JPH06214017A - Frequency modulation radar device - Google Patents

Abstract

PURPOSE:To extract only a moving object even in the case of plural reflecting objects, including stationary objects and moving objects, existing in radar beams and detect the distance and relative speed to the moving object correctly. CONSTITUTION:The reflected wave from a detected object is received by a receiving antenna 20 and supplied to a mixer 22. In the mixer 22, a receive signal is combined with a part of a transmit signal from a circulator 16 by differential operation so as to generate a beat signal. The beat signal from the mixer 22 is amplified by an amplifier 24 and supplied to an FFT signal processor 28 through a filter 26. In the FFT signal processor 28, a frequency rise part and a frequency fall part are respectively subjected to FFT processing. A target recognizer 30 detects the peak of only a moving object by the differential operation of power spectrum of the rise and fall parts, and computes the distance and relative speed to the moving object.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The frequency modulation radar device of the present invention,
Particularly, the present invention relates to a radar device mounted on a vehicle and detecting a moving object.

[0002]

2. Description of the Related Art Conventionally, various devices have been developed and installed in vehicles for the purpose of reducing driver's driving operations and improving safety, and detect distance and relative speed to surrounding objects such as preceding vehicles. The development of radar devices for this purpose is also being actively conducted. As a radar device, a device using radio waves such as millimeter waves or a device using laser light has been proposed.

In a millimeter wave radar device, for example, a frequency modulation wave whose frequency changes into a triangular shape or a trapezoidal shape with time as in the radar device disclosed in Japanese Patent Laid-Open No. 2-198380 is used. The radar device that has been proposed has been proposed. In this radar device, a beat signal is generated from a reception frequency modulated wave and a transmission frequency modulated wave reflected from an object. When the frequency of the frequency rising portion of this beat signal is fup and the frequency falling portion is fdown, fd = The relative speed to the object is calculated by (fdown−fup) / 2, and the distance to the object is calculated by fr = (fup + fdown) / 2.

[0004]

The measurement of the beat frequency in the frequency rising portion and the beat frequency in the frequency falling portion of the beat signal is performed by pulsing the beat signal at a certain threshold and counting the pulses. To be measured. However, when a plurality of reflecting objects exist in the radar beam, there is a problem that a distant object having a high reflection level is detected or an intermediate distance between the objects is detected.

That is, when the distances to a plurality of reflecting objects in the radar beam are R1, R2, and R3, the distance frequency of the beat signal is a frequency fR corresponding to each distance.
1, fR2, fR3 are mixed to form a distorted composite waveform. If you pulse this composite waveform with a constant threshold,
Only the range frequency of the object having the strongest reflection level is detected, or the frequency obtained by averaging the range frequencies is detected. Therefore, for example, when there is a stationary object such as a structure having a large reflection intensity in the distance, there is a problem that a moving object such as a vehicle that should be detected by the stationary object cannot be detected.

Of course, it is possible to use a Doppler radar to detect such a moving object such as a vehicle, but in this case, although the relative speed is detected, there is a problem that the distance to the object cannot be measured.

The present invention has been made in view of the above-mentioned problems of the prior art, and an object thereof is to provide a moving object only when a plurality of reflecting objects including a stationary object and a moving object exist in a radar beam. It is an object of the present invention to provide a frequency modulation radar device capable of accurately detecting the distance and the relative velocity between moving objects by extracting the signal.

[0008]

In order to achieve the above object, the frequency modulation radar device of the present invention is frequency-modulated having a frequency rising portion where the frequency rises with time and a frequency falling portion where the frequency falls with time. In a frequency modulation radar device that transmits and receives a carrier wave and captures an object from the frequency of the frequency rising portion and the frequency of the frequency falling portion of the beat signal, a spectrum for spectrum analysis of the frequency rising portion and the frequency falling portion of the beat signal, respectively. Analysis means, difference calculation means for calculating the difference between the power spectrum of the frequency rising portion and the power spectrum of the frequency falling portion, which have been subjected to the fast Fourier transform, and the distance to the moving object from the difference signal output from the difference calculating means, Having a calculation means for calculating the relative speed And butterflies.

[0009]

As described above, in the present invention, the power spectrum is calculated by spectrally analyzing the frequency rising portion and the frequency falling portion of the beat signal. The reflected signal from the stationary object has the same frequency spectrum in the frequency rising portion and the frequency falling portion, but in the case of a moving object, the frequency increases in the frequency rising portion and the frequency falling portion due to the Doppler effect.

Therefore, by calculating the difference between the power spectrum of the frequency rising portion and the power spectrum of the frequency falling portion, the spectrum of the stationary object is removed and only the information of the moving object is extracted.

Therefore, by calculating the distance and the relative velocity from the spectrum of the moving object, the distance and the relative velocity of only the moving object can be detected even if the stationary object and the moving object are included in the radar beam. You can

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the frequency modulation radar device according to the present invention will be described below with reference to the drawings.

FIG. 1 shows a block diagram of the configuration of this embodiment. The transmission side circuit includes a carrier wave generator 10, a frequency modulator 12, a modulation voltage generator 14, a circulator 16,
And a transmission antenna 18. Carrier wave generator 1
A carrier wave is output from 0 and supplied to the frequency modulator 12. On the other hand, the modulation voltage generator 14 outputs a triangular wave whose amplitude changes in a triangular shape, and is supplied to the frequency modulator 12 as a modulation wave. Thereby, the carrier generator 10
Is modulated in frequency, and a transmission signal whose frequency changes in a triangular shape with the lapse of time is output as shown by the solid line in FIG. This transmission signal is supplied to the transmission antenna 18 via the circulator 16,
It is radiated toward the object to be detected. On the other hand, a part of the transmission signal is supplied to the mixer of the receiving side circuit described later via the circulator 16.

The receiving side circuit includes a receiving antenna 20, a mixer 22, an amplifier 24, a filter 26, a fast Fourier transform processor (FFT signal processor) 28, and a target recognizer 3.
0, the risk determiner 32, and the alarm 34.
The reflected wave from the detected object is received by the receiving antenna 20 and supplied to the mixer 22. The received wave is shown by the dotted line in FIG. In the mixer 22, the reception signal and a part of the transmission signal from the circulator 16 are combined by a difference calculation to generate a beat signal. In FIG. 3B, the beat signal is shown, where the frequency of the rising portion (upstream section) of the triangular modulation wave is fup and the frequency of the falling portion (downstream section) of the triangular modulation wave is shown as fdown. The beat signal from the mixer 22 is amplified by the amplifier 24 and supplied to the FFT signal processor 28 via the anti-aliasing filter 26. Then, the signal subjected to the FFT processing is supplied to the target recognizer 30 and only a moving object is detected by the processing described later, and an alarm is issued when it is determined to be dangerous.

FIG. 2 is a flow chart showing the operation of this embodiment. First, it is generated by the mixer 22,
The beat signal amplified by the amplifier 24 is separated into the rising portion and the falling portion via the anti-aliasing filter 26 (S101, S102). The beat signals of the rising portion and the falling portion are supplied to the FFT signal processor 28, and FFT processing is performed on each section to calculate the power spectrum (S103). Then, the power spectrum from the FFT signal processor 28 is supplied to the target recognizer 30, a peak search of the power spectrum is performed (S104), and the peak and frequencies in the vicinity thereof are stored in the memory (S105). Figure 4 shows the F of the rising part
An example of FT signal processing is shown, and FIG. 5 shows an example of FFT signal processing in the falling portion. In both figures, the horizontal axis represents frequency and the vertical axis represents power, and there is shown a case where both a moving object and a stationary object exist within the detection range of the radar. Then, the target recognizer 30 determines the peak frequency of the rising section, the power and the peak frequency of the falling section,
The difference from the power is calculated (S106). That is, the power spectrum of the falling portion shown in FIG. 5 is inverted and added to the power spectrum of the rising portion. At this time, the detected object that is relatively stationary with respect to the own vehicle has the same frequency spectrum in the ascending portion and the descending portion, that is, fs1 = fs2 in FIGS. Since the detected object moving to the position is frequency deviation due to the Doppler effect, the frequency spectrum is deviated between the rising portion and the falling portion, that is, fm1 ≠ f in FIGS. 4 and 5.
Since the difference is m2, when the difference is calculated, the spectrum of the relative stationary object disappears and the spectrum of only the relative moving object remains, as shown in FIG.

Therefore, after the difference is calculated, it is determined whether or not there are two peaks having opposite frequencies and having frequencies close to each other (S
107), if present, further calculates the difference between the absolute values of the powers of the two peaks and compares it with a predetermined value ε. If it is determined that the wave is a reflected wave (S1
08), and shift to distance and relative velocity calculation. On the other hand, if there are no peaks of opposite signs and frequencies close to each other (for example, only a stationary object is in the detection range of the radar) or if there is a large difference in absolute value between the peaks, the above processing is repeated.

In this way, the spectrum of the moving object is detected, and the distance and relative velocity are detected. The distance and the relative speed are the above-mentioned distance frequency and relative speed frequency fd = (fdown−fup) / 2 fr = (fdown + fup) / 2 and fd = 2v / c · f0 fr = 4fm Δf / c · R, where v: Relative speed, c: speed of light, f0: center frequency, f
It is calculated by m: modulation frequency, Δf: frequency deviation width (S110).

Then, the calculated distance data and relative velocity data are supplied to the danger determiner 32. Danger determiner 3
In 2, the safety distance calculated in advance or calculated according to the running state of the own vehicle is compared with the calculated distance data, and if it is less than the safe distance, it is determined to be dangerous (S111), The driver is notified by the alarm device 34.

Further, for example, when the own vehicle is in a stopped state and a moving object is detected by the radar device of this embodiment which detects the rear of the own vehicle, the danger determiner 32 determines whether the own vehicle is in a stopped state, and It is also possible to determine whether or not a moving object is approaching and lock the door so that it will not be opened if it is dangerous.

In this embodiment, the fast Fourier transform means is used as the spectrum analysis means, but the present invention is also applicable if a frequency analyzer (spectrum analyzer) is used.

[0021]

As described above, according to the frequency modulation radar device of the present invention, it is possible to reliably detect only a moving object and improve the reliability of an alarm system or the like incorporating the radar device. be able to.

[Brief description of drawings]

FIG. 1 is a configuration block diagram of an embodiment of the present invention.

FIG. 2 is a processing flowchart of the embodiment.

FIG. 3 is an explanatory diagram of a transmission / reception signal and a beat signal of the embodiment.

FIG. 4 is an explanatory diagram of a power spectrum of a rising portion.

FIG. 5 is an explanatory diagram of a power spectrum of a descending portion.

FIG. 6 is an explanatory diagram showing a difference calculation result between an ascending portion and a descending portion.

[Explanation of symbols]

 10 carrier wave generator 12 frequency modulator 14 modulation voltage generator 16 circulator 18 transmitting antenna 20 receiving antenna 22 mixer 24 amplifier 26 filter 28 FFT signal processor 30 target recognizer 32 danger judger 34 alarm device

Claims (1)

[Claims] 1. A frequency-modulated carrier having a frequency rising portion whose frequency rises with time and a frequency falling portion whose frequency falls with time is transmitted and received.
In a frequency modulation radar device for capturing an object from the frequency of the frequency rising part and the frequency of the frequency falling part of the beat signal, spectrum analyzing means for spectrally analyzing the frequency rising part and the frequency falling part of the beat signal respectively, and a fast Fourier transform Difference calculating means for calculating a difference between the processed power spectrum of the frequency rising portion and the processed power spectrum of the frequency falling portion, and a calculating means for calculating the distance to the moving object and the relative speed from the difference signal output from the difference calculating means. And a frequency modulation radar device comprising: