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In this article, an automatic and forward method is realized to establish attributed scattering center models directly from the computer-aided design (CAD) model of the complex target. The main steps include the preprocessing of the CAD model, the separation of scattering sources, the selection of strong scattering sources, and the automatic determination of model parameters. With the proposed method, the scattering sources, scattering mechanisms, and model parameters of the scattering centers can be identified and derived, such that the complicated manual intervention is completely avoided. Moreover, the method establishes the distributed scattering center models formed by curved surfaces with large curvature radii. Therefore, the formation mechanism of the distributed scattering center is extended from typical scattering structures to a general case. Thus, the model of the attributed scattering center is extended and can be applied to describe the scattering from the real structures of the complex target. The geometric shape of the scattering source is distinguished based on the principal curvature radii, which are calculated by differential geometry theory. Thus, the frequency dependence parameter is obtained according to its corresponding relationship with the geometric shape. In addition, based on the automatic method, a technology is studied to diagnose and correct the scattering center models of a target whose CAD model is unknown or partially known. Finally, parametric models of several targets in the Moving and Stationary Target Acquisition Recognition (MSTAR) program are established, and then compared with the measured data. The results validate the effectiveness of the proposed method.

A new novel structure is proposed for cellular composite radar absorbing materials, and an equivalent method of electromagnetic scattering for the new material is also proposed for the first time. By covering the target surface with non-uniform medium cellular cell elements horizontally, the scattering characteristics of the coated target show strong surface anisotropy, leaving an imaginary space for optimizing the electromagnetic stealth performance of the coated target. In this paper, the equivalent dielectric tensor of horizontal directional composite honeycomb cell element has been calculated by using the equivalent method of electromagnetic scattering based on strong fluctuation theory (SFT) of anisotropic medium. Under the condition of plane wave irradiation with a frequency of 3 GHz, we use FEKO software to estimate the backscatter field of several typical models coated with this new structure. It has been proved that the strong fluctuation theory applied to the honeycomb composite absorbing material of the structure are effective for calculating the equivalent scattering. Based on the validity of the equivalent results, we further estimate the scattering characteristics of complex targets coated with the novel cellular medium.

This paper proposes a fast target indexing method based on target geometric models and further conceives a forward method based coarse-to-fine hierarchical synthetic aperture radar (SAR) automatic target recognition (ATR) system. The proposed fast SAR target indexing method is employed for coarse classification before the implementation of fine classification and recognition, resulting in significant acceleration of target recognition. Furthermore, the fast SAR target indexing method is purely based on target geometric models without resorting to any time-consuming electromagnetic (EM) computation, which enables the online and real-time classification. The binary target region and shadow region are selected as the indexing features, and a forward feature prediction method based on optical visibility is developed to predict the features from the target geometric model in real time. Then, the features extracted from the testing SAR image are aligned with the predicted features to establish correlation ship and a fused similarity based on four types of complementary similarity criteria is designed to further implement target indexing. The effectiveness of the proposed fast SAR target indexing method is demonstrated by using the MSTAR dataset.

A novel forward method to establish the three-dimensional parametric scattering center models is developed to extract scattering centers from the combined target/rough surface models. Both scattering centers from the ship, including single-order and higher order scattering contributions, and from the multiple interactions between the ship and random rough sea surface would be described concisely with physically relevant parameters by this proposed method. Due to the statistical nature of the random rough surface for the Monte Carlo simulation, we acquire a large number of realizations for estimations of the amplitude and position parameters to overcome the problem that single realization cannot extract scattering centers effectively. This method is validated through parametric models of the ship in free space and on the sea surface, and a good agreement has been demonstrated between the constructed and simulated radar characteristics. Furthermore, we analyze the composite target/surface model's physics and feature stability in a visually spatial range and direct connections between scattering centers and scattering sources, which would be valuable to future target recognitions and classifications. Finally, we quantitatively calculate and analyze the coupling scattering centers from interactions between the ship and the ocean-like surface that provide more abundant contour information of the inverse synthetic aperture radar (ISAR) image to facilitate contour detections.

Based on target geometric model, this paper proposes a forward approach to establish scattering center models. Different from the conventional inverse approach, which estimates scattering center models from the measured or simulated SAR image, the forward approach clearly describes the formation process of scattering centers by component separation, ray tracing and clustering technologies, and determines the model parameters by forward derivation and calculation.

With the development of radar stealth technology, electromagnetic scattering has been widely used, and the strong scattering center of military targets has been effectively suppressed by various means. At this time, the secondary scattering becoming more and more important. In this paper, the scattering field of two-dimensional perfect conductive cylinder was studied, and the curved surface diffraction field is mainly investigated. Further more, the parametric model of the curved surface diffraction field is given by function fitting method. Combined with examples, the importance of secondary scattering in high frequency region is demonstrated and the accuracy of the parametric model derived in this paper is verified.

Recent extensions are reported for the evaluation of electromagnetic scattering from electrically large perfect electric conductor target coated with uniaxial electric anisotropic multilayered media. First, the boundary conditions at the interfaces of the stratified anisotropic medium are employed to determine the complex amplitudes of the scattered fields in spectral domain, which involve a complicated coupling of type I and type II waves existing in uniaxial electric anisotropic medium. Then the scattering from the infinite coated substrate is asymptotically calculated by using the proposed spectral domain method combined with saddle point evaluation. Thereafter, the asymptotic solution is applied to derive the physical optics currents on the surface of the target. Ultimately, comparisons of the proposed asymptotic solution with the reference solutions calculated numerically confirm the validity and efficiency of the proposed solution. Employing the asymptotic solution, the evaluation of the scattering from an electrically large target coated with uniaxial electric anisotropic multi-layered media is realized.

This paper proposes a forward approach to establish parametric scattering center models for complex dielectric targets. It proposes a space ray diversity method for complex medium targets based on ray splitting tracing method. Based on the high frequency electromagnetic mechanism of complex targets, a method of calculating the equivalent action point of internal coupling action ray is proposed. This solves the problem of the forward calculation of the three-dimensional position parameters of the scattering center. Finally, the decomposition and its quantitative characterization technique of strong scattering source for complex dielectric targets are obtained, and the target scattering center model with complex dielectric has been established with clear and accurate scattering mechanism. This method greatly expands the scope of target application in the forward modeling method of attribute scattering center. Finally, a simplified wing calculation example shows the feasibility and effectiveness of the proposed method.

To better link the scattering center with the target structure, this paper forwardly deduces and analyses the component-level 3-D scattering center position of radar target under the mechanisms of single and double scattering. The ray equivalent position under the double scattering mechanism is especially deduced. This position derivation process is then applied on the models of SLICY and T72 tank to deduce and analyze their scattering center positions. The corresponding measured SAR images are used for contrast to prove the validity of the position derivation.

A method for the calculation of the scattering of the stratified uniaxial electric anisotropic media (UEAM) under point source excitation with arbitrary orientation is presented. In this method, the total field is decomposed into three parts, the radiated field of the point source in free space, the reflected field from the top interface of the UEAM and the transmitted field after multiple reflections in the anisotropic layer. The three parts are derived in spectral domain respectively and can be expressed by using Fourier transform. Then the saddle point technique (SPT) is introduced to obtain an asymptotic solution of the scattered field. Results from the asymptotic solution are compared with the results calculated by the method of moments (MOM) and the comparison shows good agreement.

The high-frequency scattering of an electrically large target can be well approximated as a sum of response from individual scattering centers. The scattering center model can provide a concise and physically relevant description of the target radar signature. We use the attribute scattering center model to represent the targets' high frequency back scattering. In this model, the backscattered field of an individual scattering center is described as a function of frequency and aspect angle, and the total scattered field from a target is then modeled as the sum of these individual scattering centers. It provides a physical description of target scattering centers via a set of parameters. Based on the limited observation data, the problems about scattering centers diagnosis and parameters modification of the complex targets' geometry model are discussed. Firstly, by comprehensive analyzing the limited observation data, we can suppose a non-accurate geometric model. Secondly, the SAR image of the geometry model can be reconstructed using a forward approach to establish parametric scattering center model. The image is compared with the limited observation data, and then adjust the correctional components' position, size and shape. As follows, the parametric scattering center model of the adjusted model is established, the SAR image of the adjusted model is reconstructed, and compared with the limited observation data again We adjust the geometry models and establish parametric scattering center model several times like these. Finally, the scattering centers are diagnosed and the parameters are modified. The modeling method is applied to a tank target, it is proved to be effective.

This work presents a new technique based on ray tracing to extract and analyze scattering centers from complex targets, which is called ray clustering. The input of this method is the target CAD model and the output is the dominant scattering centers. This method can separate the echoes from different components by clustering rays owning the different paths and establish relationship between target components and the scattering source, thus it can provide an effective approach to analyze the target characteristics. After introducing the implementation procedure of the extracting method, we present an example to demonstrate its application in characteristic analysis.

An efficient algorithm is presented for 3D volume EFIE in layered media. In the handling procedure of stabilized bi-conjugate gradient fast Fourier transform (BCGS-FFT), discrete complex image method (DCIM) is introduced to dramatically accelerate calculation of time-consuming "Sommerfeld integral" in dyadic Green's function (DGF). Before which, DGF is spit to circumvent difficulties in utilizing DCIM in volume EFIE. In this paper, a two-step pole-searching procedure is used to extract the "surface-wave poles", and then a two-level generalized pencil of function (GPOF) method is utilized to realize DCIM, which ensure DCIM agree well with numerical integration in tens of wavelengths. At last, several reported numerical examples are newly presented to demonstrate the accuracy and efficiency of this algorithm.