JP2005164287A - Frequency modulation radar system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a frequency modulation radar system which can detect a target object, while maintaining proper linearity of the modulation, coping with the variation in the modulation characteristic of a voltage controlled oscillator. <P>SOLUTION: The system is provided with: a modulation voltage generation means 1 for indicating a controlled voltage V0(t) of the voltage controlled oscillator 2; a range information calculation means 7 for calculating the range information R and S on the basis of a beat signal Wb formed from a transmission wave W1 transmitted from the voltage controlled oscillator 2 and the reflected wave W2 from the target object; a modulation wave form estimation means 8 for estimating the modulation wave form from the beat signal Wb and the range information R and S; and a modulation voltage correction means 9 for correcting the controlled voltage on the basis of the modulation wave form. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a frequency modulation radar apparatus that is mainly mounted on a vehicle and measures an inter-vehicle distance, and particularly when the modulation characteristic of a voltage-controlled oscillator for generating a transmission wave changes, the linearity of the modulation waveform is improved. The present invention relates to a frequency modulation radar apparatus capable of correcting a frequency modulation width while maintaining the frequency modulation width.

In general, an FMCW (Frequency Modulated Continuous Wave) radar applied to an inter-vehicle distance measurement device or the like is well known.
In a frequency modulation radar device using FMCW radar, based on a beat signal formed by a transmission wave and a reflected wave, distance information about the target object (an inter-vehicle distance from the host vehicle to the target object, a target object relative to the host vehicle, and the like). Relative speed) is calculated.

Usually, the distance measurement value R is calculated by the following equation using the frequency (hereinafter referred to as “beat frequency”) fb of the detected beat signal, the constant K, and the modulation frequency width B.
R = fb · K / B
Here, since the constant K and the modulation frequency width B are designed to be predetermined values in advance, the distance measurement value R can be calculated simultaneously with the detection of the beat frequency fb, but the temperature of the voltage-controlled oscillator that generates the transmission wave. It is known that the frequency modulation width B changes from a predetermined value for reasons such as change and secular change.

Therefore, in order to solve the problems such as temperature change and secular change, a frequency modulation radar apparatus configured to detect a change in the frequency modulation width B and correct the voltage waveform applied to the voltage controlled oscillator has been proposed. (For example, refer to Patent Document 1).
In this case, the distance measurement value R calculated from the beat signal is input to the distance change detection means, and the amount of change ΔR1 of the distance measurement value R over a predetermined time is calculated.

At this time, as described above, the distance measurement value R becomes a different value from the actual value when the frequency modulation width B changes. Therefore, the change amount ΔR1 based on the distance measurement value R also varies with the change of the frequency modulation width B. It may be different from the actual value.
On the other hand, the relative speed measurement value S between the host vehicle and the target object calculated based on the beat signal is input to the relative speed integration means, and the integrated value ΔR2 of the relative speed measurement value S at the same time as the predetermined time is used. calculate. Here, the relative velocity measurement value S can be calculated without depending on the frequency modulation width B.

  Therefore, in the conventional frequency modulation radar apparatus, the change amount ΔR1 depending on the change of the frequency modulation width B and the integral value ΔR2 independent of the change of the frequency modulation width B as the change amount of the distance from the own vehicle to the target object. The frequency modulation width B is corrected by calculating the difference value (ΔR1−ΔR2) of each change amount and controlling the modulation voltage so that the difference value becomes “0”. ing.

JP 2002-82164 A

In the conventional frequency modulation radar apparatus, when the relative speed of the target object with respect to the host vehicle is “0”, ΔR1 = ΔR2 = 0 regardless of the change in the frequency modulation width B, and the difference value (ΔR1−ΔR2) is obtained. Since it is always “0”, there is a problem that the frequency modulation width B cannot be corrected.
In addition, when the linearity of the modulation characteristic of the voltage controlled oscillator changes due to a change in temperature or aging, the frequency modulation width B does not necessarily change even if the linearity of the modulation characteristic changes. In the conventional frequency modulation radar device, the linearity of the modulation characteristic cannot be corrected, and particularly when the frequency of the beat signal is analyzed, the frequency spectrum representing the detection result of the target object is not sharp, Since the peak level of the frequency spectrum is lowered, there is a problem that the frequency detection performance is deteriorated.

  The present invention has been made to solve the above-described problem. When the modulation characteristic of the voltage controlled oscillator changes, the frequency modulation width can be corrected while keeping the linearity of the modulation waveform good. It is an object of the present invention to obtain a frequency modulation radar device that can be used.

  The frequency modulation radar apparatus according to the present invention includes a voltage-controlled oscillator that generates a transmission wave, an antenna that transmits the transmission wave and receives a reflected wave from a target object, and a beat signal obtained by mixing the transmission wave and the reflected wave. A modulation voltage generating means for instructing a control voltage applied to the voltage controlled oscillator, a distance information calculating means for calculating distance information about the target object based on the beat signal, a beat signal and distance information A modulation waveform estimating means for estimating the modulation waveform of the transmission wave based on the modulation waveform, and a modulation voltage for correcting the control voltage output from the modulation voltage generating means to the voltage controlled oscillator based on the modulation waveform estimated by the modulation waveform estimation means And a correcting means.

  According to the present invention, when the modulation characteristic of the voltage controlled oscillator changes, the frequency modulation width can be corrected while keeping the linearity of the modulation waveform good.

Embodiment 1 FIG.
1 is a block diagram showing a frequency modulation radar apparatus according to Embodiment 1 of the present invention.
In FIG. 1, the frequency modulation radar apparatus includes a modulation voltage generation unit 1, a voltage controlled oscillator 2, a directional coupler 3, a transmission antenna 4, a reception antenna 5, a mixer 6, and a distance information calculation unit 7. , A modulation waveform estimation means 8 and a modulation voltage correction means 9 are provided.

The modulation voltage generating means 1 instructs a modulation voltage (control voltage) V0 (t) applied to the voltage controlled oscillator 2, and the voltage controlled oscillator 2 transmits a transmission wave signal modulated based on the control voltage V0 (t). Is generated.
The directional coupler 3 distributes power of the transmission wave signal generated from the voltage controlled oscillator 2 to the transmission antenna 4 and the mixer 6.

The transmission antenna 4 radiates a transmission wave W1 based on the transmission wave signal, and the reception antenna 5 receives a reflected wave W2 from a target object (not shown). In addition, each antenna 4 and 5 may be comprised integrally as a transmission / reception antenna, and in this case, the whole apparatus can be reduced in size.
The mixer 6 mixes the transmission wave W1 and the reflected wave W2 to form a beat signal Wb.
The distance information calculation unit 7 calculates distance information regarding the target object based on the beat signal Wb.

  The distance information includes a distance measurement value (hereinafter also simply referred to as “distance”) R from the antennas 4 and 5 to a target object, and a target object relative velocity measurement value S (hereinafter simply referred to as “distance”) R and the antennas 4 and 5. Also referred to as “relative speed”.

The modulation waveform estimation means 8 estimates the modulation waveform of the transmission wave W1 based on the beat signal Wb and the distance information R and S.
The modulation voltage correction unit 9 corrects the control voltage V0 (t) output from the modulation voltage generation unit 1 to the voltage controlled oscillator 2 based on the modulation waveform estimated by the modulation waveform estimation unit 8.

Specifically, the modulation waveform estimation means 8 divides the beat signal Wb into a predetermined number of sections, performs frequency analysis for each section, and estimates the modulation waveform based on the result of the frequency analysis.
The modulation waveform estimation means 8 approximates the time differential value of the modulation waveform by a polynomial.

The modulation voltage generator 1 stores in advance a modulation voltage V0 (t) at each time t corresponding to the modulation characteristics of the voltage controlled oscillator 2, and the modulation voltage correction means 9 stores the modulation voltage V0 ( The time differential value dV0 / dt of t) may be stored.
Further, only the time differential value dV0 / dt of the modulation voltage V0 (t) is stored in the modulation voltage correction means 9, and the modulation voltage generation means 1 does not store the modulation voltage V0 (t). Alternatively, the modulation voltage V0 (t) may be generated by performing an integration operation of the time differential value dV0 / dt.

Next, the operation according to the first embodiment of the present invention shown in FIG. 1 will be described with reference to FIG.
FIG. 2 is an explanatory diagram showing the time change of the oscillation frequency f (t) of the transmission wave W1.
As shown in FIG. 2, the modulation voltage V0 (t) is set so that the modulation frequency width becomes B and the oscillation frequency f (t) changes linearly during the modulation time T. ing. In other words, it is assumed that the modulation characteristic as represented by the following formula (1) is set.

However, in equation (1) and FIG. 2, time t0 is a modulation start time at which the oscillation frequency f (t) increases as time t elapses.
Incidentally, regarding the modulation period (t0 + T ≦ t ≦ t0 + 2T) in which the oscillation frequency f (t) decreases according to the time t, the right side of the equation (1) is replaced with “−B / T”, and the following completely follows. Since it can be considered similarly, detailed description is omitted.

First, the modulation voltage V0 (t) generated by the modulation voltage generating means 1 is applied to the voltage controlled oscillator 2, and a transmission wave signal having a modulation waveform according to FIG.
However, as described above, it should be noted that the desired modulation waveform represented by the expression (1) may not be obtained due to the temperature change or aging change of the voltage controlled oscillator 2.
That is, it is considered that the actual oscillation frequency (transmission frequency) f1 (t) at each time t is generally slightly different from the set linear oscillation frequency f (t). Also, the frequency modulation width B1 that is actually output is generally considered to be different from the desired frequency modulation width B.

The transmission wave signal (modulated wave) output by the voltage controlled oscillator 2 is power-distributed by the directional coupler 3, one of which is input to the transmission antenna 4 as a transmission wave W1, and the other to the mixer 6 as a local signal. Entered.
The transmission wave W1 input to the transmission antenna 4 is radiated toward the target object, reflected by the target object, received by the reception antenna 5 as a reflected wave (reception wave) W2, and further input to the mixer 6. .

The mixer 6 mixes the transmission wave (local signal) W1 and the reflected wave W2 to generate a beat signal Wb, and inputs this to the distance information calculation means 7 and the modulation waveform estimation means 8.
The mixer 6 may be provided with a low-pass filter or the like, thereby suppressing unnecessary high-frequency components generated by the mixing action of the transmission wave W1 and the reflected wave W2.

Subsequently, the distance information calculation means 7 first performs frequency analysis processing such as FFT (Fast Fourier Transform) on the beat signal Wb, thereby detecting beat frequencies fbu and fbd in each modulation period.
Here, fbu is a beat frequency in a modulation period (t0 ≦ t ≦ t0 + T) in which the frequency fb (t) increases with the passage of time t, and fbd has a frequency fb (t with the passage of time t. ) Is a beat frequency in a modulation period (t0 + T ≦ t ≦ t0 + 2T) in which the value falls.

Based on the beat frequencies fbu and fbd detected in this way, the distance information calculation means 7 follows the calculation method of the distance R and the relative speed S in a general FMCW radar (for example, see Japanese Patent Application Laid-Open No. 11-271429). Distance information (distance R and relative speed S) for the target object is calculated.
That is, the distance measurement value R is calculated by the following equation (2).

In Equation (2), c is the speed of light, and td is the delay time from when the transmission wave W1 is reflected by the target object until it is received.
Further, the delay time td is expressed by the following equation (3) using the modulation time T, the frequency modulation width B, and the beat frequencies fbu and fbd.

  On the other hand, the relative speed measurement value S is calculated by the following equation (4).

However, in Formula (4), fd is a Doppler frequency generated by the relative speed S with respect to the target object, and fc is the center frequency of the transmission wave W1.
Further, the Doppler frequency fd is expressed as the following equation (5) using the beat frequencies fbu and fbd.

The relative velocity measurement value S and the Doppler frequency fd are expressed as “negative values” when the target object is relatively close.
The distance measurement value R and the relative speed measurement value S thus calculated are output from the distance information calculation means 7 to an external device (not shown) as a distance information signal (distance signal and speed signal) relating to the target object. .
Further, the delay time td and the Doppler frequency fd are input to the modulation waveform estimation means 8 in order to contribute to the correction process (described later) of the modulation voltage V0 (t).

Next, the modulation waveform estimation operation by the modulation waveform estimation means 8 will be specifically described with reference to FIGS. 3 and 4.
FIG. 3 is a waveform diagram showing the modulation voltage V0 (t) of the beat signal Wb, and FIG. 4 is an explanatory diagram showing the time change of the beat frequency fb (t).

In FIG. 3, the beat signal Wb of the modulation time T generated by the mixer 6 is divided into a predetermined number (for example, four).
FIG. 4 shows the beat frequencies fb1 to fb4 of the beat signal divided into four. Also, in FIG. 4, the straight line connecting the beat frequencies fb1 to fb4 (see the alternate long and short dash line) is the result of approximating the beat frequency fb (t) with a polynomial, and here, linear approximation (primary polynomial) was used. Shows the case.

The modulation waveform estimation means 8 first divides the beat signal Wb into four equal parts every time T / 4 as shown in FIG. 3, and then performs frequency analysis on each of the divided beat signals.
At this time, as shown in FIG. 4, the time change of the beat frequency fb (t) within the modulation time (observation time) T is calculated.
Here, it is defined that the time change of the beat frequency fb (t) derived as indicated by the alternate long and short dash line in FIG. 4 is expressed by the following equation (6) using the slope α and the intercept β. .

However, in Equation (6), the slope α and the intercept β are calculated by the least square method or the like based on the beat frequencies fb1 to fb4.
At this time, if the modulation waveform of the actual transmission wave W1 is modulated without losing linearity, the beat frequency Wb has no inclination within the modulation time T, the inclination α is “0”, and the intercept β Needless to say, becomes a constant value.

  Further, it is assumed that the actual oscillation frequency (transmission frequency) f1 (t) is expressed as the following equation (7) as a second-order polynomial with respect to time t.

However, in Formula (7), a2 and a1 are constants for each order.
In addition, the degree of the polynomial represented by Expression (7) is “degree on the right side” + “1” in Expression (6), that is, “2”.
At this time, it is needless to say that the constant a2 is “0” if the transmission wave W1 is modulated without losing linearity.

On the other hand, the reception frequency f2 (t) of the reflected wave W2 from the target object is the delay time td from when the transmission wave W1 having the oscillation frequency f1 (t) is radiated until it is reflected by the target object and received again. It is a delayed signal and has a frequency obtained by adding the Doppler frequency fd generated by the relative speed S to the target object.
Therefore, the reception frequency f2 (t) of the reflected wave W2 is expressed as the following formula (8).

  Further, since the beat frequency fb (t) is represented by the difference between the transmission frequency f1 (t) and the reception frequency f2 (t), the following equation (9) is used using the equations (7) and (8). ) And is easily calculated.

  Further, by comparing the equation (9) with the above equation (6), the relationship of the following equation (10) is established with respect to the slope α and the intercept β.

  By simultaneously solving the equation (10), the constants a2 and a1 are calculated as the following equation (11).

In other words, the modulation waveform estimation means 8 calculates the time change information (α, β) of the beat frequency fb (t) estimated based on the divided beat signal and the delay time td calculated by the distance information calculation means 7. Using the Doppler frequency fd, the constants a2 and a1 of the modulation waveform of the actual transmission frequency f1 (t) are calculated as in the above equation (11).
The constants a2 and a1 calculated in this way are input to the modulation voltage correction means 9 as estimated modulation waveform information.

Next, the operation of correcting the modulation voltage by the modulation voltage correction means 9 will be specifically described.
The modulation voltage correction means 9 corrects the modulation voltage based on the modulation waveform information (a2, a1) estimated by the modulation waveform estimation means 8 so that the linearity of the modulation waveform and the frequency modulation width B are properly maintained. .

  As described above, the modulation voltage correcting means 9 stores the time differential value dV0 / dt of the modulation voltage V0 (t), and the modulation voltage V0 (t) obtained by integrating the time differential value dV0 / dt is the modulation voltage. A transmission wave signal (modulated wave) is oscillated by being applied from the correction means 1 to the voltage controlled oscillator 2.

  Here, when the modulation characteristic of the voltage controlled oscillator 2 is expressed by df / dV, the time differential value df1 / dt of the actually oscillated transmission frequency f1 (t) is described by the relationship of the following equation (12). The

  Therefore, the modulation characteristic df / dV of the voltage controlled oscillator 2 is expressed by the following equation (13) using the equation (12) and the above equation (7).

  As a result, an appropriate time differential value dV1 / dt of the modulation voltage V1 (t) for obtaining the desired modulation characteristic df / dt given by the above-described equation (1) is expressed by the following equation (14). Fulfill.

  As a result, an appropriate time differential value dV1 / dt of the modulation voltage V1 (t) according to the modulation characteristic of the voltage controlled oscillator 2 is expressed by the following equation (15) using the above equations (13) and (14). Is calculated by

  Thus, the modulation voltage correction means 9 uses the modulation waveform information (a2, a1), the desired frequency modulation width B, and the modulation time (observation time) T as shown in the above equation (15). The time differential value dV0 / dt of the modulation voltage V0 (t) stored in advance is updated to the new time differential value dV1 / dt of the new modulation voltage V1 (t) after correction.

  Although the time change of the beat frequency fb (t) is approximated as a first order polynomial here, the beat frequency fb (t is calculated using a second or higher order polynomial from the viewpoint of improving accuracy with respect to a complicated change in modulation sensitivity. ) May be approximated.

Further, the beat signal Wb is divided into four to detect the time change of the beat frequency fb (t), but the number of divisions of the beat signal Wb is larger than the order of the polynomial that approximates the time change of the beat frequency fb (t). Any number can be set.
Although the beat signal Wb is equally divided, the method of dividing the beat signal Wb is not limited to the method of equally dividing the modulation time (observation time) T.

  Further, the beat signal Wb for the modulation period in which the beat frequency fb (t) increases with the lapse of time t has been described. However, for the modulation period in which the beat frequency fb (t) decreases with the lapse of time t. Even if the beat signal W is used, it can be similarly applied to the correction of the modulation voltage V0 (t), and it is needless to say that the same effect can be obtained.

  Further, the correction of the modulation voltage V0 (t) for the FMCW radar has been described. However, the present invention is not limited to the FMCW radar, and the distance R and the relative frequency are compared using the same frequency modulation while emitting the transmission wave W1 in a pulse shape. Needless to say, the present invention can also be applied to a radar that detects the speed S and has the same effect.

As described above, the relative speed S is detected by detecting the time change of the beat frequency fb (t), estimating the actual modulation waveform, and correcting the modulation voltage V0 (t) using the estimated modulation waveform. Even when “0” is “0”, the modulation voltage V0 (t) can be corrected, and the target object can be detected well.
Further, even when the linearity of the modulation waveform changes, it is possible to correct the modulation voltage V0 (t) satisfactorily, and the distance information (the target object) regarding the target object can be corrected with high accuracy and without deteriorating the detection performance. The distance R to the object and the relative speed S) of the target object can be detected.

  In addition, the beat signal Wb is divided into a predetermined number of sections, frequency analysis is performed for each section, and the modulation waveform is estimated based on the frequency analysis result. Correction for holding is possible, and the target object can be detected without impairing the detection performance.

  Further, by approximating the time differential value dV0 / dt of the modulation waveform with a polynomial, it becomes possible to estimate the modulation characteristic by eliminating the influence of noise, and the correction of the modulation voltage V0 (t) is an analytical method. Therefore, the modulation voltage V0 (t) can be corrected with higher accuracy.

1 is a block diagram showing a frequency modulation radar apparatus according to Embodiment 1 of the present invention. It is explanatory drawing which shows the time change of the oscillation frequency of the transmission wave by Embodiment 1 of this invention. It is a wave form diagram which shows the beat signal produced | generated from the mixer by Embodiment 1 of this invention. It is explanatory drawing which shows the time change of the beat frequency by Embodiment 1 of this invention.

Explanation of symbols

  1 modulation voltage generation means, 2 voltage controlled oscillator, 3 directional coupler, 4 transmission antenna, 5 reception antenna, 6 mixer, 7 distance information calculation means, 8 modulation waveform estimation means, 9 modulation voltage correction means, C beat frequency Approximate curve of time change, f (t) oscillation frequency, fb1 to fb4 Each beat frequency of the divided beat signal, R distance measurement value, S relative velocity measurement value, V0 (t) modulation voltage (control voltage), W1 transmission Wave, W2 reflected wave (received wave), Wb beat signal.

Claims (5)

A voltage controlled oscillator for generating a transmission wave signal;
An antenna for radiating a transmission wave based on the transmission wave signal and receiving a reflected wave from a target object;
A mixer for mixing the transmission wave and the reflected wave to form a beat signal;
Modulation voltage generating means for indicating a control voltage applied to the voltage controlled oscillator;
Distance information calculating means for calculating distance information about the target object based on the beat signal;
Modulation waveform estimation means for estimating a modulation waveform of the transmission wave based on the beat signal and the distance information;
A frequency modulation radar apparatus comprising: a modulation voltage correction unit that corrects a control voltage output from the modulation voltage generation unit to the voltage controlled oscillator based on the modulation waveform estimated by the modulation waveform estimation unit.   The modulation waveform estimation means divides the beat signal into a predetermined number of sections, performs frequency analysis on each section, and estimates the modulation waveform based on a result of the frequency analysis. The frequency modulation radar device according to 1.   The frequency modulation radar apparatus according to claim 1, wherein the modulation waveform estimation unit approximates a time differential value of the modulation waveform by a polynomial. The antenna is
A transmission antenna that radiates a transmission wave based on the transmission wave signal;
The frequency modulation radar apparatus according to claim 1, further comprising: a receiving antenna for receiving a reflected wave from the target object.   The frequency modulation radar apparatus according to any one of claims 1 to 3, wherein the antenna is configured by an integral transmission / reception antenna.

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