 100 according to Modification 3 of Embodiments 4 and 5 will be described with reference to FIG. In the following description, differences from the fourth and fifth embodiments will be mainly described.

  As shown in FIG. 12, in the modified example 3, the foamed resin film FP1 described in the fourth embodiment is filled between the resin film 101 and the front surface film 102, and the back surface film 103 is formed in the fifth embodiment. The holes 108 described are provided. Therefore, in Modification 3, the foamed resin film FP1 can be applied to improve the mechanical strength of the radome 100. Further, by applying the holes 108, the pressure outside the radome 100 and the radome 100 can be improved. The pressure inside 100 can be about the same.

(Embodiment 6)
The radome 100 according to the sixth embodiment will be described below with reference to FIG. In the following description, differences from the first embodiment will be mainly described.

  As shown in FIG. 13, in Embodiment 1, the resin film 101 having an uneven shape was formed inside the radome 100, but in Embodiment 6, between the front surface film 102 and the back surface film 103, It is filled with the foamed resin film FP2.

  The foamed resin film FP2 is a resin film similar to the foamed resin film FP1, has a higher foaming rate than the resin film 101, and has a foaming rate of about 50 to 800%. The dielectric constant of the foamed resin film FP1 is lower than the dielectric constant of the resin film 101, and is 1.05 to 2.4, for example.

  In the sixth embodiment, the foaming rate of the foamed resin film FP2 is not uniform and varies in the thickness direction (Z direction), and the foamed resin film FP2 goes from the front film 102 and the back film 103 toward the center of the foamed resin film FP2. And then gradually (continuously) lower. That is, the dielectric constant of the foamed resin film FP2 gradually (continuously) decreases from the center of the foamed resin film FP2 toward the front surface film 102 and the back surface film 103, respectively.

  In other words, in the thickness direction (Z direction) of the foamed resin film FP2, the foamed resin film FP2 has a first region closer to the center of the foamed resin film FP2, a second region closer to the surface film 102 than the first region, and , And has a third region closer to the back film 103 than the first region. Then, the foaming rate of the foamed resin film FP2 in the second area and the third area is higher than the foaming rate of the foamed resin film FP2 in the first area, and the dielectric constant of the foamed resin film FP2 in the second area and the third area is , Lower than the dielectric constant of the foamed resin film FP2 in the first region.

  The front surface film 102 and the back surface film 103 are partially bonded to the foamed resin film FP2 at locations other than bubbles in the foamed resin film FP2. Therefore, an adhesive for bonding the front surface film 102 and the rear surface film 103 to the foamed resin film FP2 is not necessary, and an increase in the dielectric constant inside the radome 100 can be suppressed.

  Since the resin film forming the foamed resin film FP2 has a high foaming rate, the foamed resin film FP2 has many gaps, is mechanically fragile, and has a drawback of adsorbing or absorbing various gases. Have. However, as in the sixth embodiment, the front surface film 102 and the rear surface film 103 having solvent resistance to a water-based or oil-based coating material and high environmental resistance are formed on the front surface and the back surface of the foamed resin film FP2. By doing so, such a defect can be compensated.

  As described above, since the space between the front surface film 102 and the rear surface film 103 is filled with the foamed resin film FP2, in the sixth embodiment, the equivalent dielectric constant inside the radome 100 is higher than that in the first embodiment. However, the mechanical strength of the radome 100 can be improved as compared with the first embodiment.

  The coating film 107 described in the third embodiment can be formed on the surface film 102 of the sixth embodiment.

(Embodiment 7)
The radome 100 of the seventh embodiment will be described below with reference to FIG. In the following description, differences from the first embodiment will be mainly described.

  As shown in FIG. 14, in Embodiment 7, the entire radome 100 is curved. Specifically, the radome 100 is curved so as to warp in the direction from the back film 103 to the front film 102. In order to form the radome 100 of the seventh embodiment, first, the radome 100 of FIG. 1 is prepared, and then the radome 100 is appropriately softened until the resin film 101, the front surface film 102, and the back surface film 103 are softened. This can be achieved by heating 100 and then subjecting the radome 100 to curved processing by press molding.

  Although it is technically possible to form the resin film 101 into a concavo-convex shape so that the entire resin film 101 has a curved shape, and then to bond the front surface film 102 and the back surface film 103 to the resin film 101, it is actually difficult. Is. As in the seventh embodiment, after the front surface film 102 and the back surface film 103 are bonded to the uneven resin film 101, the entire radome 100 is curved using press molding, so that the radome 100 with high processing accuracy is obtained. Can be formed.

  In this way, the curved surface-processed radome 100 can meet various vehicle design requirements.

  The technique disclosed in the seventh embodiment can also be applied to the radome 100 of the second to sixth embodiments.

  Although the invention made by the inventors of the present application has been specifically described based on the embodiments, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the invention. .

  For example, in the above embodiment, the case where the radome 100 is a bumper attached to the front of the automobile has been described, but the radome 100 may be applied to a bumper attached to the rear or the side of the automobile.

  Further, in the above-described embodiment, the case where the radome 100 that covers the radar 200 is mainly used for an automobile has been described, but such a radome 100 is used for another vehicle such as a railroad, an aircraft, or a ship. You can also

100 radome 101 resin film 101A transmissive area 101B fixed area 102 front surface film 103 back surface film 104 apex of convex portion 105 apex of concave portion 106 base material 107 coating film 108, 109 hole 200 radar 201 antenna 202 RF circuit AIR air FP1, FP2 foamed resin film

Claims (15)

A resin film having a front surface and a back surface,
A first film formed on the surface side of the resin film,
A second film formed on the back surface side of the resin film;
Have
The dielectric constant of a substance existing between the first film and the resin film and the dielectric constant of a substance existing between the second film and the resin film are respectively higher than the dielectric constant of the resin film. Low radome. The radome according to claim 1,
The resin film is a radome in which concave portions projecting to the back surface side and convex portions projecting to the front surface side are alternately repeated. The radome according to claim 2,
The radome in which the shape of the resin film between the apex of the concave portion and the apex of the convex portion is a linear shape in a cross-sectional view. The radome according to claim 2,
The radome in which the shape of the resin film between the apex of the concave portion and the apex of the convex portion is a curved shape in a cross-sectional view. The radome according to claim 2,
The said resin film is a radome which contains the 1st area | region where the said recessed part and the said convex part are repeated alternately, and the 2nd area | region which has a thickness larger than the thickness of the said resin film of the said 1st area | region. The radome according to claim 5,
The first film and the second film are formed so as to sandwich the resin film in the first region,
The radome, wherein the front surface and the back surface of the resin film in the second region are exposed from the first film and the second film. The radome according to claim 2,
The radome is a radome that is a member attached to a structure different from the radome. The radome according to claim 2,
A radome in which air is present between the first film and the resin film. The radome according to claim 8,
Air is present between the second film and the resin film,
A first hole penetrating the second film is formed in a part of the second film,
A radome in which a second hole penetrating the resin film is formed in a part of the resin film. The radome according to claim 2,
A radome in which a foamed resin film having a dielectric constant lower than that of the resin film is formed between the first film and the resin film. The radome according to claim 10,
Air is present between the second film and the resin film,
A radome in which a first hole penetrating the second film is formed in a part of the second film. The radome according to claim 1,
A radome in which the radome is curved. The radome according to claim 1,
A radome used for covering the millimeter wave radar so that the millimeter wave radar is provided on the back surface side of the resin film via the second film. The radome according to claim 13,
A coating film made of a material different from that of the first film is formed on the first film,
The radome, wherein the total thickness of the coating film and the first film is thinner than the wavelength used in the millimeter wave radar. A resin film having a front surface and a back surface,
A first film formed on the surface side of the resin film,
A second film formed on the back surface side of the resin film;
Have
The resin film is a foamed resin film,
In the thickness direction of the foamed resin film, the foamed resin film includes a first region closer to the center of the foamed resin film, a second region closer to the first film than the first region, and the first region. Has a third region closer to the second film than
A radome in which the dielectric constant of the foamed resin film in the second region and the third region is lower than the dielectric constant of the foamed resin film in the first region.

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