Ray Optical Fields Research Articles

Fast Multipole Accelerated Hybrid Finite Element-Boundary Integral-Ray-Optical Method Including Double Diffractions

This recently developed, powerful hybrid technique, which combines the finite element–boundary integral (FEBI) method and the multilevel fast multipole method (MLFMM) with the uniform geometrical theory of diffraction (UTD), allows for an efficient and accurate computation of various radiation and scattering problems. Ray-optical fields are considered by modifying the Green functions and the incident field in the boundary integral (BI) part. Within the MLFMM part, ray-optical fields are also taken into account in the translation stage on the various levels using a far-field approximation of the translation operator. Ray-optical contributions are considered on flat conducting structures and, in this article, they are extended to double-diffracted fields on pairs of straight metallic skewed edges. The corresponding formulations, as well as numerical results, are presented.

Ray Optical Electromagnetic Far-Field Scattering Computations Using Planar Near-Field Scanning Techniques

For accurate scattering computations in the far-field of flat finite objects, field based ray optical methods cannot be used directly, since the finiteness of the objects is not considered in the formulations. In this paper, planar near-field scanning techniques are used to overcome this problem. In particular, scattered ray optical fields are first computed in a scanning plane in the near-field region of the involved objects and are transformed into the far-field afterwards using field expansions in terms of spectrum density functions of outgoing waves. Since evanescent waves are avoided in the scanning plane, sampling rates less than lambda <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> /2 can be used for restricted angle range around the normal direction to the scanning plane. Reduced accuracy at grazing directions of observation is overcome by combining solutions provided by several scanning planes. The proposed approach is applied in the postprocessing stage of the recently developed hybrid method combining the uniform geometrical theory of diffraction with the finite element boundary integral technique and with the multilevel fast multipole method.

A UTD Solution for Multiple Rounded Surfaces

This paper describes the diffraction mechanism when a ray optical field is obstructed by a cascade of smooth convex obstructions. A new formulation of the uniform theory of diffraction (UTD) is presented that incorporates the slope diffraction term. The solution follows a generic approach that can be applied to arbitrary placed convex structures. It will be shown that the slope diffraction term provides the required accuracy in radio propagation predictions when more than one obstruction exists in the propagation path. The proposed solution is then compared with measurements and other analytical models with excellent agreement. It is also found that the presented slope-UTD solution seems to be superior in terms of computation time and complexity, while achieving very accurate results. In addition, when the radius of the cylinder tends to be very small, the solution approaches the UTD solution for multiple knife-edge predictions.

An approach of source equivalance for the fast analysis of high frequency radio wave problems via uniform geometrical theory of diffraction

Uniform geometrical theory of diffraction (UTD) is very efficient in the numerical analysis of electromagnetic (EM) wave problems associated with geometry of electrically large objects in comparison with ordinary numerical techniques such as method of moment (MoM) and finite difference in time domain (FDTD) because it extracts the most significant field contributions in terms of a very few ray optical fields. The UTD assumes fields radiated from a point source and suffers from difficulties in situations where the source volume is not extremely small, the object of interaction is very close to the source and only some source information is available. It is noted that discretization over the source for a numerical integration is usually required in the prior two situations, which in turn degrades the expected efficiency of UTD. This paper describes a valid approach based on an equivalent representation of a source in terms of relatively few but simple elements that can be further modeled by an equivalent point source as required in UTD solutions. The source representation is obtained through a best guess from the available source information, and has potential to improve the efficiency and applicable areas of UTD to the greatest possible extent. Numerical examples are presented to validate the proposed approach.

UTD-diffraction coefficients for higher order wedge diffracted fields

An asymptotic expansion of a multiple integral for knife-edge diffraction is derived. The expansion expresses the field in terms of single-edge diffraction. By considering this expression, a similar expansion for higher order UTD diffracted fields is proposed. By means of a set of transition functions, the result removes some of the shortcomings of the original set out of the UTD when the incident field is not a ray-optical field.

High frequency diffraction by wedges

Methods for handling high frequency fields are briefly reviewed. They are illustrated by the diffraction of a ray optical field by a curved wedge. The necessary formulas are collected or referred to for a direct application to the problem. The corresponding canonical problem, diffraction of a plane wave by a straight wedge, is presented from a point of view that shows the filiation of some diffraction factors and suggests generalization to other problems such as the diffraction by higher order wedges.

Mutual coupling between rectangular slot antennas on a conducting concave spherical surface

The surface fields excited by a horizontal magnetic source located on a conducting concave spherical surface have been formulated. The field expressions are obtained as a combination of ray-optical fields and simplified integrals under the condition that the radius of the spherical surface is much greater than the wavelength. Numerical calculations have been performed, and the calculated results for the surface fields have been corroborated with experiments. The results of these basic studies have been used in calculating the mutual coupling between rectangular slot antennas on the conducting concave spherical surface assuming the aperture field as the dominant mode in the wave guides connected with the slots. The numerical results have been compared with those for slots on a convex conducting surface. Experimental investigation of the mutual coupling has also been carried out.

High-frequency fields excited by a line source located on a concave cylindrical impedance surface

A previous study of high-frequency currents induced by a line source on a perfectly conducting concave cylindrical surface is extended to the case of nonvanishing surface impedance <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Z_{s}</tex> . Alternative field representations are formulated and evaluated asymptotically as combinations of ray-optical, whispering gallery (WG) mode, surface wave, continuous spectrum, and canonical integral contributions. Numerical calculations provide an insight into the accuracy and utility of the various formulations. Sufficiently far from the source point, a combination of ray optical fields and tightly bound WG modes was previously found to be a most appealing form when <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Z_{s} = 0</tex> . As the surface impedance becomes more dissipative, the WG modes axe weakened by attenuation and eventually render the ray optical fields adequate by themselves. A representation in terms of rays and a canonical integral is found to be useful for all parameter ranges. The canonical integral has been evaluated numerically and tabulated.