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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.

In this paper, we present a novel method that utilizes amplitude-only data of the electric field over a completely closed surface for the reconstruction of the spherical electric field, which represents a radiation source or an antenna under test (AUT) in the near-field (NF) region. The electric field exploiting genetic algorithm (GA) for global optimization is originally derived from a random initial estimate of field distribution and will gradually approximate to the exact value during iterations. When GA reaches the convergence criterion, we can calculate the far field (FF) by spherical NF-to-FF (NF-FF) transformation. The simulated and numerical results are in good agreement with each other, which shows that this method is effective over one or two closed surfaces. Furthermore, the related discussions corresponding to GA are given, confirming that the improved GA is feasible and efficient.

In this paper, a dual frequencies and bidirectional functional metasurface is presented. The functional metasurface can achieve bidirectional radiation with dual polarization at different frequencies. By independently adjusting the reflection and transmission phases, the forward and backward beam convergence can be achieved. The simulated results indicate that the gain of reflection beam can reach 24.9 dBi at 9 GHz and the gain of transmission beam can reach 26.1 dBi at 12 GHz, which is at least 13.5 dBi higher than the bare feeder.

Despite of various advantages, transmitarray antennas usually suffer from the limited bandwidth. In this paper, ultra-wideband polarization conversion elements are employed to design ultra-wideband linearly polarization transmitarray antennas. The proposed ultra-wideband transmissive polarization conversion element is a multilayered structure with asymmetric split circular ring structure in the middle layer and orthogonal metal gratings at the outermost layer. The element features ultra-wideband high efficiency transmission capability, a transmission phase coverage of 360° and good phase linearity. By employing the proposed elements, an ultra-wideband linearly polarized transmitarray antenna with dimensions of 180 mm × 180 mm is designed and its highly efficient radiation performance is demonstrated by simulation. The designed transmitarray achieves 3 dB gain bandwidth of 61 %, ranging from 12.83 GHz to 24.09 GHz. The peak simulated gain is 28.13dB at 16.5GHz. In addition, the maximum aperture efficiency of the antenna is 54.13 % and the aperture efficiency is greater than 40% from 12.4 GHz to 18.4 GHz.

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.

With the increasing coupling of secondary system components in smart substation, the operation management becomes more and more difficult. This paper proposes a graphical display approach of secondary functional components based on “information-event-function” logics. The displayed layout as well as connection relationship, which is accomplished through automatic graphing, clearly describes the logical order and assists auxiliary analysis. Based on the reasoning of the logics of layout and routing, the automatic graphing accurately describes the functional correlation of the secondary components in a simple and intuitive way. The displayed graph can be further improved by comparing it with the actual functional circuit. Several practical examples are presented to demonstrate the feasibility of the proposed approach.

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.

Based on spectral domain method (SDM), an asymptotic approach to the investigation of the reflection of electromagnetic waves from a metal plane interface separating a vacuum half-space and a anisotropic plasmas layer is presented. Firstly, the spectral formulas of type I and type II waves existing in the plasmas are deduced. Then the boundary conditions at the top and bottom interfaces of the plasmas slab are employed to determine the complex amplitudes of the scattered fields in spectral domain. By means of saddle point technique (SPT), the scattered fields in space domain are asymptotically solved out, which degrade to the reflected fields. The asymptotic solution is validated by the comparisons between the reflection coefficients obtained from the proposed solution and Titchener's method.