JP2016070916A - On-vehicle radar device and vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a structure that reduces a propagation loss due to a reflection occurring when a radio wave transmits a windshield (laminated glass) at the front of an antenna, and to curb a fall in efficiency of transmission/reception of the radio wave.SOLUTION: An on-vehicle radar device comprises: an attachment unit; and an antenna unit that transmits a transmission wave from an inside of laminated glass 12 including an innermost glass layer 121, outermost glass layer 122 and intermediate resin layer 123, and receives a reflection wave. An antenna part includes a transmission antenna. A vertically polarized wave component of the transmission wave is larger than a horizontally polarized wave component thereof. When the attachment unit is attached to a bracket, an angle θi1 of incidence upon the innermost glass layer of the transmission wave is larger than a Brewster angle θb1 in an inner surface of the innermost glass layer, and an angle θi2 of incidence upon the outermost glass layer of the transmission wave is equal to or less than a Brewster angle θb2 between the outermost glass layer and the intermediate resin layer.SELECTED DRAWING: Figure 7

Description

  The present invention relates to an on-vehicle radar device and a vehicle.

  In recent years, research on collision avoidance, driving assistance, automatic driving, and the like has been conducted using a technique of detecting an object around a vehicle using a radar. Conventionally, in an automobile, a radar is provided on a front nose. The high-frequency oscillator needs to be placed close to the antenna, and in order to avoid wind and rain, it is necessary to take measures for waterproofing and weather resistance such as protection with a Radome. On the other hand, more advanced detection techniques have been developed using both radar detection and camera images.

  US Pat. No. 8,604,968 proposes a radar-camera sensor in which a radar and a camera are housed in a single housing. The radar-camera sensor is attached to the windshield in front of the automobile rearview mirror. Radar waves are either vertically polarized waves or horizontally polarized waves.

Also in the composite sensor unit which is an external recognition device of International Publication No. 2006/035510, the image capturing unit and the transmission / reception unit are mounted on one sensor mounting board. The composite sensor unit is mounted in the vehicle interior.
US Pat. No. 8,604,968 International Publication No. 2006/035510

  When the radar device is provided in the vehicle interior, the radar wave is attenuated by reflection and absorption by the windshield. When using short-wavelength radio waves in order to increase the resolution of the radar, the effect of glass becomes large. Further, since the output of a high-frequency oscillator that can be used for in-vehicle use is restricted by laws and regulations, the output of the oscillator cannot be increased. As a result, the distance that can be monitored by the radar is shortened.

  The windshield used in passenger cars, etc. is transparent and at first glance appears to be composed of a single glass plate. Actually, however, in order to ensure the safety of passengers, two sheets of glass are laminated on a thin resin film. The laminated glass has a three-layer structure. Conventionally, it has not been recognized that the reflection is so large that it affects the radar performance between the second resin layer and the outermost glass layer. It was thought that sufficiently accurate results could be obtained by handling as a glass plate. Under that premise, even if there is a person who conceived to reduce the reflectivity by optimizing the angle of incidence of radio waves on the windshield, there are advantages to making the angle larger than the Brewster angle I can't find it. Beyond the Brewster angle, the reflectivity increases rapidly. Since the mounting angle can deviate from a predetermined angle due to the limit of the accuracy of the mounting process, it is reasonable to select a mounting angle slightly smaller than the Brewster angle. The inventor notices that such a premise is wrong, and the reflection that occurs between the second resin layer and the outermost glass layer is so large that it cannot be ignored, and it is necessary to suppress the reflection at that portion. I realized that. And the knowledge which the reflectance as the whole three-layer glass can be lowered | hung by making the incident angle of the electromagnetic wave to the innermost glass layer of a windshield larger than a Brewster angle made this invention.

  The present invention is directed to an in-vehicle radar device, and an object of the present invention is to suppress a decrease in efficiency of radio wave transmission / reception when the in-vehicle radar device is arranged in a vehicle interior.

  An in-vehicle radar device according to an exemplary embodiment of the present invention includes an innermost glass layer, an outermost glass layer, and an intermediate resin sandwiched between the innermost glass layer and the outermost glass layer. A mounting portion attached to a bracket fixed to the innermost glass layer of the laminated glass including a layer, a rearview mirror disposed inside the innermost glass layer, or a ceiling; and from the inner side of the innermost glass layer An antenna unit that transmits a transmission wave that is a millimeter-wave wave to the outside of the outermost glass layer, and receives a reflected wave that enters the innermost glass layer from the outside of the outermost glass layer; Prepare.

  The antenna unit includes a transmission antenna that transmits the transmission wave. The vertical polarization component of the transmission wave with respect to the laminated glass is larger than the horizontal polarization component. When the attachment portion is attached to a bracket, the incident angle of the transmission wave at the center of the main lobe of the transmitting antenna to the innermost glass layer is larger than the Brewster angle on the inner surface of the innermost glass layer. The incident angle of the transmitted wave to the outermost glass layer at the center of the main lobe is equal to or smaller than the Brewster angle between the outermost glass layer and the intermediate resin layer.

  The present invention is also directed to a vehicle including an in-vehicle radar device.

  The above object and other objects, features, aspects and advantages will become apparent from the following detailed description of the present invention with reference to the accompanying drawings.

  ADVANTAGE OF THE INVENTION According to this invention, in the vehicle-mounted radar apparatus arrange | positioned in a vehicle interior, the fall of the efficiency of transmission / reception of an electromagnetic wave can be suppressed.

FIG. 1 is a side view showing a simplified vehicle. FIG. 2 is a cross-sectional view of the laminated glass. FIG. 3 is a cross-sectional view of the radar apparatus attached to the laminated glass. FIG. 4 is a perspective view of the radar apparatus. FIG. 5 is a block diagram showing an outline of the configuration of the radar apparatus. FIG. 6A is a diagram illustrating a state in the proximity monitoring mode. FIG. 6B is a diagram illustrating a state of the remote monitoring mode. FIG. 7 is a diagram illustrating a state in which the transmission wave is incident on the laminated glass.

  FIG. 1 is a side view schematically showing a vehicle 1 according to an exemplary embodiment of the present invention. The vehicle 1 is a passenger car and includes an on-vehicle radar device 11 (hereinafter referred to as “radar device”).

  The radar device 11 is used for collision avoidance, driving assistance, automatic driving, and the like. The radar device 11 is attached to the inner surface of the windshield 12 of the vehicle 1 and is located in the passenger compartment 13. The vehicle compartment 13 does not need to be a space that is completely partitioned from the outside. For example, the ceiling may be open. The radar device 11 is located in front of the rearview mirror 14 attached to the windshield 12. The vehicle 1 includes a drive mechanism 15 that moves the vehicle body 10. The drive mechanism 15 includes an engine, a steering mechanism, a power transmission mechanism, wheels, and the like.

  The windshield 12 is fixed to the vehicle body 10 and is located between the inside of the passenger compartment 13 and the outside. The front glass 12 is a laminated glass in which a film is sandwiched between two glasses. Hereinafter, the windshield 12 is also referred to as “laminated glass”. The radar device 11 is fixed to the inner surface of the laminated glass 12 directly or indirectly via a mounting member such as a bracket. As another attachment form, it can also be attached to a rear view mirror or a ceiling. In the present embodiment, the radar apparatus 11 is indirectly fixed to the laminated glass 12 via a bracket.

  As shown in FIG. 2, the laminated glass 12 includes an innermost glass layer 121, an outermost glass layer 122, and an intermediate resin layer 123. The intermediate resin layer 123 is sandwiched between the innermost glass layer 121 and the outermost glass layer 122. That is, when viewed from inside the passenger compartment 13, the innermost glass layer 121, the intermediate resin layer 123, and the outermost glass layer 122 are arranged in this order. In the laminated glass 12, if these three layers are main components, other layers may be interposed. In the present embodiment, the innermost glass layer 121 and the outermost glass layer 122 are soda lime glass. The optical properties of the innermost glass layer 121 and the optical properties of the outermost glass layer 122 may be the same or different. The intermediate resin layer 123 is preferably polyvinyl butyrate (PVB). The intermediate resin layer 123 may be configured by a plurality of laminated resin layers.

  FIG. 3 is a cross-sectional view of the radar apparatus 11 attached to the laminated glass 12. Parallel diagonal lines in the details of the cross section are omitted. As described above, the radar apparatus 11 is fixed to the laminated glass 12 via the bracket 16. The radar device 11 is detachable from the bracket 16.

  The bracket 16 includes two plate portions 161 and a connecting portion 162. The two plate portions 161 are positioned so as to overlap each other, and the front end portions are connected by the connecting portion 162 in a rotatable state. The upper surface of the upper plate portion 161 is firmly fixed to the laminated glass 12 via the adhesive member 163. The bracket 16 may be fixed to the innermost glass layer 121 by other methods. The radar device 11 is fixed to the lower surface of the lower plate portion 161 using screws 164. The lower plate portion 161 is rotatable about the axis that faces in the left-right direction with respect to the traveling direction of the vehicle 1 by the connecting portion 162. With this mechanism, the angle of the lower plate portion 161 relative to the upper plate portion 161 can be selected.

  The bracket 16 further includes an adjustment bolt 165 and a spring 166. The spring 166 applies a force in a direction in which the two plate portions 161 approach each other. The position of the lower plate portion 161 relative to the upper plate portion 161 is determined by the adjustment bolt 165. Thereby, the monitoring direction in the vertical direction of the radar apparatus 11 is accurately determined. Instead of the adjustment mechanism of the bracket 16 of FIG. 3, other various mechanisms may be employed. For example, a plurality of types of brackets having different inclination angles between the upper and lower surfaces may be prepared, and those having an appropriate inclination angle may be selected according to the required angle.

  The radar apparatus 11 includes an antenna unit 21, a camera unit 22, a circuit unit 23, and a cover 24. The camera unit 22 is located above the antenna unit 21. The cover 24 covers the antenna unit 21, the camera unit 22, and the circuit unit 23. The cover 24 is attached to the antenna unit 21. The camera unit 22 is also attached to the antenna unit 21 via a member not shown. The arrangement of the antenna unit 21, the camera unit 22, and the circuit unit 23 may be changed as appropriate. For example, the camera unit 22 may be positioned below or on the side of the antenna unit 21. The cover 24 may cover the antenna unit 21, the camera unit 22, and the circuit unit 23 in various modes. For example, the cover 24 may cover the entire antenna unit 21, the camera unit 22, and the circuit unit 23, or may cover only the lower part.

  FIG. 4 is a perspective view of the radar apparatus 11. An attachment portion 241 that is attached to the bracket 16 is provided on the upper portion of the cover 24. The attachment portion 241 includes a flat surface 242 and an attachment hole 243. The flat surface 242 is in contact with the lower plate portion 161 of the bracket 16. A screw 164 is inserted into the mounting hole 243.

  As shown in FIG. 3, the circuit unit 23 includes a circuit board 23 a attached to the antenna unit 21 and a circuit board 23 b connected to the camera unit 22. The circuit board 23a and the circuit board 23b are electrically connected. The circuit board 23a mainly processes signals from the antenna unit 21, and the circuit board 23b mainly processes signals from the camera unit 22. However, the division of these functions may be changed as appropriate.

  The antenna unit 21 transmits radio waves as radar waves to the outside of the vehicle via the laminated glass 12 and receives reflected waves from the outside via the laminated glass 12. That is, the antenna unit 21 transmits a transmission wave from the inner side of the innermost glass layer 121 to the outer side of the outermost glass layer 122, and is reflected from the outer side of the outermost glass layer 122 to the inner side of the innermost glass layer 121. Receive waves.

  As shown in FIG. 4, the antenna unit 21 includes a transmission antenna unit 211 and a reception antenna unit 212. The transmission antenna unit 211 transmits a transmission wave. The receiving antenna unit 212 receives a reflected wave caused by the transmitted wave. The transmission antenna unit 211 includes a first transmission antenna 213 and a second transmission antenna 214. The first transmission antenna 213 and the second transmission antenna 214 are horn antennas. The heights of the first transmission antenna 213 and the second transmission antenna 214 in the vertical direction of the horn are the same. The lateral width of the horn of the first transmission antenna 213 is narrower than the lateral width of the horn of the second transmission antenna 214. Accordingly, the first transmission antenna 213 transmits a first transmission wave having a wide radiation range, and the second transmission antenna 214 has a radiation pattern different from that of the first transmission wave, and the radiation range is narrower than that of the first transmission wave. A second transmission wave is transmitted. That is, the transmission antenna unit 211 can transmit the first transmission wave and the second transmission wave.

  The reception antenna unit 212 includes five reception antennas 215. The plurality of receiving antennas 215 are arranged in the horizontal direction. Each receiving antenna 215 is a horn antenna. That is, all antennas included in the antenna unit 21 are horn antennas. The horns of the plurality of receiving antennas 215 have the same shape. The “longitudinal direction” and the “lateral direction” are the longitudinal direction and the lateral direction determined by design with respect to the vehicle 1, and need not be a direction exactly parallel to the direction of gravity and a direction perpendicular thereto.

  Each horn antenna of the antenna unit 21 has an electrical configuration for transmitting and receiving signals in the order of MMIC (monolithic microwave integrated circuit), transmission line (specifically, microstrip line, transducer, waveguide), and horn. Or spatially connected. By using the horn antenna, a gain can be ensured while suppressing the width of the antenna in the height direction, and the front projection area of the radar apparatus 11 can be reduced. Thereby, the radar apparatus 11 can be disposed in the vicinity of the windshield without obstructing the occupant's visual field.

  As shown in FIG. 3, the radar apparatus 11 further includes an antenna cover 25. In FIG. 4, the antenna cover 25 is omitted. The antenna cover 25 is located between the laminated glass 12 and the antenna unit 21 and covers the front of the antenna unit 21. The antenna cover 25 is molded from resin. The front surface, that is, the outer surface of the antenna cover 25 is black. Thereby, the antenna part 21 is prevented from being noticeable when viewed from the outside of the vehicle, and the aesthetic appearance of the vehicle 1 is ensured. The antenna cover 25 is inclined about 10 degrees from the direction perpendicular to the transmission direction of the transmission wave.

  The camera unit 22 includes a two-dimensional image sensor. The camera unit 22 observes the outside from the inside of the laminated glass 12. In other words, the camera unit 22 observes the outside of the vehicle from inside the passenger compartment 13. As shown in FIGS. 3 and 4, the cover 24 includes a camera window 244. The camera window 244 is transparent. The camera unit 22 observes the outside of the vehicle through the camera window 244 and the laminated glass 12.

  FIG. 5 is a block diagram showing an outline of the configuration of the radar apparatus 11. The first transmission antenna 213 and the second transmission antenna 214 are connected to the selection unit 311. The selection unit 311 is connected to the high frequency oscillator 312. As a result, the connection between the high-frequency oscillator 312 and the first transmission antenna 213 and the connection between the high-frequency oscillator 312 and the second transmission antenna 214 are switched, and high-frequency power is supplied to the first transmission antenna 213 or the second transmission antenna 214. Is done. That is, the transmission of the first transmission wave and the transmission of the second transmission wave are switched. In the present embodiment, an FMCW (Frequency Modulated Continuous Wave) method that uses a relatively narrow frequency band is employed, and the frequency of the high-frequency signal output from the high-frequency oscillator 312 varies up and down.

  Each of the five reception antennas 215 is sequentially connected to the mixer 321 and the A / D converter 322. The A / D converter 322 is connected to the selection unit 33. A reflected wave obtained by reflecting a transmission wave with an external object is incident on the reception antenna 215. A signal of a reflected wave obtained by the receiving antenna 215 and a circuit associated therewith is input to the mixer 321. A signal from the high frequency oscillator 312 is also input to the mixer 321, and both signals are combined to obtain a beat signal indicating the frequency difference between the transmitted wave and the reflected wave. The beat signal is converted into a digital signal by the A / D converter 322 and input to the selection unit 33.

  The selector 33 selects at least some of the five beat signals and inputs them to the detector 35. The detection unit 35 obtains the position, speed, and the like of the target object by performing Fourier transform on the beat signal and further performing arithmetic processing. On the other hand, an image signal from the camera unit 22 is also input to the detection unit 35. The detection unit 35 uses the information from the antenna unit 21 and the camera unit 22 to detect the type and state of the target object at a higher level.

  The selection unit 311, the high frequency oscillator 312, the selection unit 33, and the detection unit 35 are connected to the control unit 34. The control unit 34 realizes the detection operation in the detection unit 35 by controlling these components. The control unit 34 and the detection unit 35 are provided in the circuit unit 23.

  The operation of the control unit 34 includes a proximity monitoring mode and a remote monitoring mode. FIG. 6A is a diagram illustrating a state in the proximity monitoring mode, and FIG. 6B is a diagram illustrating a state in the far-field monitoring mode. 6A and 6B, the lower side corresponds to the antenna side, and the upper side corresponds to the front of the vehicle 1. A range 41 indicates a radiation range of the transmission wave. In the first transmission antenna 213 and the second transmission antenna 214, the side lobe is sufficiently smaller than the main lobe. A pattern 42 indicates an antenna pattern of the reception antenna unit 212. Reference numeral 421 indicates a main lobe, and reference numeral 422 indicates a side lobe other than the main lobe 421.

  In the proximity monitoring mode, the first transmission wave is transmitted from the first transmission antenna 213 under the control of the selection unit 311 by the control unit 34. On the other hand, signals derived from the five reception antennas 215 are input to the detection unit 35 under the control of the selection unit 33 by the control unit 34. By using signals from the five reception antennas 215 having a small arrangement interval, the spread of the main lobe 421 in the reception antenna unit 212 can be widened, while the spread of the side lobe 422 can be suppressed. As a result, the azimuth resolution is lower and the effective detection azimuth range is wider in the proximity monitoring mode than in the remote monitoring mode described later. As described above, the first transmission wave has a wider radiation range 41 than the second transmission wave. Therefore, in the proximity monitoring mode, it is possible to detect an object over a wide range.

  In the remote monitoring mode, the second transmission wave is transmitted from the second transmission antenna 214 under the control of the selection unit 311 by the control unit 34. On the other hand, of the five receiving antennas 215, only the signals derived from the three left and right and central receiving antennas 215 among the five receiving antennas 215 are input to the detecting unit 35 by the control unit 33 controlling the control unit 34. By using only signals from the three reception antennas 215 having a wide arrangement interval, the spread of the main lobe 421 in the reception antenna unit 212 can be narrowed. On the other hand, the side lobe 422 becomes large.

  However, since the radiation range 41 of the second transmission wave is narrow, the second transmission wave is not radiated in the direction of the side lobe 422 as shown in FIG. 6B. In other words, in order to detect an object located far from the front, radio waves are not irradiated to an azimuth that deviates from the front that does not require monitoring. Thereby, detection of the reflected wave in the main lobe 421 is realized while suppressing the influence of the side lobe 422. In the remote monitoring mode, the azimuth resolution is high and the effective detection azimuth range is narrow. In the remote monitoring mode, it is possible to detect an object in a remote narrow area.

  As described above, in the radar apparatus 11, the control unit 34 controls the transmission antenna unit 211, the reception antenna unit 212, and the like, so that two operation modes are executed. The radar apparatus 11 uses a condition unique to in-vehicle use, in which the range of the main lobe is changed by the receiving antenna unit 212 and it is not necessary to increase the resolution in all directions during remote monitoring. Thereby, the manufacturing cost of the radar apparatus 11 can be reduced while realizing the proximity monitoring and the remote monitoring. In the radar apparatus 11, the plurality of receiving antennas 215 used in the remote monitoring mode are included in the plurality of receiving antennas 215 used in the proximity monitoring mode, so that appropriate near and remote monitoring can be performed at low cost. Realized.

  The antenna pattern of the reception antenna unit 212 may be changed by weighting the signal from the reception antenna 215 by the selection unit 33. Furthermore, the signal from the reception antenna 215 may be selected by providing a mechanism for turning on / off the reception function of the reception antenna 215 instead of using the selection unit 33. In this case, a mechanism for turning ON / OFF reception functions as a selection unit.

  The proximity monitoring mode and the remote monitoring mode can be switched at high speed. That is, the first transmission wave and the second transmission wave are alternately transmitted under the control of the control unit 34. Actually, in order to eliminate unnecessary transmission of radio waves during calculation, the transmission stop time between the first transmission wave and the second transmission wave is the transmission time of the first transmission wave and the transmission time of the second transmission wave. Longer than any of the. For example, the transmission time for one transmission wave is 2 msec, and the transmission interval is 50 msec.

  The number of receiving antennas 215 arranged at equal intervals in the horizontal direction is not limited to five. The number of receiving antennas 215 may be six or more. By setting the number of receiving antennas 215 to 5 or more, after thinning out the receiving antennas 215 to be used, signals from three or more receiving antennas 215 having a wide arrangement interval can be used, and an object existing far away can be used. The position can be grasped. When there is only one object to be detected, the number of receiving antennas 215 after thinning may be two. Therefore, the minimum number of receiving antennas 215 in the radar apparatus 11 is 3. The minimum number of receiving antennas 215 with a wide arrangement interval after selection is two.

  If it is not necessary to detect the position of the object even in the proximity monitoring mode, the number of receiving antennas 215 used in the proximity monitoring mode may be two. For example, three receiving antennas 215 are arranged at equal intervals, signals from two adjacent receiving antennas 215 are used in the proximity monitoring mode, and signals from two receiving antennas 215 at both ends are used in the far monitoring mode. May be.

  Generally speaking, in the proximity monitoring mode, the first transmission wave is transmitted from the transmission antenna unit 211, and signals from two or more reception antennas 215 having a narrow arrangement interval among the plurality of reception antennas 215 are used. . In the remote monitoring mode, the second transmission wave is transmitted from the transmission antenna unit 211, and signals from two or more reception antennas 215 having a wide arrangement interval among the plurality of reception antennas 215 are used. In order to reduce the number of reception antennas 215, at least a part of the two or more reception antennas 215 having a wide arrangement interval is included in the two or more reception antennas having a small arrangement interval.

  The first transmission wave and the second transmission wave are vertically polarized waves with respect to the lateral direction. The first transmission wave and the second transmission wave do not need to be completely vertically polarized, but may be obliquely polarized or elliptically polarized. Generally speaking, the vertical polarization component in the lateral direction of the first transmission wave and the second transmission wave is larger than the horizontal polarization component. Usually, since the laminated glass 12 is inclined so that the upper part is located behind the lower part, the vertical polarization component in the lateral direction of the first transmission wave and the second transmission wave is the vertical polarization with respect to the laminated glass 12. It is an ingredient. Thereby, the efficiency with which a transmission wave permeate | transmits the laminated glass 12 improves. In particular, when the incident angles of the first transmission wave and the second transmission wave with respect to the laminated glass 12 are close to the Brewster angle on the inner surface of the laminated glass 12, the detection efficiency of the radar device 11 is improved. The vertically polarized wave is also called TM wave (Transverse Magnetic Wave), and refers to a polarized wave whose electric field component is perpendicular to the reflecting surface. At this time, the magnetic field component is parallel to the reflecting surface. Horizontal polarization is also referred to as TE wave (Transverse Electric Wave), and refers to polarization whose magnetic field component is perpendicular to the reflecting surface. At this time, the electric field component is parallel to the reflecting surface.

  The horn of the first transmission antenna 213 and the horn of the second transmission antenna 214 are arranged in the horizontal direction. In the present embodiment, the first transmission antenna 213 and the second transmission antenna 214 are respectively on the left and right sides of the reception antenna unit 212. To position. By arranging the first transmitting antenna 213, the second transmitting antenna 214, and the receiving antenna 215 on the left and right, a plurality of horns can be provided on one member, and the manufacturing cost of the radar apparatus 11 is reduced. Further, the orientation of each horn can be easily and accurately determined when the radar apparatus 11 is installed. In particular, by arranging the horn of the first transmission antenna 213 and the horn of the second transmission antenna 214 in the horizontal direction, the vertical direction of the first transmission antenna 213 and the vertical direction of the second transmission antenna 214 are accurately determined. Can match.

  In the first transmission antenna 213 and the second transmission antenna 214, the direction of the center of the main lobe, that is, the direction of the peak of the main lobe is preferably oriented in the horizontal direction. The first transmission antenna 213 and the second transmission antenna 214 may have the direction of the main lobe between the horizontal direction and a direction inclined twice from the horizontal direction.

  The first transmission antenna 213, the second transmission antenna 214, and the reception antenna 215 may be antennas other than the horn antenna. Any antenna that can transmit and receive millimeter waves may be used. For example, a lens antenna, an inexpensive printed antenna, a microstrip antenna, or a slit antenna can be used. It is not necessary for all antennas of the antenna unit 21 to be of the same type, and different types of antennas may be mixed.

  Next, the direction of the transmission antenna when considering the influence of both the innermost glass layer 121 and the outermost glass layer 122 of the laminated glass 12 will be described. When vertically polarized light is incident on the object at the Brewster angle, it is ideally guided into the object without being reflected. However, as will be described later, in the case of the laminated glass 12, when vertically polarized light enters the innermost glass layer 121 at a Brewster angle, it enters the outermost glass layer 122 at an angle smaller than the Brewster angle. In this case, the laminated glass 12 reflects vertically polarized waves at the interface between the outermost glass layer 122 and the intermediate resin layer 123. Therefore, by making the incident angle of the radio wave on the innermost glass layer 121 slightly larger than the Brewster angle, the incident angle of the radio wave on the outermost glass layer 122 can be made closer to the Brewster angle. As a result, due to the decrease in reflection at the interface between the outermost glass layer 122 and the intermediate resin layer 123, the total reflection by the laminated glass 12 is also reduced, and it is realized to improve the efficiency of transmission and reception of radio waves.

  FIG. 7 is a diagram illustrating a state in which a transmission wave is incident on the laminated glass 12. The incident angle of the transmission wave is such that when the mounting portion 241 is attached to the bracket 16, the transmission wave, that is, the transmission wave object at the center of the main lobe of the first transmission antenna 213 and the second transmission antenna 214. The incident angle of

In the following description, the refractive index of air _{n a,} the refractive index of the innermost glass layer 121 _{n g1,} the refractive index of the intermediate resin layer 123 _{n r} and the refractive index of the outermost glass layer 122 _{n g2,} the radio The incident angle on the innermost glass layer 121 is θ _i1 , and the incident angle on the outermost glass layer 122 is θ _i2 . Refractive index _n g1 of the glass layer 121 and _{122, n g2} is greater than the refractive index _{n r} of the intermediate resin layer 123.

  First, Equation 1 holds from Snell's law.

Therefore, when a radio wave is incident on the innermost glass layer 121 from the air layer at the Brewster angle θ _b1 , sin θ _i2 is expressed by _Equation 2.

Since tan θ _b1 is expressed by Equation 3, and sin θ _b1 is expressed by Equation 4 using tan θ _b1 , sin θ _i2 is expressed by Equation 5.

On the other hand, tan θ _b2 is expressed by Equation 6, where the Brewster angle when traveling from the intermediate resin layer 123 toward the outermost glass layer 122 is θ _b2 .

Therefore, sin θ _b2 is expressed by Equation 7.

Here, since n _g1 and n _g2 are substantially equal and n _a is smaller than n _r , the _equation 8 is derived by comparing the equations 5 and 7.

That is, when radio waves are incident on the innermost glass layer 121 at the Brewster angle θ _b1 , the outermost glass layer 122 is incident at an angle smaller than the Brewster angle θ _b2 . Therefore, it is possible to cause radio waves to enter the innermost glass layer 121 at an incident angle larger than the Brewster angle θ _b1 and to cause the outermost glass layer 122 to enter radio waves at an incident angle smaller than the Brewster angle θ _b2. It is.

In the radar apparatus 11, the innermost glass layer 121 of the first transmission wave at the center of the main lobe of the first transmission antenna 213 when the attachment portion 241 is attached to the bracket 16 using the above phenomenon in the laminated glass 12. Is larger than the Brewster angle θ _b1 on the inner surface of the innermost glass layer 121, and the incident angle of the first transmission wave on the outermost glass layer 122 at the center of the main lobe is the same as that of the outermost glass layer 122. The design is performed so that the Brewster angle θ _{b2 is} less than or equal to the intermediate resin layer 123.

Similarly, when the attachment portion 241 is attached to the bracket 16, the incident angle of the second transmission wave on the innermost glass layer 121 at the center of the main lobe of the second transmission antenna 214 is the inner surface of the innermost glass layer 121. greater than the Brewster angle theta _b1 in the incident angle of the outermost glass layer 122 of the second transmission wave at the center of the main lobe, Brewster angle between the outermost glass layer 122 and the intermediate resin layer 123 theta _b2 It is as follows.

  However, when the incident angle is larger than the Brewster angle, the reflectance increases exponentially, so the incident angles of the first transmission wave and the second transmission wave on the innermost glass layer 121 should be set too large. Is not preferred. Therefore, the difference between the incident angle of the first transmission wave and the second transmission wave on the innermost glass layer 121 and the Brewster angle at the center of the main lobe of the first transmission antenna 213 and the second transmission antenna 214 is 90 degrees. It is preferably 25% or less of the difference from the Brewster angle. Such a condition may be applied to only one of the first transmission antenna 213 and the second transmission antenna 214.

  As observed by the inventor of the present invention in the electromagnetic wave in the millimeter wave band, the electromagnetic wave in the millimeter wave band is significantly different from the refractive index in other frequency bands. Refractive index for radio waves must be used. The millimeter wave band radio wave refers to a radio wave having a wavelength in air ranging from 1 mm to 10 mm.

  The radar device 11 and the vehicle 1 can be variously modified.

  For example, the transmitting antenna and the receiving antenna may be used together. A mechanism for changing the antenna pattern may be provided in one transmission antenna, and the first transmission wave and the second transmission wave may be transmitted from one transmission antenna. Further, a proximity monitoring mode and a remote monitoring mode may be realized by providing a mechanism for changing a reception antenna pattern in one reception antenna. In other words, the number of antennas included in the antenna unit 21 can be set to 1, and the antenna unit 21 includes at least one antenna. Of course, preferably, the antenna unit 21 includes a plurality of antennas.

  The plurality of receiving antennas 215 may include a portion arranged in the vertical direction as long as it includes a portion arranged in the horizontal direction. For example, the plurality of receiving antennas 215 may be two-dimensionally arranged.

  The attachment target of the radar apparatus 11 is not limited to the windshield. The radar apparatus 11 may be attached to the rear glass and rear monitoring may be performed. The mounting position is not limited on the glass.

  The vehicle 1 is not limited to a passenger car, and may be of various uses such as trucks and trains. Furthermore, it is not limited to those of manned driving, and may be an unmanned driving vehicle such as an automatic guided vehicle in a factory.

  The configurations in the above-described embodiments and modifications may be combined as appropriate as long as they do not contradict each other.

  Although the invention has been illustrated and described in detail, the foregoing description is illustrative and not restrictive. Therefore, it can be said that many modifications and embodiments are possible without departing from the scope of the present invention.

  The radar apparatus according to the present invention can be mounted on vehicles for various purposes.

DESCRIPTION OF SYMBOLS 1 Vehicle 10 Car body 11 (For vehicle-mounted) Radar apparatus 12 Laminated glass 15 Drive mechanism 16 Bracket 21 Antenna part 22 Camera part 24 Cover 121 Innermost glass layer 122 Outermost glass layer 123 Intermediate resin layer 213 1st transmission antenna 214 2nd transmission Antenna 241 mounting part

Claims (8)

The innermost glass layer, the outermost glass layer, and the innermost glass layer of the laminated glass including an intermediate resin layer sandwiched between the innermost glass layer and the outermost glass layer, or the innermost glass layer. A mounting portion attached to a bracket fixed to a rearview mirror arranged on the inside or the ceiling;
A reflection wave that transmits a radio wave in the millimeter wave band from the inner side of the innermost glass layer to the outer side of the outermost glass layer and is incident on the inner side of the innermost glass layer from the outer side of the outermost glass layer An antenna section for receiving waves,
With
The antenna unit includes a transmission antenna that transmits the transmission wave;
The vertical polarization component of the transmission wave with respect to the laminated glass is larger than the horizontal polarization component,
When the attachment portion is attached to a bracket, the incident angle of the transmission wave at the center of the main lobe of the transmitting antenna to the innermost glass layer is larger than the Brewster angle on the inner surface of the innermost glass layer. An on-vehicle radar device, wherein an incident angle of the transmission wave at the center of the main lobe to the outermost glass layer is equal to or less than a Brewster angle between the outermost glass layer and the intermediate resin layer.   The difference between the incident angle of the transmission wave at the center of the main lobe of the transmitting antenna to the innermost glass layer and the Brewster angle is 25% or less of the difference between 90 degrees and the Brewster angle. The in-vehicle radar device according to claim 1. The antenna unit includes another transmission antenna that transmits another transmission wave having a radiation pattern different from that of the transmission wave,
When the attachment portion is attached to a bracket, the incident angle of the other transmission wave at the center of the main lobe of the other transmission antenna to the innermost glass layer is Brewster on the inner surface of the innermost glass layer. An incident angle of the other transmitted wave at the center of the main lobe to the outermost glass layer is less than or equal to a Brewster angle between the outermost glass layer and the intermediate resin layer. Item 3. The on-vehicle radar device according to Item 1 or 2.   The in-vehicle radar device according to claim 1, wherein the intermediate resin layer is polyvinyl butyrate. A camera unit for observing the outside from the inside of the laminated glass;
A cover covering the antenna unit and the camera unit;
The in-vehicle radar device according to claim 1, further comprising:   The on-vehicle radar device according to any one of claims 1 to 5, wherein each of the at least one antenna included in the antenna unit is a horn antenna, a lens antenna, a printed antenna, a microstrip antenna, or a slit antenna.   All the antennas which the said antenna part has are horn antennas, The vehicle-mounted radar apparatus in any one of Claim 1 thru | or 5. The car body,
A drive mechanism for moving the vehicle body;
A laminated glass fixed to the vehicle body and positioned between the vehicle interior and the exterior;
An in-vehicle radar device fixed directly or indirectly to an inner surface of the laminated glass, a rearview mirror disposed inside the inner surface, or a ceiling;
With
The laminated glass includes an innermost glass layer, an outermost glass layer, and an intermediate resin layer sandwiched between the innermost glass layer and the outermost glass layer,
The in-vehicle radar device transmits a transmission wave that is a radio wave in a millimeter wave band from the inner side of the innermost glass layer to the outer side of the outermost glass layer, and the innermost glass layer from the outer side of the outermost glass layer. An antenna unit that receives reflected waves incident on the inside of
The antenna unit includes a transmission antenna that transmits the transmission wave;
The vertical polarization component of the transmission wave with respect to the laminated glass is larger than the horizontal polarization component,
The incident angle of the transmission wave at the center of the main lobe of the transmitting antenna is greater than the Brewster angle at the inner surface of the innermost glass layer, and the transmission wave at the center of the main lobe The vehicle has an incident angle to the outermost glass layer that is equal to or smaller than a Brewster angle between the outermost glass layer and the intermediate resin layer.

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