JPH05180931A - Fm radar equipment - Google Patents

Abstract

(57) [Summary] [Purpose] In an FM radar device, a target can be detected without being affected by noise, and the direction of the detected target can also be obtained. [Configuration] A beat frequency signal obtained by mixing a transmission signal of an FM wave and a reception signal of a reflected wave from a target is amplified by an amplifier whose amplification factor changes proportionally according to the frequency, and then detected. , The target is detected after the level of the detected signal is compared with a preset threshold value, and at least two beams are sequentially transmitted so that some of them overlap. The direction of the target is obtained based on the level of the detection signal obtained when each beam is transmitted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is to receive a reflected wave from a target when a transmission signal of an FM wave whose frequency changes with time is transmitted and mix the reception signal and the transmission signal. The present invention relates to an FM radar device that detects a target from the obtained beat frequency signal.

[0002]

2. Description of the Related Art Conventionally, this type of FM radar device emits a frequency-modulated radio wave at a constant period toward a target,
The reflected wave from the target is received, and the distance from the frequency of the beat frequency signal generated by the phase shift between the transmitted wave and the target is measured.

[0003]

A problem to be solved by the present invention is that when an FM radar device of this kind is mounted on a traveling vehicle such as an automobile to monitor a front obstacle, a reflected wave from the road surface or a floating wave is generated. This means that it is necessary to remove the noise components that are characteristic of running vehicles such as clutter caused by the reflection from rain and snow grains.

Further, if the vehicle-mounted FM radar device can detect not only the presence / absence of a target object but also the direction of the detected target object, the driver of the traveling vehicle can be informed of the obstacle ahead. This means that more optimal information can be given.

[0005]

The present invention receives a reflected wave from a target when a transmission signal of an FM wave whose frequency changes with time is transmitted so as not to be affected by noise. Then, the beat frequency signal obtained by mixing the reception signal and the transmission signal is amplified by an amplifier whose amplification factor changes proportionally according to the frequency, and then detected, and the level of the detection signal is preset. The target is detected by performing level determination with a threshold value.

Further, according to the present invention, at least two beams are sequentially transmitted so that some of them overlap, and the direction of the target is obtained based on the level of each detection signal obtained when each beam is transmitted. I am trying.

[0007]

FIG. 2 shows a basic structure of a radar apparatus main body 1. A triangular wave generator 2 supplies a carrier wave to a sweep oscillator 3, and the sweep oscillator 3 generates an FM signal having a predetermined sweep frequency. It is given to the circulator 5 through the distributor 4 and emitted from the antenna ANT as a radio wave toward the target 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 to obtain the relative distance to the target O. A beat frequency signal is generated according to the frequency difference between the two, and the beat frequency signal is applied to an amplifier 7 having a gain characteristic proportional to the fourth power of the frequency to compensate for distance attenuation, that is, the distance to the target increases. After the reception level of the reflected signal, and thus the level of the beat frequency signal, is compensated, the distance signal S to the target O detected at that time is compensated.
It is supposed to be taken out as.

A description will be given below of a case where individual targets of a plurality of targets within the radar monitoring area are detected when the targets of the radar device 1 are detected.

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

The spectrum at that time contains a plurality of frequency components, as shown in FIG. In this case, there are four targets.

Therefore, the entire frequency range of the distance signal S is divided into a plurality of frequency bands, and as shown in FIG. 4, the channels CH1 to CH1 of the respective divided bands are divided.
Band filters 81 to 8n corresponding to CHn are arranged in parallel, the respective filter outputs are detected by the detectors 91 to 9n, and the respective detected outputs are passed through the AD converter 10 by switching the switch SW to the microcomputer 11
To sequentially detect the target and detect whether or not the target is within the distance range corresponding to the frequency band of each channel by performing the level judgment using the preset threshold. You can

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

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

The spectrum distribution of the distance signal S output from the radar apparatus main body 1 when the reflected wave from the true target O has a relatively steep pulse shape as shown in FIG. 5, but is flat. In the case of reflected waves from the road surface on the road, as shown in FIG. 6, the waves gradually change into a mountain shape over a relatively wide frequency band.

Since it is almost constant regardless of the type of road, the data by the road surface reflected wave is divided into channels and stored in the microcomputer 11 in advance, and the microcomputer 11 outputs each channel based on the distance signal S. If the arithmetic processing for subtracting the stored road surface reflection data from the data is performed, the influence of the road surface reflection can be effectively suppressed.

Further, FIG. 7 shows the spectrum distribution in the case of reflected waves from a road surface in an uphill condition and in the case of reflected waves (clutter) from floating rain and snow grains when an FM wave having 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 average of the data of all channels, the difference (or ratio) of each data between the channels, and the difference (or ratio) of each data between the adjacent channels. If it is above the preset threshold, the target,
If this is not the case, it will be possible to distinguish from noise due to clutter and perform noise removal.

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

Generally, as shown in FIG. 8, the antennas ANT-a and ANT in the two radar devices LA and LB are used.
-The emission directions of the beams B1 and B2 are set so that the beams B1 and B2 emitted from -b partially overlap with each other, and the target O in the area where the beams B and B2 are overlapped by the radar devices LA and LB, respectively. The levels of the radar output signals Sa and Sb at the time of detection are defined as la and lb, and the ratio of the sum and difference of the respective levels (la-lb) / (l
a + lb) is F, the F value and the direction angle θ of the target O
It is known that there is a constant S-shaped characteristic relationship between the and.

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 can be obtained by the radar devices LA and LB. By calculating the F value in accordance with the levels la and lb of the output signals Sa and Sb at the time of detection, the direction angle θ of the target O at that time can be obtained.

Here, 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, the directions of the respective targets can be individually detected. I have to.

FIG. 10 shows a basic structure when a plurality of targets can be individually detected together with their respective target directions.

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

In the above-mentioned structure, first, the output signal for each channel when the radar device body 1a side is in the operating state (the radar device body 1b side is inoperative at this time) is output by the microcomputer. 11 is made to read and the target is detected. Next, the radar device body 1b side is in an operating state (at this time, the radar device body 1a side is not operating)
Then, the output signal of each channel at that time is read by the microcomputer 11 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, and calculates the F value from the level of the output signal of each channel, as described above. According to the F value, 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 this time, the distance to the detected target is obtained by the channel number of the target being detected. Further, when there are a plurality of channels in which the target is 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 direction angle θ. The direction of each target is individually obtained by performing each process for finding out.

FIG. 1 shows an FM for optimally implementing the present invention.
1 shows a configuration example of a radar device. Here, in order to simplify the overall configuration, only one radar device main body 1 is provided and the antenna switch ANT-SW is switched, so that the two antennas ANT-a, The beams B1 and B2 can be alternately emitted from the ANT-b.

The triangular wave generator 2 is as follows.
A square wave oscillator 21 that generates a square wave signal with a frequency of 50 KHz, a waveform converter 22 that converts the square wave signal into a triangular wave signal, and the triangular wave signal is corrected so that the oscillation frequency in the sweep oscillator 3 changes linearly. And a linearity corrector 23. In sweep oscillator 3, sweep width 4
Generates an FM wave of 00 MHz.

Further, the band pass filter groups 81 to 8 shown in FIG.
n, the detector groups 91 to 9n and the changeover switch SW, instead of the microcomputer 11 to the DA converter 1
2, a sweep oscillator 13 that sequentially generates frequency signals divided into multiple stages according to each channel designation signal sequentially applied, and the sweep oscillation frequency signal and the distance signal S output from the radar device body 1 are mixed. Mixer 14
And a bandpass filter 8 for filtering the output signal of the mixer 14, and a detector 9 for detecting the output of the filter through an amplifier 15.

In the configuration as described above, under the control of the microcomputer 11, first, the antenna switch ANT-SW is closed to the contact a side, and then the beam B1 is emitted from the antenna ANT-a in a predetermined direction. Is done.

At this time, the target detection capability distance range is 1 to
When the distance is 100 m, the frequency range of the distance signal S is 0.2
It becomes 67-26.7 MHz. Further, the channel designation is issued from the microcomputer 11 to the DA converter 12, and the 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 in units of 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 in the pass frequency band 57.733-58.0M.
The signal is filtered by the Hz bandpass filter 8, and the filtered frequency signal is detected by the detector 9 through the amplifier 15.
The detected DC voltage signal is read by the microcomputer 11 through the AD converter 10.

At this time, the microcomputer 11 is a DA
The channel designation given to the converter 12 is sequentially changed from 1 to 99, and the output data of the AD converter 10 is read for each channel designation and sequentially stored in the internal memory.

Table 1 shows the oscillation frequency fc of the sweep oscillator 13 and the frequency range f of the distance signal S for each channel.
s, the relationship of the distance range L to the target is shown.

Next, the microcomputer 11 closes the antenna switch ANT-SW on the b contact side to emit a beam B2 from the antenna ANT-b in a predetermined direction, and in the same manner as described above, each of the channels 1 to 99. Store data in internal memory.

In this way, each of the two groups 1 to 99
When the data for the channels have been stored, the microcomputer 11 performs the above-described noise removal processing such as road surface reflection and clutter for each group, and individually detects the target in each channel. As a result, the channel in which the target is detected is selected.

Then, using the data in both groups for the selected channel, the F value is calculated as described above, the direction angle θ of the corresponding target is determined, and the detected target corresponding to the number of channels is obtained. The data of the distance L and the data of the direction angle θ are output to the outside.

[0040]

As described above, in the FM radar device according to the present invention, the beat frequency signal obtained by mixing the transmission signal and the reception signal is amplified by the amplifier whose amplification factor changes proportionally according to the frequency. Then, the target signal is detected after the level of the detected signal is compared with the preset threshold value so that the target object can be detected without being affected by noise. Can be reliably detected.

Further, according to the present invention, the direction of the detected target can also be obtained, which is the most suitable as a vehicle-mounted radar device for detecting a front obstacle or the like when the vehicle is traveling.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an FM radar device according to the present invention.

FIG. 2 is a block diagram showing a basic configuration example of a radar device main body according to the present invention.

FIG. 3 is a diagram showing a frequency spectrum characteristic of a distance signal output from the radar apparatus main body when there are a plurality of targets.

FIG. 4 is a block diagram showing a basic configuration for individually detecting a plurality of targets.

FIG. 5 is a diagram showing a frequency spectrum characteristic due to a reflected wave from a true target.

FIG. 6 is a diagram showing a frequency spectrum characteristic due to a reflected wave from a flat road surface.

FIG. 7 is a diagram showing frequency spectrum characteristics due to reflected waves from an uphill road surface and clutter.

FIG. 8 is a block diagram showing a basic configuration for causing the direction detection of a target by using two radar devices.

FIG. 9 is a diagram showing F-θ characteristics.

FIG. 10 is a block diagram showing a basic configuration example of an FM radar device according to the present invention.

[Explanation of symbols]

 1 Radar Device Main Body 2 Triangle Wave Generator 3 Sweep Oscillator 4 Divider 5 Circulator 6 Mixer 7 Amplifier 8 Bandpass Filter 9 Detector 10 AD Converter 11 Microcomputer 12 DA Converter 13 Sweep Oscillator 14 Mixer 15 Amplifier

[Table 1]

Claims (2)

[Claims] 1. A beat frequency signal obtained by receiving a reflected wave from a target when a transmission signal of an FM wave whose frequency changes with time is transmitted and mixing the reception signal and the transmission signal. In an FM radar device for detecting a target, the beat frequency signal is amplified by an amplifier whose amplification factor changes proportionally according to the frequency and then detected, and the level of the detected signal and a preset threshold value are set. The FM radar device is characterized in that the target is detected by determining the level. 2. At least two beams are sequentially transmitted so that a part thereof overlaps, and the direction of the target is obtained based on the level of each detection signal obtained when each beam is transmitted. An FM radar device according to the above item 1.