CN111649803A - Three-dimensional radar level meter based on vertical linear array and design method thereof - Google Patents

Three-dimensional radar level meter based on vertical linear array and design method thereof Download PDF

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CN111649803A
CN111649803A CN202010604582.XA CN202010604582A CN111649803A CN 111649803 A CN111649803 A CN 111649803A CN 202010604582 A CN202010604582 A CN 202010604582A CN 111649803 A CN111649803 A CN 111649803A
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array
target
distance
signal
array element
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CN111649803B (en
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马月红
王硕
朱唐永君
惠蕙
张伟涛
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Hebei Rongfa Information Technology Co ltd
Shijiazhuang Tiedao University
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Hebei Rongfa Information Technology Co ltd
Shijiazhuang Tiedao University
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F23/00—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm
    • G01F23/22—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water
    • G01F23/28—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring the variations of parameters of electromagnetic or acoustic waves applied directly to the liquid or fluent solid material
    • G01F23/284—Electromagnetic waves
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
    • G01S7/28—Details of pulse systems
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
    • G01S7/41—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00 using analysis of echo signal for target characterisation; Target signature; Target cross-section

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  • Thermal Sciences (AREA)
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Abstract

The invention discloses a three-dimensional radar level gauge based on a vertical linear array and a design method thereof, and relates to the technical field of millimeter wave radar imaging. The method comprises the following steps: selecting a proper array element, selecting a proper voltage-controlled oscillator, selecting a proper first-stage noise amplifier, a proper low-pass filter and a proper power amplifier, selecting 4 paths of 16-bit digital-to-analog conversion modules, selecting a proper digital phase compensation synthesizer, carrying out two-dimensional distance direction correction on an echo signal, and carrying out imaging by receiving a signal and inverting a response function of a target. The method can ensure high resolution and have faster imaging performance without increasing the size and cost.

Description

Three-dimensional radar level meter based on vertical linear array and design method thereof
Technical Field
The invention relates to the technical field of millimeter wave radar imaging, in particular to a three-dimensional radar level gauge based on a vertical linear array and a design method thereof.
Background
The method comprises the steps that a radio frequency front end transmits continuous waves with variable frequencies in a scanning period, echoes reflected by a target have a certain frequency difference with a transmitting signal, distance information between the radar and the target is obtained by measuring the frequency difference, the frequency-modulated continuous waves are free of a ranging blind area theoretically during receiving and transmitting, the average power of the transmitting signal is equal to the peak power, the probability of interception can be reduced, the echo signals are changed into narrow-band difference frequency signals after frequency mixing amplification, the frequency mixing signals after intermediate frequency amplification are processed, the distance and direction information of the target is extracted from a signal frequency spectrum, and the obtained different signals are imaged to obtain three-dimensional imaging of the target.
If the front-end imaging of the macro radar is to be realized, the current method adopts a synthetic aperture imaging radar or a phased array radar under a mechanical scanning mode. The mechanical scanning mode can keep a fixed bandwidth in the scanning width in the fixed direction, and can achieve a good scanning effect, but in the front-view imaging process, the rotating speed of the mechanical scanning mode is slow, so that the imaging speed is slow, and imaging at any angle cannot be achieved due to the limitation of the synthetic aperture. The synthetic aperture radar also has the defects of difficult forward looking imaging, long imaging time, incapability of imaging under the condition of static platform, requirement of high-precision motion measurement and the like.
Although the phased array radar can obtain high-resolution imaging, the phased array radar is high in cost and generally only used in the military field or the special field, and even if a UWB radar antenna is adopted, a sparse array with few array elements is adopted, and certain limitation is still achieved due to the existence of the grating lobe problem.
Disclosure of Invention
The technical problem to be solved by the present invention is how to provide a three-dimensional radar level gauge which can ensure high resolution and possess faster imaging performance without increasing size and cost.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows: a three-dimensional radar level gauge based on a vertical linear array is characterized in that: the system comprises a radio frequency front end and a digital baseband processing module, wherein the radio frequency front end is used for transmitting and receiving signals, and spectrum signals with larger energy are obtained after filtering; and the digital baseband processing module converts the obtained baseband signals and then performs phase compensation, and the output signals are corrected in the distance direction and compressed in the azimuth direction to obtain clearer three-dimensional imaging.
The further technical scheme is as follows: the radio frequency front end comprises a vertical linear antenna array consisting of two transmitting channels and four receiving channels, a frequency synthesizer and a frequency modulation continuous wave radar signal generator, and 2 x 4 receiving channels are realized by adopting a multi-transmitting multi-receiving technology.
The embodiment of the invention also discloses a design method of the three-dimensional radar level gauge based on the vertical linear array, which is characterized by comprising the following steps of:
the invention relates to a design method of a vertical linear array three-dimensional radar level gauge, which comprises the following specific steps:
the method comprises the following steps: selecting proper array elements with the size of Lx，Ly；Lx，LyThe sizes of the transmitting array element and the receiving array element are obtained;
step two: selecting a proper voltage-controlled oscillator, enabling the voltage-controlled oscillator to frequency-multiply the stable frequency generated by an external crystal oscillator to a corresponding radar carrier frequency, encoding the generated frequency-modulated continuous wave, and taking an amplified frequency-multiplied signal as a transmitting signal;
step three: selecting a proper primary noise amplifier, a proper low-pass filter and a proper power amplifier, wherein the primary noise amplifier mixes the transmitting signal to generate a beat signal, the low-pass filter filters high-frequency interference from the generated beat signal, and the power amplifier amplifies the filtered signal;
step four: selecting a digital-to-analog conversion module to meet the sampling requirement;
step five: selecting an appropriate digital phase compensation synthesizer based on
Figure BDA0002560510460000021
Adjusting the array element spacing to ensure that no grating lobe appears in the echo signal in the processing process;
step six: two-dimensional distance direction correction is carried out on echo signals, and according to the condition that the length of an array is far smaller than the distance from a target to the array, and the imaging width of the target is far smaller than the position parameter of a multi-target scattering center, the distance is xpProcessing the signal at 0 to obtain an approximation function
Figure BDA0002560510460000022
Figure BDA0002560510460000031
Carrying out Fourier transform on the baseband signal in the distance direction, and combining a distance direction correction function to obtain a time domain function of the received signal:
Figure BDA0002560510460000032
step seven: imaging by inverting the response function of the target from the received signal, at xp，yqDimension performs azimuthal compression at xpIn the dimension direction, the position x of the transmitting array elementpCorresponding to a spatial spectral domain of kxUsing stationary phase method to align xp∈[-Lx，Lx]Performing Fourier transform:
Figure BDA0002560510460000033
the above formula can be obtained:
Figure BDA0002560510460000034
wherein
Figure BDA0002560510460000035
The number of waves corresponding to the carrier frequency is indicated,
Figure BDA0002560510460000036
Figure BDA0002560510460000037
in the same way, for yqAnd (4) carrying out the same transformation, thus realizing imaging.
The further technical scheme is as follows: set at a certain position as the coordinate (X)P0, 0) array element transmitting waveform is marked as s (T), the width of coding sub-pulse is T, and the coding sequence is marked as T
Figure BDA0002560510460000038
Each receiving array element receiving processing unit consists of a filter bank module, and the set target is located at (x)n，yn，HnN 1, 2) has a radar cross-sectional area σnWhen the array element (0, y) is receivedpAnd 0, p ═ 1, 2, 3, 4) can be expressed as:
Figure BDA0002560510460000041
wherein:
Figure BDA0002560510460000042
Figure BDA0002560510460000043
Figure BDA0002560510460000044
wherein c is the speed of light,
Figure BDA0002560510460000045
for the nth scattering center to the transmitting array element (x)p0, 0) and receiving array element (0, yp, 0) and distance
Figure BDA0002560510460000046
And
Figure BDA0002560510460000047
the distances from the transmitting array element and the receiving array element to the p-th scattering center on the target are respectively
Figure BDA0002560510460000048
Figure BDA0002560510460000049
According to the fact that the signals transmitted by the array elements are orthogonal to each other in the time zone, the pair of the array elements for a certain receiving array element is positioned at (0, y)pAnd 0) the output baseband signal of the pulse compression of the p-th filter is:
Figure BDA00025605104600000410
in the formula rp(t) a pulse compression output waveform represented as the p-th array element transmit waveform;
in order to better obtain echo signals, the aperture of an array antenna is utilized, DOA echo signals are processed in the direction of arrival, the echo signals reach adjacent array elements and have a fixed wave path difference, phase change is determined by the wavelength of transmitted electromagnetic waves, the distance between the array elements and the incident angle, the phase difference comprises DOA information, the DOA can be estimated by estimating the phase difference, and the direction information of a target is obtained;
the distance between the array elements is d, the included angle between the target echo direction and the normal direction of the antenna is theta, the wave path difference of the adjacent array elements is dsin theta, and the corresponding phase difference can be expressed as:
Figure BDA0002560510460000051
wherein f is0Calculating a corresponding beam pointing angle theta in a reverse manner according to the phase difference information, wherein the carrier frequency is c is the speed of light;
forming directional receiving wave beams in a desired direction through receiving array elements, performing phase compensation on incident signals in a certain direction through a phase compensator to enable the incident signals to form wave beam directional receiving in the certain direction, achieving wave beam directional target, enabling the array antenna to receive maximum energy, converting frequency-converted baseband signals, and performing phase compensation to obtain output signals; the normalized directivity function is expressed as:
Figure BDA0002560510460000052
wherein N is the number of array elements and the radar working wavelength, d is the array element interval, and theta is the beam pointing angle;
θowhen the directional function satisfies the beam pointing angle theta ═ thetaoWhen the directional diagram function F (θ) is 1, that is, the directional diagram points in the direction of the angle θ;
to ensure that the received signal does not exhibit grating lobes, care should be taken in the range of beam pointing angles,
Figure BDA0002560510460000053
the conditions for not outputting grating lobes are as follows:
Figure BDA0002560510460000054
after the working wavelength lambda of the radar is determined, the above formula can be satisfied only by adjusting the array element spacing d, and the grating lobe can be ensured not to appear.
The further technical scheme is as follows: compressing the obtained signal in the distance direction
Figure BDA0002560510460000055
Is a transmitting array element (x)p0, 0) to the nth scattering center,
Figure BDA0002560510460000056
for receiving the distance from the array element to the target, and hence the distance
Figure BDA0002560510460000057
The correction of (2) is converted into the correction of the distances Rp and Rq, the distances of the two parts can be respectively corrected at the same time because the propagation distances of the two parts are mutually independent, and the distance of the emitting array can be corrected because the length of the emitting array is far less than the distance from a target to the array
Figure BDA0002560510460000058
And performing Taylor series expansion nearby, and omitting high-order terms more than the cubic term to obtain:
Figure BDA0002560510460000061
wherein
Figure BDA0002560510460000062
Under far field conditions, the width of the target imaging region is far less than the position width of the multi-target scattering center:
Figure BDA0002560510460000063
wherein in the formula
Figure BDA0002560510460000064
Representing the distance from the center of the target to the center of the array,
Figure BDA0002560510460000065
represents the scattering center distance walking amount caused by the scattering center parameters of the target in squint,
Figure BDA0002560510460000066
and expressed as corresponding distance bending amount, for the determined target, after the pulse compression signals received by each array element are subjected to distance correction, the envelope delays are completely the same and are all determined by the distance from the scattering center to the center of the array.
The further technical scheme is as follows: inverting the response function d of a target by receiving a signalpq(t，xn，yq) Realize radar imaging along xp，xqBy compressing the maximum transverse dimension of the target in the x-axis and y-axis directions, the imaging problem of the target can be decomposed into two one-dimensional imaging problems, so that the two one-dimensional imaging problems are respectively along the x-axis and the y-axispAnd yqThe dimension pair signal is compressed in the direction of direction, the corresponding space spectrum domain is found according to the position of the transmitting array element, and the x is processed by the stationary phase methodpAnd performing Fourier transform to realize imaging.
Adopt the produced beneficial effect of above-mentioned technical scheme to lie in: the array element numbers of the transmitting array and the receiving array in the level meter are respectively n-2 and p-4, so that under the constraint condition of orthogonal phase coding waveform, 8 space observation channels can be obtained by single receiving and transmitting, and the function of a receiving and transmitting planar array is completed. By increasing the sensitivity of the radio frequency front end, the energy of the echo signal can be larger, high-resolution imaging is facilitated, meanwhile, the area, the power consumption and the size are saved, and the design of the level meter is easy to implement. The signal is decomposed in the signal processing process, so that errors can be reduced, and the echo signal is optimized in the signal processing process. In conclusion, the level meter is convenient to integrate, low in power consumption and suitable for portable and movable scenes.
Drawings
The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
FIG. 1 is a schematic block diagram of a level gauge according to an embodiment of the present invention;
FIG. 2 is a flow chart of a design method according to an embodiment of the present invention;
FIG. 3 is a diagram of the position relationship between array elements in the method according to the embodiment of the present invention;
fig. 4 is a schematic block diagram of a synthesizer in the method according to an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention are clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, but the present invention may be practiced in other ways than those specifically described and will be readily apparent to those of ordinary skill in the art without departing from the spirit of the present invention, and therefore the present invention is not limited to the specific embodiments disclosed below.
The embodiment of the invention discloses a vertical array three-dimensional radar level gauge and a design method thereof, which can be used for the continuous measurement of near-distance non-contact solid and liquid.
As shown in FIG. 1, an embodiment of the present invention discloses a vertical linear array based three-dimensional radar level gauge, which mainly comprises a radio frequency front end and a digital baseband processing module. The radio frequency front end mainly transmits and receives signals, a spectrum signal with larger energy is obtained after filtering, the digital baseband processing module converts the obtained baseband signal and then performs phase compensation, and an output signal is subjected to distance direction correction and azimuth direction compression to obtain clearer three-dimensional imaging.
The radio frequency front end module comprises a vertical linear antenna array consisting of two transmitting channels and four receiving channels, a frequency synthesizer and a Frequency Modulated Continuous Wave (FMCW) radar signal generator, and 2 x 4 receiving channels are realized by adopting a multi-transmitting and multi-receiving technology, so that the angular resolution is doubled.
As shown in FIG. 2, the embodiment of the present invention discloses a design method of a three-dimensional radar level gauge based on a vertical linear array, comprising the following steps:
the method comprises the following steps: selecting proper array elements with the size of Lx，Ly。
Step two: and selecting a proper voltage-controlled oscillator to enable the voltage-controlled oscillator to frequency-multiply the stable frequency generated by the external crystal oscillator to a corresponding radar carrier frequency, encoding the generated frequency-modulated continuous wave, and taking the amplified frequency-multiplied signal as a generation transmitting signal.
Step three: selecting a proper primary noise amplifier, a proper low-pass filter and a proper power amplifier, wherein the primary noise amplifier mixes the transmitting signal to generate a beat signal, the low-pass filter filters high-frequency interference from the generated beat signal, and the power amplifier amplifies the filtered signal.
Step four: and 4 paths of 16-bit digital-to-analog conversion modules are selected, the sampling rate of the digital-to-analog conversion modules can reach 10MHZ, the baseband signals are more accurate, and the sampling requirement can be met.
Step five: selecting an appropriate digital phase compensation synthesizer based on
Figure BDA0002560510460000081
The distance between array elements is adjusted to ensure that grating lobes do not appear in the echo signal in the processing process, and the scanning angle does not exceed 60 DEG
Step six: two-dimensional distance direction correction is carried out on echo signals, and according to the condition that the length of an array is far smaller than the distance from a target to the array, and the imaging width of the target is far smaller than the position parameter of a multi-target scattering center, the distance is xpProcessing the signal at 0 to obtain an approximation function
Figure BDA0002560510460000082
Figure BDA0002560510460000083
Carrying out Fourier transform on the baseband signal in the distance direction, and combining a distance direction correction function to obtain a time domain function of the received signal:
Figure BDA0002560510460000084
step seven: imaging by inverting the response function of the target from the received signal, at xp，yqDimension performs azimuthal compression at xpIn the dimension direction, the position x of the transmitting array elementpCorresponding to a spatial spectral domain of kxUsing stationary phase method to align xp∈[-Lx，Lx]Performing Fourier transform:
Figure BDA0002560510460000091
the above formula can be obtained:
Figure BDA0002560510460000092
wherein
Figure BDA0002560510460000093
The number of waves corresponding to the carrier frequency is indicated,
Figure BDA0002560510460000094
Figure BDA0002560510460000095
in the same way, for yqAnd (4) carrying out the same transformation, thus realizing imaging.
The level meter transmitting signal is a same-frequency-band time domain orthogonal phase coding broadband signal, and the carrier frequency is 77 GHz. Selecting proper coordinates, and recording the coordinates of a certain transmitting array element as (X)P0, 0), the array element transmitting waveform is denoted as s (T), the code sub-pulse width is T, and the code sequence is denoted as
Figure BDA0002560510460000096
Each receiving array element receiving processing unit of the level meter consists of a filter bank module, and the set target is located at (x)n，yn，HnN 1, 2) has a radar cross-sectional area σnWhen the array element (0, y) is receivedpAnd 0, p ═ 1, 2, 3, 4) can be expressed as:
Figure BDA0002560510460000097
wherein:
Figure BDA0002560510460000098
Figure BDA0002560510460000099
Figure BDA0002560510460000101
wherein c is the speed of light,
Figure BDA0002560510460000102
for the nth scattering center to the transmitting array element (x)p0, 0) and receiving array element (0, yp, 0) and distance
Figure BDA0002560510460000103
And
Figure BDA0002560510460000104
the distances from the transmitting array element and the receiving array element to the p-th scattering center on the target are respectively
Figure BDA0002560510460000105
Figure BDA0002560510460000106
According to the fact that the signals transmitted by the array elements are orthogonal to each other in the time zone, the pair of the array elements for a certain receiving array element is positioned at (0, y)pAnd 0) the output baseband signal of the pulse compression of the p-th filter is:
Figure BDA0002560510460000107
in the formula rp(t) a pulse compression output waveform represented as the p-th array element transmit waveform.
In order to better obtain echo signals, the aperture of an array antenna is utilized, the echo signals are processed by adopting direction of arrival (DOA), the echo signals reach adjacent array elements and have a fixed wave path difference, the phase change is determined by the wavelength of transmitted electromagnetic waves, the distance between the array elements and the incident angle, the phase difference comprises direction of arrival information, and the DOA can be estimated by estimating the phase difference to obtain the direction information of a target. As shown in fig. 3, the distance between the array elements is d, the included angle between the target echo direction and the antenna normal direction is θ, the wave path difference between adjacent array elements is dsin θ, and the corresponding phase difference can be expressed as:
Figure BDA0002560510460000108
wherein f is0And c is the carrier frequency, and the corresponding beam pointing angle theta is calculated reversely according to the phase difference information.
The directional receiving wave beam is formed in the expected direction through the receiving array element, the phase compensation is carried out on the incident signal in a certain direction through the phase compensator, the incident signal can form wave beam directional receiving in a certain direction, the wave beam directional target is achieved, the array antenna energy receiving is maximum, the frequency-converted baseband signal is converted, then the phase compensation is carried out, and the output signal is obtained. The normalized directivity function is expressed as
Figure BDA0002560510460000111
Wherein, N is the number of array elements and the radar working wavelength, d is the array element interval, and theta is the beam pointing angle.
θoFor the angle between the azimuth and the antenna normal, as shown in fig. 4, when the directivity function satisfies the beam pointing angle θ ═ θoWhen the pattern function F (θ) is 1, the pattern is directed in the direction of the angle θ.
It should be noted that, to ensure that grating lobes do not occur in the received signal, the range of beam pointing angles should be noted,
Figure BDA0002560510460000112
the conditions for not outputting grating lobes are as follows:
Figure BDA0002560510460000113
after the working wavelength lambda of the radar is determined, the above formula can be satisfied only by adjusting the array element spacing d, and the grating lobe can be ensured not to appear. The scanning angle can not exceed 60 degrees, and the scanning angle is usually taken
Figure BDA0002560510460000114
Compressing the obtained signal in the distance direction
Figure BDA0002560510460000115
Is a transmitting array element (x)p0, 0) to the nth scattering center,
Figure BDA0002560510460000116
for receiving the distance from the array element to the target, and hence the distance
Figure BDA0002560510460000117
The correction of (2) is converted into the correction of the distances Rp and Rq, and because the propagation distances of the two parts are independent of each other, the two parts of the distances can be simultaneously and respectively corrected, because the length of the transmitting array is far less than the distance from the target to the array, and the distances can be corrected
Figure BDA0002560510460000118
And performing Taylor series expansion nearby, and omitting high-order terms more than the cubic term to obtain:
Figure BDA0002560510460000119
wherein
Figure BDA00025605104600001110
Under far field conditions, the width of the target imaging area is far less than the position width of the multi-target scattering center
Figure BDA00025605104600001111
Wherein in the formula
Figure BDA0002560510460000121
Representing the distance from the center of the target to the center of the array,
Figure BDA0002560510460000122
represents the scattering center distance walking amount caused by the scattering center parameters of the target in squint,
Figure BDA0002560510460000123
expressed as the corresponding amount of distance bending. For a determined target, after the pulse compression signals received by each array element are subjected to distance correction, the envelope delays are completely the same and are determined only by the distance from the scattering center to the center of the array.
Inverting the response function d of a target by receiving a signalpq(t，xn，yq) Can realize radar imaging along xp，xqThe imaging problem of the target can also be decomposed into two one-dimensional imaging problems by compressing the maximum transverse dimension of the target in the x-axis and the y-axis in the direction, so that the maximum transverse dimension is respectively along the x-axis and the y-axispAnd yqThe dimension compresses the signal azimuthally. Finding out corresponding spatial spectrum domain according to the position of the transmitting array element, and using the stationary phase method to xpAnd performing Fourier transform to realize imaging.
The array element numbers of the transmitting array and the receiving array in the level meter are respectively n-2 and p-4, so that under the constraint condition of orthogonal phase coding waveform, 8 space observation channels can be obtained by single receiving and transmitting, and the function of a receiving and transmitting planar array is completed. By increasing the sensitivity of the radio frequency front end, the energy of the echo signal can be larger, high-resolution imaging is facilitated, meanwhile, the area, the power consumption and the size are saved, and the design of the level meter is easy to implement. The signal is decomposed in the signal processing process, so that errors can be reduced, and the echo signal is optimized in the signal processing process. In conclusion, the level meter is convenient to integrate, low in power consumption and suitable for portable and movable scenes.

Claims (6)

1. A three-dimensional radar level gauge based on a vertical linear array is characterized in that: the system comprises a radio frequency front end and a digital baseband processing module, wherein the radio frequency front end is used for transmitting and receiving signals, and spectrum signals with larger energy are obtained after filtering; and the digital baseband processing module converts the obtained baseband signals and then performs phase compensation, and the output signals are corrected in the distance direction and compressed in the azimuth direction to obtain clearer three-dimensional imaging.
2. The vertical linear array based three-dimensional radar level gauge according to claim 1, wherein: the radio frequency front end comprises a vertical linear antenna array consisting of two transmitting channels and four receiving channels, a frequency synthesizer and a frequency modulation continuous wave radar signal generator, and 2 x 4 receiving channels are realized by adopting a multi-transmitting multi-receiving technology.
3. A design method of a three-dimensional radar level gauge based on a vertical linear array is characterized by comprising the following steps:
the invention relates to a design method of a vertical linear array three-dimensional radar level gauge, which comprises the following specific steps:
the method comprises the following steps: selecting proper array elements with the size of Lx，Ly；Lx，LyThe sizes of the transmitting array element and the receiving array element are obtained;
step two: selecting a proper voltage-controlled oscillator, enabling the voltage-controlled oscillator to frequency-multiply the stable frequency generated by an external crystal oscillator to a corresponding radar carrier frequency, encoding the generated frequency-modulated continuous wave, and taking an amplified frequency-multiplied signal as a transmitting signal;
step three: selecting a proper primary noise amplifier, a proper low-pass filter and a proper power amplifier, wherein the primary noise amplifier mixes the transmitting signal to generate a beat signal, the low-pass filter filters high-frequency interference from the generated beat signal, and the power amplifier amplifies the filtered signal;
step four: selecting a digital-to-analog conversion module to meet the sampling requirement;
step five: selecting an appropriate digital phase compensation synthesizer based on
Figure FDA0002560510450000011
Adjusting the array element spacing to ensure that no grating lobe appears in the echo signal in the processing process;
step six: two-dimensional distance direction correction is carried out on echo signals, and according to the condition that the length of an array is far smaller than the distance from a target to the array, and the imaging width of the target is far smaller than the position parameter of a multi-target scattering center, the distance is xpProcessing the signal at 0 to obtain an approximation function
Figure FDA0002560510450000021
Figure FDA0002560510450000022
Carrying out Fourier transform on the baseband signal in the distance direction, and combining a distance direction correction function to obtain a time domain function of the received signal:
Figure FDA0002560510450000023
step seven: imaging by inverting the response function of the target from the received signal, at xp，yqDimension performs azimuthal compression at xpIn the dimension direction, the position x of the transmitting array elementpCorresponding to a spatial spectral domain of kxUsing stationary phase method to align xp∈[-Lx，Lx]Performing Fourier transform:
Figure FDA0002560510450000024
the above formula can be obtained:
Figure FDA0002560510450000025
wherein
Figure FDA0002560510450000026
The number of waves corresponding to the carrier frequency is indicated,
Figure FDA0002560510450000027
Figure FDA0002560510450000028
in the same way, for yqAnd (4) carrying out the same transformation, thus realizing imaging.
4. The vertical linear array based three-dimensional radar level gauge design method of claim 3, comprising the steps of:
set at a certain position as the coordinate (X)P0, 0) array element transmitting waveform is marked as s (T), the width of coding sub-pulse is T, and the coding sequence is marked as T
Figure FDA0002560510450000031
Each receiving array element receiving processing unit consists of a filter bank module, and the set target is located at (x)n，yn，HnN 1, 2) has a radar cross-sectional area σnWhen the array element (0, y) is receivedpAnd 0, p ═ 1, 2, 3, 4) can be expressed as:
Figure FDA0002560510450000032
wherein:
Figure FDA0002560510450000033
Figure FDA0002560510450000034
Figure FDA0002560510450000035
wherein c is the speed of light,
Figure FDA0002560510450000036
for the nth scattering center to the transmitting array element (x)p0, 0) and receiving array element (0, yp, 0) and distance
Figure FDA0002560510450000037
And
Figure FDA0002560510450000038
the distances from the transmitting array element and the receiving array element to the p-th scattering center on the target are respectively
Figure FDA0002560510450000039
Figure FDA00025605104500000310
According to the fact that the signals transmitted by the array elements are orthogonal to each other in the time zone, the pair of the array elements for a certain receiving array element is positioned at (0, y)pAnd 0) the output baseband signal of the pulse compression of the p-th filter is:
Figure FDA00025605104500000311
in the formula rp(t) a pulse compression output waveform represented as the p-th array element transmit waveform;
in order to better obtain echo signals, the aperture of an array antenna is utilized, DOA echo signals are processed in the direction of arrival, the echo signals reach adjacent array elements and have a fixed wave path difference, phase change is determined by the wavelength of transmitted electromagnetic waves, the distance between the array elements and the incident angle, the phase difference comprises DOA information, the DOA can be estimated by estimating the phase difference, and the direction information of a target is obtained;
the distance between the array elements is d, the included angle between the target echo direction and the normal direction of the antenna is theta, the wave path difference of the adjacent array elements is dsin theta, and the corresponding phase difference can be expressed as:
Figure FDA0002560510450000041
wherein f is0Calculating a corresponding beam pointing angle theta in a reverse manner according to the phase difference information, wherein the carrier frequency is c is the speed of light;
forming directional receiving wave beams in a desired direction through receiving array elements, performing phase compensation on incident signals in a certain direction through a phase compensator to enable the incident signals to form wave beam directional receiving in the certain direction, achieving wave beam directional target, enabling the array antenna to receive maximum energy, converting frequency-converted baseband signals, and performing phase compensation to obtain output signals; the normalized directivity function is expressed as:
Figure FDA0002560510450000042
wherein N is the number of array elements and the radar working wavelength, d is the array element interval, and theta is the beam pointing angle;
θowhen the directional function satisfies the beam pointing angle theta ═ thetaoWhen the directional diagram function F (θ) is 1, that is, the directional diagram points in the direction of the angle θ;
to ensure that the received signal does not exhibit grating lobes, care should be taken in the range of beam pointing angles,
Figure FDA0002560510450000043
the conditions for not outputting grating lobes are as follows:
Figure FDA0002560510450000044
after the working wavelength lambda of the radar is determined, the above formula can be satisfied only by adjusting the array element spacing d, and the grating lobe can be ensured not to appear.
5. The vertical linear array based three-dimensional radar level gauge design method of claim 4, comprising the steps of:
compressing the obtained signal in the distance direction
Figure FDA0002560510450000045
Is a transmitting array element (x)p0, 0) to the nth scattering center,
Figure FDA0002560510450000046
for receiving the distance from the array element to the target, and hence the distance
Figure FDA0002560510450000047
The correction of (2) is converted into the correction of the distances Rp and Rq, the distances of the two parts can be respectively corrected at the same time because the propagation distances of the two parts are mutually independent, and the distance of the emitting array can be corrected because the length of the emitting array is far less than the distance from a target to the array
Figure FDA0002560510450000051
And performing Taylor series expansion nearby, and omitting high-order terms more than the cubic term to obtain:
Figure FDA0002560510450000052
wherein
Figure FDA0002560510450000053
Under far field conditions, the width of the target imaging region is far less than the position width of the multi-target scattering center:
Figure FDA0002560510450000054
wherein in the formula
Figure FDA0002560510450000055
Representing the distance from the center of the target to the center of the arrayAfter the separation, the water is separated from the water,
Figure FDA0002560510450000056
represents the scattering center distance walking amount caused by the scattering center parameters of the target in squint,
Figure FDA0002560510450000057
and expressed as corresponding distance bending amount, for the determined target, after the pulse compression signals received by each array element are subjected to distance correction, the envelope delays are completely the same and are all determined by the distance from the scattering center to the center of the array.
6. The vertical linear array based three-dimensional radar level gauge design method of claim 5, comprising the steps of:
inverting the response function d of a target by receiving a signalpq(t，xn，yq) Realize radar imaging along xp，xqBy compressing the maximum transverse dimension of the target in the x-axis and y-axis directions, the imaging problem of the target can be decomposed into two one-dimensional imaging problems, so that the two one-dimensional imaging problems are respectively along the x-axis and the y-axispAnd yqThe dimension pair signal is compressed in the direction of direction, the corresponding space spectrum domain is found according to the position of the transmitting array element, and the x is processed by the stationary phase methodpAnd performing Fourier transform to realize imaging.
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