JPH0216997B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to an automotive radar, and particularly to an improvement in the portion that processes beat signals from transmitted waves and received waves.

Prior Art and Problems It is desirable for automotive radars to be able to reliably detect only desired targets, such as cars or pedestrians traveling ahead, and to not malfunction due to clutter such as surrounding buildings or cliffs. However, in the case of an automobile radar, the received waves include waves reflected from clutter in addition to signals reflected from the target, so if all the received waves are subjected to detection processing, the above-mentioned malfunction will occur. Therefore, a method has been proposed in which components below a certain level corresponding to the clutter level are cut out from the beat signals of the transmitted and received waves, and the level is also set relatively high to avoid radar malfunctions as much as possible. . However, because the level is set high, there is a problem in that targets with very low reflection coefficients, such as humans, cannot be detected even if they are present at a short distance. Of course, if the level is set low, such targets can be detected, but it becomes difficult to distinguish them from clutter.

Purpose of the Invention The present invention has been made to improve the above drawbacks, and its purpose is to improve the detection performance of the radar while preventing malfunctions as much as possible by devising the above-mentioned level settings.

Structure of the Invention As shown in FIG. 1, when a car 2 equipped with an automotive radar 1 travels on a straight road, the radar received waves are easily affected by clutter such as a building 3 next to the road or an oncoming car 4. Currently, automotive radar 1
Considering a clutter with a reflection coefficient δ located at an azimuth θ and a distance R from , and if the clutter level is expressed by the output voltage Vc of the preamplifier that amplifies the beat signal, the following equation is obtained from the radar equation.

Vc ² =k×{G(θ)} ² ×δ/R ⁴ ×{G _P (fb)} ² ...
...(1) However, k is a constant, G(θ) is a transmitting/receiving antenna directivity, G _P (fb) is a value determined from the frequency characteristics of the preamplifier, and the mixer conversion efficiency is assumed to be constant.

According to equation (1) above, the clutter level Vc is inversely proportional to the square of the distance R, so at first glance it seems that the clutter level increases as the distance gets closer, but as can be seen from Figure 1, the closer the distance As the azimuth angle θ of clutter increases, the clutter level decreases as the distance approaches, due to the relationship with the antenna directivity and the frequency characteristics of the preamplifier where the gain decreases on the low frequency side. Figure 2 shows that the transmitting and receiving antenna is a horn antenna with an antenna beam angle of 8°, and the preamplifier characteristics are
The equation (1) is calculated assuming that 6 dB/octave, and the above situation is illustrated with the clutter level on the vertical axis and the distance R on the horizontal axis.

In this way, the clutter level is not independent of distance, and becomes smaller as the distance gets closer. The present invention has been made with attention to such points, and the detection distance is divided into a plurality of areas such as a short distance of 0 to 25 m and a long distance of 25 to 50 m, and the detection distance is By setting the value of the threshold level as low as possible, it is intended to improve the detection performance particularly at short distances. Figure 3 shows how the reception level pattern of humans and cars changes with distance, where 5 is the car radar, 6 is the car pattern, 7 is the human pattern, and 8
is at Kuratsuta level. Threshold for distinguishing between clutter and targets at long distances
Although it is impossible to detect a human at a short distance with V _th1 , it is possible to detect a human being at a short distance by setting the threshold V _th2 for short distance.

FIG. 4 is an explanatory diagram of the configuration of the present invention. A frequency modulated wave with a predetermined frequency change is transmitted from a transmitting section 10, and a beat signal of a part of the transmitted wave and a received wave is generated at a receiving section 11. This beat signal is input to a plurality of band pass filters 12a to 12n provided corresponding to the distance, and a beat signal corresponding to the distance is extracted.
Added to a to 13n. Each gate circuit is given a threshold level V _tha to V _tho depending on the distance, and only the beat signal above that level is input to the processing means 14 to detect a target or perform processing as necessary. Distance, speed, etc. are required.

Embodiment of the Invention FIG. 5 is a block diagram of essential parts showing an example of the hardware configuration of the automotive radar of the present invention.

In the figure, a frequency modulated wave (continuous wave) whose frequency changes in the shape of a triangular wave, for example, is emitted from the Gunn oscillator 20.
is transmitted via the transmitting antenna 21, and
A part of it is taken out by the directional coupler 22 and added to the mixer circuit 23, where it is sent to the receiving antenna 24.
A beat signal is generated by mixing with the received wave from. This beat signal is amplified in a preamplifier 25 according to a predetermined amplification factor, and is input to a short-distance bandpass filter 26 and a long-distance bandpass filter 27. The short-distance bandpass filter 26 passes only a beat signal having a frequency corresponding to a short distance of, for example, 25 m or less, and its output is input to one input terminal of the comparator 28 . In addition, a long-distance bandpass filter 27
is for passing only a beat signal of a frequency corresponding to a long distance, for example, 25 m to 50 m, and its output is input to one input terminal of the comparator 29.

For example, as shown in the flowchart of FIG. 6, the microcomputer 30 reads a steering signal indicating the steering angle through the input port 31 (step S1), and when it is determined from the steering signal that the vehicle is traveling in a straight line (step S1).
S2), sends the digital value of the threshold level V _th2 to the D/A converter 32 to hold the other input terminal of the comparator 28 at the threshold level V _th2 (step S3),
Threshold level on D/A converter 33
V _th1 digital value is sent to comparator 29
set the other input terminal to the threshold level.
Hold V _th1 . That is, threshold levels V _th1 and V _th2 are set as shown by the dashed line in FIG. 7. The comparator 28 outputs the output of the short-range bandpass filter 26 when it is larger than the threshold level V _th2 , and the comparator 29 outputs the threshold value V th2.
When the output of the long distance bandpass filter 27 is larger than V _th1 , it is output.

The output levels of the comparators 28 and 29 are detected by level detection circuits 34 and 35, respectively, and a comparator 36 determines which level is higher. The microcomputer 30 reads the determination result via the input port 37 (step S5), and when the output level of the comparator 28 is higher, it switches the analog switch 39 to the comparator 28 side via the output port 38. (Step S7) On the other hand, when the output of the comparator 29 is larger, the analog switch 39 is switched to the comparator 29 side (Step S8).
Then, the count value of the pulse counter 40 is continued (step S9), and the distance and speed to the target are calculated (step S10).

Further, when the microcomputer 30 determines that the vehicle is traveling on a curve based on the steering signal (step S2), it outputs a curve threshold level V' _th2 to the D/A converter 32, for example, as shown by the solid line in FIG. (Step S11), and the analog switch 39 is switched to the comparator 28 side (Step S12). This is because when driving on a curve, the clutter level at long distances becomes abnormally high, so only short distances are detected, and it is also taken into consideration that the clutter level increases somewhat even at short distances.

In addition, in Fig. 4, 41 is ROM, 42 is
RAM, which is used to store programs, threshold levels, etc.

FIG. 8 is a block diagram showing another example of the hardware configuration of the automotive radar of the present invention, in which the same reference numerals as in FIG. 5 indicate the same parts, and 70 is a pulse counter. Further, FIG. 9 is a flowchart showing an example of the software configuration of this embodiment.

The difference between this embodiment and the previous embodiment is that the hardware configuration is such that the level detection circuits 34, 3
5. Eliminate the comparator 36, input port 37 and analog switch 39, use the pulse counter 40 exclusively for the comparator 28, and add a new pulse counter 70 to count the output pulses of the comparator 29.
The software configuration is such that when driving in a straight line, the counts of both pulse counters 40 and 70 are read to calculate the distance to the target, and when driving on a curve, the counts of pulse counter 40 are read and processed. It's where you're doing it. In the previous embodiment, when the analog switch 39 is switched to either the short distance or the long distance, it is difficult to detect it unless a beat signal of a higher level is generated on the other side. According to the present invention, if it is above the clutter level, it can be detected immediately.

Effects of the Invention As explained above, according to the present invention, since the threshold level for target detection is changed according to the distance, malfunctions are prevented as much as possible and the detection performance of the radar is improved, especially the detection performance at short distances. will be greatly improved. Therefore, it is effective as a multi-purpose radar, such as a short-range detection system for detecting people and dangerous objects on the road, and an inter-vehicle distance control system for automobiles. Also,
Since the beat frequency band is divided using a bandpass filter, there is also the effect of reducing the influence of the ground clutter level, which has a relatively wide frequency band.
Note that detection performance can be further improved by increasing the number of bandpass filters.

[Brief explanation of drawings]

1 to 3 are diagrams for explaining the principle of the present invention, FIG. 4 is a diagram for explaining the configuration of the present invention, FIG. 5 is a block diagram of essential parts showing an example of the hardware configuration of the automotive radar of the present invention, and FIG. 6 5 is a float chart showing an example of the software configuration of the embodiment, FIG. 7 is an explanatory diagram of the threshold level, and FIG. 8 is a main part block diagram showing another example of the hardware configuration of the automotive radar of the present invention. , FIG. 9 is a flowchart showing an example of the software configuration of the embodiment of FIG. 20 is a Gunn oscillator, 21 is a transmitting antenna, 22
is a directional coupler, 23 is a mixer circuit, 24 is a receiving antenna, 25 is a preamplifier, 26 is a short-range bandpass filter, 27 is a long-range bandpass filter, 28 and 29 are comparators, 30 is a microcomputer, 31 , 37 is the input port, 3
2 and 33 are D/A converters, 34 and 35 are level detection circuits, 36 is a comparator, 38 is an output port, 39 is an analog switch, 40 and 70 are pulse counters, 41 is a ROM, and 42 is a RAM.

Claims (1)

[Claims] 1. A transmitting section that transmits a frequency modulated wave with a predetermined frequency change, a receiving section that mixes a part of the transmitted wave from the transmitting section and the received wave to obtain a beat signal, and inputting the output of the receiving section. A plurality of bandpass filters each having a different pass band, and a plurality of bandpass filters provided corresponding to each bandpass filter and outputting the bandpass filter output when the output is equal to or higher than a predetermined threshold level. a gate circuit, and processing means for processing the output signal of the gate circuit to detect at least the presence or absence of a target, and the passband of the plurality of bandpass filters has a frequency band of the beat signal divided into a plurality of frequency bands. For use in automobiles, the threshold level of the gate circuit corresponds one-to-one to the regions when divided into regions, and the threshold level of the gate circuit is set to be larger as the gate circuit corresponds to a bandpass filter with a higher passband. Radar.