JP3995816B2 - Radar equipment - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a radar apparatus used in a vehicle collision prevention system and the like.
[0002]
[Prior art]
As components such as a vehicle collision prevention system, an in-vehicle radar device that detects a distance from an object such as a preceding vehicle or an oncoming vehicle has been developed. Recently, electronic scanning and mechanical scanning type radar devices capable of detecting not only the distance to an object but also the direction in which the object is seen from the host vehicle are being developed.
[0003]
In the electronic scanning radar device, antenna devices that radiate beams in different directions and receive the reflected waves are arrayed adjacent to each other with their directions slightly shifted, and the time for each antenna device is shifted. By sequentially transmitting and receiving beams, it is configured to detect which antenna device, that is, in which direction the reflected wave is generated. The direction of the object that caused the reflected wave can also be detected by mechanical scanning that mechanically deflects the direction of one transmitting / receiving antenna device.
[0004]
For example, Japanese Patent No. 2567332 of the present applicant discloses a method for accurately detecting the direction of an object that has caused a reflected wave by performing a weighted averaging process of the reception level on the reflected wave in each direction. . Further, in this type of radar apparatus, in order to prevent erroneous detection due to noise, a predetermined threshold is set with respect to the reception level of the reflected wave, and only a reception signal having a level exceeding the predetermined value is regarded as a reflected wave. A received signal at a level below this threshold is discarded as noise.
[0005]
[Problems to be solved by the invention]
As a vehicle-mounted radar device, downsizing is an important issue, and in particular, downsizing of an antenna that occupies a considerable portion of the entire radar device is an important technical issue. However, as the antenna device is reduced in size, there arises a problem that the ratio of the gain of the side lobe to the main lobe increases. The ratio of the gain of the side lobe is particularly large when a reflected wave of a beam radiated from one antenna is received by another adjacent antenna in order to realize high directional resolution with a small number of antennas.
[0006]
As described above, when the ratio of the gain of the side lobe increases, the reflected wave detected only by the side lobe off the front of the antenna exceeds the threshold, and it is detected by the main lobe, that is, at the front of the antenna. There is a problem that it is recognized as if it is an existing object, and the accuracy of detecting the direction is lowered. Accordingly, a main object of the present invention is to provide a radar apparatus that improves the detection accuracy of the direction of an object by reducing the influence of side lobes.
[0007]
The radar apparatus according to the present invention includes an antenna gain characteristic holding unit that holds the antenna gain characteristic of the antenna, and a direction in which a received signal of a maximum level is obtained or a direction of the maximum level among the directions in which the beam is radiated and received . tentatively regarded as a direction of the object the direction obtained by weighted average at each level for two or three directions received signal of large level is obtained including the received signal, in the holding and the maximum level Based on the antenna gain characteristics in each direction, calculate the received signal component in the direction considered as the direction of the object included in the received signal in each direction, and subtract the calculated component from the received signal obtained in each direction. And an unnecessary component removing means for removing the side lobes.
[000 8 ]
DETAILED DESCRIPTION OF THE INVENTION
According to good optimal embodiment of the present invention, the antenna gain property is a plurality of types held in accordance with a combination status of the transmit and receive antennas. According to another preferred embodiment of the present invention , there is provided a direction detecting means for calculating a weighted average value of directions by the received signal from which the unnecessary component is removed, and detecting the calculated value as a final object direction. I have.
[0009]
According to yet another preferred embodiment of the present invention, a radar apparatus radiation beam to a plurality of directions it is mounted on a vehicle, division manner when a plurality of antennas arranged facing different directions Done. According to yet another preferred embodiment of the invention, the beam emitted in a plurality of directions is a beam of FM signals.
[0010]
【Example】
FIG. 2 is a functional block diagram showing a schematic configuration of an in-vehicle radar device according to an embodiment of the present invention, in which A1 to A5 are antennas exemplified by a transmission / reception antenna for convenience of illustration, and TR1 to TR5 are transmission / reception circuits. PS is a processor.
[0011]
Five antennas A1, A2,... A5 are installed in front of the vehicle with their directions slightly shifted in order of arrangement, and beams B1, B2,. They are arranged so that they partially overlap each other. Under the control of the processor PS, a transmission signal generated by one of the transmission / reception circuits TR1 to TR5 is radiated as a transmission beam from the one corresponding to the antennas A1 to A5. A reflected wave generated by an object ahead of the vehicle such as a preceding vehicle, an oncoming vehicle, or a guard rail on the shoulder is received by one of the antennas A1 to A5 that radiates a transmission beam, and is supplied to a corresponding transmission / reception circuit.
[0012]
The processor PS controls transmission / reception timings of the five transmission / reception systems (hereinafter referred to as “transmission / reception channels # 1 to # 5”) in which transmission / reception is performed in a time-division manner, and transmission / reception circuits TR1 to TR5 of each transmission / reception channel. Receive and process the information about the reflected wave obtained in (1). For example, if this radar apparatus is an FM radar apparatus that transmits an FM signal and receives the reflected wave, the processor PS transmits as information on the received reflected wave from the transmission / reception circuits TR1 to TR5 of each transmission / reception channel. The frequency and the amplitude (level) of the beat signal generated by mixing the signal and the reflected wave are received. The frequency of the beat signal indicates the distance to the object, and the level of the beat signal indicates the reception level of the reflected wave.
[0013]
In FIG. 2, in order to avoid complication of illustration, the influence of the side lobe is omitted for each of the radiation beams B1 to B5. However, in an actual small vehicle-mounted antenna, as illustrated as an antenna gain in FIG. 1A, side lobes of a considerably large level appear on both sides of the main lobe in the gain characteristics of the antennas A1 to A5. . In addition, the installation angles of the antennas A1 to A5 of the five transmission / reception channels # 1 to # 5 are maintained at equal angular intervals as shown in the figure as θ1, θ2,. .
[0014]
In the example of FIG. 1, if an object such as a preceding vehicle is present at a position (direction, angle) illustrated by a solid triangle mark in (A), the reception level of the reflected wave generated by this object is (B) as illustrated. That is, no reflected wave is received by the leftmost antenna A1, and the four antennas A2, A3, A4, A5 arranged on the right side thereof are illustrated by reception levels L2, L3, L4, L5, respectively. A reflected wave having such a magnitude is received. Each reception level in (B) is a value when the lateral width of the object is sufficiently smaller than the width of the spread of the radiation beam, that is, between each gain characteristic curve in (A) and the object position. Illustrated by the height of the intersection.
[0015]
The conventional threshold radar apparatus uses all received signals that are regarded as reflected waves because it has a level higher than the preset threshold value α for reflected wave detection in consideration of the noise level and the like. According to the formula, the weighted average value Θ of the angle was calculated, and this was set as the reception position of the object.
Θ = (L2θ2 + L3θ3 + L4θ4 + L5θ5) / (L2 + L3 + L4 + L5) As a result, the weighted average value Θ is an intermediate value between the angles θ3 and θ4 as illustrated by white triangles in FIG. (A) A large deviation occurs from the object position indicated by the filled triangle in FIG.
[0016]
The cause of such a large shift will be described as follows with reference to FIG. That is, in the case of the transmission / reception channel # 2, the main lobe of the antenna A2 does not cover the object position, and only the side lobe covers the object position in the vicinity of the angle θ4.
[0017]
As a result, in this transmission / reception channel # 2, it is recognized as if there is an object that has generated a reflected wave of level L2 almost in front of the antenna A2 (position at the angle θ2 of the center of the main lobe). This is because the conventional radar apparatus does not have a function of discriminating whether the received signal of level L2 is due to the main lobe or the side lobe.
[0018]
On the other hand, in the radar apparatus of this embodiment, the gain characteristics of the antennas A1 to A5 as exemplified in FIG. 1A are held in advance in a data memory built in the processor PS. The processor PS has a function of discriminating whether each received signal is a main lobe or a side lobe from the gain characteristics of each antenna being held and the reception level of each transmission / reception channel.
[0019]
First, the processor PS checks the reception level of each transmission / reception channel, and the beam radiation direction (angle θ4) of the transmission / reception channel # 4 at which the maximum reception level is obtained is the direction of the object that generated the reflected wave. Temporarily consider. Next, based on the maximum reception level L4 and the gain characteristics of each antenna read from the built-in memory, the processor PS, for each transmission / reception channel from which the reception signal is obtained, includes a component due to the side lobe included in each reception signal. Is calculated.
[0020]
That is, the processor PS, for the transmission and reception channels # 2, calculates the ratio ρ of the main lobe and the antenna A 2 side lobes of the antenna A 4 at the position of the angle .theta.4. The processor PS calculates the component due to the side lobe included in the reception signal of the transmission / reception channel # 2 by multiplying the ratio ρ thus calculated by the reception level L4.
[0021]
The processor PS calculates the component of the received signal detected only by the main lobe by subtracting the component due to the side lobe thus calculated from the received signal of the transmission / reception channel # 2 and removing it. In the example of FIG. 1, since the component due to the side lobe is substantially equal to L2, the level of the received signal after subtraction is equal to or less than the threshold value α.
[0022]
For the adjacent transmission / reception channel # 3, since the side lobe of the antenna A3 does not exist at the position of the angle θ4, the component due to the side lobe is immediately calculated as zero. As a result, the subtraction of the component due to the side lobe is not performed from the reception signal of the transmission / reception channel # 3, and the level of the reception signal remains L3. Also for the transmission / reception channel # 5, for the same reason as in the case of the transmission / reception channel # 3, subtraction of components by side lobes is not performed, and the level L5 of the reception signal is maintained as it is.
[0023]
Thus, after the subtraction by the received signal component by the side lobe is performed, the received signal exceeding the threshold value α is the received signal of the levels L3, L4, and L5 of the transmission / reception channels # 3, # 4, and # 5. Thus, the weighted average value Θ is calculated. That is,
Θ = (L3θ3 + L4θ4 + L5θ5) / (L3 + L4 + L5)
[0024]
The weighted average value Θ calculated in this way is a value between the angles θ4 and θ5 and in the vicinity of θ4, as illustrated by the solid triangle mark in FIG. ) Is close to the object position exemplified in FIG.
[0025]
The configuration in which only the received signal component due to the side lobe is removed as an unnecessary component has been described above. However, even for antennas that have a large main lobe spread and can only radiate a wide beam, a configuration that removes received signal components as unnecessary components from the center of the main lobe at a predetermined angle or more away from the center. Can be adopted.
[0026]
For example, a case is assumed where an antenna having a gain characteristic including only a main lobe as indicated by a solid line as shown by a dotted line in FIG. Each main lobe circumscribes a gain characteristic composed of a main lobe and a side lobe similar to that shown in FIG. In this case, if the width of the object is sufficiently narrow compared to the beam width, as illustrated in FIG. 3B, a reception signal substantially similar to that in FIG. It is possible to apply a removal process of unnecessary components that is almost the same as described above. As a result of this unnecessary component removal processing, the substantial gain characteristic of the antenna becomes sharp, the spatial resolution is increased, and the detection accuracy of the object direction is improved.
[0027]
In view of the above-described purpose, the antenna gain characteristic held in the data memory of the processor PS does not need to be a continuous curve, and discrete data for several discrete angles is sufficient.
[0028]
Further, a configuration in which the conventional reflected wave detection threshold value α is used as it is, and the direction of the object is calculated by performing weighted averaging only for transmission / reception channels in which the reception signal after the sidelobe component is removed exceeds the threshold value α. Explained. However, in addition to or instead of the above-described reflected wave detection threshold value α, a new threshold value β dedicated to weighted averaging is introduced, and the reception level after removing the sidelobe components is the new threshold value β. It is also possible to adopt a configuration in which the object direction is calculated by weighted averaging only for the transmission and reception channels where a received signal with a level exceeding 1 is obtained.
[0029]
As such a threshold value β, a value that is smaller than the maximum reception level by a predetermined value γ (dB) can be set by paying attention to the transmission / reception channel from which the reception signal of the maximum level is obtained.
[0030]
Further, the embodiment of the present invention has been described by taking the case where the gain characteristics of the respective antennas are all the same as an example. However, as disclosed in the above-mentioned applicant's patent No. 2567332, the operation of receiving the reflected wave of the beam radiated from an arbitrary antenna with the same antenna or with another adjacent antenna is performed. When mixed, the gain characteristics of the antennas differ depending on the combination of the transmission / reception antennas.
[0031]
In this case, various antenna gain characteristics corresponding to the transmission / reception antenna combinations are stored in the data memory in advance, and the antenna gain characteristics corresponding to the operation being selected for the transmission / reception antenna combinations are read from the memory. Based on the side lobe, the received signal component may be calculated.
[0032]
In addition, the configuration in which the maximum received signal obtained from a plurality of directions is tentatively regarded as the direction of the object is illustrated. However, as the provisional object direction, other appropriate ones such as a weighted average value calculated for two or three transmission / reception channels from which a high-level received signal is obtained can be applied.
[0033]
Furthermore, although the present invention has been described by taking a radar apparatus that performs electronic scanning as an example, it is obvious that the present invention can also be applied to a radar apparatus configured to perform mechanical scanning.
[0034]
【The invention's effect】
As described above in detail, the radar apparatus according to the present invention is based on the gain characteristics being held and the peripheral portion of the side lobe and main lobe included in the received signal of the antenna in each direction from the maximum level of the received signal. Since the component is calculated as an unnecessary component, and the calculated component is subtracted from the received signal obtained in each direction , the side lobe and the wide main lobe significantly affect the spatial resolution. As a result, the detection accuracy of the direction of the object is greatly improved.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram for explaining the operation of an embodiment of the present invention.
FIG. 2 is a functional block diagram showing a configuration of a radar apparatus according to the embodiment.
FIG. 3 is a conceptual diagram for explaining the operation of another embodiment of the present invention.
[Explanation of symbols]
θ1 to θ5 Antenna direction L1 to L5 of each transmission / reception channel Reception level α of each antenna Reflected wave detection threshold β Center of gravity calculation threshold A1 to A5 Antenna of each transmission / reception channel
TR1 to TR5 Transmit / receive circuit for each transmit / receive channel PS processor

Claims (6)

In a radar apparatus that includes an antenna that emits a beam in a plurality of directions and receives a reflected wave from an object as a reception signal, and detects an object that has caused the reflected wave,
Antenna gain characteristic holding means for holding antenna gain characteristics in each direction consisting of a main lobe and side lobes of the antenna;
Among the directions in which the beam is radiated and received, each level in the direction in which the maximum level received signal is obtained or in two or three directions in which a large level received signal including this maximum level received signal is obtained. in regarded as the direction of the tentatively object the direction obtained by weighted average, based on the respective direction of the antenna gain characteristics in the maximum level and the holding of the object included in each direction of the received signal A radar comprising: an unnecessary component removing means for calculating a received signal component based on a side lobe in a direction regarded as a direction and subtracting the calculated component from a received signal obtained in each direction apparatus. In a radar apparatus that includes an antenna that emits a beam in a plurality of directions and receives a reflected wave from an object as a reception signal, and detects an object that has caused the reflected wave,
Antenna gain characteristic holding means for holding the antenna gain characteristic of the main lobe in each direction of the antenna;
Among the directions in which the beam is radiated and received, each level in the direction in which the maximum level received signal is obtained or in two or three directions in which a large level received signal including this maximum level received signal is obtained. in regarded as the direction of the tentatively object the direction obtained by weighted average, based on the respective direction of the antenna gain characteristics in the maximum level and the holding of the object included in each direction of the received signal A radar apparatus comprising: an unnecessary component removing unit that calculates a received signal component in a direction regarded as a direction and subtracts the calculated component from a received signal obtained in each direction and removes the calculated component. In either claim 1 or 2,
The antenna gain characteristics are radar apparatus, wherein a plurality of kinds held in accordance with a combination status of the transmit and receive antennas. In any one of claims 1 to 3,
A radar apparatus, comprising: a direction detection unit that calculates a weighted average value of directions based on a received signal from which the unnecessary component has been removed, and detects the calculated value as a final object direction. In any one of claims 1 to 4,
The radar apparatus is mounted on a vehicle, and the radiation of the beam in the plurality of directions is performed in a time-sharing manner from a plurality of antennas arranged in different directions. In any one of claims 1 to 5,
The radar apparatus according to claim 1, wherein the beams emitted in the plurality of directions are FM signal beams.

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