JPH11271428A - Fm-cw radar apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an FM-CW radar apparatus in which a desired frequency modulation can be maintained when a change by aging exists, by a method wherein beat-signal frequency spectrums in every small section are compared and a control signal is corrected when the linearity of modulation at a transmitting signal collapses. SOLUTION: A voltage-controlled oscillator 11 outputs an oscillation frequency which is proportional to a control voltage given by a D/A converter 20. Electromagnetic waves are radiated from a transmitting antenna 13. A reflected wave signal from a target received by a receiving antenna 14 is mixed with a transmitted signal by a mixer 16, and the beat signal of both signals is fetched. An FFT processor 22 to which the signal is inputted generates the frequency spectrum of the beat signal between the up section and the down section of triangular waves. A correction device 23 finds and compares the Q value of a frequency spectrum A and that of a frequency spectrum B between a small section A and a small section B which are found by the FFT processor 22. The Q values are large in a region in which the linearity of a modulation is maintained, and they are small in a region in which the linearity collapses. As a result, when the Q value A < the Q value B (or the Q value A > the Q value B), the control voltage in the small section B (or A) is corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an FM-CW radar device.

[0002]

2. Description of the Related Art An FM-CW radar device is disclosed in
As disclosed in Japanese Patent Application Publication No. 72078, a continuous wave signal subjected to frequency modulation is transmitted as a transmission signal, and the transmission signal is reflected by a target object and mixed with the transmission signal to return to a beat. A signal is generated, and the position and relative speed of the target are detected from the frequency of the beat signal.

As a transmission signal generator in an FM-CW radar device, a voltage controlled oscillator (VCO) whose output frequency is controlled in accordance with a bias voltage is generally used. V
Since the relationship between the control voltage and the oscillation frequency in CO is known in advance, desired frequency modulation can be achieved by adjusting the control voltage.

Incidentally, the relationship between the control voltage and the oscillation frequency is often affected by the temperature. In the FM-CW radar device, generally, triangular wave modulation is often performed, and a beat signal is detected in a section where the modulation is performed linearly. It becomes impossible to accurately detect.

Therefore, in the technique disclosed in Japanese Patent Application Laid-Open No. Sho 62-177468, the relationship between the oscillation frequency and the control voltage is stored in advance in consideration of the influence of temperature, so that even if the temperature changes, the appropriate Frequency modulation.

[0006]

However, the relationship between the control voltage and the oscillation frequency, that is, the voltage-frequency characteristic is affected not only by the temperature but also by the number of years of use. Also,
The degree of change in characteristics due to temperature is not always the same for each VCO. Therefore, desired frequency modulation cannot be performed only by storing in advance the relationship between the control voltage and the oscillation frequency in consideration of only the influence of temperature as in the related art.

Further, it is conceivable to store the voltage-frequency characteristics in advance in accordance with aging and individual temperature changes based on the same technical idea as in the prior art, but this is not practical. .

[0008] The present invention is applied to the case where there is aging,
It is an object of the present invention to provide an FM-CW radar device that can maintain a desired frequency modulation even when the amount of temperature change differs for each.

[0009]

SUMMARY OF THE INVENTION An FM-CW radar apparatus according to the present invention transmits a frequency-modulated continuous wave signal as a transmission signal, and the transmission signal is reflected by a target object and returns. What is claimed is: 1. An FM-CW radar device for detecting a target from a beat signal frequency with a transmission signal, comprising: a voltage control type oscillator for outputting a transmission signal, wherein the output signal frequency changes in accordance with an applied voltage; Control means for applying a control voltage to the voltage-controlled oscillator so that a transmission signal subjected to linear frequency modulation is repeatedly output from the type oscillator, and time-division of the linear frequency modulation section into a plurality of small sections. Compare the beat signal frequency spectrum for each small section detected by the spectrum detection means that detects the beat signal frequency spectrum for each small section with the spectrum detection means. Characterized by comprising a correction means for correcting the control voltage in accordance with the result.

If the linearity of the modulation in the linear modulation area is maintained, the frequency spectrum of the beat signal detected in each small section in the linear modulation area matches. Conversely, if the linearity is broken, the beat signal frequency spectrum of each small section does not match. Therefore, by comparing the beat signal frequency spectrum for each small section, the state of maintaining the linearity of the modulation in the transmission signal can be detected,
If it is determined that the linearity is broken, the control voltage applied to the voltage-controlled oscillator is corrected, so that the linearity of the modulation in the transmission signal is always maintained.

When comparing the frequency spectrum of the beat signal, it is desirable to compare the Q value of the spectrum. In a small section in which the linearity of the modulation is high, the spectrum becomes sharp and the Q value becomes large. Therefore, if the control voltage is corrected in a small section in which the Q value of the spectrum is small, the linearity of the entire linear modulation region becomes high.

It is desirable to determine the direction of correction of the control voltage, that is, whether to perform the correction for increasing or decreasing the voltage, based on the magnitude of the beat signal frequency in each of the two selected small sections.

Further, when the beat signal frequency in one small section where the Q value of the frequency spectrum is small is smaller than the beat signal frequency in the other small section, control is performed to increase the transmission signal frequency in one small section. When the voltage is corrected and the beat signal frequency in one small section is higher than the beat signal frequency in the other small section, it is desirable to correct the control voltage in a direction to lower the transmission signal frequency in one small section.

With this correction, the linearity of the linear modulation region is maintained with high accuracy.

[0015]

FIG. 1 is a block diagram showing an embodiment of the present invention. The front-end unit 10 of the FM-CW radar device 1 includes a transmitting unit and a receiving unit, and the transmitting unit includes a voltage-controlled oscillator 11 and a buffer amplifier 12.
And a transmission antenna 13.

The voltage controlled oscillator 11 has a D / A (to be described later).
With the control voltage provided from the converter 20, the frequency f0
(For example, 76 GHz), a signal obtained by subjecting a carrier to triangular wave modulation with a frequency modulation width ΔF, ie, a frequency f0 ±
A modulated wave (transmission signal) of ΔF / 2 is output. The modulated wave is amplified by the buffer amplifier 12 and radiated from the transmission antenna 13 as an electromagnetic wave. Part of the transmission signal is provided to the mixer 16 of the reception unit as a local signal for reception detection.

The voltage-controlled oscillator 11 has an output oscillation frequency proportional to the control voltage.

FIG. 2 shows an oscillation frequency with respect to a control voltage of a general voltage-controlled oscillator. The horizontal axis represents the control voltage, and the vertical axis represents the oscillation frequency. The solid line 30 is a voltage-frequency characteristic curve of the voltage controlled oscillator. As can be seen from this figure, since the oscillation frequency changes linearly between F0 and F1 with respect to the control voltage between the control voltages V0 and V1, the oscillation frequency control is normally performed using this region.

However, the voltage-frequency characteristics may change depending on the temperature and the number of years of use, for example, as indicated by alternate long and short dash lines 31 and 32. Thus, if the voltage-frequency characteristics change from the initial state, normal modulation cannot be performed. However, in this embodiment,
Since the control voltage is corrected by a correction device described later, desired frequency modulation can be maintained.

The voltage-controlled oscillator 11 is supplied with a digital triangular wave signal generated by the triangular wave generator 24 and converted by the D / A converter 20 into an analog voltage signal. The triangular wave generator 24 outputs a triangular wave of a preset frequency and amplitude in digital form, but can appropriately correct the output waveform based on a command from the corrector 23.

The receiving section of the front end section 10 includes a receiving antenna 14, an RF amplifier 15, a mixer 16, an amplifier 17, and a filter 18. The transmission signal reflected by the target is received by the reception antenna 14 as a reception signal. After the received signal is amplified by the RF amplifier 15, it is mixed with the transmitted signal by the mixer 16, and the beat signal of both signals is extracted. The beat signal is output from the front end unit 10 via the amplifier 17 and the filter 18,
The signal is converted into a digital signal by the A / D converter 21 and input to the FFT processing device 22.

The FFT processing device 22 performs FFT processing in each of the up section and the down section of the triangular wave, and generates a frequency spectrum of a beat signal in each section. The frequency of the beat signal obtained here is input to the external processing device 25 and used for detecting a target.

That is, the following processing is performed in the external processing device 25. In the triangular wave modulation FM-CW system, the beat frequency when the relative speed is zero is fr, the Doppler frequency based on the relative speed is fd, the beat frequency in a section where the frequency increases (up section) is fb1, and the section in which the frequency decreases ( Assuming that the beat frequency in the down section is fb2, fb1 = fr-fd (1) fb2 = fr + fd (2) holds.

Therefore, if the beat frequencies fb1 and fb2 in the up and down sections of the modulation cycle are measured separately, fr and fd can be obtained from the following equations (3) and (4).

Fr = (fb1 + fb2) / 2 (3) fd = (fb2-fb1) / 2 (4) If fr and fd are obtained, the distance R and the velocity V of the target are calculated by the following (5) ( It can be obtained by equation (6).

R = (C / (4 · ΔF · fm)) · fr (5) V = (C / (2 · f0)) · fd (6) where C is the speed of light, and fm is FM modulation frequency.

FIGS. 3 (a), 3 (b) and 3 (c) show the transmission / reception frequency, beat signal frequency and beat when the voltage-frequency characteristic of the voltage controlled oscillator 11 is linear in a desired control voltage section, respectively. 5 is a waveform showing a signal spectrum. Here, for the sake of simplicity, the case where the relative speed of the target is zero is shown, and fb1 = fb2 = f
r.

FIGS. 4 (a), (b) and (c)
Are waveforms showing the transmission / reception frequency, the beat signal frequency, and the beat signal spectrum when the voltage-frequency characteristics of the voltage controlled oscillator 11 cannot maintain the linearity in the desired control voltage section due to the influence of temperature or the like. This figure also shows a case where the relative speed of the target is zero. As is apparent from comparison of FIG. 4A with the proper waveform shown in FIG. The frequency has been declining.
For this reason, the beat signal frequency which should originally take a uniform value as shown in FIG. 3B becomes non-uniform as shown in FIG. 4B. As a result, the FFT frequency spectrum becomes less sharp as shown in FIG. 4C than in FIG. 3C, and the position of the apex is shifted, so that an accurate beat signal frequency cannot be detected.

Therefore, such a state is detected by the correction device 23 and the control voltage is corrected, so that the linearity of the up and down sections of the modulated waveform is maintained.

In order to correct the control voltage by the correction device 23, the FFT processing device 22 performs an FFT process different from the FFT process for detecting a target. That is, F
The FT processing device 22 performs the FFT processing in each of the up section and the down section of the triangular wave modulation cycle for detecting the target as described above, but also corrects the control voltage for the voltage controlled oscillator 11. In order to do so, the up section or the down section is further time-divided into two small sections, and the FFT processing is also performed on each of the small sections A and B.

FIGS. 5 (a), 5 (b) and 5 (c) show the voltage-frequency characteristics of the voltage-controlled oscillator 11 as shown in FIG. Is a waveform showing a transmission / reception frequency, a beat signal frequency, and a beat signal spectrum when the frequency spectrum is no longer maintained. The up section is divided into two small sections A and B, and the FFT processing is performed on each of the divided sections. Has been generated.

The frequency spectrums A and B, which are the result of the FFT processing in the small sections A and B, are
The correction device 23 performs predetermined processing on the frequency spectra A and B, and issues a correction command to the triangular wave generator 24 based on the processing result.

FIG. 6 is a flowchart showing the operation of the correction device 23.

In step 61, the frequency spectrums A and B, which are the results of the FFT processing in the small sections A and B obtained by the FFT processing device 22, are fetched. In step 62, it is determined whether or not a target (target) exists using the frequency spectrum A or B captured in step 61. That is, if the peak value of the frequency spectrum A or B is equal to or less than a predetermined value,
It is determined that the target does not exist, and the process returns to step 61 without executing the following control voltage correction processing.

If it is determined in step 62 that the target is present, the flow advances to step 63 to determine how the frequency spectra A and B overlap. As described above, as long as the linearity of the modulation in the up section or the down section of the transmission signal is maintained, the frequency spectrums of the small sections in these sections are almost the same even if the FFT processing is performed. . Therefore, if the frequency spectra A and B are substantially the same, there is no need to correct the control voltage, and the correction processing in step 64 and subsequent steps is performed without performing the correction processing in step 64 and subsequent steps.
Return to 1. The frequency spectrums A and B are shown in FIG.
In the case where there is a deviation as shown in FIG.

In step 64, the frequency spectrum A
For each of B and B, the Q value indicating the sharpness of the spectrum waveform is obtained, and the two are compared. As already mentioned Q
The value is large in a region where the linearity of the modulation is maintained, and is small in a region where the linearity is broken.

In the example shown in FIG. 5, as shown in FIG. 5A, the linearity of the small section A is better maintained than that of the small section B. Therefore, as shown in FIG. In addition, the frequency spectrum in the small section A has a sharper waveform than the frequency spectrum in the small section B. Therefore, the Q value (A) of the frequency spectrum A is larger than the Q value (B) of the frequency spectrum B. In this case, the process proceeds to step 67 or 68 via step 66, and
Is corrected. Conversely, the Q value (B) is the Q value (A)
If it is larger, step 6 is performed to correct the small section A.
After step 5, go to step 69 or 70.

In steps 65 and 66, the frequencies (A) and (B) of the peak values of the frequency spectra A and B are
And are compared respectively. In step 66, FIG.
When the frequency (A) is higher than the frequency (B) as in (c), the transmission signal frequency in the small section B is lower than the ideal frequency as shown in FIG. The process proceeds to step 67 to raise the value, and outputs a plus correction command to the triangular wave generator 24 so that the output waveform gradually increases in the small section B.

On the other hand, if the frequency (A) is smaller than the frequency (B), the process goes to step 68 to output a minus correction command so that the output waveform of the triangular wave generator 24 gradually decreases in the small section B. I do.

By this correction, the linearity of the modulation in the small section B is restored. The amount of the correction may be appropriately selected. When the correction value is set to a small value, the desired correction can be finally achieved by repeating the correction a plurality of times.

In step 65, if the frequency (A) is higher than the frequency (B), the transmission signal frequency in the small section A is higher than the ideal frequency. Triangular wave generator 2
4, a minus correction command is output so that the output waveform gradually decreases in the small section A. If the frequency (A) is lower than the frequency (B), the process proceeds to step 70 and outputs a plus correction command so that the output waveform of the triangular wave generator 24 gradually increases in the small section A. This allows
The linearity of the modulation in the small section A is restored.

Although the present embodiment is a case of triangular wave modulation, the present invention can be applied to another modulation method in which linear modulation is repeated, for example, sawtooth modulation.

The case where the linear section is divided into two small sections of A and B has been described. However, the linear section is divided into three or more small sections, and the frequency spectrum in each small section is based on the same idea as in the present embodiment. The control voltage correction may be performed by performing processing based on the control voltage.

In the FFT processing unit 22, the FFT processing for control voltage correction and the FFT processing inherent in the radar apparatus are separately performed.
Predetermined arithmetic processing may be performed on the FT processing result, and the result may be used as the original FFT data of the radar device.

[0045]

As described above, the FM-C of the present invention
According to the W radar device, the state of maintaining the linearity of the modulation in the transmission signal is detected by comparing the beat signal frequency spectrum of each small section, and when it is determined that the linearity is broken, the voltage control type is used. Since the control voltage applied to the oscillator is corrected, the linearity of the modulation in the transmission signal is always maintained. Moreover, this correction can be achieved regardless of the reason why the linearity of the modulation is lost. That is, even if the linearity is lost due to the temperature, or if the linearity is lost due to aging, automatic correction is performed.
Therefore, the target is not lost or misidentified, and the detection accuracy of the FM-CW radar device can be maintained satisfactorily.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing voltage-frequency characteristics of a voltage controlled oscillator.

FIG. 3 is a waveform chart showing the operation of the FM-CW radar device of the embodiment.

FIG. 4 is a waveform chart showing the operation of the FM-CW radar device of the embodiment.

FIG. 5 is a waveform chart showing the operation of the FM-CW radar device of the embodiment.

FIG. 6 is a flowchart showing the operation of the correction device.

[Explanation of symbols]

1 ... FM-CW radar device, 10 ... Front end part,
11 voltage-controlled oscillator, 22 FFT processor, 23
... Correction device, 24 ... Triangular wave generator, 25 ... External processing device.

Claims (5)

[Claims] 1. A frequency-modulated continuous wave signal is transmitted as a transmission signal, and the target is determined based on a beat signal frequency of the reception signal and the transmission signal, the transmission signal being reflected by the target and returning. In the FM-CW radar device for detecting, a voltage-controlled oscillator for outputting the transmission signal, wherein an output signal frequency changes according to an applied voltage; and linear frequency modulation is repeatedly performed from the voltage-controlled oscillator. Voltage control means for applying a control voltage to the voltage-controlled oscillator so that the transmitted signal is output, and dividing the linear frequency modulation section into a plurality of small sections by time to obtain a beat signal frequency spectrum for each small section. Comparing the detected spectrum detecting means with the beat signal frequency spectrum for each of the small sections detected by the spectrum detecting means, and responding to the comparison result. FM-CW radar apparatus is characterized in that a correcting means for correcting the control voltage Te. 2. The FM-controller according to claim 1, wherein said correction means corrects the control voltage based on a magnitude of a Q value of a frequency spectrum of a beat signal in each of the small sections. CW radar device. 3. The method according to claim 1, wherein the correction means selects any two of the plurality of small sections, and corrects the control voltage of a small section having a small Q value of the frequency spectrum. The FM-CW radar device according to claim 2, wherein 4. The FM-CW according to claim 3, wherein the correction direction of the control voltage is determined based on the magnitude of the beat signal frequency of each of the two selected small sections.
Radar equipment. 5. The correction means according to claim 1, wherein the beat signal frequency of one of the two small sections having a smaller Q value of the frequency spectrum is lower than the beat signal frequency of the other small section. In this case, the control voltage is corrected in a direction to increase the transmission signal frequency of the one small section, and when the beat signal frequency of the one small section is larger than the beat signal frequency of the other small section, 5. The FM-CW radar device according to claim 4, wherein the control voltage is corrected so as to decrease a transmission signal frequency in the one small section.