CN104459691A - Two-dimensional short-range microwave holographic imaging method - Google Patents

Abstract

The invention discloses a two-dimensional short-range microwave holographic imaging method. According to the method, parameter data of an objective scattered field and parameter data of an objective incident field are obtained through actual measuring or a simulation mode, the more real objective scattered field and the more real objective incident field can be obtained, and the irrationality that an incident field is assumed as spherical waves or cylindrical waves in the short-range millimeter wave holographic imaging technology is overcome; the least square solution of an overdetermined equation utilized in an objective image is solved and serves as two-dimensional Fourier transform of an objective function, the range of the imaging objective can be enlarged, and the imaging definition and the accuracy of an objective at different background environments can be improved.

Description

A kind of two-dimentional short range microwave holography formation method

Technical field

The invention belongs to microwave holography imaging field, be specifically related to a kind of two-dimentional short range microwave holography formation method.

Background technology

Microwave holography is one inversion technique fast, and it is extended by traditional light holographic technique, and the main amplitude of measurement target scattered field and the phase place of relying on obtains objective holographic figure, then obtains target microwave imagery through inverting.At present, microwave holography formation method is mainly short range millimeter wave holographic imaging method, and first the method uses spherical wave or cylindrical wave to substitute incident field, and by being arranged at the transmitting and receiving antenna of target the same side, gathers the backscatter data of target; Then direct two-dimensional Fourier transform is carried out to these scattering datas, then be multiplied by a phase compensation term; Reconstruct target is drawn after finally two-dimensional inverse Fourier transform being carried out to the result after compensation.But said method exists following not enough: (1) replaces incident field owing to using spherical wave or cylindrical wave, and this substituting for short range imaging is irrational, and incident field should be definite numeric form, so make image quality decline; (2) because transmitting and receiving antenna is placed in target side together, so can only collect backscatter data, thus image quality declines again further; (3) scattering data used when object reconstruction and incident field data directly carry out Fourier transform without after effective process, gained is image blurring resolution rate variance; (4) there is the sampling to x, y direction wave number in imaging formula during object reconstruction, error is large, and only uses backscatter data to solve target density function, differs larger with the optimum solution of target density function.

Summary of the invention

Technical matters to be solved by this invention is the deficiency that the resolution of existing short range microwave holography formation method existence is low, provides a kind of two-dimentional short range microwave holography formation method.

For solving the problem, the present invention is achieved by the following technical solutions:

A kind of two-dimentional short range microwave holography formation method, comprises the steps:

Step 1, sets emitting antenna and the X-axis of receiving antenna and the start-stop position of Y-axis and scanning pattern respectively;

Step 2, target to be reconstructed placed between the transmit antennas and the receive antennas, emitting antenna, receiving antenna and target form 1 two-port network, and wherein emitting antenna and receiving antenna are as Two-port netwerk;

Step 3, the target treating reconstruct according to the setup control emitting antenna of step 1 and receiving antenna scans, and obtains 4 S parameter on each of the scanning positions thus;

Step 4, removes target to be reconstructed, and scans target according to the setup control emitting antenna of step 1 and receiving antenna, obtains the Near-field Data of 4 coupling S parameter and 4 corresponding objective planes thus on each of the scanning positions;

Step 5, deducts 4 coupling S parameter of step 4 gained respectively by the target current location scattering data of step 3 gained i.e. 4 S parameter, obtain 4 corresponding calibration S parameter of each scanning position;

Step 6, substitutes into the Near-field Data of 4 of step 3 gained objective planes respectively in scattering parameter computing formula and draws 4 scattering parameters;

4 of step 5 gained calibration S parameter and corresponding step 6 gained 4 scattering parameters are updated in target density parameter calculation formula, obtain 4 overdetermined equations by step 7;

Step 8, the least square solution of the over-determined systems that 4 overdetermined equations of solution procedure 7 gained form;

Step 9, obtains target density parameter after carrying out two-dimentional inverse Fourier transform, reconstruct target thus to the result of the least square solution of step 8 gained.

In above-mentioned steps 1, described emitting antenna and receiving antenna are half-wave dipole antenna or electromagnetic horn.

In above-mentioned steps 3, adopt rectangular node division methods to obtain 4 S parameter of each scanning position, namely interval delta x, the Δ y of transmitting and receiving antenna scanning X, Y direction are as rectangle X, Y direction mesh spacing, i.e. 4 S parameter of each rectangular node correspondence.In like manner, in step 4, also adopt rectangular node division methods to obtain 4 coupling S parameter of each scanning position, namely interval delta x, the Δ y of transmitting and receiving antenna scanning X, Y direction are as rectangle X, Y direction mesh spacing, corresponding 4 the coupling S parameter of each rectangular node.

In above-mentioned steps 6, described scattering parameter computing formula is:

$g_0(x,y,\stackrel{\‾}{z})=\frac{E_{\mathrm{inc}}(x,y,\stackrel{\‾}{z})e^{-j{k}_b\sqrt{{(x^2+y^2+(D-\stackrel{\‾}{z})}^2}}}{\sqrt{x^2+y^2+{(D-\stackrel{\‾}{z})}^2}}$ ①

In formula, for target exists the scattering parameter of position, D is the z-axis position coordinates of receiving antenna, and e represents exponential function, and j represents the imaginary number in plural number, for the Near-field Data of the objective plane of position, k _bfor scattering wave number during driftlessness.

In above-mentioned steps 7, described target density parameter calculation formula is:

$\mathrm{\ρ}(x,y,\stackrel{\‾}{z})=F{T}_{2D}^{-1}\left\{\frac{E_{\mathrm{sca}}(k_x,k_y)}{G_0(k_x,k_y,\stackrel{\‾}{z})}\right\}$ ②

In formula, for target exists the target density parameter of position, represent two-dimensional inverse Fourier transform; E _sca(k _x, k _y) be calibration S parameter take Fourier coefficient as k _x, k _ytwo-dimensional Fourier transform acquired results, for scattering parameter take Fourier coefficient as k _x, k _ytwo-dimensional Fourier transform result.

In such scheme, in described step 3, in target current location scattering data and step 4, the Near-field Data of objective plane is all obtained by software emulation method.

Compared with prior art, the present invention has the following advantages:

1, the supplemental characteristic of target scattering field and incident field is obtained by true measurement or analog form, more real target scattering field and incident field can be obtained, thus solve in short range millimeter wave holographic imaging technology and suppose that incident field is the irrationality of spherical wave or cylindrical wave; Solve in target image utilize over-determined systems least square solution as the two-dimensional Fourier transform of objective function, the scope of imageable target can be expanded and improve sharpness and the precision of the imaging of target under different background environments;

2, Fast Fourier Transform (FFT) (FFT) implementation algorithm is adopted greatly can to improve the efficiency of algorithm, the gridding method processing target holographic data of being drawn by FFT, correct for the grid dislocation caused by scanister system noise and external influence factor, thus effectively eliminate grid and to misplace the aliasing effect caused, improve sharpness and the image quality of object reconstruction image;

3, the mode adopting FEKO and MATLAB software to combine realizes, FEKO software simulation mode is first used to obtain the supplemental characteristic of target scattering field and incident field, again the data obtained is sent in MATLAB software and process, significantly reduce again experimental cost while experimental result can being drawn quickly like this and improve simulation accuracy; Instead of simple codes implement simulation, reduce embodiment cost, shorten the embodiment cycle, embodiment efficiency can be improved.

Accompanying drawing explanation

Fig. 1 is a kind of process flow diagram of two-dimentional short range microwave holography formation method.

Fig. 2 is data gridding process schematic diagram.

Embodiment

A kind of two-dimentional short range microwave holography formation method, as shown in Figure 1, specifically comprises the steps:

Step 1, sets emitting antenna and the X-axis of receiving antenna and the start-stop position of Y-axis and scanning pattern respectively.Described emitting antenna and receiving antenna are half-wave dipole antenna or electromagnetic horn.

Step 2, target to be reconstructed placed between the transmit antennas and the receive antennas, emitting antenna, receiving antenna and target form 1 two-port network, and wherein emitting antenna and receiving antenna are as Two-port netwerk.

Step 3, the target treating reconstruct according to the setup control emitting antenna of step 1 and receiving antenna scans, and obtains 4 S parameter on each of the scanning positions thus.Adopt rectangular node division methods to obtain 4 S parameter of each scanning position, namely interval delta x, the Δ y of transmitting and receiving antenna scanning X, Y direction are as rectangle X, Y direction mesh spacing, i.e. 4 S parameter of each rectangular node correspondence.

Step 4, removes target to be reconstructed, and scans target according to the setup control emitting antenna of step 1 and receiving antenna, obtains the Near-field Data of 4 coupling S parameter and 4 corresponding objective planes thus on each of the scanning positions.Adopt rectangular node division methods to obtain 4 coupling S parameter of each scanning position, namely interval delta x, the Δ y of transmitting and receiving antenna scanning X, Y direction are as rectangle X, Y direction mesh spacing, corresponding 4 the coupling S parameter of each rectangular node.

Step 5, deducts 4 coupling S parameter of step 4 gained respectively by the target current location scattering data of step 3 gained i.e. 4 S parameter, obtain 4 corresponding calibration S parameter of each scanning position.

Step 6, substitutes into the Near-field Data of 4 of step 3 gained objective planes respectively in scattering parameter computing formula and draws 4 scattering parameters.

Described scattering parameter computing formula is:

$g_0(x,y,\stackrel{\‾}{z})=\frac{E_{\mathrm{inc}}(x,y,\stackrel{\‾}{z})e^{-j{k}_b\sqrt{{(x^2+y^2+(D-\stackrel{\‾}{z})}^2}}}{\sqrt{x^2+y^2+{(D-\stackrel{\‾}{z})}^2}}$ ①

In formula, for target exists the scattering parameter of position, D is the z-axis position coordinates of receiving antenna, and e represents exponential function, and j represents the imaginary number in plural number, for the Near-field Data of the objective plane of position, k _bfor scattering wave number during driftlessness.

4 of step 5 gained calibration S parameter and corresponding step 6 gained 4 scattering parameters are updated in target density parameter calculation formula, obtain 4 overdetermined equations by step 7.

Described target density parameter calculation formula is:

$\mathrm{\ρ}(x,y,\stackrel{\‾}{z})=F{T}_{2D}^{-1}\left\{\frac{E_{\mathrm{sca}}(k_x,k_y)}{G_0(k_x,k_y,\stackrel{\‾}{z})}\right\}$ ②

In formula, for target exists the target density parameter of position, represent two-dimensional inverse Fourier transform.E _sca(k _x, k _y) be calibration S parameter take Fourier coefficient as k _x, k _ytwo-dimensional Fourier transform acquired results, for scattering parameter take Fourier coefficient as k _x, k _ytwo-dimensional Fourier transform result.

Step 8, the least square solution of the over-determined systems that 4 overdetermined equations of solution procedure 7 gained form.

Step 9, obtains target density parameter after carrying out two-dimentional inverse Fourier transform, reconstruct target thus to the result of the least square solution of step 8 gained.

A kind of two-dimentional short range microwave holography formation method, it can be divided into following three parts substantially: one, the measurement of S parameter and incident field data.Two, process the data solved, make it meet algorithm requirement.Three, the data reconstruction target image after process is used.

Although S parameter and incident field all can be obtained by simulation method or actual measurement method, the time a large amount of due to practical measurement requirement and cost, thus adopt simulation method in the present embodiment.Simulation method mainly adopts electromagnetic computing software simulated target scattered field and incident field, then utilizes the data reconstruction target image of acquisition.Adopt electromagnetic computing software FEKO and MATLAB to combine in the present embodiment and realize emulation, FEKO is the three-dimensional full-wave electromagnetic simulation software that first item introduces multilevel fast multipole (MLFMM), provide the integrated analysis from the scattering properties of Antenna Design, dual-mode antenna and target and a few cover near-field scattering characteristics simulating solutions, have very comprehensive function.FEKO simulated target scattered field and incident field step: (1) scattered field parameter calculates: in FEKO, arrange antenna is half-wave dipole antenna, and in the EDITFEKO module of FEKO, in TG card, antenna x is set, y-axis coordinate variable, MATLAB calls FEKO and changes TG card x in the EDITFEKO module of FEKO, y-axis coordinate carrys out control antenna and has moved two-dimensional raster scan to target, emitting antenna, receiving antenna and target form a two-port network, two antennas are as Two-port netwerk, 4 S parameter calculating this two-port network are target current location scattering data, (2) incident field is measured: in the CADFEKO module of FEKO, arrange the Near-field Data calculating objective plane or the Near-field Data arranging FE calorimeter calculation objective plane in EDITFEKO module.

Fast Fourier Transform (FFT) (FFT) implementation algorithm can be adopted to improve efficiency of algorithm, and in order to better use FFT, the data that the present invention utilizes the process of gridding method to obtain.The S parameter of each scanning position, must form corresponding rectangular node according to its coordinate position.When measuring incident field data, also must adopt rectangular node form, and grid position is consistent with S parameter.Namely in step 3, adopt rectangular node division methods to obtain 4 S parameter of each scanning position, namely interval delta x, the Δ y of transmitting and receiving antenna scanning X, Y direction are as rectangle X, Y direction mesh spacing, i.e. 4 S parameter of each rectangular node correspondence; In like manner, in step 4, also adopt rectangular node division methods to obtain 4 coupling S parameter of each scanning position, namely interval delta x, the Δ y of transmitting and receiving antenna scanning X, Y direction are as rectangle X, Y direction mesh spacing, corresponding 4 the coupling S parameter of each rectangular node.Make each computing walked be all based on rectangular node like this, the target density function grid value finally obtained just represents target pixel value.See Fig. 2.

S parameter and incident field data are after gridding process, S parameter after process is deducted coupling S parameter and draw calibration S parameter, incident field data are substituted into scattering function computing formula simultaneously and draw corresponding scattering function, respectively two-dimensional fast fourier transform is done to the calibration S parameter drawn and scattering function again, finally substitute into the density function that objective function computing formula just can obtain target, image can be obtained by the amplitude function of density function.

Combine for FEKO and MATLAB software below and realize this method, this method is described in more detail:

(1) utilize FEKO software constitution and implementation example realistic model to carry out Initialize installation to this software, namely position and the attribute of the sweep velocity of the reference position of X-axis and Y-axis, the initial anglec of rotation, X-axis and Y-axis, scan aperture and scan mode and scanning target are set; Also tackle the transmission frequency of antenna simultaneously, the attribute of background media is arranged;

(2) in FEKO, S parameter calculates: antenna adopts half-wave dipole antenna, emitting antenna, receiving antenna and target form a two-port network, two antennas are as Two-port netwerk, MATLAB completes two-dimensional raster scan by calling FEKO control antenna, and in scanning process, MATLAB reads 4 S parameter that FEKO solves this two-port network and is target current location scattering data and saves;

(3) in FEKO, remove set reconstruct target, and re-execute step (2) survey calculation coupling S parameter data; The Near-field Data calculating objective plane is set simultaneously in the CADFEKO module of FEKO or the Near-field Data that objective plane calculated by FE calorimeter is set in EDITFEKO module; These data are read by MATLAB simultaneously and save;

In described step (2), (3), in order to better use FFT, we consider the data utilizing the process of gridding method to obtain.The S parameter of each scanning position, must form corresponding rectangular node according to its coordinate position.Antenna scanning x, y direction interval delta x, Δ y are as rectangle x, y direction mesh spacing, and the corresponding rectangle net scale value of each S parameter value as shown in Figure 2.Make each computing walked be all based on rectangular node like this, the target density function grid value finally obtained just represents target pixel value.When measuring incident field data, also must adopt rectangular node form, and grid position is consistent with S parameter.

(4) 4 S parameter that step (2) obtains are deducted respectively the coupling S parameter that step (3) obtains and draw corresponding S calibration parameter, the incident field data that step (3) obtains are drawn corresponding scattering function for scattering function computing formula, the while of 4 S calibration parameters and corresponding scattering function, target density function computing formula is by composition over-determined systems, the least square solution solving this over-determined systems is the two-dimensional Fourier transform of objective function, just obtains objective function through two-dimensional inverse Fourier transform.

The mode that the present embodiment (1) adopts FEKO and MATLAB software to combine is to realize this algorithm, FEKO software is used to obtain scattered field and the incident field data of target, sent in MATLAB software by the data obtained and process, which significantly reduces again embodiment cost and improves simulation accuracy while can drawing embodiment result quickly.(2) Fast Fourier Transform (FFT) (FFT) is adopted to improve the efficiency of this algorithm; (3) before reconstruct target image, gridding process is carried out to the data collected, effectively can improve the quality of gained target image.The proposition of this algorithm realization method can promote the fast development of modern microwave imaging technique effectively.

Claims (6)

1. a two-dimentional short range microwave holography formation method, is characterized in that, comprise the steps:

Step 1, sets emitting antenna and the X-axis of receiving antenna and the start-stop position of Y-axis and scanning pattern respectively;

Step 2, target to be reconstructed placed between the transmit antennas and the receive antennas, emitting antenna, receiving antenna and target form 1 two-port network, and wherein emitting antenna and receiving antenna are as Two-port netwerk;

Step 3, the target treating reconstruct according to the setup control emitting antenna of step 1 and receiving antenna scans, and obtains 4 S parameter on each of the scanning positions thus;

Step 4, removes target to be reconstructed, and scans target according to the setup control emitting antenna of step 1 and receiving antenna, obtains the Near-field Data of 4 coupling S parameter and 4 corresponding objective planes thus on each of the scanning positions;

Step 5, deducts 4 coupling S parameter of step 4 gained respectively by the target current location scattering data of step 3 gained i.e. 4 S parameter, obtain 4 corresponding calibration S parameter of each scanning position;

Step 6, substitutes into the Near-field Data of 4 of step 3 gained objective planes respectively in scattering parameter computing formula and draws 4 scattering parameters;

4 of step 5 gained calibration S parameter and corresponding step 6 gained 4 scattering parameters are updated in target density parameter calculation formula, obtain 4 overdetermined equations by step 7;

Step 8, the least square solution of the over-determined systems that 4 overdetermined equations of solution procedure 7 gained form;

Step 9, obtains target density parameter after carrying out two-dimentional inverse Fourier transform, reconstruct target thus to the result of the least square solution of step 8 gained.

2. one according to claim 1 two-dimentional short range microwave holography formation method, is characterized in that, in step 1, described emitting antenna and receiving antenna are half-wave dipole antenna or electromagnetic horn.

3. one according to claim 1 two-dimentional short range microwave holography formation method, it is characterized in that, in step 3, rectangular node division methods is adopted to obtain 4 S parameter of each scanning position, namely interval delta x, the Δ y of transmitting and receiving antenna scanning X, Y direction are as rectangle X, Y direction mesh spacing, i.e. 4 S parameter of each rectangular node correspondence;

In like manner, in step 4, also adopt rectangular node division methods to obtain 4 coupling S parameter of each scanning position, namely interval delta x, the Δ y of transmitting and receiving antenna scanning X, Y direction are as rectangle X, Y direction mesh spacing, corresponding 4 the coupling S parameter of each rectangular node.

4. one according to claim 1 two-dimentional short range microwave holography formation method, is characterized in that, in step 6, described scattering parameter computing formula is:

$g_0(x,y,\stackrel{\‾}{z})=\frac{E_{\mathrm{inc}}(x,y,\stackrel{\‾}{z})e^{-{\mathrm{jk}}_b\sqrt{{(x^2+y^2+(D-\stackrel{\‾}{z}))}^2}}}{\sqrt{x^2+y^2+{(D-\stackrel{\‾}{z})}^2}}$ ①

In formula, for target exists the scattering parameter of position, D is the z-axis position coordinates of receiving antenna, and e represents exponential function, and j represents the imaginary number in plural number, for the Near-field Data of the objective plane of position, k _bfor scattering wave number during driftlessness.

5. one according to claim 1 two-dimentional short range microwave holography formation method, is characterized in that, in step 7, described target density parameter calculation formula is:

$\mathrm{\ρ}(x,y,\stackrel{\‾}{z})={\mathrm{FT}}_{2D}^{-1}\left\{\frac{E_{\mathrm{sca}}(k_x,k_y)}{G_0(k_x,k_y,\stackrel{\‾}{z})}\right\}$ ②

In formula, for target exists the target density parameter of position, represent two-dimensional inverse Fourier transform; E _sca(k _x, k _y) be calibration S parameter take Fourier coefficient as k _x, k _ytwo-dimensional Fourier transform acquired results, for scattering parameter take Fourier coefficient as k _x, k _ytwo-dimensional Fourier transform result.

6. one according to claim 1 two-dimentional short range microwave holography formation method, is characterized in that, in described step 3, in target current location scattering data and step 4, the Near-field Data of objective plane is all obtained by software emulation method.