Study For Ultra Wide Band Microwave Imaging Of Conductor Objects

Ultra wide band(UWB) microwave imaging of conductor object,is of great importance in military and civil realm.While the stealth material is widely applied in military object,the narrowband radar can't work efficiently.But the stealth material,usually excellent in narrowband,is not uniformly good in ultra bandwidth.Adopting UWB pulse as the incident wave to detect object,is the effective means against the stealth.In civil sensing,the advantages such as installing easily,transmitting conveniently,etc,are realized by adopting the monostatic radar to detect;therefore the monostatic imaging is worth way in the microwave imaging.In this paper,the UWB microwave monostatic imaging based on the optimization method is proposed to achive metal object imaging.There are several characters in proposed method:1.the necessary scattering field singal is the back-propagated scattering signal,the imaging is accomplished by single-illumination single-view way,the number of the required radar is one. 2.while applying the optimization method,by processing the scattering signal and the incident signal,the pre-estimation of the size of the object can be attained.3.for enough employing the UWB signal,results of all efficient frequency are matched to associate the image and the scattering information in optimization method,and the better image of the illuminated part of the object is provided.The microwave imaging is inverse scatter problem,for the scatter and inverse scatter,the relation between the incident field,the scattering field and the object shap parameters can be recast to the same integral equation.The important differenct between the scatter and inverse scatter is that the scattering field can be computed directly while the object shape information is known,vice versa,the object shape information can't be obtained directly for the known scattering field.While the integral equation is not approximated, the optimization method is the efficient way to solve the microwave imaging problem.When the UWB pulse microwave monostatic imaging is worked out with the optimization method,the follow problems need to be analyzed:1.the relation between the object shape or electric parameters and the UWB information obtained from the monostatic radar.2.the pre-estimated size of the object.3.the selection and the spreads of the shape function.4.the determination of the size and the number of the mesh in time domain algorithm and the control of the price of the imaging.5.the efficience and fitness of the optimization method.In chapter2,the numerical discrete model of the scatter integral equation is described detailedly,and the simplification of imaging is discussed in different options.In time domain,the realation between the object shape and the information procured by processing the incident field and the scattering field is analyzed,therefore the model corresponding to the discrete result of the frequency domain is established.Moreover,the difference of the solving in both domain is presented.When the contour of the object is equal approximately to the wave length of the incident wave,the amplitude of the back propagation wave is fluctuated with difference between the wave length and the object contour,so the estimated way to the object contour is deduced, which also is base of the estimation of the object size.To synthesize all above, the mathematical model and the computation flow of time domain UWB pluse microwave monostatic imaging are generated,simultaneously,the couplings among the modules of the model are eliminated as possible for optimizing further.The optimization algorithm is analyzed in chapter 3,the random optimization methods and the traditional optimization methods are discussed, including the advantage and the disadvantage of optimization method.For the random optimization method,the correlation between the type and the performance of the algorithms is tested,at the same time,the standard of the performance is determined unambiguously.While the border of the solution space is transversed,the several schemes are provided for the different stage of the optimization procedure.At last,the optimization performance of the common optimization algorithms is evaluated as the test standard.Because the optimization method is not coupled with the solving problem,the performance result is valid in imaging. The estimation of the object size is narrated,and the customization of the object shape function in two dimension and three dimension also is analyzed. Because the settings of the ranges of the object size parameters in optimization method is correlated with the size esitimation and the shape function,the ranges of the parameters can be assigned quantitatively acoording to the estimation of the size when the shape function is fixed.In time domain imaging,the importantest is how to determine the number of the mesh of the computing scope,the size of the mesh and the improvement of the optimization method in imaging,which is described in chapter5.Based on the content of the chapter4,the range of the computing scope is come out automatically while taking the extreme circumstance into consideration.The size of the mesh can be determined by the rate of the estimated size and the precision of the imaging,then the whole range of the numerical computation is found out automatically.The precision of the imaging is adjusted as the requirement,the incident field series is generated acoording to the band of the real incident field and the precision of the imaging in the time domain scattering computation,so the price of the computation can be evaluated. Without any prior knowledge of the object size,the setting of the imaging is deduced,moreover,the precision and the price of the imaging can be balanced. The coefficents of the shape function is corresponding to the contour of the simulated object,but the procedure of mapping the coefficients to the contour is to discretizate real to integer,thus the real code of the coefficients is redundancy,further more,the unsteady solution must be filtered out in the project design.Comparing with the real code optimization method,the integer code can be more efficient to solve the problem of the discretization and filter out the unsteady solution.The UWB microwave imaging based on the optimization method is the discrete problem,when adopting the integer code, the image quality is same as that of the read code and imaging's speed goes higher.In addition,in scattering computation,the far field is obtained by the near-to-far field transformation that is data projection from the close surface to the line,because the information of data is redundant,the fast near-to-far field transformation whose projection data is sampled on the close surface is proposed in this paper.The fast transformation is independent to the coordinate and the type of the simulated problem,speeds up the computation in multstatic scattering and antenna design.The narrated above is summed up in chapter6,consequently the UWB pluse microwave monostatic imaginig is realized.At last,the images of two dimension and three dimension are presented,simultaneously,the results of the imaging experiment are analyzed,moreover,in especial occasions,how to hasten imaging is presented as well as the results and analysis.Summarizing the improvement of each step,inverse scattering is actualized by the UWB pluse microwave monostatic imaging.Monostatic minimizes the requirement of the imaging,is beneficial means for application. The improvement of the optimization method,speeds up the imaging,and come out higher quality image at the same price.