CN108427114B - Loss-compensated frequency division multiplexing millimeter wave three-dimensional imaging device and method - Google Patents
Loss-compensated frequency division multiplexing millimeter wave three-dimensional imaging device and method Download PDFInfo
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Abstract
The invention discloses a loss compensated frequency division multiplexing millimeter wave three-dimensional imaging device and a method, wherein the method comprises the following steps: the control unit, the radio frequency unit and the antenna array are connected in sequence; the radio frequency unit comprises a frequency multiplier array, a power divider array, a millimeter wave receiving and transmitting array, an electronic switch array, a quadrature mixer array and a splitter array; the frequency multiplier array is connected with the power divider array, one path of output of the power divider array is connected with the millimeter wave receiving and transmitting array, the other path of output of the power divider array is connected with the orthogonal mixer array, and the orthogonal mixer array is connected with the splitter array; the invention has the beneficial effects that: the backward scattering data model of the target object is equivalent to an angular spectrum formula for calculating the light field propagation process, and in the image reconstruction process, the propagation loss of millimeter waves in space is compensated, and the quality of millimeter wave three-dimensional imaging is improved.
Description
Technical Field
The invention belongs to the field of millimeter wave imaging, and particularly relates to a loss-compensated frequency division multiplexing millimeter wave three-dimensional imaging device and method.
Background
Millimeter waves with the frequency in the range of 30 GHz-300 GH are particularly suitable for being applied to the field of human body security inspection by virtue of excellent characteristics of good clothing penetrability, high imaging resolution, non-ionizing radiation and the like. Related millimeter wave three-dimensional imaging devices and methods become current research hotspots.
In the existing products, widely applied three-dimensional millimeter wave imaging technologies are divided into two categories: holographic imaging techniques and range migration techniques.
The millimeter wave holographic imaging technology is derived from the optical holographic technology, the scattered spherical wave of a near-field target object is decomposed into superposition of a plurality of plane waves, and the reconstruction of the target object image is completed through four steps of two-dimensional Fourier transform, phase compensation, wave number domain interpolation and three-dimensional inverse Fourier transform by utilizing the acquired amplitude and phase information of the scattered wave front of the target object. Compared with the early digital reconstruction technology based on Fresnel approximation, the imaging resolution is greatly improved.
The millimeter wave range migration technology is derived from a range migration method of a synthetic aperture radar, the acquired backward scattering data of the target object are multiplied by a phase reference index term in a frequency domain and moved to a target object plane parallel to the aperture plane, and then residual radial curvature is eliminated, so that a target object image is obtained. The key point is to approximate the double integral of the index term related to the two range migration on the plane to the double integral of the transverse wave number domain after the phase compensation by utilizing the stationary phase method and the conversion of the product of the time convolution and the frequency domain.
However, in the image reconstruction process, the traditional holographic imaging technology and the range migration technology ignore the propagation loss of electromagnetic waves in space, and inevitably influence the quality of near-field millimeter wave three-dimensional imaging.
Disclosure of Invention
In order to solve the defects in the prior art, the invention provides a loss-compensated frequency division multiplexing millimeter wave three-dimensional imaging device and a loss-compensated frequency division multiplexing millimeter wave three-dimensional imaging method. In the image reconstruction process, the propagation loss of millimeter waves in space is compensated, the radial positioning of the target object is realized, and the quality of millimeter wave three-dimensional imaging is improved.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
the invention discloses a loss compensated frequency division multiplexing millimeter wave three-dimensional imaging device, which comprises: the control unit, the radio frequency unit and the antenna array are connected in sequence;
the radio frequency unit comprises a frequency multiplier array, a power divider array, a millimeter wave receiving and transmitting array, an electronic switch array, a quadrature mixer array and a splitter array;
the frequency multiplier array is connected with the power divider array, one path of output of the power divider array is connected with the millimeter wave receiving and transmitting array, the other path of output of the power divider array is connected with the orthogonal mixer array, and the orthogonal mixer array is connected with the splitter array;
the control unit controls the output of periodic multi-frequency signals to the frequency multiplier array; the control unit receives the analog signals of the splitter array, converts the analog signals into digital signals, and then reconstructs and displays the image of the target object.
Further, the control unit comprises a central processing unit, a multi-frequency signal synchronous generator, a multi-path data acquisition card and a display;
the central processing unit is respectively connected with the multi-frequency signal synchronous generator, the multi-path data acquisition card and the display through the data transmission bus; the multi-frequency signal synchronous generator is connected with the frequency multiplier array, and the multi-path data acquisition card is connected with the splitter array.
Further, the multi-frequency signal synchronous generator outputs single-frequency signals of N channels to the radio frequency unit, and the frequencies of the output signals of each channel are different and distributed at equal intervals; the frequency of the output signal of each channel is unchanged in one subcycle; in the next sub-period, the frequency of all channel output signals realizes rotation; each channel traverses all the signals of N frequencies over N subcycles.
Further, the millimeter wave receiving and transmitting array comprises a transmitter array and a receiver array, and the transmitter array receives N channels of millimeter wave signals output by the power divider array and transmits the N channels of millimeter wave signals to the electronic switch array; the receiver array receives the output of the electronic switch array and transmits the output to the quadrature mixer array.
Further, the quadrature mixer array includes N90 ° phase shifters and 2N mixers; for each channel, the phase shifter shifts the phase of the output signal of the power divider array by 90 degrees and then transmits the shifted phase to the second mixer, the first mixer directly receives the output signal of the power divider array, the two mixers also simultaneously receive the return signal of the channel output by the millimeter wave transceiver array, and the amplitude and phase information of the signals obtained after mixing are output to the splitter array.
Further, the antenna array comprises N transmitting antennas and N receiving antennas, and the N transmitting antennas and the N receiving antennas are distributed in an equidistant plane.
Further, the splitter array receives amplitude signals and phase information of N channels simultaneously, and 2N input channels are provided in total, and M input channels selected each time are directly transmitted to the multi-channel data acquisition card until all 2N input channels are acquired.
The invention discloses a loss compensated frequency division multiplexing millimeter wave three-dimensional imaging method, which comprises the following steps: the back scattering data received by one receiving antenna in the antenna array is equivalent to the form of an angular spectrum formula for calculating the light field propagation process, and a three-dimensional image of the target object is reconstructed by means of Fourier transformation and inverse transformation operation contained in the angular spectrum formula.
Further, the method comprises the following steps:
step 1: backscatter data s (x 0 ，y 0 Performing conjugate processing on the k) and then performing transverse two-dimensional Fourier transformation to obtain S * (k x ，k y ，k)；
wherein ,x0 Representing the horizontal axis position of the receiving antenna in the plane of the antenna array, y 0 The vertical axis position of the receiving antenna on the plane of the antenna array is shown, and k represents the signal wave number of the corresponding channel of the receiving antenna; k (k) x Wavenumbers representing the horizontal axis; k (k) y Wavenumbers representing the vertical axis; * Representing conjugate operation;
step 2: will S * (k x ，k y K) multiplying a phase compensation factor, and converting the phase of the back scattering data to the phase of the nearest distance between the target object area and the antenna array along the radial axis;
step 3: interpolation processing is carried out on the data obtained in the step 2, and wave number domain data F (k) of the reflection coefficient of the target object is obtained x ，k y ，k z )；k z Wavenumbers representing radial axes;
step 4: for wave number domain data F (k) x ，k y ，k z ) Performing transverse two-dimensional inverse Fourier transform to obtain data
/>
Step 5: for data
Radial one-dimensional Fourier transform is carried out to obtain data
Step 6: multiplying the data obtained in the step 5 with a set index term to compensate the frequency shift of the target object at different radial distances;
multiplying the obtained data with a set constant term to carry out amplitude compensation on the attenuation loss;
multiplying the data by
And the result is conjugated, so that phase correction is realized, and the reflection coefficients of each point of the target object are obtained; and meanwhile, the radial resolution determined by the signal bandwidth is utilized to realize the positioning of the target object on the radial axis.
Further, the phase compensation factor in the step 2 is specifically
wherein ,z0 The nearest distance between the target object area and the antenna array along a radial axis, wherein the radial axis is orthogonal to a transverse plane where the antenna array is positioned; k (k) z Representing the wave number of the radial axis, an
The invention has the beneficial effects that:
(1) According to the invention, the backward scattering data model of the target object is equivalent to an angular spectrum formula for calculating the light field propagation process, so that the propagation loss of millimeter waves in space is compensated in the image reconstruction process, and the quality of millimeter wave three-dimensional imaging is improved.
(2) When the radial wave number domain of the three-dimensional image is converted into the space domain, fourier positive transformation is used, and radial resolution determined by combining signal bandwidth is used, so that the positioning of the target object in the radial distance is realized.
(3) The invention uses a frequency division multiplexing signal system, combines a radio frequency unit consisting of a frequency multiplier array, a power divider array, a millimeter wave receiving and transmitting array, an electronic switch array, a quadrature mixer array and a branching device array and a planar antenna array, so that all channels can work simultaneously, and the imaging time is shortened.
Drawings
Fig. 1 is a schematic diagram of a frequency division multiplexing millimeter wave three-dimensional imaging system with loss compensation according to the present invention;
FIG. 2 is a schematic diagram of the spatial positions of an antenna array and a target;
FIG. 3 is a two-dimensional gray scale map of a backscatter data set;
FIG. 4 is a two-dimensional gray scale plot of the backscattered data after completion of a transverse two-dimensional Fourier transform;
FIG. 5 (a) is a three-dimensional curved surface view of a projection of a reconstructed three-dimensional image on a transverse plane before correction;
FIG. 5 (b) is a three-dimensional curved surface view of the projection of the reconstructed three-dimensional image on the transverse plane after the correction process;
FIG. 6 (a) is a two-dimensional gray scale map of a projection of a reconstructed three-dimensional image on a transverse plane prior to a correction process;
FIG. 6 (b) is a two-dimensional gray scale map of the projection of the reconstructed three-dimensional image on the transverse plane after the correction process;
FIG. 7 is a two-dimensional gray scale map of each section of the reconstructed image along the radial axis;
fig. 8 is a flow chart of a loss compensated frequency division multiplexing millimeter wave three-dimensional imaging method of the invention.
Detailed Description
The invention is further described below with reference to the drawings and the detailed description.
It should be noted that the specific data given in the present invention are exemplary, and do not limit the technical content of the present invention, and those skilled in the art may set the specific data according to actual needs.
The invention discloses a loss compensated frequency division multiplexing millimeter wave three-dimensional imaging device, which comprises: control unit, radio frequency unit and antenna array as shown in fig. 1.
The control unit comprises a central processing unit, a multi-frequency signal synchronous generator, a multi-path data acquisition card and a display.
The central processing unit sends control data to the multi-frequency signal synchronous generator to enable the multi-frequency signal synchronous generator to output periodic multi-frequency signals;
the central processing unit receives the data of the multipath data acquisition card and reconstructs an image of the target object;
the central processing unit sends the image data of the target object to the display, so that the display displays the image of the target object in real time.
The multi-frequency signal synchronous generator outputs single-frequency signals of 32 channels to the radio frequency unit, and the frequencies of the output signals of all the channels are different and distributed at equal intervals. The frequency of the output signal of each channel is unchanged during one sub-period. In the next sub-period, the frequency of all channel output signals is rotated. Each channel traverses through 32 sub-periods for a signal of 32 frequencies in its entirety.
The round robin fashion is shown as a matrix in equation 1:
wherein the number of rows of the matrix represents 32 channels and the number of columns of the matrix represents 32 subcycles; f (f) 1 ,f 2 ,f 3 …f 32 The frequency points are distributed at equal intervals, the difference between every two adjacent frequencies is set to 4.6875MHz, and f 1 ＝862.5MHz，f 32 ＝1007.8125MHz。
The multipath data acquisition card comprises an analog-digital converter with 16 channels, and the analog signals output by the splitter array are converted into digital signals and transmitted to the central processing unit.
The radio frequency unit comprises a frequency multiplier array, a power divider array, a millimeter wave transceiver array, a 2-group electronic switch array, a quadrature mixer array and a splitter array.
The frequency multiplier array receives the single-frequency signals of 32 channels output by the multi-frequency signal synchronous generator in the control unit, and outputs broadband millimeter waves of 27.6-32.25 GHz frequency bands to the power divider array after 32 times of frequency multiplication.
The millimeter wave signals of each channel are divided into two paths by the power divider array, one path of millimeter wave signals are output to the millimeter wave receiving and transmitting array, and the other path of millimeter wave signals are output to the quadrature mixer array.
The millimeter wave receiving and transmitting array comprises a transmitter array and a receiver array, and the transmitter array receives 32 channel millimeter wave signals output by the power divider and transmits the 32 channel millimeter wave signals to 32 inputs of the first group of electronic switch arrays; the receiver array receives the 32 outputs of the second set of electronic switch arrays and transmits them to the quadrature mixer array.
The 2 groups of electronic switch arrays are used for connecting the millimeter wave receiving and transmitting arrays and the antenna arrays, and the number of transmitting antennas and receiving antennas contained in the antenna arrays is 4096; the first group of electronic switch arrays are connected with the transmitter array and the transmitting antenna array, and the second group of electronic switches are connected with the receiving antenna array and the receiver array, so that the antenna array traverses 32 channel signals.
The quadrature mixer array includes 32 90 phase shifters and 64 mixers. For each channel, the phase shifter shifts the phase of the output signal of the power divider array by 90 degrees and transmits the shifted phase to the second mixer, the first mixer directly receives the output signal of the power divider array, the two mixers also simultaneously receive the return signal of the channel output by the millimeter wave transceiver array, and the amplitude and phase information obtained after mixing are output to the splitter array.
The splitter array receives the amplitude signals and the phase information of 32 channels simultaneously, and has 64 input channels in total, and 16 input channels selected each time are directly transmitted to the multi-channel data acquisition card until all the 64 input channels are acquired.
The antenna array comprises 4096 transmitting antennas and 4096 receiving antennas, the transmitting antennas and the receiving antennas are distributed at equal intervals along the horizontal axis and the vertical axis of the antenna plane in a 64 multiplied by 64 array, the intervals between the transmitting antennas and the receiving antennas are all 0.0025m, and the aperture size is 0.1575 multiplied by 0.1575m. Each pair of transmit and receive antennas is located in close proximity, which may be approximately the same location in the plane of the antennas. The antenna plane is set at the origin at a radial axis position perpendicular to the antenna plane.
The target was set to be 2 square metal plates placed at different radial positions, each 0.0175 x 0.0175m in size, 0.1m and 0.35m in radial position, respectively, with the plane of the metal plates parallel to the plane of the antenna.
The spatial positions of the antenna array and the target are shown in fig. 2.
The back scattering data received by one receiving antenna in the antenna array can be expressed as superposition of secondary reflection spherical waves of the target object:
wherein ,s(x0 ，y 0 K) represents the back-scattered data received by one of the receiving antennas in the antenna array, x 0 Representing the horizontal axis position of the receiving antenna on the plane of the antenna array, y 0 Represents the vertical axis position of the receiving antenna on the plane of the antenna array, k represents the signal wave number of the corresponding channel of the receiving antenna, and
f represents the signal frequency of the corresponding channel, c represents the propagation speed of electromagnetic waves in air; f (x, y, z) represents the reflection coefficient of a certain point on the target object, x represents the position of the point on the transverse horizontal axis, y represents the position of the point on the transverse vertical axis, z represents the position of the point on the radial axis, z is perpendicular to the transverse plane formed by x and y, the transverse plane formed by x and y is parallel to the plane of the antenna array, and the antenna array is positioned at the origin of the radial axis; r represents a receiving antennaTo the position of the point on the object, and +.>
When the signal frequency of each channel is the center frequency of the broadband signal, a two-dimensional amplitude gray scale map of the backscatter data set is shown in fig. 3.
According to the scalar diffraction theory of optics, the propagation of the light field can be expressed as:
wherein ,U(x0 ，y 0 0) represents the field at the observation point, i.e. the receiving antenna; u (x, y, z) represents the secondary wave source, i.e. the field at a point of the object; lambda represents the wavelength, an
cos θ represents a tilt factor, and +.>
Field U (x) of a receiving antenna 0 ，y 0 0) can be used with the backscatter data s (x 0 ，y 0 The field U (x, y, z) of the secondary wave source can be expressed by the reflection coefficient f (x, y, z) of the target at that point, and thus equation (2) can be equivalently:
wherein ,s* (x 0 ，y 0 K) is the backscatter data s (x 0 ，y 0 Conjugation of k); f (f) * (x, y, z) is the conjugate of the reflection coefficient f (x, y, z); k 'is the number of incoming returns, and k' =2k; z 0 =0.1m is the closest distance between the target area and the antenna array along the radial axis.
The propagation of the light field can also be expressed using an angular spectrum formula:
wherein ,A(kx ，k y Z) represents the mapping of the secondary wave source U (x, y, z) in the transverse wave number domain; k (k) x Wavenumbers representing the transverse horizontal axis; k (k) y The wave number of the transverse vertical axis is indicated.
Thus, equation (4) may be equivalently in the form of an angular spectrum equation:
wherein ,F(kx ，k y Z) represents the reflection coefficient conjugate f * (x, y, z) transverse two-dimensional fourier transform.
Let variable z' =z-z 0 Substituting formula (6) to obtain:
from equation (7), it can be seen that for the back-scattered data s (x 0 ，y 0 K) performing a series of operations, the reflection coefficient f (x, y, z) of the target object can be obtained, thereby realizing three-dimensional image reconstruction.
The invention discloses a loss compensated frequency division multiplexing millimeter wave three-dimensional imaging method, as shown in fig. 8, comprising the following steps:
step 1: transverse two-dimensional fourier transform of backscatter data
For backscatter data s (x 0 ，y 0 And k) performing conjugate processing and then performing transverse two-dimensional Fourier transform:
wherein ,S* (k x ，k y K) represents the back-scattered data s (x 0 ，y 0 An expression of the conjugation of k) in the frequency domain; FT (FT) 2D { } represents a transverse two-dimensional fourier transform operator.
After the backscattering data of the center frequency is subjected to transverse two-dimensional Fourier transform, a two-dimensional gray scale diagram of the data is shown in FIG. 4.
Step 2: phase compensation
Will S * (k x ，k y K) is multiplied by a phase compensation factor to obtain:
wherein ,kz Represents radial wave number, and
the effect of this step is to scale the phase of the backscatter data to the nearest distance along the radial axis of the target area and the antenna array (z=z 0 ) Is a phase of (a) of (b).
Step 3: interpolation processing
The wave number domain back scattering data obtained in the above steps are uniformly distributed in the transverse wave number domain, but are unevenly distributed in the radial wave number domain, and in order to obtain radial space domain data by using radial one-dimensional fourier transform subsequently, interpolation processing is required to be performed on the data obtained in the formula (8):
wherein ,F(kx ，k y ，k z ) Wave number domain data representing reflection coefficients of the target object; stolt []Indicating interpolation of the data in brackets.
Step 4: transverse two-dimensional inverse Fourier transform
Performing transverse two-dimensional inverse Fourier transform on wave number domain data of the reflection coefficient of the target object to obtain:
wherein ,
the data in brackets is shown as being subjected to a transverse two-dimensional inverse fourier transform.
Step 5: radial one-dimensional Fourier transform
Performing radial one-dimensional Fourier transform on the data obtained in the previous step to obtain:
where FT { } represents radial one-dimensional fourier transform of the data in brackets.
After this step, a three-dimensional curved surface image projected on a transverse plane by the three-dimensional image is reconstructed, and a two-dimensional gray scale image is shown in fig. 5 (a).
Step 6: correction processing
The data obtained in the last step is firstly combined with an index term
Multiplying to compensate the frequency shift of the target object at different radial distances; and then->
Multiplying, and compensating the amplitude of the attenuation loss; finally multiply by->
And the result is conjugated to realize phase correction. The following expression is finally obtained:
wherein ,
f c is the center frequency of the wideband signal transmitted by each channel.
Equation (12) is the inverse of equation (7) and achieves three-dimensional image reconstruction of the object from the backscatter data. A three-dimensional curved surface image projected on a transverse plane of the reconstructed three-dimensional image is shown in fig. 5 (b), and a two-dimensional gray scale image is shown in fig. 6 (b).
The closest distance of the target object along the radial axis to the antenna plane is z 0 =0.1m, the radial resolution determined by the signal bandwidth is δ z The coordinate values of the radial tangential plane of the reconstructed image obtained by the method are=0.03125m, and the two-dimensional gray-scale map of the tangential plane of the reconstructed image at the radial axes 0.1m, 0.13125m, 0.1625m, 0.19375m, 0.225m, 0.25625m, 0.2875m, 0.31875m and 0.35m is shown in fig. 7.
While the foregoing description of the embodiments of the present invention has been presented in conjunction with the drawings, it should be understood that it is not intended to limit the scope of the invention, but rather, it is intended to cover all modifications or variations within the scope of the invention as defined by the claims of the present invention.
Claims (10)
1. The loss compensated frequency division multiplexing millimeter wave three-dimensional imaging method is characterized by comprising the following steps of: the back scattering data received by a certain receiving antenna in the antenna array is equivalent to the form of an angular spectrum formula for calculating the light field propagation process, and a three-dimensional image of the target object is reconstructed by virtue of Fourier transform and inverse transform operation contained in the angular spectrum formula;
step 1: transverse two-dimensional fourier transform of backscatter data
For backscatter data s (x 0 ,y 0 And k) performing conjugate processing and then performing transverse two-dimensional Fourier transform:
wherein ,S* (k x ,k y K) represents the back-scattered data s (x 0 ,y 0 An expression of the conjugation of k) in the frequency domain; FT (FT) 2D { } represents a transverse two-dimensional fourier transform operator;
step 2: phase compensation
Will S * (k x ,k y K) is multiplied by a phase compensation factor to obtain:
wherein ,kz Represents radial wave number, and
the effect of this step is to scale the phase of the backscatter data to the nearest distance along the radial axis of the target area and the antenna array (z=z 0 ) Is a phase of (2);
step 3: interpolation processing
The wave number domain back scattering data obtained in the above steps are uniformly distributed in the transverse wave number domain, but are unevenly distributed in the radial wave number domain, and in order to obtain radial space domain data by using radial one-dimensional fourier transform subsequently, interpolation processing is required to be performed on the data obtained in the formula (8):
wherein ,F(kx ,k y ,k z ) Wave number domain data representing reflection coefficients of the target object; stolt []Indicating that interpolation processing is carried out on the data in brackets;
step 4: transverse two-dimensional inverse Fourier transform
Performing transverse two-dimensional inverse Fourier transform on wave number domain data of the reflection coefficient of the target object to obtain:
wherein ,
representing the transversal two-dimensional inverse fourier transform of the data in brackets;
step 5: radial one-dimensional Fourier transform
Performing radial one-dimensional Fourier transform on the data obtained in the previous step to obtain:
wherein FT { } represents performing radial one-dimensional fourier transform on the data in brackets;
step 6: correction processing
The data obtained in the last step is firstly combined with an index term
Multiplying to compensate the frequency shift of the target object at different radial distances; and then->
Multiplying, and compensating the amplitude of the attenuation loss; finally multiply by->
And the result is conjugated to realize phase correction; the following expression is finally obtained: />
wherein ,
f c is the center frequency of the wideband signal transmitted by each channel.
2. A loss-compensated frequency division multiplexing millimeter wave three-dimensional imaging device realized by the loss-compensated frequency division multiplexing millimeter wave three-dimensional imaging method according to claim 1, characterized in that,
comprising the following steps: the control unit, the radio frequency unit and the antenna array are connected in sequence;
the radio frequency unit comprises a frequency multiplier array, a power divider array, a millimeter wave receiving and transmitting array, an electronic switch array, a quadrature mixer array and a splitter array;
the frequency multiplier array is connected with the power divider array, one path of output of the power divider array is connected with the millimeter wave receiving and transmitting array, the other path of output of the power divider array is connected with the orthogonal mixer array, and the orthogonal mixer array is connected with the splitter array;
the control unit controls the output of periodic multi-frequency signals to the frequency multiplier array; the control unit receives the analog signals of the splitter array, converts the analog signals into digital signals, and then reconstructs and displays the image of the target object.
3. A loss-compensated, frequency division multiplexed millimeter wave three-dimensional imaging device of claim 2,
the control unit comprises a central processing unit, a multi-frequency signal synchronous generator, a multi-path data acquisition card and a display;
the central processing unit is respectively connected with the multi-frequency signal synchronous generator, the multi-path data acquisition card and the display through the data transmission bus; the multi-frequency signal synchronous generator is connected with the frequency multiplier array, and the multi-path data acquisition card is connected with the splitter array.
4. A loss-compensated frequency division multiplexing millimeter wave three-dimensional imaging device according to claim 3, wherein said multi-frequency signal synchronizing generator outputs single-frequency signals of N channels to the radio frequency unit, and the frequencies of the output signals of each channel are different and distributed at equal intervals; the frequency of the output signal of each channel is unchanged in one subcycle; in the next sub-period, the frequency of all channel output signals realizes rotation; each channel traverses all the signals of N frequencies over N subcycles.
5. The loss-compensated frequency division multiplexing millimeter wave three-dimensional imaging device of claim 2, wherein said millimeter wave transceiver array comprises a transmitter array and a receiver array, said transmitter array receiving N channels of millimeter wave signals output by said power divider array and transmitting said signals to said electronic switch array; the receiver array receives the output of the electronic switch array and transmits the output to the quadrature mixer array.
6. The loss-compensated frequency division multiplexing millimeter wave three-dimensional imaging device of claim 2, wherein said quadrature mixer array comprises N90 ° phase shifters and 2N mixers; for each channel, the phase shifter shifts the phase of the output signal of the power divider array by 90 degrees and then transmits the shifted phase to the second mixer, the first mixer directly receives the output signal of the power divider array, the two mixers also simultaneously receive the return signal of the channel output by the millimeter wave transceiver array, and the amplitude and phase information of the signals obtained after mixing are output to the splitter array.
7. The loss-compensated frequency division multiplexing millimeter wave three-dimensional imaging device of claim 2, wherein said antenna array comprises N transmitting antennas and N receiving antennas distributed in equidistant planes.
8. The loss-compensated frequency division multiplexing millimeter wave three-dimensional imaging device of claim 2, wherein the splitter array receives the amplitude signals and the phase information of N channels simultaneously, and there are 2N input channels in total, and M input channels selected each time are directly transmitted to the multi-channel data acquisition card until all 2N input channels are acquired.
9. The loss-compensated frequency division multiplexing millimeter wave three-dimensional imaging method of claim 1, comprising the steps of:
step 1: backscatter data s (x 0 ,y 0 Performing conjugate processing on the k) and then performing transverse two-dimensional Fourier transformation to obtain S * (k x ,k y ,k)；
wherein ,x0 Representing the horizontal axis position of the receiving antenna in the plane of the antenna array, y 0 The vertical axis position of the receiving antenna on the plane of the antenna array is shown, and k represents the signal wave number of the corresponding channel of the receiving antenna; k (k) x Wavenumbers representing the horizontal axis; k (k) y Wavenumbers representing the vertical axis; * Representing conjugate operation;
step 2: will S * (k x ,k y K) multiplying a phase compensation factor, and converting the phase of the back scattering data to the phase of the nearest distance between the target object area and the antenna array along the radial axis;
step 3: interpolation processing is carried out on the data obtained in the step 2, and wave number domain data F (k) of the reflection coefficient of the target object is obtained x ,k y ,k z )；k z Wavenumbers representing radial axes;
step 4: for wave number domain data F (k) x ,k y ,k z ) Performing transverse two-dimensional inverse Fourier transform to obtain data
Step 5: for data
Radial one-dimensional Fourier transform is carried out to obtain data
Step 6: multiplying the data obtained in the step 5 with a set index term to compensate the frequency shift of the target object at different radial distances;
multiplying the obtained data with a set constant term to carry out amplitude compensation on the attenuation loss; wherein the obtained data is obtained by multiplying the data obtained in the last step with a set index term;
multiplying the data by
And the result is conjugated, so that phase correction is realized, and the reflection coefficients of each point of the target object are obtained; and meanwhile, the radial resolution determined by the signal bandwidth is utilized to realize the positioning of the target object on the radial axis.
10. The loss-compensated frequency division multiplexing millimeter wave three-dimensional imaging method according to claim 1, wherein the phase compensation factor in step 2 is specifically
wherein ,z0 The nearest distance between the target object area and the antenna array along a radial axis, wherein the radial axis is orthogonal to a transverse plane where the antenna array is positioned; k (k) z Representing the wave number of the radial axis, an
Wherein k represents the signal wave number of the corresponding channel of the receiving antenna; k (k) x Wavenumbers representing the horizontal axis; k (k) y The wave number of the vertical axis is indicated. />
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