A quantitative electromagnetic imaging method based on target multi-frequency spatial spectrum stitching

Abstract

The present invention discloses an electromagnetic quantitative imaging method based on target multi-frequency spatial spectrum splicing, the purpose of which is to solve the problem of poor imaging accuracy caused by multi-frequency spatial spectrum aliasing in traditional diffraction tomography methods, realize geometric imaging and physical imaging of the target, and belong to the field of radar imaging. The present invention first performs spatial two-dimensional Fourier transform processing on the backscattered echo signal to obtain a spectrum domain signal, then performs coordinate transformation and interpolation on the spectrum domain signal, and then processes the real part and imaginary part of the spectrum domain signal respectively to obtain a dielectric parameter spectrum domain and a conductivity spectrum domain, and then performs de-aliasing processing on the multi-frequency dielectric parameter spectrum domain and the conductivity spectrum domain to obtain a multi-frequency spliced ​​dielectric parameter spectrum domain and a conductivity spectrum domain of the target, reduce the influence of the aliased spectrum domain on the imaging performance of the target, and finally obtain the geometric imaging and physical imaging of the target body.

Description

Technical Field

[0001] The present invention proposes an electromagnetic quantitative imaging method based on target multi-frequency spatial spectrum stitching. The proposed imaging method uses multi-frequency measurement of the target to obtain backscattering field data, then eliminates aliasing spectra in the spectral domain, and finally obtains geometric imaging and physical imaging of the target, which belongs to the field of radar imaging. Background Art

[0002] The backscattered echo data received by the radar is used to invert and reconstruct the position, shape, size and electrical parameters of the target, and the dielectric parameters or conductivity profile of the reconstructed area are obtained, which can be widely used in mine clearance engineering, civil engineering, archaeological applications, early warning identification, etc.

[0003] There are three types of radar measurement configurations. The first is to perform a one-dimensional scan along the survey line. The transmitting antenna moves along the survey line M times at a fixed interval. Each time it moves, the receiving antenna receives the scattered echo of the detection area at N measurement points in the direction of the survey line, and obtains M×N channels of scattering data, that is, the Multiple-Input Multiple-Output (MIMO) mode; the second is that the transmitting antenna and the receiving antenna move along the survey line at fixed intervals respectively, and the receiving antenna receives the scattered echo of the detection area at M observation positions, and obtains M channels of scattering data; the third is that the transmitting antenna is fixed at one position to transmit electromagnetic waves to the detection area, and the receiving antenna receives the scattered echo at M observation positions, and obtains M channels of scattering data, that is, the Single-Input Multiple-Output (SIMO) mode. The spatial spectra obtained by the three radar measurement configurations are different, but they all need to solve the spatial spectrum aliasing problem first. This patent takes the MIMO radar detection mode as an example, and can obtain imaging results in the azimuth and range directions, but the scope of application is not limited to the MIMO radar detection mode.

[0004] Among radar imaging methods, inverse scattering imaging is a research hotspot. The nonlinear inverse scattering imaging method can reconstruct the target object with high accuracy, but in the imaging process, it is necessary to perform step-by-step iterative operations, which is computationally intensive and not suitable for engineering applications. Therefore, a reasonable approximation is used under certain specific conditions to obtain a linear inverse scattering imaging method. The theoretical basis of the linear inverse scattering imaging method is diffraction tomography. This method is based on Fourier transform and linear Born approximation, and is based on electromagnetic scattering theory. By analyzing the correspondence between the electromagnetic parameters of the target and multi-angle scattering data in the spatial-spectral domain, the electromagnetic parameter information, position, and shape information of the target can be obtained.

[0005] The traditional diffraction tomography method directly superimposes the multi-frequency target spatial spectrum without considering the spectrum aliasing problem. Since there are aliasing areas in the multi-frequency spatial spectrum, the aliasing spectrum accumulated multiple times will interfere with the results of quantitative electromagnetic imaging. Even if the frequency step interval can be reasonably set to reduce the impact of spatial spectrum aliasing on the accuracy of quantitative imaging, the imaging result still has errors and the problem cannot be fundamentally solved. In order to obtain accurate target geometric information and physical parameters, it is necessary to utilize or discard the aliasing spectrum. The present invention proposes an electromagnetic quantitative imaging method based on the splicing of target multi-frequency spatial spectrum. Summary of the invention

[0006] The technical problem to be solved by the present invention is to reduce the influence of multi-frequency spatial spectrum aliasing on the accuracy of target electromagnetic quantitative imaging, so as to overcome the defects of the prior art.

[0007] The method of the present invention comprises the following technical measures:

[0008] An electromagnetic quantitative imaging method based on target multi-frequency spatial spectrum stitching includes the following steps:

[0009] Obtain the backscattered echo signal and perform two-dimensional Fourier transform to obtain the scattering field spectrum domain signal;

[0010] The scattering field spectrum domain signal is subjected to coordinate transformation and cubic interpolation processing to obtain the target multi-frequency spatial spectrum;

[0011] Process the target multi-frequency spatial spectrum to obtain the scattering field dielectric parameter spectrum domain and the scattering field conductivity spectrum domain;

[0012] De-aliasing is performed on the scattered field dielectric parameter spectrum domain and the scattered field conductivity spectrum domain respectively, and then accumulation and splicing are performed to obtain the target multi-frequency splicing dielectric parameter spectrum domain and the target multi-frequency splicing conductivity spectrum domain;

[0013] A two-dimensional inverse Fourier transform is performed on the target multi-frequency splicing dielectric parameter spectrum domain and the target multi-frequency splicing conductivity spectrum domain to obtain the target imaging.

[0014] The step of acquiring the backscattered echo signal and performing a two-dimensional Fourier transform to obtain a scattering field spectrum domain signal comprises:

[0015] Obtaining the incident two-dimensional Green's function of the backscattered echo signal, determining the target contrast function, and defining the spectral domain Fourier transform of the target contrast function to obtain the backscattered field signal;

[0016] Perform two-dimensional Fourier transform on the backscattered field signal to obtain the scattered field spectral domain signal.

[0017] The coordinate transformation and cubic interpolation processing of the scattered field spectrum domain signal are performed to obtain the target multi-frequency spatial spectrum, including:

[0018] Convert from the two-dimensional spatial domain form to the two-dimensional spectral domain form, and perform coordinate transformation on the scattering field dielectric parameter spectrum domain and the scattering field conductivity spectrum domain;

[0019] The scattering field dielectric parameter spectrum domain and the scattering field conductivity spectrum domain after coordinate transformation are subjected to cubic interpolation processing to obtain the target multi-frequency spatial spectrum.

[0020] The processing of the target multi-frequency spatial spectrum to obtain the scattering field dielectric parameter spectrum domain and the scattering field conductivity spectrum domain includes:

[0021] According to the target contrast function, the real part and imaginary part of the target multi-frequency spatial spectrum are processed to obtain the dielectric parameter spectrum domain signal and the conductivity spectrum domain signal respectively.

[0022] The anti-aliasing process comprises:

[0023] The scattering field dielectric parameter spectrum domain and the scattering field conductivity spectrum domain are analyzed respectively, and the aliasing region of the scattering field dielectric parameter spectrum domain and the aliasing region of the scattering field conductivity spectrum domain are determined according to the overlapping region judgment standard;

[0024] Anti-aliasing is performed on the aliasing region of the scattering field dielectric parameter spectrum domain and the aliasing region of the scattering field conductivity spectrum domain respectively.

[0025] The overlapping area judgment criteria specifically include:

[0026] The frequencies of the beam vectors in the x-direction of the spectrum domain are compared. When the positive root value of the sum of the squares of the two-dimensional spectrum domain coordinates at the current moment frequency is less than and equal to the beam vector in the x-direction at the previous moment frequency, it is determined to be an aliasing area.

[0027] The overlapping area judgment criteria are specifically:

[0028]

[0029] is the sum of the squares of the two-dimensional spectral domain coordinates at the current frequency, k0(f n-1 ) is the wave number vector in the x direction at the frequency of the previous moment.

[0030] Performing a two-dimensional inverse Fourier transform on the target multi-frequency spliced ​​dielectric parameter spectrum domain and the target multi-frequency spliced ​​conductivity spectrum domain to obtain target imaging includes:

[0031] Perform multiplication processing on the target multi-frequency spliced ​​conductivity spectrum domain;

[0032] The target multi-frequency splicing dielectric parameter spectrum domain and the target multi-frequency splicing conductivity spectrum domain after multiplication are obtained and subjected to two-dimensional inverse Fourier transform to obtain the geometric imaging, dielectric parameter distribution and conductivity distribution of the target in space.

[0033] The multiplication processing of the target multi-frequency splicing conductivity spectrum domain includes:

[0034] Get the electromagnetic wave frequency at the current moment and multiply it with the target multi-frequency spliced ​​conductivity spectrum domain at the current moment.

[0035] The present invention can achieve the following technical effects:

[0036] The present invention first performs a spatial two-dimensional Fourier transform process on the backscattered echo signal to obtain a spectral domain signal, which is the first Fourier transform process. Then, coordinate transformation and interpolation are performed on the spectral domain signal, and then the real part and imaginary part of the spectral domain signal are processed respectively to obtain a dielectric parameter spectrum domain and a conductivity spectrum domain, and then the multi-frequency dielectric parameter spectrum domain and the conductivity spectrum domain are subjected to a de-aliasing process to obtain a multi-frequency spliced ​​dielectric parameter spectrum domain and a conductivity spectrum domain of the target, reduce the influence of the aliased spectrum domain on the imaging performance of the target, perform a two-dimensional inverse Fourier transform on the target multi-frequency spliced ​​dielectric parameter spectrum domain and the target multi-frequency spliced ​​conductivity spectrum domain, which is the second Fourier transform, and finally obtain the geometric imaging and physical imaging of the target body. The whole process only performs two Fourier transforms, maintaining a low amount of calculation. It can be seen that after the aliased spectrum is eliminated, the contour of the imaging target is more accurate. It solves the problem of poor imaging accuracy caused by multi-frequency spectrum aliasing in traditional diffraction tomography methods, realizes geometric imaging and physical imaging of the target, has good imaging performance, low cost, fast imaging speed, and has strong engineering application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is a flow chart of the present invention;

[0038] Figure 2 A flowchart of an embodiment of the present invention;

[0039] Figure 3 Schematic diagram of spectral domain filling configured for multi-frequency MIMO radar detection mode;

[0040] Figure 4a It is the spectrum domain diagram of dielectric parameters after multi-frequency accumulation;

[0041] Figure 4b It is the conductivity spectrum after multi-frequency accumulation;

[0042] Figure 5a The dielectric parameters and conductivity results of the diffraction tomography of the present invention;

[0043] Figure 5b Dielectric parameters and conductivity results for conventional diffraction tomography. DETAILED DESCRIPTION

[0044] Figure 1This is a flow chart of electromagnetic quantitative imaging based on target multi-frequency spatial spectrum stitching of the present invention. Figure 1 , the method proposed by the present invention is further explained. The specific steps and effects of the present invention are as follows:

[0045] Step 1: 101 is to obtain a backscattered echo signal and perform a two-dimensional Fourier transform to obtain a scattered field spectrum domain signal, wherein the scattered echo signal is a TM wave.

[0046] Step 2: 102 is to perform coordinate transformation and cubic interpolation processing on the scattered field spectrum domain signal. In the coordinate transformation part, the coordinates of the scattered field spectrum domain signal are transformed from a two-dimensional spatial domain form to a two-dimensional spectrum domain form. After the coordinate transformation processing, there is a unique correspondence between the coordinates, and then the spectrum domain is interpolated, and the interpolation adopts a cubic interpolation method. The target multi-frequency spatial spectrum is obtained.

[0047] Step 3: 103 is to process the target multi-frequency spatial spectrum to obtain the scattering field dielectric parameter spectrum domain and scattered field conductivity domain

[0048] Step 4: 104 is to perform de-aliasing processing on the scattered field dielectric parameter spectrum domain and the scattered field conductivity spectrum domain respectively, and then perform accumulation splicing processing to obtain the target multi-frequency splicing dielectric parameter spectrum domain and the target multi-frequency splicing conductivity spectrum domain.

[0049] Step five: 105 is to perform a two-dimensional inverse Fourier transform on the target multi-frequency splicing dielectric parameter spectrum domain and the target multi-frequency splicing conductivity spectrum domain to obtain the target imaging.

[0050] Combination Figure 2 , the embodiments of the above steps are further explained.

[0051] Regarding the above step one, in one of the embodiments, specifically, a two-dimensional Green's function of the incident backscattered echo signal is obtained, a target contrast function is determined, and a spectral domain Fourier transform of the target contrast function is defined to obtain a backscattered field signal; and a two-dimensional Fourier transform is performed on the backscattered field signal to obtain a spectral domain signal of the scattered field.

[0052] More specifically, the backscattered echo signal is a TM wave, and the TM wave incident two-dimensional Green function is:

[0053]

[0054] where ρ R represents the distance from the receiving antenna to the target, ρ represents the distance from the target to the receiving antenna, ω represents the frequency of the electromagnetic wave, It represents the component of the wave number vector in the z direction when the electromagnetic wave propagates in the air. represents the component of the wave number vector in the x direction when the electromagnetic wave propagates in the air, ε0 and μ0 represent the dielectric parameter and magnetic permeability in free space respectively, and k x represents the x-coordinate spectrum domain form of the receiving antenna, (x R ,z R ) represents the receiving antenna coordinates, and (x,z) represents the target coordinates.

[0055] Define the transmit antenna coordinates (x T ,z'), receiving antenna coordinates (x R ,z'), the distance from the receiving antenna to the target and the distance from the transmitting antenna to the target are ρ R and ρ T , the x-coordinate spectral domain forms of the receiving and transmitting antennas are k x and k' x , using the two-dimensional Green function of TM wave incidence, the scattered field has the following form:

[0056]

[0057] in, Represents the target contrast function. Define the target ratio function spectral domain Fourier transform:

[0058]

[0059] Formula (2) gives

[0060]

[0061] The Fourier transform of the scattered field in the spectral domain can be defined as

[0062]

[0063]

[0064] According to formula (6), formula (4) can be deduced to obtain

[0065]

[0066] Therefore, formula (7) can be derived as follows:

[0067]

[0068] Regarding the above step 2, in one embodiment, the two-dimensional spatial domain form may be transformed into the two-dimensional spectral domain form, and the scattering field dielectric parameter spectral domain and the scattering field conductivity spectral domain may be coordinate transformed;

[0069] The multi-frequency MIMO mode configuration method realizes the spatial spectrum filling of the objective function such as Figure 3As shown, that is, the scattering data from (o,k x ,k' x ) domain to (o,k” x ,k” z ) domain, where (o,k x ,k' x ) is a two-dimensional spatial form, (o,k” x ,k” z ) is in the form of two-dimensional spectrum domain;

[0070] k” x =k x -k' x ,k” z =-γ res -γ' res (9)

[0071] M×N channels of scattering data can be obtained under multi-aperture scanning of the array antenna. Here, the apertures of the transmitting and receiving arrays are made to coincide, that is, the transmitting aperture and the receiving aperture have the same aperture extension length and sampling interval.

[0072] In fact, (o,k x ,k' x ) domain to (o,k” x ,k” z ) domain, ideally, the spectrum domain filling form for single-frequency incidence is an area composed of three semicircles: the first semicircle is a semicircle with a center of (0,0) and a radius of 2k0; the second semicircle is a semicircle with a center of (-k0,0) and a radius of k0; the third semicircle is a semicircle with a center of (k0,0) and a radius of k0.

[0073] Ideally, in the multi-aperture scattered echo, the frequency component is f min The target spectral domain form filled with the components is shown in the shadow in the figure. When a broadband signal is used for detection, the spectral domain filling forms of different frequency components are combined together to form the spectral domain support of multi-channel scattering data. Figure 3 The frequency component f is also given in max The target volume spectral domain is filled with components. Because Figure 3 The scanning scene in the figure can only obtain the backscattered echo of the target body, so in the spectral domain filling diagram here, only k" can be filled z The area of ​​the negative semi-axis.

[0074] The scattering field dielectric parameter spectrum domain and the scattering field conductivity spectrum domain after coordinate transformation are subjected to cubic interpolation processing to obtain the target multi-frequency spatial spectrum.

[0075] Due to k x -k' x Any straight line in the spectral domain and k"x -k" z There is a unique correspondence between the coordinates of the domains, and the spectral domain can be interpolated after the coordinates are transformed.

[0076]

[0077] Finally, cubic interpolation is used to obtain the target contrast function spectrum after coordinate transformation.

[0078] For the above step three, in one of the embodiments, the target multi-frequency spatial spectrum is processed to obtain the scattered field dielectric parameter spectrum domain and the scattered field conductivity spectrum domain, specifically: according to the target contrast function, the real part and the imaginary part of the target multi-frequency spatial spectrum are processed to obtain the dielectric parameter spectrum domain signal and the conductivity spectrum domain signal respectively.

[0079] According to the contrast function expression, the real part of the spectrum domain signal represents the dielectric parameter spectrum domain, and the imaginary part of the spectrum domain signal represents the conductivity spectrum domain. The conductivity spectrum domain is a function related to the frequency of the electromagnetic wave, so the following expression can be obtained:

[0080]

[0081]

[0082] The scattered field dielectric parameter spectrum domain and the scattered field conductivity spectrum domain are spectral domain signals. The interpolation part in the embodiment of step 2 can be processed uniformly in the scattered field dielectric parameter spectrum domain and the scattered field conductivity spectrum domain, and the anti-aliasing part in step 4 needs to be processed separately.

[0083] With respect to the above step 4, in one embodiment, the anti-aliasing process is specifically: analyzing the scattered field dielectric parameter spectrum domain and the scattered field conductivity spectrum domain respectively, and determining the aliasing region portion of the scattered field dielectric parameter spectrum domain and the aliasing region portion of the scattered field conductivity spectrum domain according to the overlapping region judgment criterion;

[0084] Anti-aliasing is performed on the aliasing region of the scattering field dielectric parameter spectrum domain and the aliasing region of the scattering field conductivity spectrum domain respectively.

[0085] The Fourier transform result of the scattered field signal obtained in the embodiment of step 1 can be regarded as the energy addition of the spectrum at different frequencies from the spectrum domain; the single frequency spectrum domain area is expressed as

[0086]

[0087] Among them, k0(f n ) is the frequency f n The component of the wave number vector in the x direction when the electromagnetic wave propagates in the air.

[0088] However, due to the existence of overlapping areas between multi-frequency spectral domains, directly accumulating the spectrum leads to reduced imaging accuracy. The overlapping area judgment criteria specifically include: comparing the frequencies of the beam vectors in the spectral domain in the x-direction, and when the positive root value of the sum of the squares of the two-dimensional spectral domain coordinates at the current moment frequency is less than and equal to the beam vector in the x-direction at the previous moment frequency, it is judged to be an aliasing area.

[0089] The aliasing region is represented by

[0090]

[0091] The aliased spectrum domain will be discarded, and the remaining spectrum domains will be accumulated and spliced ​​to obtain the dielectric parameter spectrum domain and the conductivity spectrum domain as shown in Figure 4.

[0092] With respect to the above step 5, in one embodiment, performing a two-dimensional inverse Fourier transform on the target multi-frequency spliced ​​dielectric parameter spectrum domain and the target multi-frequency spliced ​​conductivity spectrum domain to obtain the target imaging includes:

[0093] Since the spectral domain of conductivity is a function related to the frequency of electromagnetic waves, it is necessary to multiply the current electromagnetic wave frequency when performing a two-dimensional inverse Fourier transform, and multiply the target multi-frequency spliced ​​conductivity spectrum to obtain the current electromagnetic wave frequency and the current target multi-frequency spliced ​​conductivity spectrum for multiplication.

[0094] The target multi-frequency splicing dielectric parameter spectrum domain and the target multi-frequency splicing conductivity spectrum domain after multiplication are obtained and subjected to two-dimensional inverse Fourier transform to obtain the geometric imaging, dielectric parameter distribution and conductivity distribution of the target in space.

[0095] Perform a two-dimensional inverse Fourier transform on the spectral domain signal in Figure 4

[0096]

[0097]

[0098] Accumulate and splice multiple frequencies separately and Perform a two-dimensional inverse Fourier transform in the spectral domain, where k x -k' x =k" x (f) and -γ res -γ' res =k" z (f) It is worth noting that since the spectral domain of conductivity is a function related to the frequency of electromagnetic waves, it is necessary to multiply it by the current electromagnetic wave frequency when performing a two-dimensional inverse Fourier transform to obtain the geometric imaging of the target in space and the distribution of its dielectric parameters and conductivity. Figure 5a The dielectric parameters and conductivity results of the diffraction tomography of the present invention are shown. Figure 5b Dielectric parameters and conductivity results for conventional diffraction tomography.

[0099] The present invention provides the following specific examples, and the performance of the method proposed in the present invention is verified in combination with the examples.

[0100] The finite difference frequency domain (FDFD) method is used to perform forward calculation of the target in the air, and the multi-frequency MIMO radar detection method is used. Then, the imaging method of formula (8) is used for imaging processing. The transmitting and receiving antennas are located at 0m on the y-axis, the transmitting antennas are evenly arranged along the x-axis from -1.5m to 1.5m, and the receiving antennas are from -1.55m to 1.55m, with a spacing of 0.1m. 31×32 channels of scattering data can be obtained. The working frequency band is 1GHz-2.35GHz, with an interval of 30MHz. Under the same scanning geometry, the wider the bandwidth, the larger the spectral domain filling area of ​​the target body, and the better the imaging result. The imaging target is a metal rectangular target (vertex coordinates (-0.245, 2.4), (-0.5, 2.25), (-0.35, 2), (-0.1, 2.15), ε r =1,σ=10 5 mS / m) and a strong scattering cylinder (center (0.3, 1.8), radius 0.15m, ε r =10, σ=0mS / m), the imaging result is shown in FIG4 , where the dotted line portion is the actual position of the target.

[0101] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. An electromagnetic quantitative imaging method based on target multi-frequency spatial spectrum stitching, characterized in that: The following steps are involved: Obtain the backscattered echo signal and perform two-dimensional Fourier transform to obtain the scattering field spectrum domain signal; The scattering field spectrum domain signal is subjected to coordinate transformation and cubic interpolation processing to obtain the target multi-frequency spatial spectrum; Process the target multi-frequency spatial spectrum to obtain the scattering field dielectric parameter spectrum domain and the scattering field conductivity spectrum domain; De-aliasing is performed on the scattered field dielectric parameter spectrum domain and the scattered field conductivity spectrum domain respectively, and then accumulation and splicing are performed to obtain the target multi-frequency splicing dielectric parameter spectrum domain and the target multi-frequency splicing conductivity spectrum domain; A two-dimensional inverse Fourier transform is performed on the target multi-frequency splicing dielectric parameter spectrum domain and the target multi-frequency splicing conductivity spectrum domain to obtain the target imaging.

2. The electromagnetic quantitative imaging method based on target multi-frequency spatial spectrum stitching according to claim 1, characterized in that: The step of acquiring the backscattered echo signal and performing a two-dimensional Fourier transform to obtain a scattering field spectrum domain signal comprises: Obtaining the incident two-dimensional Green's function of the backscattered echo signal, determining the target contrast function, and defining the spectral domain Fourier transform of the target contrast function to obtain the backscattered field signal; Perform two-dimensional Fourier transform on the backscattered field signal to obtain the scattered field spectral domain signal.

3. The electromagnetic quantitative imaging method based on target multi-frequency spatial spectrum stitching according to claim 1, characterized in that: The coordinate transformation and cubic interpolation processing of the scattered field spectrum domain signal are performed to obtain the target multi-frequency spatial spectrum, including: Convert from the two-dimensional spatial domain form to the two-dimensional spectral domain form, and perform coordinate transformation on the scattering field dielectric parameter spectrum domain and the scattering field conductivity spectrum domain; The scattering field dielectric parameter spectrum domain and the scattering field conductivity spectrum domain after coordinate transformation are subjected to cubic interpolation processing to obtain the target multi-frequency spatial spectrum.

4. The electromagnetic quantitative imaging method based on target multi-frequency spatial spectrum stitching according to claim 1, characterized in that: The processing of the target multi-frequency spatial spectrum to obtain the scattering field dielectric parameter spectrum domain and the scattering field conductivity spectrum domain includes: According to the target contrast function, the real part and imaginary part of the target multi-frequency spatial spectrum are processed to obtain the dielectric parameter spectrum domain signal and the conductivity spectrum domain signal respectively.

5. The electromagnetic quantitative imaging method based on target multi-frequency spatial spectrum stitching according to claim 1, characterized in that: The anti-aliasing process comprises: The scattering field dielectric parameter spectrum domain and the scattering field conductivity spectrum domain are analyzed respectively, and the aliasing region of the scattering field dielectric parameter spectrum domain and the aliasing region of the scattering field conductivity spectrum domain are determined according to the overlapping region judgment standard; Anti-aliasing is performed on the aliasing region of the scattering field dielectric parameter spectrum domain and the aliasing region of the scattering field conductivity spectrum domain respectively.

6. The electromagnetic quantitative imaging method based on target multi-frequency spatial spectrum stitching according to claim 5, characterized in that: The overlapping area judgment criteria specifically include: The frequencies of the beam vectors in the x-direction of the spectrum domain are compared. When the positive root value of the sum of the squares of the two-dimensional spectrum domain coordinates at the current moment frequency is less than and equal to the beam vector in the x-direction at the previous moment frequency, it is determined to be an aliasing area.

7. The electromagnetic quantitative imaging method based on target multi-frequency spatial spectrum stitching according to claim 5, characterized in that: The overlapping area judgment criteria are specifically: is the sum of the squares of the two-dimensional spectral domain coordinates at the current frequency, k0(f n-1 ) is the wave number vector in the x direction at the frequency of the previous moment.

8. The electromagnetic quantitative imaging method based on target multi-frequency spatial spectrum stitching according to claim 1, characterized in that: Performing a two-dimensional inverse Fourier transform on the target multi-frequency spliced ​​dielectric parameter spectrum domain and the target multi-frequency spliced ​​conductivity spectrum domain to obtain target imaging includes: Perform multiplication processing on the target multi-frequency spliced ​​conductivity spectrum domain; The target multi-frequency splicing dielectric parameter spectrum domain and the target multi-frequency splicing conductivity spectrum domain after multiplication are obtained and subjected to two-dimensional inverse Fourier transform to obtain the geometric imaging, dielectric parameter distribution and conductivity distribution of the target in space.

9. The electromagnetic quantitative imaging method based on target multi-frequency spatial spectrum stitching according to claim 8, characterized in that: The multiplication processing of the target multi-frequency splicing conductivity spectrum domain includes: Get the electromagnetic wave frequency at the current moment and multiply it with the target multi-frequency spliced ​​conductivity spectrum domain at the current moment.

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