JP2860558B2 - FM radar equipment - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an FM radar device for measuring a distance from a target.

Conventional technology Recently, an FM-CW radar device is mounted on a running vehicle such as a car or a train, and the distance to another car or an obstacle, etc., and the relative speed are measured. 2. Description of the Related Art Systems are being developed to prevent a collision by giving an alarm to a driver or applying an automatic brake.

The operation principle of the FM-CW radar device is as follows.

As shown in FIG. 2, a signal of the fundamental frequency fo is linearly increased to fo + Δf at a period Tm, and is modulated by a triangular wave to linearly decrease to the original fo (fm = 1 / Tm is a modulation). Frequency, Δf is the frequency shift width), the frequency-modulated signal is emitted as a transmission wave Tw toward the radar monitoring area, and the reflected wave Rw from the target existing in the monitoring area is
To receive.

Comparing the received wave Rw with the previous transmitted wave Tw on the same time axis, the phase shifts according to the round trip time td of the radio wave, focusing on that the frequency difference fr at that time is proportional to the distance to the target The distance to the target is determined by measuring the frequency difference fr.

Further, the relative speed can be calculated by calculating a temporal change (dx / dt) of the distance (x) to the obtained target.

Conventionally, as this kind of FM-CW radar device, the transmission signal Tw
Developed by the same applicant to measure the frequency of the signal according to the frequency difference fr between the transmitted and received signals obtained by mixing the received and received signals Rw with the spectrum analysis based on the principle of heterodyne frequency measurement. (See JP-A-57-201873).

FIG. 4 shows a configuration of a conventional FM-CW radar device using a spectrum analysis formula.

In the configuration shown in the figure, the frequency modulation section 1 frequency-modulates the signal of the fundamental frequency fo in the oscillator 3 in accordance with the triangular modulation signal Sm from the modulation signal generation circuit 2 and outputs the frequency output from the oscillator 3. The modulated signal is distributed by the power distributor 4, most of which is supplied to the circulator 5, and part of the modulated signal is supplied to the mixer 6. The signal provided to the circulator 5 is guided to the antenna ANT and emitted to free space as a radio wave.

Then, the reflected wave from the target O is received by the antenna ANT, and the received signal is provided to the mixer 6 through the circulator 5, where it is mixed with the transmission signal, and the output signal of the mixer 6 is amplified by the amplifier 7, From the amplifier 7, a signal of the reception frequency fr is obtained according to the frequency difference between the transmission and reception signals.

Next, the signal of the reception frequency fr and the signal of the local oscillation frequency fv from the local oscillator 17 are mixed in the mixer 10,
A signal having a frequency fd according to the difference (or sum) between the reception frequency fr and the local oscillation frequency fv output from the mixer 10 is supplied to the bandpass filter 12 through the amplifier 11.

Then, the signal that has passed through the bandpass filter 12 is provided to the detector 14 through the amplifier 13, and the detected voltage signal is converted into digital data by the A / D converter 15,
The data is the arithmetic and control circuit (microcomputer)
9 'and read into the internal memory.

At this time, the local oscillation frequency fv of the local oscillator 17 is continuously changed through the D / A converter 16 by the control signal output from the arithmetic control circuit 9 ', and the frequency fd of the signal output from the mixer 10 is changed to a plurality of channels. The voltage is varied so as to correspond to each other, and the detected voltage by the detector 14 is converted into digital data by the A / D converter 15 for each channel, and is sequentially stored in the internal memory of the arithmetic and control circuit 9 '. Obtain data group by analysis.

The arithmetic and control circuit 9 'determines a channel in which the reception frequency fr and the local oscillation frequency fv resonate and the detection voltage is in the high level state from the spectrum distribution information, and the reception frequency fr in the resonance state at that time. Find the distance to the target according to the value of.

Then, using such a conventional spectrum analysis formula
In the FM-CW radar apparatus, a mixer 10, an amplifier 11, and a
Band filter 12, amplifier 13, detector 14, D / A converter 16
In addition, since a component including the local oscillator 17 is required, the entire configuration is complicated.

In the conventional device, the processing speed of spectrum analysis by channel scanning depends on the pass band width of the band filter 12, and the processing speed increases as the pass band width of the band filter 12 decreases to increase the distance resolution. Will be slow.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above points, and has as its object to provide an FM radar apparatus capable of quickly performing spectrum analysis processing with multiple resolutions with a simple configuration.

Configuration In order to achieve the object, the present invention is characterized in that a signal according to a frequency difference between a transmission signal and a reception signal is subjected to spectrum analysis by a maximum entropy method.

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

FIG. 1 shows an example of a basic configuration when an FM-CW radar device is used. A frequency modulating unit 1 comprising an oscillator 3 for modulating, a power divider 4 for distributing the frequency-modulated transmission signal, and a transmission signal given from the power divider 4 are given to an antenna ANT to be emitted as radio waves, A circulator 5 for providing a mixer 6 with a reception signal from the antenna ANT reflected by the target O, the mixer 6 for mixing the reception signal with a transmission signal provided from the power divider 4, and an output signal of the mixer 6 An amplifier 7 for amplification, an A / D converter 8 for converting an output signal of the amplifier 7 into a digital signal, and reading digital data output from the A / D converter 8 Then, the spectrum analysis is performed by the maximum entropy method, and the distance from the target O is determined from the plurality of spectrum-analyzed channel data in accordance with the high-level data channel, and the A / D conversion is performed. And an operation control circuit (microcomputer) 9 for controlling the data sampling period in the device 8.

Here, the maximum entropy method (MEM: Maximum Entropy
Method) performs a spectrum analysis by estimating an autocorrelation function having a large lag that cannot be measured by itself from finite measurement data so that the information entropy is maximized according to a predetermined algorithm. It is known per se.

Further, according to the maximum entropy method, spectrum analysis can be performed on a short signal of one cycle or less, and the resolution of the spectrum is high.

Thus, in such a configuration, the fourth
As in the case of the configuration shown in the figure, a signal of the reception frequency fr is obtained from the amplifier 7 according to the frequency difference between the transmission and reception signals.

The signal of the reception frequency fr is output to the arithmetic control circuit 9.
Are sampled at a predetermined cycle in the A / D converter 8 whose sampling cycle is controlled by the control signal from the control signal, and are converted into digital data.

The converted digital data related to the reception frequency fr is read into the arithmetic and control circuit 9 and stored in the internal memory.

When predetermined data is stored in the internal memory, the arithmetic control circuit 9 performs a spectrum analysis by using the data to execute an arithmetic process according to a predetermined algorithm based on a maximum entropy method.

At this time, as shown in FIG. 3, the channel CHx (x =
Spectrum distribution information is obtained from a group of level data in each spectrum divided for each of (1, 2, 3,...).

In FIG. 3, Sr is an antenna ANT output from the amplifier 7.
The signal represents a reception frequency fr proportional to the distance between the target and the target O, that is, a beat frequency signal between the transmission signal and the reception signal.

Then, the arithmetic control circuit 9 selects one channel of the high level data (or the high level data when there are a plurality of targets) from the plurality of spectrum-analyzed channel data. Of a plurality of channels), and the distance from the target is determined according to the channel.

Specifically, a number is assigned to a plurality of channels to be subjected to spectrum analysis, and the number of a channel of data in a high level state from among the plurality of channel data.
Knowing Nx (Nx = 1, 2, 3,...), The distance Lx between the target and the maximum measurement distance Lm of the target in the FM-CW radar device and the total number of channels n for spectrum analysis are calculated as follows: In accordance with the following.

Lx = Lm × Nx / n (1) Note that the maximum measurement distance Lm is determined by a modulation frequency, a frequency shift width, and the like in the modulation signal.

In the FM radar apparatus according to the present invention configured as described above, the number of spectrums analyzed by the maximum entropy method is determined so as to divide the maximum measurement distance Lm into the total number of channels n, and a plurality of channels subjected to spectrum analysis are determined. , The channel number Nx of the data in the high level state is detected, and the distance Lx to the target can be obtained by multiplying the channel number Nx by a constant (Lm / n).

As described above, according to the present invention, the reception frequency fr according to the frequency difference between the transmission and reception signals in proportion to the distance from the target in the FM-CW radar main body is determined by the arithmetic control circuit 9 in the spectrum by the maximum entropy method. Because it is obtained by analysis, the overall processing speed does not slow down due to filter processing as in the case of performing spectrum analysis using a conventional bandpass filter, and the spectrum analysis is performed with high resolution It can be performed at high speed, and there is a degree of freedom in setting the total number n of spectrum-analyzed signals. By setting the total number n of channels to be large, the distance resolution can be easily increased.

At this time, if a microcomputer for high-speed processing is used as the arithmetic control circuit 9, the spectrum analysis can be performed at a higher speed.

Further, in the present invention, since the spectrum analysis by the maximum entropy method is performed by the arithmetic processing in the arithmetic control circuit 9, there is no need for any component for performing the channel scanning at the time of the spectrum analysis as in the related art. The overall configuration is simplified.

Effects As described above, in the FM radar device according to the present invention, the transmission signal obtained by frequency-modulating the signal of the fundamental frequency according to the modulation signal and the reception signal by the reflected wave from the target are mixed,
When the distance between the target and the target is determined from the frequency of the signal according to the frequency difference between the transmitted and received signals, the signal obtained by mixing the transmitted signal and the received signal is determined using the maximum entropy method. The spectrum is analyzed while dividing the channels according to the frequency, and the distance between the target and the target is determined in accordance with the high-level data channel from the plurality of spectrum-analyzed channel data. In this case, in particular, in the present invention, a plurality of channels subjected to spectrum analysis are numbered, and a channel number Nx (Nx = 1, 2, 3,,) of data in a high level state from among the plurality of channel data. …) And the maximum measuring distance Lm
From the total number of channels n subjected to the spectrum analysis, the distance Lx between the target and the target is calculated as Lx = Lm × Nx / n. This has an excellent advantage that the distance to the target can be measured at a high speed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an FM radar apparatus according to the present invention, FIG. 2 is a characteristic diagram of transmission and reception signals in the FM radar apparatus, and FIG. FIG. 4 is a characteristic diagram showing a signal of the reception frequency fr proportional to the distance and a channel subjected to spectrum analysis, respectively.
FIG. 1 is a block diagram showing a conventional FM-CW radar apparatus based on spectrum analysis. 1 ... frequency modulation section, 2 ... modulation signal generation circuit, 3 ...
Oscillator, 4 ... Power divider, 5 ... Circulator, 6
... mixer, 7 ... amplifier, 8 ... A / D converter, 9 ...
… Calculation control circuit

Claims (1)

(57) [Claims] 1. A signal according to a frequency difference between a transmission signal and a reception signal obtained by mixing a transmission signal obtained by frequency-modulating a signal of a fundamental frequency in accordance with a modulation signal and a reception signal by a reflected wave from a target. In the FM radar system that obtains the distance between the target and the target from the frequency of the signal, the signal obtained by mixing the transmission signal and the reception signal is divided into channels according to the frequency using the maximum entropy method. A means for performing spectrum analysis and a means for obtaining a distance from a target according to a channel of data at a high level among a plurality of channel data subjected to spectrum analysis are provided. Numbering is performed to select the channel of the data that is in the high level state from among the multiple channel data. Number Nx (Nx = 1,2,3, ...) out comparatively and from the maximum measurement distance Lm and spectrum analysis is the total number of channels n was, the distance Lx between the target, Lx = Lm × / Nx /
An FM radar device characterized in that it is obtained as n.