CN115047484B

CN115047484B - Radar ranging method

Info

Publication number: CN115047484B
Application number: CN202210690649.5A
Authority: CN
Inventors: 张涛; 邹进贵
Original assignee: Wuhan University WHU
Current assignee: Wuhan University WHU
Priority date: 2022-06-17
Filing date: 2022-06-17
Publication date: 2024-06-14
Anticipated expiration: 2042-06-17
Also published as: CN115047484A

Abstract

The invention relates to a radar ranging method. Comprising the following steps: performing primary measurement based on a frequency modulation continuous wave ranging principle, performing Fourier transform on measurement data to obtain a coarse precision distance obtained in an echo signal, and obtaining a corresponding primary phase value; performing second measurement based on the frequency modulation continuous wave ranging principle, and obtaining a corresponding second phase value after performing Fourier transformation on the measurement data; and obtaining a phase difference by differencing the first phase value and the second phase value, and obtaining precision coefficients of precise absolute distance=coarse precision distance data+phase difference. Wherein the wavelength required to satisfy the frequency difference of the two measurements is equal to twice the FFT well resolution. The accuracy of the absolute distance of the target can be improved by more than two orders of magnitude after the two measurements only by skillfully designing the radar frequency for the two measurements, namely, the accuracy from the original centimeter level to the meter level is improved to sub-millimeter, so that the requirement of remote modeling can be met, and the deformation monitoring of the target can be performed.

Description

Radar ranging method

Technical Field

The invention relates to a ranging method, in particular to a radar ranging method.

Background

The microwave radar has long acting distance, good penetrability and wide acting range. For fm continuous wave radar, the absolute distance is generally obtained by fourier transforming an original sample of a set of intermediate frequency data, and the accuracy of this absolute distance depends on the maximum unblurred distance and the length of the result after fourier transformation, in fact, the final implementation is on the sweep bandwidth of the electromagnetic wave used, i.e. the distance resolution r=c/2B, C is the speed of light, and B is the sweep bandwidth. Current microwave radar bandwidths are typically tens of megahertz to several gigahertz, so the absolute range accuracy is in the order of centimeters to meters. Although the ranging accuracy can be improved by improving the scanning bandwidth, this effect is extremely limited by technical restrictions such as limitation of electromagnetic wave resources, limitation of devices, limitation of antennas, and the like.

Although the absolute ranging accuracy of the microwave radar is limited, the absolute ranging accuracy can only reach the centimeter level generally, the microwave radar can realize the relative displacement measurement with the sub-millimeter level or even higher accuracy through an interference technology. This benefits from the phase information contained in the echo signals.

Assuming a wavelength of 10 cm for radar, modern digital processing techniques are readily capable of obtaining phase information with an accuracy better than 0.2 degrees (about 0.0035 radians), and thus a relative displacement accuracy better than 10 x 0.2/360=0.0056 cm. However, in the prior art, the measurement accuracy is limited to measuring relative displacement and is not used for measuring absolute distance. Because the phase information in the echo signal has a wrapping phenomenon (or phase ambiguity), it cannot be directly used to measure the absolute distance of the target.

Disclosure of Invention

The invention mainly solves the technical problems existing in the prior art; the method is easy to implement, can effectively improve the absolute distance measurement precision of the microwave radar, changes the condition that the microwave radar is difficult to accurately measure the absolute distance, and can generate a precise point cloud by matching with the imaging radar. The radar ranging method can be widely applied to aspects such as target displacement monitoring, target precise model establishment and the like.

The technical problems of the invention are mainly solved by the following technical proposal:

a radar ranging method, comprising:

Performing primary measurement based on a frequency modulation continuous wave ranging principle, performing Fourier transform (FFT) on measurement data to obtain a coarse precision distance obtained from an echo signal, and obtaining a corresponding primary phase value;

Performing second measurement based on the frequency modulation continuous wave ranging principle, and obtaining a corresponding second phase value after performing Fourier transformation on the measurement data;

And obtaining a phase difference by differencing the first phase value and the second phase value, and obtaining precision coefficients of precise absolute distance=coarse precision distance data+phase difference.

Wherein the wavelength required to satisfy the frequency difference of the two measurements is equal to twice the FFT well resolution. In the radar ranging method, the wavelength of the electromagnetic wave used in the first measurement is L1, the frequency is F1, the sweep bandwidth is B, the phase of the frequency is W1, the coarse ranging resolution Rc=C/2B, C is the light speed, and the target distance is D;

The first FFT is performed on the measured data, and then the target falls into the FFT well with sequence number INT (D/Rc), the target falls into the FFT well with distance D _coarse =int (D/Rc) x Rc, and the first phase value W1 at the FFT transformation well of INT (D/Rc).

In the radar ranging method, the electromagnetic wave with the wavelength of L2 is used for the second measurement, and the data of the second measurement is subjected to the second FFT to obtain the second phase W2 at the INT (D/Rc) FFT trap of the FFT data of the second measurement result.

In the radar ranging method, the wavelength satisfying the frequency difference between the two measurements is equal to twice the resolution of the FFT trap, i.e. L1-l2= (l1×l2×b)/C, or L2-l1= (l1×l2×b)/C.

In one radar ranging method described above, the wavelength satisfying the frequency difference of the two measurements is equal to twice the FFT well resolution, i.e., C/(F1-F2) =c/B, or C/(F2-F1) =c/B. In the above radar ranging method, the precision coefficient includes a circumference ratio Pi, a light speed C, and a sweep bandwidth B, and the accurate absolute distance is based on an entire number of circles N when the wavelength is C/B and D is measured, where the difference between the wavelengths measured by C/B is:

When N is even, d=d _coarse + (W1-W2) ×c/2B)/Pi

When N is an odd number, d=d _coarse + (2 (W1-W2) -1) (C/2B)/Pi

Wherein D _coarse is obtained by FFT of the first measurement data, W1-W2 is obtained by phase difference of two measurements, C is constant of light velocity, and B is bandwidth.

Therefore, the invention has the following advantages: the accuracy of the absolute distance of the target can be improved by more than two orders of magnitude after the two measurements only by skillfully designing the radar frequency for the two measurements, namely, the accuracy from the original centimeter level to the meter level is improved to sub-millimeter, so that the requirement of remote modeling can be met, and the deformation monitoring of the target can be performed.

Drawings

FIG. 1 is a schematic diagram of a method of the present invention;

Detailed Description

The technical scheme of the invention is further specifically described below through examples and with reference to the accompanying drawings.

Examples:

The method adopts the method of inter-frequency multi-time measurement, is based on the frequency modulation continuous wave technology, obtains coarse precision distance information by measuring echo signals once, and obtains the accurate absolute distance of the target by extracting the phase of the inter-frequency signals. By using the method, the distance of all observable targets in the visual angle can be measured at one time, the precision is determined by the phase resolution of the radar, and generally, the distance can be easily better than 0.1mm.

1. First, the principle is described with reference to a non-imaging real aperture radar.

Assuming that the wavelength of the electromagnetic wave used for the first measurement is L1, the frequency is F1, the target distance is D, and the sweep bandwidth is B, the coarse ranging resolution rc=c/2B, C is the speed of light. And performing FFT on the measured data, wherein the serial number of the FFT well in which the target falls is INT (D/Rc), namely, the target falls into the FFT well with the distance of D _coarse =INT (D/Rc) and D _coarse is the coarse precision value of the absolute distance. What we require is D, the difference between it and D _coarse is:

ds=d-D _coarse =d-INT (D/Rc) ×rc, and the exact distance D of the target can be known by finding Ds.

At this time, at the FFT well of INT (D/Rc), the phase value W1 at this point can be obtained.

In order to obtain Ds, a second measurement is performed, and the electromagnetic wave used at this time has a wavelength of L2 and a frequency of F2 satisfying the requirement

L1-l2= (L1 x L2 x B)/C, or L2-l1= (L1 x L2 x B)/C, which are not different, but the order of L1 and L2 is different, which is basically such that the wavelength of the frequency difference of the two measurements is equal to twice the FFT well resolution, in engineering practice, an equivalent formula can be used, namely:

C/(F1-F2) =C/B, or C/(F2-F1) =C/B

The frequency can be converted after simplification, and in fact, f2=f1+b or f1=f2+b is the case.

It should be noted that according to the conventional ranging concept, the wavelength of the frequency difference between the two measurements should be made to coincide with the resolution of the FFT trap. However, this implementation has a certain technical obstacle, and the bandwidth requirements on the radar frequency synthesis range and the radio frequency power amplifier, the low noise amplifier, the antenna and the like are too high. By adopting the scheme, the technical difficulty is greatly reduced, and the correct residual phase can be obtained by only adding an odd-number period compensation step in the later calculation.

The swept bandwidth of the second measurement is still B.

Since the bandwidth used for the second measurement is B for the first measurement, after the second measurement is FFT, the target still falls into the FFT bin at a distance of D _coarse =int (D/Rc) ×rc. However, since the wavelengths used for the two measurements are different, at the INT (D/Rc) FFT trap of the FFT data of the second measurement result, the phase W2 is not equal to W1, and the phase difference W1-W2 between W1 and W2 is the phase of the difference between the frequencies used for the first measurement and the second measurement, since the difference between the wavelengths of the two measurements is C/B, that is, twice the FFT distance resolution, there is:

D= (n+nd) ×c/2b=n×c/2b+nd×c/2b, N is the number of whole cycles when D is measured at wavelength C/B, is a natural number, nd is the number of remaining cycles when D is measured at wavelength C/B, and is a fraction of 0 or more and less than 1.

Conventionally, we can only get the number of Nd remaining cycles, while N is ambiguous and cannot be measured directly. Nd is the number of remaining cycles measured with the wavelength C/B as the measuring scale, and W1-W2 is the phase of the difference between the frequencies used for the first measurement and the second measurement, nd=w1-W2 since the difference between the two measurements is C/B.

Since the first measurement has been used before, the rough distance D _coarse of the target is obtained by FFT, whereas the resolution of D _coarse (FFT well resolution) is C/2B, and we set the wavelength of the frequency difference used for the two measurements to be the C/B relationship, therefore:

N*C/2B＝D_coarse

Since the resolution of the FFT trap is twice the wavelength of the frequency difference, when N is even, the phase difference of the frequency difference can be directly used to calculate the exact distance, and when N is odd, the phase difference of the frequency difference needs to be compensated for an odd period, and the number of compensated periods is nd×2-1.

In combination with all of the above, it is possible to obtain when N is even:

D＝D_coarse+(W1-W2)*(C/2B)/Pi

when N is an odd number:

D＝D_coarse+(2*(W1-W2)-1)*(C/2B)/Pi

(wherein Pi is the circumferential rate)

Wherein D _coarse is obtained by FFT of the first measurement data, W1-W2 is obtained by phase difference of two measurements, C is constant of light velocity, pi is constant of circumference ratio, and B is bandwidth, which is a known quantity set by people. Thus, the accurate distance of the target is obtained.

If a plurality of targets exist in the received reflected signal, the received reflected signal can be processed respectively according to the method to obtain the accurate distances of the targets respectively.

In the following, by way of illustration, for convenience of description, it is illustrated that the difference frequency wavelength of the two measurements is equal to the FFT-well resolution. O1 and O2 are observation targets. The abscissa is FFT trap (FFT Bins), which is the ranging accuracy achieved by the common radar, and the length of each grid is Rc=C/2B, wherein B is the sweep bandwidth, and C is the light speed. After the original signal is subjected to FFT, two peaks appear at FFT Bins and FFTBins, corresponding to target O1 and target O2, respectively. The rough coordinates of the targets O1 and O2 are 3 and 7, respectively. The waveforms shown at W1-W2 are waveforms of the difference frequency of the two measurements. Since the wavelength of the frequency difference between the two measurements is C/B at the time of design, the phase portion in the FFT result of the data of the two measurements is subtracted, and the phase difference at the FFT well where the target is located reflects Nd of the target, nd1 and Nd2 for the O1 and O2 targets, respectively.

In short, it is a ruler used in measurement, the large lattice scale of which is the FFT trap of the single measurement, and the fine small scale is the phase difference of the two measurements.

Since FFTBins has limited distance resolution, the result of FFT falls on n FFT Bins for all targets (n is a natural number) with distances between n×rc and (n+1) ×rc. And the phase difference of O1 from this position is Nd1.

For imaging radars (such as synthetic aperture radars), only the processed data source is changed from FFT results to complex images, that is, the data processed by non-imaging radars is measured data of two times, namely, the data processed by the imaging radars are respectively a one-dimensional array of FFT results, the data processed by the imaging radars are complex images imaged twice with different frequencies and are two-dimensional arrays, and the processing methods are not different.

Finally, because of some delay in signal transmission and processing, it is necessary to measure the true value of the range by other means (e.g., a calibrated laser range finder) to obtain the systematic error of the radar for correction.

2. Specific example 1 using the above method is described below.

The embodiment adopts a precise ranging real-aperture linear frequency modulation radar ranging method.

The first measurement sweep frequency ranges from 10GHz to 10.3GHz

Center frequency f1=10.15 GHz, center wavelength l1=c/f1= 0.02055665m

Bandwidth b=10.3-10=10.6-10.3=0.3 GHz

FFT well resolution rc=c/2b=0.5m

The second measurement frequency of frequency sweep f2=f1+b=10.45 GHz, frequency sweep range is 10.3GHz-10.6GHz

The frequency difference between the two measurements was b=0.3 GHz, corresponding to a wavelength of 1.0m.

The first measurement is carried out by using the frequency F1 to obtain an original data array R1, and FFT is carried out on the obtained original data R1 to obtain a rough distance information array T1.

Each amplitude peak in the T1 array indicates a target echo at the FFT-well. The peaks are found in array T1, each peak representing a target.

Searching Index (position) Index of each peak in the T1 array, and then roughly separating the corresponding target from the Index is:

D_coarse＝Index*0.5

And carrying out second measurement by using the frequency F2 to obtain an original data array R2, and carrying out FFT on the obtained original data R2 to obtain T2.

Extracts the phase value W1 of the element at Index in the T1 array and the phase value W2 of the element at Index in the FT array,

Obtaining the phase difference of the two measurements:

pd=w1-W2, if the result is negative, add one circle to the result:

Pd＝Pd+2*Pi

The angle is then converted to the number of weeks:

Nd＝Pd/Pi/2

The parity according to Index is handled separately:

When Index is even, the phase difference of the frequency difference can be directly used for calculating the precise distance, and when Index is odd, the phase difference of the frequency difference needs to be compensated for in odd cycles, and the number of cycles after compensation is Nd 2-1.

Finally, converting the number of weeks into a distance, and combining the distance with the rough distance to obtain a precise distance:

D＝Index*0.5+Nd*C/B

D is the exact distance of the point.

The accurate distance of all targets in the field of view can be obtained by performing the above processing on each FFT peak.

Since microwave signals have some delays in processing, these delays can be systematic errors of the instrument. Before use, the calibrated precise distance measuring equipment is used for obtaining the difference E between the original measuring result of the radar and the real distance, and the E is treated as a system error to obtain the real distance:

True distance dr=d-E

For example, there is a goal that the index of the FFT peak in the T1 array is 100 (counted from 1) and the index number is even, then:

D_coarse＝Index*0.5＝100*0.5＝50m

And f1[100] =1+1.732 i, f2[100] =1.732+1i

Then pd=w1-w2= 0.5236

Nd＝0.5236/Pi/2＝0.08333

D＝50+0.08333*C/B＝50.08333m

Assume that measured e=0.03 m

The distance the radar finally outputs to the target is:

Dr＝D-E＝50.05333m

For another example, there is a goal that the index of the FFT peak in the T1 array is 101 (counted from 1) and the index number is odd, then:

D_coarse＝Index*0.5＝101*0.5＝50.5m

And f1[101] = 1-1.732i, f2[101] = -1+2i

Then pd=w1-w2= 3.219

Nd＝0.5236/Pi/2＝0.5095

D＝50.5+(2*0.5095-1)*C/B＝50.519m

Assume that measured e=0.03 m

The distance the radar finally outputs to the target is:

Dr＝D-E＝50.489m

2. Specific example 2 using the above method is described below.

The embodiment adopts a precise range imaging radar for range finding.

The first measurement sweep frequency ranges from 10GHz to 10.3GHz

Center frequency f1=10.15 GHz, center wavelength l1=c/f1= 0.02055665m

Bandwidth b=10.3-10=10.6-10.3=0.3 GHz

FFT well resolution rc=c/2b=0.5m

The first measurement is performed with frequency F1 to obtain a single vision complex image C1, which is actually a two-dimensional complex array.

Each strong scattering point (high amplitude point) in the C1 array indicates where there is a target echo. The strong scattering points of interest are found in array F1, each representing a target. Assume that the distance to the first point of interest indexes (location) index_X, and the azimuth dimension Index is index_Y

The rough distance of its corresponding target is:

D_coarse＝Index_X*0.5

The second measurement is performed with frequency F2 to obtain a single vision complex image C2, which is actually a two-dimensional complex array.

Extracting the phase value W1 of the element in the [ index_X, index_Y ] in the C1 array and the phase value W2 of the element in the [ index_X, index_Y ] in the F2 array,

Obtaining the phase difference of the two measurements:

pd=w1-W2, if the result is negative, add one circle to the result:

Pd＝Pd+2*Pi

The angle is then converted to the number of weeks:

Nd＝Pd/Pi/2

processing according to the parity of index_X:

When index_x is even, the phase difference of the frequency difference can be directly used to calculate the exact distance, and when index_x is odd, the phase difference of the frequency difference needs to be compensated for in odd cycles, and the number of cycles after compensation is Nd X2-1.

D＝Index*0.5+Nd*C/B

D is the exact distance of the point.

The accurate distance of all targets in the visual field can be obtained by processing each strong scattering point.

True distance dr=d-E

For example, with one goal, the Index in the C1 array is [100,200] (counting from 1), and index_X Index is even, then:

D_coarse＝Index*0.5＝100*0.5＝50m

And f1[100] =1+1.732 i, f2[100] =1.732+1i

Then pd=w1-w2= 0.5236

Nd＝0.5236/Pi/2＝0.08333

D＝50+0.08333*C/B＝50.08333m

Assume that measured e=0.03 m

The distance the radar finally outputs to the target is:

Dr＝D-E＝50.05333m

for another example, there is a goal that the Index of its FFT peak in the T1 array is [101,220] (counting from 1), index_x Index is odd, then:

D_coarse＝Index*0.5＝101*0.5＝50.5m

And f1[101] = 1-1.732i, f2[101] = -1+2i

Then pd=w1-w2= 3.219

Nd＝0.5236/Pi/2＝0.5095

D＝50.5+(2*0.5095-1)*C/B＝50.519m

Assume that measured e=0.03 m

The distance the radar finally outputs to the target is:

Dr＝D-E＝50.489m

The specific embodiments described herein are offered by way of example only to illustrate the spirit of the invention. Those skilled in the art may make various modifications or additions to the described embodiments or substitutions thereof without departing from the spirit of the invention or exceeding the scope of the invention as defined in the accompanying claims.

Claims

1. A radar ranging method, comprising:

Obtaining a phase difference by performing difference on the first phase value and the second phase value, and obtaining accurate absolute distance = coarse accuracy distance data + phase difference accuracy coefficient;

The precision coefficient comprises a circumference ratio Pi, a light speed C and a sweep frequency bandwidth B, wherein the accurate absolute distance is based on the whole circle number N when the wavelength is C/B and D is measured, and the difference between the wavelengths measured by the C/B is the difference between the two times:

When N is even, d=d _coarse + (W1-W2) ×c/2B)/Pi

When N is an odd number, d=d _coarse + (2 (W1-W2) -1) (C/2B)/Pi

Wherein D _coarse is obtained by FFT of the first measurement data, W1-W2 is obtained by phase difference of two measurements, C is constant of light velocity, and B is bandwidth;

Wherein the wavelength required to satisfy the frequency difference of the two measurements is equal to twice the FFT well resolution.

2. The radar ranging method according to claim 1, wherein the electromagnetic wave used for the first measurement has a wavelength of L1, a frequency of F1, a sweep bandwidth of B, a phase of the frequency of W1, a coarse ranging resolution rc=c/2B, C being a speed of light, and a target distance of D;

3. A radar ranging method according to claim 2, wherein the electromagnetic wave with a wavelength of L2 is used for the second measurement, and the measured data is subjected to the second FFT to obtain the second phase W2 at the INT (D/Rc) FFT trap of the FFT data of the second measurement result.

4. A radar ranging method according to claim 3, wherein the wavelength satisfying the frequency difference of the two measurements is equal to twice the FFT well resolution, i.e. L1-l2= (l1×l2×b)/C, or L2-l1= (l1×l2×b)/C.

5. A radar ranging method according to claim 3, characterized in that the wavelength satisfying the frequency difference of the two measurements is equal to twice the FFT-well resolution, i.e. C/(F1-F2) =c/B, or C/(F2-F1) =c/B.