JP3031094B2 - Frequency modulation radar equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a frequency-modulated radar device,
In particular, the present invention relates to a radar device that is mounted on a vehicle and detects a moving object.

[0002]

2. Description of the Related Art Conventionally, various devices have been developed and mounted on vehicles for the purpose of reducing driving operations and improving safety of a driver, and detecting a distance and a relative speed to a surrounding object such as a preceding vehicle. The development of radar equipment for performing this is also being actively pursued. As a radar device, a device using a radio wave such as a millimeter wave or a device using a laser beam has been proposed.

In a millimeter wave radar device, a frequency modulation wave whose frequency changes in a triangular shape or a trapezoidal shape with the passage of time, such as the radar device disclosed in Japanese Patent Laid-Open No. 2-198380, is used. Radar systems have been proposed. In this radar device, a beat signal is generated from the reception frequency modulation wave and the transmission frequency modulation wave reflected from the object, and when the frequency of the frequency rising portion of the 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]

Here, the measurement of the beat frequency of the rising frequency portion and the beat frequency of the falling frequency portion of the beat signal is performed by pulsing the beat signal at a certain threshold and counting the pulses. Measured. However, when a plurality of reflective objects exist in the radar beam, there are problems that a distant object having a large 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 the frequency fR corresponding to each distance.
1, fR2 and fR3 are mixed to form a distorted composite waveform. When this composite waveform is pulsed at a certain threshold,
Either only the distance frequency of the object having the highest reflection level is detected, or a frequency obtained by averaging the distance frequencies is detected. Therefore, for example, when there is a stationary object such as a structure having a large reflection intensity in a distant place, there has been a problem that a moving object such as a vehicle which should be originally detected cannot be detected due to the influence of the stationary object.

Of course, in order to detect such a moving object such as a vehicle, a Doppler radar may be used. In this case, although the relative speed is detected, there is a problem that the distance to the object cannot be measured.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above-mentioned problems of the related art, and has as its object to provide a method for controlling 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-modulated radar device that can extract the distance and accurately detect the distance and the relative speed between the moving objects.

[0008]

In order to achieve the above object, a frequency modulation radar apparatus according to the present invention is frequency-modulated having a frequency rising portion in which the frequency rises with time and a frequency falling portion in which the frequency falls with time. In a frequency modulation radar apparatus that transmits and receives a carrier wave and captures an object from the frequency of the frequency rising part and the frequency of the frequency falling part of the beat signal, the spectrum for spectrum analysis of the frequency rising part and the frequency falling part of the beat signal respectively. Analysis means, a relative stationary object and
In order to identify the relative moving object, a difference calculating means for calculating a difference between the power spectrum of the power spectrum and the frequency falling section of the fast Fourier transform frequency rising portion, before the differential signal output from the difference calculation means
Calculating means for calculating the distance to the relative moving object and the relative speed.

[0009]

As described above, according to the present invention, the power spectrum is calculated by performing spectrum analysis on the frequency rising portion and the frequency falling portion of the beat signal. The reflected signal from a stationary object has the same frequency spectrum in the frequency rising part and the frequency falling part, but in the case of a moving object, the frequency is different between the frequency rising part and the frequency falling part due to the Doppler effect.

Therefore, by calculating the difference between the power spectrum of the frequency rising part and the power spectrum of the frequency falling part, 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 speed from the spectrum of the moving object, the distance and the relative speed of only the moving object can be detected even if the stationary object and the moving object are included in the radar beam. Can be.

[0012]

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

FIG. 1 is a block diagram showing the configuration of this embodiment. The transmitting side circuit includes a carrier generator 10, a frequency modulator 12, a modulation voltage generator 14, a circulator 16,
And a transmission antenna 18. Carrier generator 1
From 0, a carrier is output and supplied to the frequency modulator 12. On the other hand, a triangular wave whose amplitude changes in a triangular shape is output from the modulation voltage generator 14 and supplied to the frequency modulator 12 as a modulation wave. Thereby, the carrier wave generator 10
Is frequency-modulated, and a transmission signal whose frequency changes in a triangular shape with time as shown by a solid line in FIG. 3A is output. This transmission signal is supplied to the transmission antenna 18 via the circulator 16,
It is emitted toward the object to be detected. On the other hand, a part of the transmission signal is supplied to a mixer of a reception-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, a danger determiner 32, and an alarm 34.
The reflected wave from the detected object is received by the receiving antenna 20 and supplied to the mixer 22. FIG. 3 (A) shows the received wave by a dotted line. In the mixer 22, the received signal and a part of the transmitted signal from the circulator 16 are combined by a difference operation to generate a beat signal. FIG. 3B shows a beat signal, in which the frequency of the rising part (upward section) of the triangular modulated wave is indicated by fup, and the frequency of the falling part (downward section) of the triangular modulated wave is indicated by 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 the moving object is detected by the processing described later, and an alarm is issued when it is determined that the moving object is dangerous.

FIG. 2 is a flowchart showing the operation of this embodiment. First, generated by the mixer 22,
The beat signal amplified by the amplifier 24 is separated into an ascending portion and a descending portion via the anti-aliasing filter 26 (S101, S102). The ascending and descending beat signals are supplied to the FFT signal processor 28, which performs FFT processing on each section to calculate a power spectrum (S103). Then, the power spectrum from the FFT signal processor 28 is supplied to the target recognizing device 30 to perform a peak search of the power spectrum (S104), and further store the peak and its neighboring frequencies in a memory (S105). FIG.
An example of the FT signal processing is shown, and FIG. 5 shows an example of the FFT signal processing in the descending portion. In both figures, the horizontal axis represents frequency, and the vertical axis represents power, and shows a case where both a moving object and a stationary object exist in the radar detection range. Then, the target recognizer 30 outputs 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 part shown in FIG. 5 is inverted and added to the power spectrum of the rising part. 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. Is shifted by the Doppler effect, the frequency spectrum is shifted between the rising part and the falling part, that is, fm1 ≠ f in FIGS.
Since the difference is m2, when the difference is calculated, the spectrum of the relatively stationary object disappears as shown in FIG. 6, and the spectrum of only the relatively moving object remains.

Therefore, after the difference is calculated, it is determined whether or not there are two peaks having opposite signs and close in frequency (S
107), if present, the difference between the absolute values of the powers of the two peaks is further calculated and compared with a predetermined value ε, and is equal to or less than the predetermined value ε, that is, the absolute values of the two peaks are sufficiently equal, and If it is determined that it is a reflected wave (S1
08), and proceeds to distance and relative speed calculation. On the other hand, when there is no peak with a reverse frequency and a frequency close to that (for example, when only a stationary object is within the radar detection range), or when there is a large difference between the absolute values of the peaks, the above process is repeated.

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

The calculated distance data and relative speed data are supplied to the danger determiner 32. Danger detector 3
In Step 2, the safety distance calculated in advance or calculated according to the traveling state of the vehicle and the calculated distance data are compared in magnitude, and if the distance is equal to or less than the safety distance, it is determined that there is danger (S111). The driver is notified by the alarm 34.

For example, when the own vehicle is stopped and a moving object is detected by the radar device of the present embodiment that detects the rear of the own vehicle, the danger determiner 32 determines whether the own vehicle is in the stopped state, It is also possible to determine whether a moving object is approaching or not, and to lock the door so as not to open it in a dangerous case.

In this embodiment, the fast Fourier transform means is used as the spectrum analyzing means, but the present invention can be realized by using a frequency analyzer (spectral analyzer).

[0021]

As described above, according to the frequency modulation radar apparatus of the present invention, only a moving object can be reliably detected, and the reliability of an alarm system or the like incorporating the radar apparatus is improved. be able to.

[Brief description of the 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 a rising part and a falling part.

[Explanation of symbols]

 Reference Signs List 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 determiner 34 alarm

Claims (1)

(57) [Claims] 1. Transmitting and receiving a frequency-modulated carrier having a frequency rising portion in which the frequency rises with time and a frequency falling portion in which the frequency falls with time,
In a frequency modulation radar apparatus for capturing an object from a frequency of a frequency rising part and a frequency of a frequency falling part of the beat signal, a spectrum analyzing means for performing spectrum analysis on a frequency rising part and a frequency falling part of the beat signal, respectively , A difference calculating means for calculating a difference between a power spectrum of a frequency rising part and a power spectrum of a frequency falling part which has been subjected to fast Fourier transform processing to identify an object and a relative moving object; and a difference signal output from the difference calculating means. From the relative
And a calculating means for calculating a distance to the moving object and a relative speed.