JPH06168400A - Radar for automobile - Google Patents

Abstract

PURPOSE:To freely select the installation height of an antenna and to reduce the influence of reflection from a road surface and an unwanted reflecting object. CONSTITUTION:A radar device 4 is fitted to the bumper part of the front end of an automobile 1. The gain of the antenna is provided with a vertical directivity pattern 7. The vertical directivity pattern 7 is provided with gain characteristics proportional to cosec<2>theta relating to the angle of elevation theta so as to prevent the useless reflecting object such as an overpass and a tunnel ceiling, etc., from being detected thereafter to prevent erroneous operations from being performed. Thus, an object 6 from a certain height (h) can be detected with a certain reception strength regardless of a distance R and the inter-vehicle distance with the proceeding automobile 3 travelling on a road 2 or the like can be effectively detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automotive radar mounted on a vehicle for forward monitoring.

[0002]

2. Description of the Related Art Conventionally, a radar for forward monitoring is used by being mounted on a vehicle for the purpose of preventing collision. Such automotive radars are used as collision warning devices and inter-vehicle distance control devices by measuring distances and relative velocities with vehicles and obstacles ahead using millimeter-wave radio waves. By using the automotive radar, it is possible to enhance the safety in running the vehicle even when the visibility is poor such as rain or snow.

In automotive radars, the antenna is located at the front end of the vehicle. In typical prior art, the frequency is 24 GH
A parabolic antenna having directivity with a pencil beam width of 4 ° in z is attached to the center of the radiator. The parabolic surface is formed by an elongated strip plate having a gap in order to ensure the air permeability of the front surface of the radiator.

In the above-mentioned prior art, since the antenna of the automobile radar is mounted on the front surface of the radiator, the antenna is located at a relatively high position from the road surface on which the vehicle is traveling. Therefore, if the directivity pattern is directed forward, the influence of reflection from the road surface and unnecessary reflection from the overpass, tunnel ceiling, etc. is small. However, in recent years, due to changes in automobile design aimed at reducing air resistance, the front grill has become narrower, and the structure is such that the air supplied to the radiator is also taken in from the lower side. The area is getting bigger. For this reason, automobile radars for forward monitoring are more likely to be mounted inside bumpers.

[0005]

When mounting an automotive radar in a bumper, an antenna is mounted at a position lower than the road surface. For this reason, the influence of the reflection on the road surface becomes large, and in order to prevent malfunction, it is conceivable to mount the antenna with the directional beam facing upward. However,
When the directional beam of the antenna is directed upward, the influence from the overpass, the tunnel ceiling, etc. becomes large, and the probability of malfunctioning by detecting the reflected wave from the unnecessary reflector is increased.

An object of the present invention is to increase the degree of freedom in selecting the mounting height of the antenna by improving the directivity of the antenna, and to detect only the object within a certain height range from the road surface. It is an object of the present invention to provide an automotive radar that can reduce the number of malfunctions and malfunctions.

[0007]

SUMMARY OF THE INVENTION The present invention is an automotive radar that radiates a radio wave from an antenna in front of a vehicle and receives a reflected wave to monitor the front of the vehicle. The gain for the vehicle is smaller than that for the upward direction, and the upward gain has an asymmetric pattern in which the upward gain changes in proportion to cosec ² θ with respect to the elevation angle θ.

[0008]

According to the present invention, the directivity in the vertical plane of the antenna of the automotive radar for monitoring the front of the vehicle has an asymmetric pattern in which the downward gain is smaller than the upward gain. As a result, even if the mounting height of the antenna is low from the road surface, the influence of reflection on the road surface can be reduced. The gain above the antenna is
Since it changes in proportion to cosec ² θ, the reception level reflected from the object is kept constant within a certain height range from the road surface regardless of the distance, and the height is constant from the road surface. It is possible to reduce the influence of unnecessary reflection from the above-mentioned overpass, the ceiling of the tunnel, etc. and prevent malfunction.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a state in which an automobile radar according to an embodiment of the present invention is used. The vehicle 1 is traveling on the road 2, and the vehicle 3 is traveling forward in the traveling direction.
The radar device 4 is attached to the bumper at the front end of the vehicle 1, and the measurement result is displayed to the driver by the display device 5. The measurement result of the radar device 4 can also be used as an input to an inter-vehicle distance control device, a collision prevention device, or the like.

The radar device 4 detects an object 6 having a distance R to the front and a height h from the road 2 at the same reception level even if the distance R is different as long as the height h is constant. Therefore, it has an asymmetric vertical directivity pattern 7. In the vertical directivity pattern 7, the gain in the direction parallel to the road surface of the road 2 is the largest, and the upward gain is cos with respect to the elevation angle θ.
In proportion to ec ² , the downward gain shows a change smaller than the upward gain. As a result, the influence of the reflection on the road surface of the road 2 can be reduced, and malfunctions due to unnecessary reflection from above can be reduced.

FIG. 2 shows a more specific structure of the radar device 4. A transceiver 10 is provided near the center of the radar device 4. A transmitting antenna 11 is provided on one side in the horizontal direction with the transceiver 10 in the middle. The transmitting antenna 11 includes a primary radiator 12 to which transmission power is applied from the transceiver 10 and a cylindrical parabolic reflector 13 that reflects the radio wave radiated from the primary radiator 12. Transceiver 1
A receiving antenna 14 is provided on the other horizontal side of 0. The receiving antenna 14 has an injector 15 and a cylindrical parabolic reflector 16. The reflected wave returning to the vicinity of the receiving antenna 14 is reflected by the cylindrical parabolic reflecting mirror 16 and collected in the injector 15 near its focal position. The received signals collected by the injector 15 are input to the receiver side of the transceiver 10. Such a transmitting antenna 11
The receiving antenna 14 has the asymmetric vertical directivity pattern 7 as described above and the horizontal directivity pattern 17 symmetrical in the horizontal direction.

FIG. 3 shows the principle of the present invention. An aerial surveillance radar (hereinafter abbreviated as "ASR") in which the directivity in the vertical plane requires the cosec ² θ characteristic as described above.
The general use state of is shown. The present invention is an application technique of an asymmetric beam of an aircraft radar. In the ASR 20, it is desirable that the intensity of the reflected wave from the aircraft 22 flying at a constant height H from the ground 21 is constant regardless of the distance L. The relationship between L, H and θ is expressed by the following first equation.

L = H × cosec θ (1) Further, the following second equation is known as a radar equation representing the maximum received effective power of a general radar.

[0014]

[Equation 1]

Here, Pr is the maximum received effective power per unit area of the object, Pt is the radiated power, λ is the wavelength, and G is the absolute gain of the antenna. Absolute gain G of this antenna
Becomes a function of the elevation angle θ in this case, and is expressed as the following third equation.

G = G (θ) (3) Substituting the above-mentioned first and third equations into the second equation to rearrange them yields the following fourth equation.

[0017]

[Equation 2]

From the fourth equation, if G (θ) is represented by the following fifth equation, the maximum received effective power Pr can be constant regardless of the elevation angle θ if the height H is constant. I understand.

G (θ) = K × cosec ² θ (5) Here, K is a constant represented by the following sixth equation.

[0020]

[Equation 3]

That is, the fact that the directivity of the gain G (θ) is proportional to cosec ² θ as in the fifth equation means that the same height H is obtained.
It is a condition that the intensity of the reflected wave from the aircraft 22 flying in the field is constant regardless of the distance L.

The asymmetric pattern of directivity in the vertical plane as described above is realized by the configuration shown in FIG.
That is, by making the shape of the reflecting surface of the cylindrical parabolic reflector 13 asymmetric with respect to the primary radiator 12, co
A pattern that changes according to sec ² θ is realized. Alternatively, by shifting the position of the primary radiator 12, the shape of the cylindrical parabolic reflecting mirror 13 is made asymmetrical and cosec ^{2 is set.}
It is also possible to realize a θ pattern.

FIG. 5 shows the internal structure of the transceiver 10 shown in FIG. Inside the transceiver 10, a transmitter 25 and a receiver 2
6 is included. A directional coupler 27 is provided between the transmitter 25 and the transmitting antenna 11. A directional coupler 28 is provided between the receiving antenna 14 and the receiver 26. The transmission signal 29 s from the transmitter 25 passes through the directional coupler 27 and is guided to the transmission antenna 11. The reception signal 29r received by the reception antenna 14 is input to the receiver 26 via the directional coupler 28. In the pulse radar method in which the transmission signal 29s is a pulse having a very narrow width, the backscattered wave from the object is temporally separated from the transmission wave and the distance to the object is obtained from the time difference, the transmission antenna is used. 11 is also used for reception, and the directional coupler 27 is used.
The synthesizing signal 29t can be input to the receiver 27 via the and 28 to improve the receiving sensitivity.

FIG. 6 shows a method of obtaining a distance by the FM radar method. In the FM radar method, the transmitted wave 31 is transmitted at F with a cycle T.
The frequency is modulated like a saw tooth so that the frequency shifts up to. When the transmitted wave 32 is received with a delay of time t,
The deviation of the frequency is f, and as shown in FIG.
A beat signal 33 having a beat frequency f is obtained. At this time, the distance L to the object is given by the following seventh formula.

[0025]

[Equation 4]

Here, c represents the propagation velocity of the radio wave. Figure 5
According to the configuration shown in (1), such an FM radar method can also be realized.

In this embodiment, cylindrical parabolic reflectors are used for both transmission and reception as the antenna, but it goes without saying that other shapes of reflection mirrors may be used.

[0028]

As described above, according to the present invention, the directivity in the vertical plane of the antenna of the automobile radar is made into an asymmetric pattern in which the downward gain is smaller than the upward gain. Even if the antenna is mounted at a position lower than the road surface, the influence of road surface reflection can be reduced.
Also, the gain above the antenna is cos with respect to the elevation angle θ.
Since it is changed in proportion to ec ² θ, the intensity of the reflected wave from the object of constant height is constant regardless of the distance to the object, and the distance between the object and The relative velocity can be measured accurately.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a schematic directional characteristic in a vertical plane according to an embodiment of the present invention.

FIG. 2 is a perspective view showing the directional characteristics of the radar device shown in FIG.

FIG. 3 is a diagram for explaining directional characteristics of an airport surveillance command radar.

FIG. 4 is a cross-sectional view of the transmitting antenna 11 shown in FIG.

5 is a block diagram showing a schematic electrical configuration of the transceiver 10 shown in FIG.

FIG. 6 is a time chart showing an operating state of the radar apparatus 4 of the embodiment shown in FIG.

[Explanation of symbols]

 1, 3 vehicle 2 road 4 radar device 6 object 7 vertical directivity pattern 10 transceiver 11 transmitter antenna 12 primary radiator 13, 16 cylindrical parabolic reflector 14 receiving antenna 15 injector 17 horizontal directivity pattern 25 transmitter 26 receiver 27, 28 directional coupler

Claims (1)

[Claims] 1. In an automotive radar that radiates a radio wave from an antenna in front of a vehicle and receives a reflected wave to monitor the front, the directivity in the vertical plane of the antenna is such that the downward gain is the upward gain. An automotive radar characterized by having an asymmetric pattern that is smaller than that of, and whose upward gain changes in proportion to cosec ² θ with respect to an elevation angle θ.