For low-observable targets, particularly those treated with material coatings, edge diffraction is an influential scattering mechanism. Although scattering center (SC) models can provide an effective sparse representation of local scattering mechanisms, the evolution from diffraction fields to SC models has not been systematically derived or quantitatively described for arbitrarily shaped edges and material coating conditions, which limits the accurate parameter characterization of edge diffraction SCs. Accordingly, this paper proposes an automated forward modeling method for coated edge diffraction SCs, grounded in the physical theory of diffraction (PTD). Spatial radiation expressions for straight edge and curved edge diffraction SCs are derived based on PTD and impedance boundary conditions. Then, geometric topology and visibility analyses are integrated to automatically identify, classify, and separate effective edge structures for given incidence directions. On this basis, physical correspondence from edge geometry, incidence conditions, and coating material properties to SC parameters is established, revealing the physical formation mechanisms of SCs and leading to an interpretable modeling method for edge diffraction from complex coated scatterers. Validated through comparisons with high-frequency methods and full-wave numerical simulations for typical edge diffraction structures and complex coated targets, the proposed method supports efficient and physically interpretable edge diffraction SC characterization, supporting physics-based analysis of target scattering responses.

The scarcity of real Synthetic Aperture Radar (SAR) images, coupled with significant discrepancies between simulated and real samples, constrains the performance of Automatic Target Recognition (ATR). Thus, this paper proposes an efficient, physically rigorous, and lightweight realistic SAR image generation method for limited real-sample scenarios by integrating the scattering center model with flow matching. First, a GPU-accelerated forward modeling rapidly generates physically interpretable target scattering features from CAD models within tens of milliseconds. Based on this, a structure-constrained flow matching network incorporating a global self-attention mechanism is designed. Using scattering-derived physical scattering skeleton as structural prior, the network effectively reconstructs the complex scattering distributions and nonlinear background noise in real SAR images while ensuring the accuracy of the target’s electromagnetic characteristics. Experiments on the SAMPLE dataset demonstrate that this method outperforms traditional generative adversarial networks (GAN) models on key metrics (FID, KID, LPIPS). In few-shot scenarios classification tasks, classifiers trained on our synthesized images achieve accuracy close to those of real data, demonstrating that our method effectively bridges the domain gap between synthetic and real data, enabling direct application to downstream tasks.

A continuously tunable reflective metasurface is proposed for the dynamic generation of vortex beams in the microwave band. Each meta-atom integrates a voltage-controlled varactor diode, enabling near-continuous reflection phase modulation through external bias control. To address phase instability caused by position-dependent biasing vias in large-scale metasurface arrays, a symmetric blind-via design strategy is employed to effectively suppress parasitic-induced phase perturbations. The designed metasurface achieves approximately 340° continuous reflection phase coverage over the frequency range from 5.75 to 7.25 GHz. By programming spatial phase distributions, multiple complex beam types, including conventional vortex beams, focused vortex beams, and non-diffracting vortex beams, can be dynamically generated using a single metasurface configuration. Full-wave simulations validate stable phase control and consistent beamforming performance across the operating band. The proposed metasurface provides a practical and scalable solution for multifunctional wavefront manipulation, with potential applications in microwave antennas, wireless communication, and radar systems.

This paper proposes a forward modeling method for multibounce bistatic attributed scattering centers (BASCs) of complex targets. The key innovation is to establish the relationship between ray-path increments and apparent scattering positions using the Doppler frequency induced by turntable motion. First, ray tracing and ray clustering techniques are incorporated into a geometrical optics–physical optics (GO–PO) method to record ray paths and their interaction mechanisms. Then, ray-path increments are generated by simulating small-angle turntable motion and mapped to scattering-center positions through the Doppler-frequency relationship. Finally, the total scattering field is parameterized using the BASC model to reconstruct target characteristics. Acute dihedral and aircraft models are used to analyze multibounce scattering sources and construct BASCs, with results showing good agreement with Method of Moments (MoM) and high-frequency simulations. The modeling process enables an efficient and quantitative description of multibounce scattering behaviors under bistatic radar.

A double-metasurface phase modulation architecture is proposed and designed for wide-angle and high-efficiency retroreflection and backscattering enhancement. In order to overcome the intrinsic mutual constraint between the angular coverage and aperture efficiency in designing a retroreflector by using a single metasurface, a double-metasurface structure is developed to separate the design requirement for different incident angles, thus enabling the enhancement of retroreflection efficiency. The first, to the best of our knowledge, metasurface focuses the incident plane waves from arbitrary directions into different spots on the second reflective metasurface, enabling spatially decoupled phase modulation and thus enhancing angular retroreflection. Further, to address the inherent degradation of retroreflection efficiency caused by focal spot distribution and overlapping, a multi-spot phase modulation method accounting for the spot energy distribution is developed and employed. A retroreflector operating at 10 GHz is designed, fabricated, and measured to experimentally validate the proposed method. The designed retroreflector demonstrates stable retroreflection (3-dB) across the full-azimuth range (φinc = 0° ∼ 360°) and a broad elevation range (θinc = -20° ∼ 20°) under dual-linear polarization (dual-LP, TE/TM) waves. The peak aperture efficiency of wide-angle retroreflection reaches over 50.0%, approaching the achievable upper limit for double-metasurface structure. The proposed retroreflector offers a promising solution for wide-angle, high-efficiency backscattering enhancement, with potential applications in asset tracking, satellite navigation, and related fields.

Synthetic Aperture Radar (SAR) serves as a pivotal tool in the realm of earth observation. Despite multiple scattering structures that can form dominant scattering sources, current interpretation and identification methods lack the capability to effectively reveal the scattering mechanism and structures with complex paths. In this paper, we present a 3D forward modeling approach for scattering centers (SCs) formed by multiple reflections, based on target geometry and high-frequency scattering mechanisms.

This paper presents an approach for predicting the near-field electromagnetic (EM) scattering of complex targets coated with anisotropic media, utilizing the physical optics (PO) method. In this method, the PO near-field integral representation is derived by using the Green's function for localized expansions, which allows for a more efficient and accurate representation of the scattering problem. The Green's function formulation is critical in solving the EM field interactions at the surface of the target, where the anisotropic coating significantly alters the behavior of the incident and scattered waves. To calculate the reflection coefficient of the anisotropic media-coated targets, the spectral domain approach is employed, in combination with boundary conditions, along with the PO near-field integral representation. This hybrid method enables an effective analysis of the near-field EM scattering phenomena for targets covered with anisotropic coatings. The use of spectral domain techniques allows for the decomposition of the scattered field into manageable components, simplifying the complex interactions between the incident field and the anisotropic material. Compared to traditional numerical methods, the results show that the proposed approach is both computationally efficient and accurate, reducing the computational resources and time required for the analysis. Furthermore, the proposed method can easily be extended to analyze electrically large and complex objects, especially in scenarios involving anisotropic coatings. This makes the approach particularly valuable for real-world applications in areas such as radar cross-section (RCS) analysis, where complex target geometries and material properties need to be considered. Overall, the method provides a reliable and scalable solution for near-field EM scattering analysis in complex coated structures.

In this article, a forward approach is proposed to establish the 3-D scattering center (SC) model for dielectric-perfect electrically conducting (PEC) composite targets (including nested targets). First, various-order SCs are separated from computer-aided design (CAD) models by ray tracing and clustering technology applicable for the dielectric-PEC composite target; in particular, the multiple refraction-containing coupling scattering mechanisms are involved in the scattering of nested targets. Furthermore, a set of forward methods (FMs) is developed to determine the parameters of 3-D attribute SCs, including amplitude, frequency factor, position, and length. The method addresses the challenge of deriving the model parameters of multi-order refraction-containing coupling SCs generated by multiple bounces and complex propagation media. Finally, this approach is validated by establishing the parametric model of several composite targets (including nested targets), and the synthetic aperture radar (SAR) image reconstructed by the model behaves a good agreement with the result of the RLGO algorithm in FEKO. This approach provides a clear physical image of the SC formation process. It helps construct a target feature database and enables radar target recognition via image-domain characteristics and physically relevant model parameters.

A novel approach for modeling and analyzing angular glint errors (AGEs) based on scattering center (SC) forward model is proposed in this communication. Target scattering is decomposed into coherent superposition of 3-D SCs using ray-tracing and diversity techniques. The parametric formula for AGE calculation based on SCs is derived through the phase gradient method (PGM). Accounting for the effects of weak scattering mechanisms on phase-front variations and modeling accuracy, such as coating surface scattering and edge diffraction, a forward calculation process for the amplitude and position of relevant SCs is developed grounded in high-frequency electromagnetic (EM) theory. The proposed approach is validated through simulations of typical scattering structures and complex targets, revealing the relationship between SC types and AGE. This work provides a systematic framework for AGE analysis and explores the potential of SC-based AGE modeling through coating materials in EM intelligent control.

A novel forward parametric modeling method to construct the scattering center model (SCM) for coated targets above dielectric rough surfaces. Compared to traditional scattering center analysis methods, the proposed method takes full account of actual environmental conditions, including targets with coating and rough surfaces for electromagnetic (EM) parameters, and analyzing EM scattering by forward parametric modeling. Initially, the rough surface is randomly generated by Monte Carlo method, which simulates a three dimensional (3D) rough surface model by Gaussian spectrum, and different permittivity is used to characterize the surface in realistic. Subsequently, the complex integrated model, which includes the rough surface and the target, is discretized into a collection of multiple scattering sources by a forward approach with ray tracing and ray diversity techniques. Finally, comparing the reconstructed radar cross section (RCS) and inverse synthetic aperture radar (ISAR) images, the numerical examples show the effectiveness of the proposed method.

This letter presents a systematic method for improving the aperture efficiency (AE) of transmitarray antenna (TA) without increasing the profile through modulation of dual metasurface transmitarrays. The first metasurface transmitarray intercepts more energy from the feed source and redistributes the intercepted energy over the second transmitarray through phase modulation, thereby improving spillover and taper efficiencies simultaneously. The phase efficiency is improved through the modulation of second metasurface transmitarray. The method overcomes mutual constraint between spillover efficiency and taper efficiency in traditional TA with single metasurface TA (TA-SM). To demonstrate the effectiveness of the method, two TAs [termed as TA-SM and dual metasurface TA (TA-DM)] with identical focal-length-to-diameter (F/D) of 0.625 are designed, fabricated, measured, and compared. The TA-SM with single transmitarray is a traditional TA with optimal AE, and the TA-DM with dual transmitarrays is designed based on the proposed method. Finally, at 14 GHz, the TA-DM realizes peak AE of 67.8% with low profile (F/D=0.625) and achieves maximum AE improvement of 20.6% compared to TA-SM (realized AE of 47.2%). Besides, the TA-DM has 1 dB gain bandwidth of 22.9%. The proposed method is a good candidate for the design of high gain and low profile antenna in long-distance communication.

This paper proposes a unified spectral-domain framework for high-frequency scattering analysis of complex targets coated with biaxially electric anisotropic medium (BEAM) under arbitrary near-field excitation. First, arbitrary electromagnetic sources are rigorously decomposed into spectral-domain plane-wave superpositions via Fourier analysis, enabling seamless integration with layered anisotropic boundary conditions. For BEAM-coated complex targets discretized into surface facets, the propagation matrices are explicitly derived for infinite planar interfaces under plane wave spectrum incidence, enabling single-facet modeling of electromagnetic interactions. Finally, based on the physical optics (PO) method, a Green's function modification tailored for scattering fields on illuminated facets is introduced, and saddle-point spectral-spatial asymptotic evaluation is employed to enable scattering field calculations for near-field excitation and reception scenarios. Compared with Titchener's method, the proposed method is validated, and the simulation results of representative shapes coated with the BEAM layer demonstrate the correctness and effectiveness of the algorithm.

A novel method is proposed for designing a low sidelobe level (SLL) transmitarray antenna (TA) with high aperture efficiency (AE). In this method, two phase-only metasurface plates are cascaded and coordinated to achieve amplitude modulation and phase alignment. The first phase-only metasurface plate is employed to realize the Chebyshev amplitude distribution of low sidelobes over the aperture of the second phase-only metasurface plate, where the aperture field phase can be subsequently aligned. The phase-only metasurface-based aperture amplitude modulation can effectively avoid energy loss, and it can simultaneously enhance the spillover efficiency to compensate for taper efficiency loss resulting from sidelobe suppression, thereby achieving low sidelobes while avoiding the loss of AE. Besides, to facilitate the specific design of Chebyshev distribution through phase modulation, a fast and efficient method is developed. Finally, to demonstrate the effectiveness of the proposed method, two TAs (termed TA1 and TA2, respectively) are designed, fabricated, measured, and compared. TA1 is a TA with optimal AE, and TA2 is designed based on the proposed method of low sidelobes without the loss of AE. Finally, TA2 achieves SLL of -27.2 dB (7.8 dB lower than TA1), a gain of 25.48 dB, and AE of 49.18% (0.26 dB and 3% lower than TA1, respectively). The proposed design method overcomes the loss of AE during sidelobe suppression, which presents new guidance for designing a low sidelobe TA with high AE.

The increasing detection frequency of modern radars makes the effect of the roughness of the target surface on its scattering characteristics not negligible. In this paper, a forward parametric modeling method for the scattering center of surface rough targets based on ray tracing and diversity technology is proposed, and the influence of roughness on the scattering characteristics of the simplified tank is analyzed.

The diffraction of anisotropic impedance wedges plays a key role in radar detection, electromagnetic (EM) wave propagation, and high-frequency antenna design. Existing numerical methods are limited by their complexity and high resource demands, restricting their practical engineering applications. This study presents a numerical matching approach grounded in high-frequency EM theory, deriving a simplified expression for the Maliuzhinets wedge special function and constructing an effective diffraction spectrum through enhanced boundary condition constraints. The method significantly broadens the scope of the Uniform Theory of Diffraction (UTD), overcoming challenges associated with large-angle deviations from normal or grazing incidence. Numerical results confirm the method's accuracy and efficiency in solving diffraction fields for anisotropic impedance wedges at arbitrary wedge and skew incident angles.

The structure with multiple reflections is commonly observed in radar targets and can form dominant scattering sources. However, their scattering centers (SCs) tend to deviate from the expected target region and display instability with changing observation angles, complicating SC analysis and interpretation. To elucidate the mapping relationship between apparent SC and target geometry with multiple reflections, this article proposes a forward approach to establish the 3-D parametric SC model for complex targets, particularly those with deep cavities. The forward-constructed model is a concise combination of clear physical parameters that are characterized by robust inferential and descriptive capabilities. Specifically, we first utilize ray tracing and clustering techniques to discretize the scattering of a target into several component-level scattering sources. Then, for each source, a set of physically relevant parameters is calculated in a forward (cause-to-effect) manner, incorporating a deeper understanding of the high-frequency mechanisms. This direct quantitative deductive modeling approach allows for the simultaneous attachment of scattering mechanisms and target information to the SC model. Meanwhile, the physical formation process of the SC type (localized or distributed) and 3-D position is explicated in multiple scattering scenarios. Finally, the efficacy of this forward modeling is validated through comparisons between the model-reconstructed and high-frequency (or full-wave) simulated high-resolution range profiles (HRRPs) or synthetic aperture radar (SAR) images of cavities and complex targets. In addition, those numerical examples also demonstrate the interpretation capabilities of the proposed forward model.

Machine learning assisted synthetic aperture radar (SAR) automatic target recognition (ATR) methods have gained widespread attention and application. Among them, the methods based on the convolutional neural network (CNN) have achieved good results under standard operating conditions (SOC) because the CNN can automatically extract and learn the image feature from the SAR image. Still, they show poor performance under extended operating conditions (EOC) due to the change of the radar imaging conditions, especially when the depression angle of radar imaging changes a lot. Compared to the image features, the scattering center (SC) can provide a concise and physically relevant description of the target scattering characteristics. To achieve a good recognition performance under both SOC and EOC, we propose a SAR ATR method based on the scattering center features and Graph Neural Networks with Feature-wise Linear Modulation (GNN-FiLM). By quantifying and representing scattering features with the physical parameters of SCs, the scattering center features are introduced into the training of GNN-FiLM in the form of a graph. The structure features and physical information are extracted and learned by the GNN-FiLM. Experiment results on the Moving and Stationary Target Acquisition and Recognition (MSTAR) and simulation datasets demonstrate that our method can perform well in recognition experiments of three-class targets. Especially under EOC of large depression variant on the MSTAR dataset, our method can obtain about 91.5% accuracy which is better than other deep learning based methods.

In this letter, an efficient method is proposed for analyzing electromagnetic scattering from complex targets coated with anisotropic metal composites. The method discretizes electromagnetic scattering on the complex target's surface into a superposition of triangular surface element scattering. Initially, the plane wave spectrum expansion method derives the dual-spectral-domain integral representation of the scattering from triangular surface elements on the anisotropic metal composites coated slab model. Then, the saddle point evaluation is utilized to perform the asymptotic evaluation of the integral; the reflection coefficient can be obtained in the spatial domain. Finally, the equivalent electromagnetic current of the triangular surface elements is solved using the Stratton-Chu equation. Furthermore, the electromagnetic scattering of complex targets coated with anisotropic metal composites is obtained through the physical optics method. The numerical results, including radar cross section comparisons for typical slab, cube, and fighter models, demonstrate the accuracy and efficiency of the proposed method. The anisotropic metal composites can enhance the stealth capability of the fighter, which possesses excellent structural stealth performance.

Theoretical and experimental studies reveal that, in the high-frequency domain, a target's total electromagnetic scattering field can be decomposed into re-radiations from localized "scattering sources," known as scattering centers. Using the Stratton-Chu surface integral formula, it is understood that radiation from non-uniform electromagnetic flow near surface discontinuities and boundaries corresponds to edge diffraction, while radiation from uniform flow on smoothly curved surfaces corresponds to geometric optical reflection. Radar images typically show "bright spots" that correlate with these surface reflections and edge diffraction. To improve the accuracy of radar target scattering characteristic acquisition and to enhance the scattering center model by incorporating edge diffraction mechanisms, it is essential to advance electromagnetic modeling precision and comprehensiveness. This paper introduces an enhanced forward modeling method for scattering centers that integrates edge diffraction mechanisms. Building on the surface scattering mechanism and incremental length diffraction theory, this method first automatically classifies target edges as edge diffraction scattering centers based on geometric models. It then calculates the amplitude, frequency, position, and other attributes of each edge scattering center using the target's geometric parameters and edge diffraction coefficients.The effectiveness and accuracy of this forward edge diffraction modeling method are validated by comparing the reconstructed radar cross section (RCS) and synthetic aperture radar (SAR) data with simulation results obtained from the Method of Moments (MOM). This method addresses the forward scattering center modeling of target edges and provides critical support for the detection and identification of low-observable targets.

An efficient method for analyzing the electromagnetic(EM) scattering behavior of the biaxial anisotropic media in monostatic radar. The electromagnetic scattering characteristics of the anisotropic media are described in tensor permittivity, which can increase the difficulty of calculation, and reflection coefficient is included in the efficient calculation of radar cross section (RCS). Therefore, the relationship between electric and magnetic fields in anisotropic media is obtained by substituting the tensor permittivity into Maxwell equation. The reflection coefficients are calculated using the spectral domain method (SDM) and the saddle point evaluation (SPE). Then the electromagnetic scattering field is analyzed through the physical optics (PO) method. In order to verify the accuracy and efficiency of the proposed algorithm in this paper, the results of the proposed method are compared with the numerical reference solution in detail.