Geometrical Theory Of Diffraction Method Research Articles

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.

Double effects between reflection and edge-diffraction in NURBS-UTD method

ABSTRACTSecond-order ray types in uniform geometrical theory of diffraction method are studied in this paper where non-uniform rational B-spline technique is introduced to construct targets. Reflection-edge diffraction ray type and edge diffraction-reflection ray type which are always appeared in multi-scatterer environments are investigated. Ray paths are found through numerical optimization based on Fermat’s principle. Ray fields carried by these kinds of rays are calculated based on single effected ray fields to discuss their contribution to the total ray fields. It can be seen that the consideration of reflection-edge diffraction effect and edge diffraction-reflection effect can improve the computational precision slightly in calculation of radiation patterns. Numerical results show the validation and the improvement.

Study on Interface Scheme for Non-Uniform Rational B-Spline Uniform Geometrical Theory of Diffraction Method

ABSTRACTAn interface scheme is presented to analyze radiation pattern of complex antennas for non-uniform rational B-spline-uniform geometrical theory of diffraction method. Antennas are represented as the distribution of vectorial fields around antennas in free space which can be achieved either from electromagnetic algorithms, software simulations, or practical measurements. The given scheme can be applied on common PC to analyze the radiation pattern of large-scale antenna mounted around electrically large targets efficiently especially when the structure of the antenna is unknown.

Expandable shipboard decoy including adequate RCS by using trihedral corner reflectors

The purpose of this study is to design expandable shipboard decoys by using right angle trihedral corner reflectors (TCRs). It is expected that they show larger radar cross section values than the ships themselves in X-band. Due to practical impacts, they should be made of lightweight materials in rational dimensions. Furthermore it must be realised in expandable structure. Hence, some kind of conductive textiles are used as the base material. The subject covers two different types of scenarios in specific angular sectors and suitable configuration is proposed for each. In each scenario, various types of TCR configurations are introduced to find the best response. Simulations are performed by CST Microwave Studio software tool based on geometrical theory of diffraction method. The optimum configurations of geometrical models with limited dimensions are evaluated based on actual measured data. The simulated and measured results are in very good agreement.

Scattering of inhomogeneous plane waves by a truncated cylindrical cap

Scattered fields of the inhomogeneous plane waves from a truncated cylindrical cap are obtained. Also the uniform diffracted fields are performed in terms of the Fresnel functions. Reflected and diffracted fields are obtained by using the physical optics and the geometrical theory of diffraction methods, respectively. All the mentioned results are plotted numerically for various numerical parameters.

Study on Curved Wedge Diffraction in NURBS‐UTD Method

ABSTRACTThe curved wedge diffraction in nonuniform rational b‐spline (NURBS)‐uniform geometrical theory of diffraction method is studied in this article. The curved wedge is denoted as a NURBS curve while it is also treated as the intersection of two NURBS surfaces. Basic aspects are managed through numerical measures, and parameters used in the calculation of ray field are achieved by using the mathematic definition of NURBS and basic knowledge of differential geometry. Good results are achieved in the examples given and with the contribution of the wedge diffracted ray field to the total ray field, the computational accuracy can be slightly improved. Numerical results show the validation and the improvement. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:2317–2321, 2013

Quasihybrid scheme of nonuniform rational B‐spline–uniform geometrical theory of diffraction method for radiation of antennas

AbstractThe nonuniform rational B‐spline–uniform geometrical theory of diffraction (NURBS‐UTD) method is studied in this paper. To deal with arbitrary wire antennas without analytical directional functions, a quasihybrid scheme is presented to discuss the radiation pattern of wire antennas mounted around electrically large targets. The NURBS technique is introduced to construct targets, the wire antennas, and electrically large targets are analyzed by method of moment (MoM) and NURBS‐UTD, respectively. Information from results of ray tracing is chosen as interface between MoM and NURBS‐UTD to form quasihybrid scheme. The practicability and validity can be seen from examples given. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:2963–2967, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26374

Directly Connected Hybrid Finite Element–Boundary Integral–Ray-Optical Models

The hybrid finite element–boundary integral–uniform geometrical theory of diffraction method with acceleration by the multi-level fast multi-pole method is extended in a way that allows the application of the hybrid method to problems, where the finite element–boundary integral–multi-level fast multi-pole method parts of the model can be directly connected to uniform geometrical theory of diffraction regions. This becomes possible by an appropriate utilization of Huygens' principle, together with the fact that the regions exterior to the introduced Huygens surface is free of any fields and can thus be filled with arbitrary materials. As such, the appropriate materials are chosen in order to obtain simple enough bodies, which can be treated by the uniform geometrical theory of diffraction. Since some of the boundary integral basis functions typically touch flat parts of these bodies, the image principle is employed for the accurate evaluation of the corresponding boundary integrals. Numerical results for radiation and scattering problems are presented and compared to reference numerical data. The obtained results prove the feasibility of the procedure and considerable computation time and memory savings.

Advances in hybrid finite element – boundary integral – multilevel fast multipole – uniform geometrical theory of diffraction method

Abstract. Numerical modeling of problems including composite metallic/dielectric objects with arbitrary shapes and electrically large conducting objects within a common environment is performed in an optimum way with the recently developed powerful hybrid numerical method, which combines the Finite Element Boundary Integral (FEBI) method and the Multilevel Fast Multipole Method (MLFMM) with the Uniform Geometrical Theory of Diffraction (UTD), giving full electromagnetic coupling between all involved objects. In this contribution, the hybrid FEBI-MLFMM-UTD method is extended to double diffracted fields on pairs of straight metallic edges, formulated with the hard and soft scalar diffraction coefficients of UTD. The diffraction points on each pair of edges are determined by an iterative three-dimensional parametric realization of the generalized Fermat's principle. The divergence factor of the double diffracted field is computed by multiplying the appropriate divergence factors of the single diffracted UTD fields on each edge for the particular case. Thereby, the ray caustic distance of the diffracted field at the second edge is determined by linear interpolation between the radii of curvature in the two principal planes of the incident astigmatic ray tube. Further, fast near-field computation in the postprocessing stage of the hybrid method is extended in each translation domain to ray optical contributions due to the presence of electrically large objects, according to the hybridization of MLFMM with UTD. Formulations and numerical results will be presented.

Interference effects in the light scattering by transparent plates

We examine the effect of interference on the light scattering by transparent plates of arbitrary refractive index with moderate to large width-to-thickness ratios using a scattering model developed within the framework of the geometrical theory of diffraction (GTD). The GTD method bridges the gap between the geometric optics and the resonance region, thus allowing us to investigate the light scattered by plates of very large size down to the size of a few wavelengths. In particular, we study the dependence of the angular distribution of the intensity and the linear polarization on the geometrical dimensions of the plate.

Deemphasizing low frequency defects in GTD analysis of pulsed signal scattering by a perfectly conducting flat strip

Geometrical theory of diffraction (GTD) based wavefront, resonance and hybrid formulations of transient scattering by targets, while adequate to generate resonance frequencies, yield incorrect late time scattered fields because of the early time (high-frequency) nature of GTD asymptotics. Thus, impulsive signals are improperly treated in this manner. However, for signals with low frequency cutoff, deemphasizing the low frequency range may eliminate the troublesome portions of the GTD algorithm. This is confirmed here for plane wave scattering by a perfectly conducting flat strip when the exciting pulse has a raised cosine shape. The solution is now stabilized and compares very well with an exact solution obtained by eigenfunction expansion. This suggests that the GTD method can be employed with confidence for transient scattering responses for a class of input pulses with sufficiently weak low frequency content.

Monopole antenna patterns on finite size composite ground planes

Geometrical theory of diffraction methods have been used to develop models and to predict the patterns of communications, navigation, and identification (CNI) blade antennas mounted on finite size composite ground planes. The computed patterns agree extremely well with measurements. It has been shown, both analytically and experimentally, that very minor differences between patterns of antennas mounted on perfectly conducting and composite ground planes appear for conductivities equal to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> s/m.