Physical Optics Method Research Articles

A Fast, Hybrid, Time-Domain Discontinuous Galerkin-Physical Optics Method for Composite Electromagnetic Scattering Analysis

To accelerate the solution of transient electromagnetic scattering from composite scatters, a novel hybrid discontinuous Galerkin time domain (DGTD) and time-domain physical optics (TDPO) method is proposed. The DGTD method is used to solve the accurate scattering field of the multi-scale objects region, and a hybrid explicit-implicit time integration method is also used to improve the efficiency of multi-scale problems in the time domain. Meanwhile, the TDPO method is used to accelerate the speed of surface current integration in an electrically large region. In addition, the DGTDPO method considers the mutual coupling between two regions, and effectively reduces the number of numerical calculations for the other space of the composite target, thereby significantly reducing the computer memory consumption. Numerical results certified the high efficiency and accuracy of the hybrid DGTDPO. According to the results, in comparison with the DGTD algorithm in the entire computational domain, the DGTDPO method can reduce computing time and memory by 90% and 70% respectively. Meanwhile, the normalized root mean square deviation (NRMSD) of the time-domain, high-frequency approximation method is over 0.2, and that of the DGTDPO method is only 0.0971. That is, compared with the approximation methods, the hybrid method improves the accuracy by more than 64%.

Influence of multiple reflections in simulation of scattering electromagnetic wave by objects of complex shape

Microwave imaging technique allows obtaining images of hidden objects in structures and media using microwaves. This technique has various applications such as: nondestructive testing, medical imaging, concealed weapon detection, through-the-wall imaging, etc. Obtaining radar images in these applications is based on processing phase and amplitude of the reflected signal recorded over an aperture (a microwave hologram). To design and evaluate the effectiveness of modern radars, to test the developed reconstruction algorithms, microwave holograms of various objects obtained under different conditions are required. Obtaining microwave holograms by experimental methods is associated with measuring the scattering fields of real objects. Such experiments are rather laborious and expensive. Therefore, the problem of modeling the processes of scattering of electromagnetic waves by the objects of study is very important. Since the implementation of rigorous methods for solving the scattering problem is associated with large computational costs, it is sometimes advisable to use various simplifications and assumptions to analyze scattering fields on objects of complex spatial configuration. One of these methods is the physical optics method, which is a very common method for calculating fields scattered from objects of various shapes. The physical meaning of the approximation of the physical optics approach is that the field on the surface of the scattering object is taken to be equal to the field in the absence of the object. In other words, multiple reflections of an electromagnetic wave between different parts of the object are not taken into account. The aim of this work is to study the influence of the effects of re-reflection of an electromagnetic wave and to reveal the dependence of the accuracy of the calculation of the scattered field, performed by the physical optics method, on the shape of scattering objects. A comparison of microwave holograms obtained by the physical optics method with the results of calculations using the computational electromagnetic software product FEKO is carried out. It was found that for objects consisting of separate elements, spatially separated in a plane parallel to the registering plane, rereflections have the strongest effect on the recorded microwave hologram of an object if a distance between the elements equal to about 65% of the wavelength. In general, for such objects, the degree of influence of multiple reflections is small, and they can be ignored when modeling microwave holograms. For objects consisting of separate elements spatially spaced in a direction perpendicular to the registering plane, the influence of multiple reflections is approximately five times greater than for the previous case. The greatest effect is observed when the distance between the elements is equal to 30% of the wavelength. Under such conditions, ignoring re-reflections when modeling microwave holograms can lead to incorrect results when reconstructing them. When modeling scattering by spatially extended solid objects, the degree of influence of re-reflections depends on the shape of the object: if the side of the object oriented to the registering plane of the microwave hologram is convex, then the influence is minimal, and if it is concave, re-reflections must be taken into account.

Electromagnetic Occlusion Algorithm Based on FPGA and Panel Grouping and Its Optimization

With the development of digital signal processing and advanced algorithms, real‐time signal processing based on FPGA and DSP is suitable for high‐speed radar signal processing. With the rapid development of science and technology, war has entered the information age guided by high technology, and advanced science and technology has played a vital role in the trend of war. In recent years in the modern war, many countries invest a lot of research effort on the stealth technology, and advanced stealth technology can use a variety of technical means to alter or weaken the feature information of the target, confuse the enemy radar detection system effectively, reduce the chance of being detected to the largest extent, and prolong the lifecycle of aircraft and weapons. This research mainly discusses the electromagnetic occlusion algorithm and its optimization based on FPGA and panel grouping. The FPGA model selected for this study is XC6VLX240T‐1FF1156I. Because the amount of data processed here is not very large, the cache part directly uses the on‐chip storage resources of the FPGA, and the AD device is used to perform analog‐to‐digital/digital‐to‐analog conversion on the signal and perform digital up‐down conversion. For a facet, it is necessary to first verify whether it is a bright facet and set the flag to mark it, then the facet needs to be occluded with the triangular facet marked as a bright facet, and all bright facets that have been marked need to be traversed. Open MP parallelization of the occlusion algorithm is as follows: The physical optics method is used to calculate the target RCS, and the focus of parallelism is placed on the part with a large amount of calculation. When using Open MP to design a program on a multicore computer, each group is assigned a thread to give full play to the core computing power. The total field is scattered and superimposed by each surface element. This part uses the parallel processing mode of Open MP, which allows the panel judgment in the group to be carried out at the same time. This part requires schedule to allocate resources and use different parallel mechanisms for different calculations to optimize debugging. In the angular range where there is multiple scattering at 0° ≤ φ ≤ 90°, the calculation results and the measurement results are in good agreement, and when the two planes are simulated with 1820 triangular faces, the fast multiple scattering in this paper only needs 4 minutes. This research has realized the general radar signal processing method based on FPGA structure, and the design has important engineering realization significance.

Line source diffraction by double strips with different fractional boundary conditions

In this study, the cylindrical wave diffraction by double strips with different lengths and boundary conditions are investigated. The scattered fields are found by the Numerical-Analytical Approach. The double-strip structure satisfies integral boundary conditions which are the generalization of Dirichlet and Neumann boundary conditions. The electric field, current distribution, and Total Radar Cross Sections are investigated. The results are compared with other methods and previous findings such as the Method of Moments and Physical Optics. The theoretical and numerical analyses indicate that the fractional order, the position of the line source have tremendous effects on the total-field distributions.

Improved Hybrid Algorithm for Composite Scattering From Multiple 3D Objects Above a 2D Random Dielectric Rough Surface

In this paper, an improved hybrid scheme combining the method of moment (MoM) and physical optic (PO) is proposed to analyze composite scattering from multiple 3D conductingobjects above a 2D random rough dielectric surface. In the calculation scheme, rough surface scattering is calculated using the PO method and target scattering is calculated by the MoM. The coupling interactions between the multiple targets are considered using the domain distribution method (DDM), where the matrix equations are constructed upon each individual target and are then presented and solved as a whole. The contribution from rough surface scattering, which is calculated by the PO method, is coupled with the impedance matrix, and the unknowns must be considered only in the MoM region. Most of the composite scattering problems are computing interactions between objects and rough surface, and solving the complex impedance matrix equation in the MoM part. To solve these two problems, first, the combined multilevel fast multipole algorithm (MLFMA) and the fast far field approximation (FaFFA) are introduced to accelerate interactions between objects and rough surface, where the near area on the rough surface is computed by MLFMA, while the far area is computed by FaFFA. In addition, to further improve the efficiency, the adaptive integral method (AIM) is employed to solve the impedance matrix equation of the MoM part in the scheme. The results are compared to those obtained with the traditional MoM-PO method, showing that the hybrid method proposed in this paper can maintain a high accuracy with a much smaller computational time and fewer resource requirements. The numerical results obtained under several different conditions are presented and discussed in this paper.

Iterative MLFMA-MADBT Technique for Analysis of Antenna Mounted on Large Platforms

A hybrid technique combining the multi-level fast multipole algorithm (MLFMA) and the modified adaptive division beam tracing (MADBT) is presented to analyze the radiation patterns of the antennas mounted on large-scale complex platforms. In this technique, the MLFMA is used to characterize the antenna and the transition region that cannot be analyzed accurately by high-frequency asymptotic methods. The MADBT method is used to analyze the contribution of the platforms to the entire radiation pattern by tracing all beams effectively. By applying the beam-based MADBT method instead of the conventional current-based physical optics (PO) method to the platforms, the multi-bounce effects inside the platforms are considered, which enhances the accuracy of the radiation patterns, especially for the complex platforms with corner reflector. An iteration method is proposed to model the interaction between the antennas and the platforms strictly. The proposed iterative MLFMA-MADBT method is mesh-independent and can avoid the matrix-vector production (MVP) of the iterative MLFMA-PO method in each iteration. These characters significantly reduce the memory and time consumption in computation while keeping high accuracy. Numerical results are presented to demonstrate the accuracy and efficiency of the proposed hybrid technique.

Hybrid PO-SBR-PTD method for composite scattering of a vehicle target on the ground

In this paper, a hybrid method of physical optics (PO) shooting and bouncing ray (SBR) physical theory of diffraction (PTD), is adopted to investigate the composite scattering of a vehicle target on the ground. Where the scattering of ground is calculated by the PO method, the scattering of the vehicle target is computed by the SBR-PTD method, and the mutual couplings between them are solved by the ray tracing technique. In addition, an octree data structure is used to accelerate the ray tracing progress. A forward-backward ray tracing technique is employed to ensure the accuracy of the illuminated facet identification. In numerical simulation, the monostatic and bistatic scattering of a reduced-scale vehicle target are calculated by the SBR-PTD method and compared with the simulation results with the multilevel fast multipole method (MLFMM) in commercial software FEKO. And the composite scattering from a reduced-scale vehicle target on the planar ground by our PO-SBR-PTD method is also compared with the MLFMM. The results show that our methods can greatly reduce the computational time and memory requirement while keeping a satisfactory accuracy. Finally, the composite scattering from the vehicle target on the rough ground is demonstrated and analyzed for different incident parameters.

Блочный принцип построения и оценки снижения ЭПР непоглощающих широкополосных 2-битных анизотропных цифровых метапокрытий.

The block principle of constructing of coding matrices for non-absorbing flat digital anisotropic meta-coatings (MC) used to reduce monostatic RCS of objects is considered. The essence of this principle consists in 2-bit coding of the tilt angles of the anisotropy axes of the MC modules so that four arbitrary adjacent modules of the MC form two pairs of antiphase modules. The use of the block principle in the development of a MC provides a reduction of monostatic RCSs on cross polarization due to cancellation of interference waves. The reduction of the monostatic RCS of a MC at matched polarization (co-RCS) is due to the twist-effect. Simultaneously with cancellation and twist-effect, diffuse wave scattering is implemented in the developed digital MCs. The proposed 2-bit anisotropic MCs make it possible to achieve a more effective reduction of monostatic co-RCS (in relation to the traditionally accepted level of minus 10 dB) in a wide frequency band, for different polarization planes of the incident wave. The impedance and full-wave models of the two main blocks of digital anisotropic MCs are developed. An asymptotic representation of the polarization scattering matrix is obtained for the impedance model of the MC block using the method of physical optics. The algorithm for calculating the frequency characteristics (FC) of monostatic co-RCS of impedance models of MC blocks is implemented in the Octave program. Full-wave models of MC blocks are built using the HFSS program. Layouts of two main MC blocks were made. Monostatic co-RCSs of the blocks are measured in the 7÷17.5 GHz frequency band for different polarizations of the incident wave. It is shown that the calculated and measured frequency characteristics of monostatic RCS of the models and layouts of blocks of 2-bit anisotropic MCs are in good agreement. The calculated and measured levels of monostatic RCS reduction of the main blocks are at least 12.5 - 13.5 dB at different co-polarizations in the band from 10.2 to 17.5 GHz and higher (based on the results of calculations).

Comprehensive optimization design of aerodynamic and electromagnetic scattering characteristics of serpentine nozzle

Comprehensive optimization design of serpentine nozzle with trapezoidal outlet was studied to improve its aerodynamic and electromagnetic scattering performance. Serpentine nozzles with different center offsets and different ratios of the bases of the trapezoidal outlet were generated based on curvature control regulation. Computational Fluid Dynamics (CFD) simulations have been conducted to obtain the flow field in the nozzle, and Forward-Backward Iterative Physical Optics (FBIPO) method was applied to study the electromagnetic scattering characteristics of the nozzle. Guarantee Convergence Particle Swarm Optimization (GCPSO) algorithm based on Radial Basis Function (RBF) neural network was used to optimize the geometry of the nozzle in consideration of its aerodynamic and electromagnetic scattering characteristics. The results show that the GCPSO method based on RBF can be used to optimize the aerodynamic characteristics of the internal flow and the scattering characteristics of the cavity of the serpentine nozzle with irregular outlet. The optimized model has a higher center offset and a lower ratio of the bases of the trapezoidal outlet after optimization compared to the original model. The optimized model leads to a slight change in aerodynamic performance, with a total pressure recovery coefficient increase of 0.31% and a discharge coefficient increase of 0.41%. In addition, the Radar Cross Section (RCS) decreases also by around 83.33% and the overall performance is significantly improved, with a decrease of the optimized objective function by around 38.74%.

Synthesis of contoured beam multifeed reflector antenna for optimum coverage

AbstractA synthesis procedure for realizing contoured beams in multifeed reflector antenna is proposed. The proposed procedure solves the synthesis problem so that the maximum gain and low ripple together with low cross polarization are achieved. To this end, first, the relation between the physical parameters of the antenna and the gain loss over the contour is investigated. Then, the maximum achievable gain is approximated, which is needed to study the next issue, that is the optimization procedure. A new optimization procedure is presented, through which the desired contoured beam is achieved. The synthesis procedure employs physical optic (PO) method, which is time‐consuming. To reduce the computational time, which is another focus of the analysis, we introduce an efficient method for computing the PO integral. Through this method, the 3D PO integral is mapped to a 2D integral. The procedure is applied to Brazil coverage. Results show that the cross‐polarization is below −20 dB and the gain deviation is less than 1 dB over the contour, which is suitable for satellite communications.

A Field Equivalence between Physical Optics and GO-Based Equivalent Current Methods for Scattering from Circular Conducting Cylinders

A Field Equivalence between Physical Optics and GO-Based Equivalent Current Methods for Scattering from Circular Conducting Cylinders

Simulation and Feature Extraction of the Dynamic Electromagnetic Scattering of a Hypersonic Vehicle Covered with Plasma Sheath

Based on the detection platform of space-borne radar (SBR), the dynamic electromagnetic (EM) scattering characteristics of a hypersonic vehicle covered with plasma sheath are calculated and analyzed by the physical optics (PO) method. Using the angle-time conversion method, the dynamic radar cross section (DRCS) of the vehicle in horizontal flying path and different flying states is solved in the range of L-band to X-band. The relevant effective statistical features are extracted from the time-scale matrix of DRCS based on continuous wavelet transform (CWT). The numerical results show that: At different flying altitudes, the backscattering radar cross section (BRCS) of the hypersonic vehicle covered with plasma sheath has irregular fluctuation and large range reduction in the head region of the vehicle. Generally, the higher the incident EM wave frequency is, the more detailed the fluctuation characteristics of the DRCS can be reflected. Within the same radar illuminate angle range, the time consumed by the vehicle DRCS is inversely proportional to the flying height and flying speed and is directly proportional to the detection altitude of the SBR. Besides, the different kinds of statistical eigenvalues extracted from DRCS will play an important role in hypersonic targets classification and recognition.

Scattering of Electromagnetic Waves With Orbital Angular Momentum on Metallic Sphere

In this letter, theory concerning scattering of electromagnetic (EM) waves with orbital angular momentum (OAM) is presented, in which a metallic sphere illuminated by OAM waves is adopted to simplify the study. Based on the series expansion and the physical optics (PO) methods, expressions of incident and scattered OAM waves are obtained. To get the expansion coefficients of the scattered fields, boundary conditions and Debye potentials are applied to establish the relationship between incident and scattered fields. Besides, a full EM wave simulation of the scattered field has been accomplished by the computer simulation technology (CST), the measurement of scattered field is done in an anechoic chamber. The simulated results are in good consistency with numerical calculations, demonstrating the interaction between the OAM EM waves and the metallic target sphere effectively. This letter also paves the way for research on scattering of complex targets of OAM waves, and for future studies on target detection.

ISAR Image Algorithm Using Time-Domain Scattering Echo Simulated by TDPO Method

In this letter, we propose an inverse synthetic aperture radar (ISAR) imaging method using time-domain (TD) scattering echo simulated by time-domain physical optics (TDPO) method. First, the TD pulse plane wave is taken as the incident wave and the transient scattering echo data matrix is obtained by using the TDPO method under different look angles of the target. Then, demodulation, pulse compression, and azimuth inverse fast Fourier transform (FFT) are performed on the echo data matrix to obtain the ISAR image under small bandwidth small angle. In this letter, considering the fact of TD pulse signals emitted by radar, electromagnetic scattering modeling method is adopted to obtain more accurate TD scattering echoes. This method combines the electromagnetic scattering algorithm and radar imaging algorithm effectively and is closer to practical application. Finally, ISAR images are given to verify the feasibility and fidelity of the presented method.

Analyzing the Electromagnetic Scattering Characteristics of a Hypersonic Vehicle Based on the Inhomogeneity Zonal Medium Model

A new electromagnetic (EM) calculation model, the inhomogeneity zonal medium model (IZMM) (based on the physical optics (PO) method), is proposed to calculate and analyze the EM scattering characteristics of hypersonic vehicle covered with a plasma sheath. First, the flow field of the plasma sheath is divided into nonuniform calculation subregions with different spacing sizes. The shape of the external flow field of the aircraft is modeled by fitting with a paraboloid and circular platform with different radii. Then, the electron density, temperature, and pressure distribution are obtained by collecting data from different points in the flow field of the sheath. Finally, a piecewise PO method is used to calculate the backscattering radar cross section (BRCS) of the hypersonic vehicle covered with plasma sheath from L-band to X-band. The numerical results show that the EM scattering characteristics of a target spacecraft covered with a plasma sheath can be described more accurately by using zoned medium model simulation. Under different flying conditions, the BRCS of hypersonic vehicle covered with a plasma sheath appears to be reduced to different degrees in the S-band and the band range of 7-11 GHz, and a large attenuation of BRCS occurs in the head area of the aircraft. The research results enrich the EM modeling method of hypersonic vehicles, overcome some shortcomings of the existing PO method, and provide technical support and innovative ideas for the accurate analysis of the EM scattering characteristics of hypersonic targets.

The electromagnetic scattering modelization of metallic object in rectangular waveguide by hybrid method (MOM–PO–GTD)

ABSTRACT This article deals with a new hybrid approach combining a Moment Method (MOM), with the Geometrical Theory of Diffraction (GTD), this approach evaluates the currents surface on the microstrip antenna placed in the rectangular Electric Magnetic Electric Magnetic(EMEM) Waveguides. The incident field is taken as a TEM polarized plane wave in the principal plane. The new hybrid current function based on the Geometrical Theory of Diffraction (GTD), consists in approximating the total current on a homogenous metallic pattern on two steps; in the inside of the metal is dominated by the Physical Optic (PO) method, and the edges, tips effects are described by the GTD method. A set of test functions (sinusoidal or triangular or others) used in the MoM method is replaced by one and unique test function, to get a rapid convergence and less computation time. The new hybrid method can be applied to different structures to calculate scattering for validation proposes. The result of this new method electromagnetic variables current and filed distributions are in agreement with those given by the MoM method. An accurate gain in precision and time, memory resources are obtained.

Features of spectral dependence of single scattering characteristics for crystalline clouds

Extinction, scattering, absorption coefficients, and single-scattering albedo as basic characteristics of single scattering are considered. The results of calculating of extinction and single-scattering albedo for randomly oriented crystals (plates and columns, their aggregates, droxtals, and also mixture of 8 types of cloud crystals) taken from scientific sources are presented. The Mie theory and the physical optics method are used by us to calculate these characteristics for spheres and large crystals. At visible and IR radiation regions, the features of extinction, scattering, absorption, and single-scattering albedo are discussed for various microphysical parameters of spheres, large plates and columns taking into account their orientation. The difference in their behavior is due to variations in the physico-chemical properties of the particles even for the identical shaped crystals. With the same concentration of the particles, the spectral dependence of the optical characteristics (especially for the extinction coefficient) for the large plates is more pronounced (by some orders of magnitude) than for the small particles. Particular attention is paid to the Christiansen spectral regions. In the work, the main focus is made on the consideration of the large horizontally oriented plates. For them, the analytical expressions are presented to calculate the absorption coefficient and the extinction coefficient.

Multilevel Second-Order Physical Optics Method for Calculating the High-Frequency Scattered Fields

The multilevel physical optics (MLPO) method is an effective method for performing the simulation of scattering patterns from a range of frequencies and aspect angles. However, the number of plane patches used to discretize the surfaces of the scatterers will increase with the frequency. Therefore, workloads of the domain decomposition and the calculation of the physical optics integral are too heavy. In order to improve efficiencies, this letter proposes the multilevel second-order physical optics (MLSO-PO) method, which combines the quadratic discretization with the multilevel technology. The workload of the domain decomposition will be reduced greatly, since there has been a decrease in the number of patches. Furthermore, we implement closed-form formulas with the complementary error function to avoid highly oscillatory phenomena. Numerical experiments are provided to benchmark the efficiencies of the MLSO-PO method.

A new BGK model to compute the scattering characteristics of electromagnetic waves by weakly ionized dusty plasma shroud

The dynamics theory of dust charging in the Bhatnagar–Gross–Krook (BGK) model is changed, and the updated expression of the complex permittivity for weakly ionized dusty plasma is derived. Then, by using the physical optics method, the radar-cross section (RCS) of electrically large blunt cones covered by dusty plasma with weak ionization is calculated under the new complex permittivity and compared with the traditional results. The numerical results indicate that the new values of the RCS are significantly smaller than their traditional values. In addition, the influence of dust plasma parameters on the scattering characteristics of EM waves is discussed under the new BGK model. The results enriched the physical mechanisms of the scattering characteristics of weakly ionized dusty plasma shroud and provide a theoretical basis for future studies.

Optimal Design of Cooperative Penetration Trajectories for Multiaircraft

At present, two kinds of shortages exist in the research on cooperative combat. One is that radar detection threat (which cannot be ignored) is rarely considered. The other is that limited efforts have been made on the cooperative penetration trajectories under the conditions of long distance, vast airspace, and wide speed range. In order to offset the shortages of the research on cooperative combat, the penetration trajectory optimization method considering the influence of aircraft radar cross-section (RCS) and the cooperative penetration strategy is proposed in this study. Firstly, the RCS data are calculated by the physical optics (PO) method. The radar detection threat model is established considering the influence of the aircraft RCS. Then, a trajectory optimization framework with the dynamic model, constraint conditions, and optimal objectives is formed. Using the hp-adaptive Radau pseudospectral method, the optimal control problem for a single aircraft flight is solved. Finally, a cooperative penetration strategy is proposed to solve the cooperative penetration problem of multiaircraft. The impact time and angle constraints are given, and the virtual target point is introduced for terminal guidance. Two cases are simulated and verified. Simulation results demonstrate that the proposed method is effective. The single aircraft can effectively penetrate, and the multiaircraft can fulfill the requirement of cooperative impact time and angle under the condition of meeting the minimum threat of radar detection.