JP2513466B2 - FM radar device - Google Patents

Description

TECHNICAL FIELD The present invention relates to an improvement of an FM radar device.

2. Description of the Related Art Generally, an FM radar device emits a frequency-modulated radio wave at a constant period toward a target, receives a reflected wave from the target, and produces a beat due to a phase shift between the received wave and the transmitted wave. The distance from the signal frequency to the target is measured, but when such an FM radar device is mounted on a traveling vehicle such as an automobile to monitor the presence of obstacles ahead, the radar It is necessary to be able to detect a plurality of targets in the surveillance area while individually identifying them. Also, not only the relative distance to the target,
If the direction of the detected target can also be obtained, it becomes possible to give the driver more optimum information regarding the front obstacle.

The present invention has been made in view of the above points, and in particular, is suitable for an in-vehicle radar device to detect a plurality of targets individually and detect the targets to detect the direction of each of the detected targets. The present invention provides an FM radar device with expanded capability.

Configuration Hereinafter, one embodiment of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 2 shows a concrete configuration of the FM radar device,
In the radar device main body 1, a carrier wave is given to a sweep oscillator 3 from a triangular wave generator, and an FM signal with a predetermined sweep frequency from the sweep oscillator 3 is given as a radio wave from an antenna ANT given to a circulator 5 through a distributor 4. It is designed to be fired toward the mark O. Further, the reflected wave from the target O received by the antenna ANT is given to the mixer 6 through the circulator 5, where it is mixed with the transmitted wave given from the distributor 4, and both frequencies corresponding to the relative distance to the target O are mixed. It produces a beat frequency signal due to the difference. Since the reception level of the reflected wave from the target O is attenuated in inverse proportion to the fourth power of the distance to the target O, the frequency signal has the optimum gain characteristic that is proportional to the fourth power of the frequency. Is provided to the amplifier 7 having a distance compensation, that is, the reception level of the reflected signal and the level of the beat frequency signal decrease as the distance to the target increases, and the detected object is detected. The distance signal S for the mark O is taken out.

When performing detection of a target using such an FM radar device, the basic principle for individually detecting a plurality of targets will be described below.

When a plurality of targets having different relative distances are present in the radar monitoring area, the radar device body 1 is proportional to the reflected wave from each target at a frequency corresponding to the distance to each target. A distance signal S in which amplitude signals are mixed is obtained.

The spectrum at that time contains a plurality of frequency components as shown in FIG. In this case, the target is 4
It shows when there is one.

Therefore, the entire frequency range of the distance signal S is divided into a plurality of frequency bands, and band filters 81 to 8n corresponding to the respective channels CH1 to CHn of the divided bands are arranged in parallel as shown in FIG. , The respective filter outputs are respectively detected by the wave detectors 91 to 9n, and the respective wave detection outputs are sequentially read by the microcomputer 11 via the AD converter 10 by switching the switch SW, and preset for each channel there. By performing the level determination using the threshold value, it is possible to respectively detect whether or not the target is within the distance range corresponding to the frequency band of each channel.

By adopting such means, it becomes possible for the FM radar device to individually detect a plurality of targets within the radar monitoring area with their relative distances.

Next, the basic principle of removing noise such as road reflection and clutter will be described below.

The spectrum distribution of the distance signal S output from the radar device body 1 is the fifth when the reflected wave from the true target O is used.
As shown in Figure (a), the pulse shape is relatively steep,
In the case of reflected waves from the road surface on a flat road, as shown in (b) of the figure, it gradually changes into a mountain shape over a relatively wide frequency band. Since it is almost constant regardless of the type of road tail, the data of the road surface reflected wave is divided into channels and stored in the microcomputer 11 in advance, and the output data of each channel based on the distance signal S in the microcomputer 11 is used. If the arithmetic processing for reducing the stored road surface reflection data is performed, the influence of the road surface reflection can be effectively suppressed.

Fig. 5 (c) shows the spectrum distribution due to the reflected wave from the road surface in the uphill condition and the reflected wave (clutter) from the floating rain and snow grains when the FM wave with an extremely high carrier frequency is transmitted. As shown in the figure, it has a comparatively gentle mountain shape, and the characteristic is obviously different from that due to the reflected wave from the true target O shown in FIG. Therefore, the microcomputer 11 calculates the difference (or ratio) of the average of the data of all channels from each channel data and the difference (or ratio) of each data between adjacent channels, and the result is set in advance. If it is above the threshold value, it can be determined that it is a target, and if not, it can be determined as noise due to clutter, etc., and noise can be removed.

Next, the basic principle for detecting the direction of the target will be described below.

Generally, as shown in FIG. 6, two radar devices LA and LB are used.
Each of the beams B1 and B2 emitted from the antennas ANT-a and ANT-b in FIG.
The emission direction of B2 is set, and the level of each radar output signal Sa, Sb when the target O in the area where the beams overlap is detected by each radar device LA, LB is la, lb.
And the ratio of the sum and difference of each level (la-lb) / (la +
It is known that there is a constant S-shaped characteristic relationship as shown in FIG. 7 between the F value and the direction angle θ of the target O, where lb) is F.

Therefore, if the relationship between F and θ is previously obtained by actual measurement and the F-θ characteristic is stored in the memory, the same target O is detected by each radar device LA, LB. Level l of each output signal Sa, Sb at
By calculating the F value according to a and lb, the direction angle θ of the target O at that time can be obtained.

In the present invention, in particular, even if a plurality of targets exist in the area where the beams B1 and B2 of the radar devices LA and LB overlap each other, it is possible to individually detect the directions of the respective targets. There is.

FIG. 8 shows a basic configuration example in which a plurality of targets can be individually detected together with their respective target directions.

Here, two FM radar devices having the function of individually detecting the target according to the configuration of FIG. 4 are installed side by side so as to share the microcomputer 11, and the radar device main body on one side A is used.
The beam emission direction of each antenna is set so that the beam B1 emitted from the antenna ANT-a of 1a and the beam B2 emitted from the antenna ANT-b of the radar main body 1b on the other side B partially overlap each other. There is. Further, the corresponding band-pass filters 81 to 8n on the A and B sides are set to have the same frequency band.

In such a configuration, first, the microcomputer 11 reads the output signal for each channel when the radar device body 1a side is in the operating state (the laser device body 1b side is inoperative at this time). Then, the target is detected. Next, the microcomputer 11 reads the output signal for each channel when the laser device main body 1b side is in the operating state (the laser device main body 1a side is not operating at this time) to detect the target. As a result, the microcomputer 11 finds out the channel in which the target is detected on the same channel on both sides of A and B, calculates the F value from the level of the output signal of each channel, and then calculates the F value. According to the above, the corresponding θ value is read from the table set in the internal memory in advance, and the direction angle of the detection target in that channel is obtained.

At that time, the distance to the detected target is obtained by the number of the channel in which the target is detected. Further, when there are a plurality of sets of channels in which the targets are respectively detected in the same channel, that is, when a plurality of targets are detected over different distance ranges, the F value is calculated for each set to determine the azimuth angle θ. The direction of each target is individually obtained by performing each process for putting out.

FIG. 1 shows a specific example of the configuration of an FM radar device for optimally implementing the present invention. Here, only one radar device main body 1 is provided in order to simplify the overall configuration. 2 by switching the antenna switch ANT-SW
The beams B1 and B2 can be alternately emitted from the one antenna ANT-a and ANT-b. In this case, the triangular wave generator 2 is a square wave oscillator 21 that generates a square wave signal having a frequency of 50 KHz, and the square wave signal is converted into a triangular wave signal. The waveform converter 22 and a linearity corrector 23 that corrects the triangular wave signal so that the oscillation frequency of the sweep oscillator 3 changes linearly. The sweep oscillator 3 generates an FM wave with a sweep width of 400 MHz.

In addition, the band pass filter groups 81 to 8n and the detector group 9 shown in FIG.
Instead of the configurations of 1 to 9n and the changeover switch SW, a sweep oscillator 13 that sequentially generates frequency signals divided into other stages in accordance with each channel designation signal sequentially provided from the microcomputer 11 via the DA converter 12. , The sweep oscillation frequency signal and the distance signal S output from the radar device body 1.
A mixer 14 that mixes with a bandpass filter 8 that filters the output signal of the mixer 14, and an amplifier 15 that outputs the filter.
And a detector 9 for detecting the signal through.

In such a configuration, under the control of the microcomputer 11, the antenna switch ANT-SW is first closed to the contact a side, and then the beam B1 is emitted from the antenna ANT-a in a predetermined direction. At this time, when the target detection capability distance range is set to 1 to 100 m, the frequency range of the distance signal S is 0.267 to 26.7 MHz. Further, a channel designation is issued from the microcomputer 11 to the DA converter 12, and a DC voltage signal suitable for the channel designation is given to the sweep oscillator 13. The sweep oscillator 13 oscillates 99 kinds of frequency signals divided every 267 KHz within the frequency range of 31.3 to 57.466 MHz according to the channel designation signal. The frequency signal output from the sweep oscillator 13 and the distance signal S are mixed in the mixer 14, and the mixed output is the pass frequency band.
The band-pass filter 8 of 57.733 to 58.0 MHz filters, the filtered frequency signal is detected by the detector 9 through the amplifier 15, and the detected DC voltage signal is read into the microcomputer 11 through the AD converter 10. Be done. At this time, the microcomputer 11 sequentially changes the channel designation given to the DA converter 12 from 1 to 99, reads the output data of the AD converter 10 for each channel designation, and sequentially stores it in the internal memory.

The following table shows the relationship between the oscillation frequency fc of the sweep oscillator 13, the frequency range fs of the distance signal S, and the distance range L to the target for each channel.

Next, the microcomputer 11 is an antenna switch AN
The T-SW is closed on the b contact side to emit a beam B2 from the antenna NAT-b in a predetermined direction, and each data in channels 1 to 99 is stored in the internal memory in the same manner as described above.

When the data of channels 1 to 99 in each of the two groups is stored in this way, the microcomputer 11 performs the above-described noise removal processing such as road reflection and clutter for each group, and then the target in each channel. Is individually detected. As a result, the channel in the detection state of the target is detected. Then, using the data in both groups for the selected channel, the F value is calculated as described above, the azimuth angle θ of the corresponding target is determined, and the distance L of the detected target according to the number of channels is calculated. And the data of the direction angle θ thereof are output to the outside.

Effects As described above, in the present invention, the distance to the target detected for each channel is not obtained by complicated arithmetic processing as in the conventional art, and no arithmetic processing is performed.
The beat frequency signal as a radar output signal is swept for each channel and detected, and the level of each signal detected is simply compared with the threshold value set for each channel in advance to detect the target with the distance resolution set by each channel. In order to detect the presence or absence directly and to make a multi-channel system to detect the presence or absence of the target according to the distance, the radar output without the configuration of multiple channels using a multi-filter Each channel has a simplified configuration by achieving multi-channel by only one system configuration in which a signal obtained by sequentially mixing a signal with a channel-divided sweep frequency signal and passing through a bandpass filter is detected. The target can be detected efficiently with the distance resolution set by Cormorant has the advantage.

At this time, in particular, according to the present invention, the reception level of the reflected signal and thus the level of the beat frequency signal decreases as the distance to the target increases, so that the amplification rate is compared in accordance with the beat frequency. Since the distance attenuation compensation of the signal level is performed by amplifying it by the amplifier that changes dynamically, the detection level of the beat frequency signal for which the distance attenuation compensation is performed is compared with the threshold value. Even if there is a target in, the detection can be surely performed.

Furthermore, the invention of the present application enables to obtain the direction of a target to be detected by sequentially transmitting at least two beams so that some of them are overlapped by using one radar device main body. Thus, with a simplified configuration, the direction of each target detected with the distance resolution set by each channel can be efficiently obtained, and the position of the target detected in the radar monitoring area can be specified. It is advantageous as an on-vehicle radar device for detecting an obstacle in front of the vehicle while traveling.

[Brief description of drawings]

FIG. 1 is a block configuration diagram showing an embodiment of an FM radar device according to the present invention, FIG. 2 is a block diagram showing the basic configuration of the FM radar device body, and FIG. 3 is an FM when there are a plurality of targets.
The figure which shows the frequency spectrum characteristic of the distance signal output from the radar apparatus main body, FIG. 4 is the block diagram which shows the basic structure for making a plurality of targets individually detected, FIG. 5 (a)
Shows a frequency spectrum characteristic of a reflected wave from a true target, (b) shows a frequency spectrum characteristic of a reflected wave from a flat road surface, and (c) shows a frequency spectrum characteristic of an uphill road surface. FIG. 6 is a diagram showing a frequency spectrum characteristic by reflected waves, clutter, etc., FIG. 6 is a block diagram showing a basic configuration for performing direction detection of a target by using two radar devices, and FIG. 7 is an F-θ characteristic. FIG. 8 is a block diagram showing a basic configuration example of the FM radar device according to the present invention. 1 ... Radar device main body, 2 ... Triangular wave generator, 3,13 ...
Sweep oscillator, 4 …… Distributor, 5 …… circulate, 6,
14 ... Mixer, 7,15 ... Amplifier, 8,81-8n ... Band filter, 9,91-9n ... Detector, 10 ... AD converter, 11 ... Microcomputer, 12 ... DA conversion vessel

Claims (2)

(57) [Claims] 1. A relative distance to a target by receiving a reflected wave from the target when a transmission signal is generated by an FM wave whose frequency changes with time and mixing the transmission signal and the reception signal. To obtain the beat frequency signal corresponding to, and to perform the distance attenuation compensation of the signal level by amplifying the beat frequency signal with an amplifier whose amplification factor changes proportionally according to the frequency, and to specify the channel. A sweep oscillator that generates a frequency signal divided for each channel according to the mixer, and a mixer that mixes an oscillation frequency signal for each channel and a beat frequency signal that has been subjected to distance attenuation compensation and is output from the radar device body, A bandpass filter that filters the mixed frequency signal, a detector that detects the frequency signal that has passed through the filter, and a level of the detected signal are predicted. FM radar device configured as compared to the set threshold values for each channel for each channel by means for detecting the presence or absence of target. 2. A relative distance to a target by receiving a reflected wave from the target when the transmission signal is an FM wave whose frequency changes with time and mixing the transmission signal and the reception signal. A beat frequency signal corresponding to the signal is obtained, and the beat frequency signal is amplified by an amplifier whose amplification factor changes proportionally according to the frequency to perform distance attenuation compensation of the signal level, and at least two beams are Radar device body that transmits sequentially so as to partially overlap, sweep oscillator that generates frequency signals divided for each channel according to channel designation, oscillation frequency signal for each channel and output from radar device body A mixer that mixes the beat frequency swing that has been subjected to the distance attenuation compensation, a bandpass filter that filters the mixed frequency signal, and A detector that detects the frequency signal that has passed through the filter and a means that detects the presence or absence of a target for each channel by comparing the level of the detected signal with a threshold value set in advance for each channel. An FM radar device comprising: means for determining the direction of the detected target based on the level of each detection signal in the same channel where the target is detected when the beams are transmitted so as to overlap.