JP2655127B2 - FMCW radar equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radar apparatus using microwaves and millimeter waves, and more particularly to an FMCW type radar apparatus in which a continuous wave signal is frequency-modulated.

[0002]

2. Description of the Related Art In a conventional radar apparatus, a microwave and a millimeter wave are sent to a moving body, and a Doppler shift or a beat frequency component of a reflected wave returning from the moving body is detected to determine a distance to the moving body and a distance to the moving body. It measures a moving object and a relative speed. FIG. 4 shows a configuration diagram of a radar apparatus using FMCW modulation which is conventionally known. By inputting the triangular wave modulation signal from the modulation signal generator 6 to the voltage controlled oscillator (VCO unit) 1, the triangular wave FM with respect to the transmission center frequency
The modulation is applied, and the modulated transmission signal is amplified by the RF amplifier 2 and transmitted through the directional coupler 3 and the circulator 4 from the antenna 5 to the moving body. The received wave reflected by the moving object is received by the antenna unit 5 and branched by the circulator unit 4 to the mixer unit 9.

[0003] The mixer unit 9 includes the directional coupler 3.
The same frequency signal as the transmission wave extracted from the transmission signal is input as a local oscillation signal, and the reception wave is converted into a beat frequency corresponding to a difference frequency from the transmission wave by being mixed with the local oscillation signal. The beat signal is amplified by the low-frequency amplifier 10, A / D-converted by the AD converter 11, and then subjected to a Fourier transform for performing spectrum analysis of the beat frequency in the FFT circuit 12, and the output thereof is an arithmetic processing unit including a microprocessor. 13, where the distance and speed are calculated and output.

When triangular wave modulation is applied, the frequency of the output beat signal changes every half the modulation period, as shown in FIG. 5, and the distance R and speed V of the moving object increase in frequency. When the beat frequency component detected at the time of sweeping is fu and the beat frequency component detected at the time of sweeping when lowering the frequency is fd, it can be calculated by the following equation. R = {(Tm · C) / (4 · ΔF)｝ ｛(fu + fd) / 2} (1) V = (C / 2fo) ｛(fu−fd) / 2｝ (2) where C is The speed of light, ΔF is the maximum frequency shift, Tm is the cycle of triangular wave modulation, and fo is the transmission center frequency. In the drawing, W1 indicates a transmission wave, and W2 indicates a reception wave.

In this conventional FMCW radar device, when the output beat signal is δf, the local oscillation signal fL, which is a transmission wave,
O lower frequency f1 = fLO-δf and higher frequency f
The signal of 2 = fLO + δf is simultaneously down-converted by the mixer, and the lower frequency f1 at the time of the sweep to increase the frequency, the high frequency component f2 at the time of the sweep to lower the frequency is a desired reception frequency component, and the other signals are so-called image signals. It is a noise component and becomes an interference wave. Thus in particular, the distance may detects distant location will be a distance detection capability by the noise caused by image band and the reception level that a low down. If another radar or the like is nearby, the possibility of interference increases by the amount of the image band.

[0006] In the example JP-5-297122 and JP 5-2 4 0947 JP to prevent the effects of interference from other radar is this latter problem, when subjected to disturbance, the disturbance A method of recognizing and deleting the result from a result output and a method of correcting the influence of an interference wave by signal processing have been proposed. However, in the case of performing data processing after receiving these interference waves, data processing is frequently performed when the probability of interference increases, and necessary data can be obtained at the correct timing because more data is deleted. It becomes difficult.

Therefore, it is required to reduce the noise in the former image band, and at the same time, suppressing the image band is effective in lowering the probability of interference in the latter. For this reason, it is conceivable that a beat frequency is obtained by mixing an input received signal from an antenna with local signals having phases different from each other by 90 degrees in two different mixers.
At this time, the output signal from each mixer appears as a signal having a phase shift of 90 degrees. However, the phase shift is reversed at frequencies higher and lower than the local oscillation signal.
If the output signal is further shifted by 90 degrees and combined, the mixer output frequency is the same, but the signal waveform is different in phase between the local signal and the local signal, so it becomes a signal that overlaps and strengthens the canceling signal and suppresses the image band components. Becomes possible.

[0008]

However, such a configuration is a circuit configuration often used as a radio communication circuit, but a circuit having a low output frequency is required to generate a local oscillation signal having a phase difference of 90 degrees. It is not widely used because it is difficult to produce hybrids. In particular, in a radar apparatus using FMCW modulation, the desired reception band differs in the upper and lower directions of the reception input frequency and the local oscillation frequency depending on the state of the triangular wave frequency modulation. Cannot be realized. For this reason, the fact is that image suppression cannot be performed using the conventional technique as it is.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to reduce the noise in an image band by suppressing an image band generated in a mixer, and to suppress interference from another radar device in the image band. Is to provide.

[0010]

SUMMARY OF THE INVENTION An FMCW radar apparatus according to the present invention comprises first and second mixers for inputting a local oscillation signal having a phase different from that of a received wave by 90 degrees and outputting a beat frequency signal. First and second FFT circuits for Fourier transforming the outputs of the first and second mixers, respectively, and an operation for calculating the distance and speed of the object based on the values obtained from the first and second FFT circuits A processing unit.

Also, according to the present invention, the received wave
A 90-degree hybrid for demultiplexing into signals having a phase difference of 0 degrees, first and second mixers for inputting a demultiplexed received wave input and a local oscillation signal and outputting a beat frequency signal, First and second FFT circuits for Fourier transforming the output of the second mixer, and an arithmetic processing unit for calculating the distance and speed of the object based on the values obtained from the first and second FFT circuits. The configuration is provided with.

[0012] Here, the arithmetic processing unit performs the first and second F-mode operations during sweeping when the triangular wave frequency of the FMCW modulation increases.
A process of calculating the sum of the opposing real part and imaginary part, and the sum of the imaginary part and real part of the FT circuit, and performing a spectrum analysis on the sum to obtain the peak frequency;
At the time of the sweep in which the triangular wave frequency of the W modulation becomes low, the difference between the real part and the imaginary part facing each other of the first and second FFT circuits and the difference between the imaginary part and the real part are calculated, and their spectrum analysis is performed. The processing is performed to obtain the peak frequency, and the distance and speed of the object are calculated based on each peak frequency obtained by the processing.

[0013]

The FFT operation is performed on each of beat frequency signals having a phase difference of 90 degrees, which are two mixer output signals, and the sum and difference of the real part and the imaginary part of each signal are obtained. Is calculated. On this occasion,
The desired reception band can be selected and the image band can be suppressed by switching the calculation between sweeping when increasing the frequency of the transmission output of the triangular wave frequency modulation and sweeping when lowering the frequency, thereby reducing the noise in the image band. And interference from other radars can be suppressed.

[0014]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a configuration of an embodiment of the present invention, and the same reference numerals are given to portions equivalent to those of the conventional FMCW radar device shown in FIG. That is, the voltage controlled oscillator (V
By inputting a triangular wave modulation signal from the modulation signal generator 6 to the CO unit 1, the transmission center frequency is subjected to triangular wave FM modulation, and the modulated transmission signal is amplified by the RF amplification unit 2, and the directivity is increased. The signal is transmitted from the antenna unit 5 to the moving body through the coupler 3 and the circulator 4. The received wave reflected by the moving object is received by the antenna unit 5, extracted by the circulator unit 4, and branched by the in-phase branching circuit 7 into two.

On the other hand, the same frequency signal as the transmission wave extracted from the directional coupler 3
Are output as two local signals having the same amplitude and different phases by 90 degrees. These two local signals and the received waves branched by the in-phase branching circuit 7 are input to mixers 9A and 9B provided individually, and mixed here, and beat frequencies are output from the mixers 9A and 9B. You. This output is connected to the amplifier 10
A, 10B, and are amplified by the AD converters 11A, 11B.
The signal is A / D converted at B and input to the FFT circuits 12A and 12B.

In the FFT circuits 12A and 12B, a fast Fourier transform is performed, and respective outputs of a real part and an imaginary part are output from each. The real part output and the imaginary part output are input to an arithmetic processing unit 13 composed of a microprocessor, where the arithmetic processing is performed, and the output of distance and speed is output as data. In the arithmetic processing unit 13, the FFT circuit 12 is synchronized with the sweep of the triangular wave frequency modulation.
The image frequency can be suppressed by taking the sum and difference of the real part output and the imaginary part output from A and 12B.

FIG. 2 shows the processing flow. here,
For example, it is assumed that the 90-degree hybrid 8 is connected so that the local signal of the mixer 9A is ahead of the local signal of the mixer 9B by 90 degrees in phase. The real part output results obtained by Fourier transforming the outputs of the mixers 9A and 9B by the FFT circuits 12A and 12B are respectively "real number 1" and "real number 2", and the imaginary part outputs are "imaginary number 1" and "imaginary number 2", respectively. .

Then, at the time of sweeping when the frequency becomes high during the triangular wave frequency modulation, the sum of "real number 1" and "imaginary number 2" and the sum of "real number 2" and "imaginary number 1" are calculated for each frequency component, and Spectral analysis is performed using the sum of these as a real part and an imaginary part, respectively, and the peak frequency is searched for, and this is set as fu. In addition, at the time of sweeping when the frequency becomes low during the triangular wave frequency modulation, the difference between “real number 1” and “imaginary number 2” and the difference between “imaginary number 1” and “real number 2” are calculated for each frequency component, and Is analyzed as a real part and an imaginary part, respectively, and the peak frequency is searched, and this is set as fd.
Then, these values fu and fd are calculated by the above-mentioned equations (1),
By substituting into (2), the distance R and the velocity V can be obtained.

At this time, by performing the above-described calculation, a signal component higher than the local oscillation signal is obtained as a reception band during the sweep operation in which the frequency becomes low, and a signal bandwidth lower than the local oscillation signal is suppressed as the image frequency. become. Further, at the time of the sweep in which the frequency becomes higher, a frequency lower than the local oscillation signal is obtained as the reception band, and the higher frequency is suppressed as the image frequency. This makes it possible to lower the noise level in the image band,
In addition, the probability of occurrence of interference is reduced.

In the FMCW radar apparatus, since a microwave or a millimeter wave is used as described above, there is no particular problem in manufacturing a 90-degree hybrid. Also, FM
In the CW radar device, a fixed 90-degree hybrid cannot be used because the desired reception band differs in the upper and lower portions of the reception input frequency and the local oscillation frequency depending on the state of the triangular wave frequency modulation. This can be accommodated.

Here, in the present invention, 9
Since it is only necessary to obtain a beat signal having a phase difference of 0 degrees, for example, as shown in FIG.
The transmission wave from the directional coupler is branched into two by the in-phase branching circuit 7 to generate a local oscillation signal, and these are respectively sent to the mixer circuits 9A,
The beat frequency may be obtained by inputting it to 9B.
In FIG. 3, parts equivalent to those in FIG. 1 are denoted by the same reference numerals, and detailed description is omitted.

[0022]

As described above, according to the present invention, a beat frequency signal of a received wave input is obtained by local signals having phases different from each other by 90 degrees, and these signals are subjected to Fourier transform, respectively, and the obtained values are obtained. Since the distance and the speed of the object are calculated based on the above, it is possible to suppress the image band, reduce the noise in the image band, and suppress interference from other radars.

Also, according to the present invention, the received wave input is demultiplexed into signals having phases different from each other by 90 degrees by using a 90-degree hybrid, and the beat frequency signal is obtained by a local oscillation signal. Can be suppressed.

According to the present invention, particularly in the arithmetic processing section, a desired reception band is selected by switching the operation between a sweeping operation for increasing the frequency of the transmission output of the triangular wave frequency modulation and a sweeping operation for lowering the frequency, thereby selecting the desired reception band. This makes it possible to suppress noise, reduce the noise in the image band, and suppress interference from other radars.

[Brief description of the drawings]

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

FIG. 2 is a flowchart for explaining a calculation flow in a calculation processing unit.

FIG. 3 is a block diagram of another embodiment of the present invention.

FIG. 4 is a block diagram illustrating an example of a conventional FMCW radar device.

FIG. 5 is a diagram showing a relationship between a frequency sweep and its beat frequency in the FMCW radar device.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 voltage controlled oscillator 2 amplifier 3 directional coupler 4 circulator 5 antenna unit 6 modulation signal generator 7 in-phase branch circuit 8 90-degree hybrid 9A, 9B mixer 10A, 10B amplifier 11A, 11B AD converter 12A, 12B FFT circuit 13 arithmetic Processing unit

Claims (2)

(57) [Claims] In a radar apparatus using FMCW modulation, first and second mixers for inputting a local oscillation signal having a phase different from that of a received wave by 90 degrees and outputting a beat frequency signal, and a first and a second mixer, First and second FFT circuits for Fourier transforming the output of the second mixer, respectively;
An arithmetic processing unit for calculating the distance and the speed of the object based on the values obtained from the first and second FFT circuits , wherein the local oscillation signal separates a transmission wave and hybridizes by 90 degrees.
Signals with 90 degrees phase difference
And the arithmetic processing unit is a triangular wave frequency of FMCW modulation.
The first and second FFT circuits during a sweep when the number is high
The sum of the opposite real and imaginary parts of, and the imaginary and real parts
And calculate the sum of
Processing to obtain the peak frequency and the FMCW modulation
At the time of sweeping when the triangular wave frequency becomes low, the first and second F
The difference between each opposing real and imaginary part of the FT circuit, and the imaginary part
Calculate the difference between
Processing to obtain the peak frequency by performing
Target based on each peak frequency obtained by
An FMCW radar apparatus characterized in that it is configured to calculate the distance and the speed of the vehicle. 2. A radar apparatus using FMCW modulation.
And split the received wave input into signals with 90 degrees phase difference
90 degree hybrid that waves,
Input the local oscillator signal and output the beat frequency signal
First and second mixers, and the first and second mixers.
A first and a second to Fourier transform the output of the mixer, respectively.
From the first and second FFT circuits.
An operation to calculate the distance and speed of the target object based on the obtained values
And an arithmetic processing unit, wherein the arithmetic processing unit performs FMCW modulation.
During the sweep in which the triangular wave frequency becomes high, the first and second
The sum of the opposing real and imaginary parts of the FFT circuit, and the imaginary number
Calculate the sum of the
Processing to obtain the peak frequency by performing
During the sweep in which the triangular wave frequency of CW modulation becomes low,
The difference between each opposing real and imaginary part of the second FFT circuit;
And the difference between the imaginary and real parts, respectively, and
To obtain the peak frequency by analyzing the spectrum of
Based on each peak frequency obtained by these processes.
This configured distance to the object, the calculation of the speed in the line Migihitsuji to have
An FMCW radar device characterized by the following .