Heuristic Diffraction Coefficient Research Articles

A new time-domain heuristic diffraction coefficient for characterization of diffracted and transmitted field with UWB applications

In this paper, a novel heuristic diffraction coefficient in the frequency-domain (FD) for non-perfectly conducting wedges and buildings is proposed. The six-terms diffraction coefficient which is an extension of the four-terms UTD coefficient is proposed to include the effect of transmitted ray for a lossy dielectric wedge with arbitrary low wedge angle, thus, attaining the continuity of the total field all around the structure. This new six-terms UTD diffraction coefficient is verified with the earlier available finite-difference time-domain (FDTD) result. Further, the time-domain (TD) solution based on the classical frequency domain result is proposed for UWB applications in indoor environments. Finally, a case of double diffraction for two consecutive buildings scenario is presented based on slope diffraction and their corresponding TD solution is also presented. The different input pulses and building materials are considered to test the overall behavior of the TD model. All the TD results are verified with inverse fast Fourier transform (IFFT) of the FD results in both the soft and hard polarization and the results are found to be in very good agreement. The channel impulse response is also presented to determine the distortion on the input pulse. The computational efficiency of the proposed TD solutions is demonstrated by comparing them with IFFT-FD solutions.

Heuristic UTD Diffraction Coefficient for Three-Dimensional Dielectric Wedges

This article presents a heuristic diffraction coefficient for 3-D dielectric wedges of arbitrary angles. First, the proposed diffraction coefficient is derived for 2-D wedges with soft and hard polarization, by enforcing continuity of the total field at every shadow boundary associated with the multiply reflected fields inside the wedge. The accuracy of the proposed heuristic 2-D solution is verified comparing with the UTD solution derived from Maliuzhinets' exact integration. Then, it is extended to 3-D wedges for arbitrary polarizations and incident/scattered directions by transforming ray-fixed to edge-fixed coordinate systems. The total field predicted using the proposed heuristic diffraction coefficient is continuous for arbitrary angle 3-D dielectric wedges, including interior wedges, and is close to the geometrical optics field far from the shadow boundaries. The proposed method is validated against a Method-of-Moment solution. Finally, we show the method can significantly improve the accuracy of ray-tracing modeling of wave propagation in arched tunnels.

A Novel Symmetrical Heuristic Coefficient for Urban Microcellular Environments

A novel heuristic diffraction coefficient is presented which is perfectly reciprocal and symmetrical. The prediction obtained using proposed coefficient is compared with that obtained using rigorous Maliuzhinets' solution. It is shown that the proposed coefficient is more efficient than available diffraction coefficient. The comparison is made for both soft and hard polarization. Further, the applicability of proposed coefficient in complex urban scenario is demonstrated by applying the coefficient in the city of Ottawa.

A Finite Edge GTD Analysis of the H-Plane Horn Radiation Pattern

The earlier geometrical theory of diffraction (GTD) approach to the H-plane horn radiation problem is reconsidered with spherical source excitation. Corner diffraction terms are included to provide a GTD model for the finiteness of the horn edges. A new heuristic corner slope diffraction (CSD) coefficient for a finite edge in a conducting plane is presented. The H-plane horn pattern, obtained with the addition of the corner diffraction and the new CSD terms to the earlier infinite edge GTD approach, is found to be in better agreement with measured results compared to earlier GTD formulations.

Millimeter-Wave Propagation in Indoor Corridors

In this letter, ray-based models for both line-of-sight (LOS) and non-line-of-sight (NLOS) indoor corridors are presented and compared with results of propagation measurements performed at millimeter (mm)-waves in the 60-GHz frequency band. It is shown that in the LOS corridor case, signals propagate like in free space and in a guided fashion in near and far zones, respectively. A nine-ray model (LOS path plus four first-order and four second-order reflections from the corridor walls, ground, and ceiling) is found to be suitable in characterizing propagation signals in far zone in this environment. In the NLOS corridor case, multiray models with a heuristic diffraction coefficient are used in the field simulation. Results show that a model with eight rays is adequate in characterizing both average power and variation of signals. However, in characterizing the average decay of signal power, only two diffracted rays are needed. Also, empirical models given for NLOS corridors cases indicate that diffraction is the dominant propagation phenomenon in the environment. Furthermore, multipath power distributions are investigated. It is found that Rayleigh and double-Rayleigh distributions are the bounds for both the LOS and NLOS data. Multiple-Rayleigh distribution can fit the measurement data very accurately.

A Heuristic Diffraction Coefficient for the Corner of a Dielectric Slab

A heuristic diffraction coefficient for the corner of a semi-infinite dielectric slab angular sector is presented. The corner diffraction coefficient is constructed based on the solution of a canonical problem using a physical optics formulation: a plane surface wave hitting the corner of the slab. The corner diffraction coefficient is expressed in terms of edge diffraction coefficients. It has a very simple form that can be easily extended to other types of excitations. The effectiveness of the proposed method is demonstrated by comparison with other techniques based on physical optics and experiments. The proposed corner diffraction coefficient can be used within geometrical theory of diffraction solution techniques for planar antennas.

Heuristic edge diffraction coefficient for the surface field of an equal curved face wedge: TE plane wave illumination

We present a diffraction coefficient for calculating the field on the surface of a perfectly conducting two-dimensional curved face wedge, illuminated by a TE plane wave. The surface field consists of a geometrical optics (GO) field supplemented by a creeping wave launched by edge diffraction. The GO field is that which would exist on the circular cylinder of which the wedge face is a part, subject to the same illumination. The diffracted field takes the form of a creeping wave and is related to the incident field at the edge by the new diffraction coefficient /spl Delta/. /spl Delta/ is found by requiring the sum of the diffracted and GO fields to equal the correct field determined by numerical methods in a range of representative cases. /spl Delta/ is found to be a function of distance close to the edge and then becomes constant with increasing distance; thus, our method is valid for all distances from the edge, including zero. We have developed relatively simple analytic expressions for /spl Delta/ as a function of plane wave incidence direction, wedge angle, radius of curvature of the surfaces and distance of the field point from the edge. These expressions have been found to give good prediction of surface magnetic field for cases different from those for which the original data was calculated.

Influence of diffraction coefficient and corner shape on ray prediction of power and delay spread in urban microcells

For a low base-station (BS) antenna located on one street, signals propagate into crossing and parallel streets by reflection and diffraction at corners of buildings. Therefore, in order to accurately predict the received signals, it is necessary to properly model the diffraction coefficient at the building edge and to accurately represent the shape and the electrical properties of the building near the corner. This paper compares ray-tracing predictions to measurements of received power and root mean square (rms) delay spread and shows the need for a diffraction coefficient having larger values than suggested by the commonly used heuristic diffraction coefficient. A new heuristic diffraction coefficient is proposed that has higher diffracted field strength in the deep shadow region and in the region between the two shadow boundaries. The proposed diffraction coefficient shows better agreement with measurements of both received power and delay spread compared to the commonly used heuristic diffraction coefficient. The influence of building shape near the corner and its electrical properties on the ray-tracing predictions are also presented. The shape is shown to have an important role in accurately predicting both received power and delay spread.

A new heuristic diffraction coefficient for lossy dielectric wedges at normal incidence

A new heuristic diffraction coefficient is proposed for dielectric wedges with losses. This new diffraction coefficient, based on the uniform theory of diffraction (UTD), is valid for incidence orthogonal to the edge and when losses are such that the field transmitted through the wedge can be neglected. This applicability range fits typical scenarios for urban propagation models. Our results are compared to those predicted by using the diffraction coefficients of R.J. Luebbers (see IEEE Trans. Antennas Propagat., vol.AP-32, p.70-76, 1984) and P.D. Holm (see IEEE Trans. Antennas Propagat., vol.48, p.1211-19, 2000), and the rigorous diffraction coefficient (RDC) of G.D. Maliuzhinets (see Sov. Phys. Dokl., vol.3, no.4, p.752-5, 1958). Comparisons with a diffraction coefficient derived from the finite-difference time-domain (FDTD) simulations are also presented for right angle wedges. Parallel and perpendicular field polarizations are tested. The new heuristic diffraction coefficient shows clear improvement in agreement with the RDC and the FDTD results. Moreover, the proposed diffraction coefficient is as simple to compute as Luebbers' and Holm's coefficients.

A three-dimensional UTD heuristic diffraction coefficient for complex penetrable wedges

A three-dimensional heuristic diffraction coefficient, useful to predict the electromagnetic field scattered from penetrable wedges of complex geometry, is presented. The model, based on a modification of the exact uniform theory of diffraction (UTD) metallic wedge diffraction coefficient, allows the analysis of a large class of penetrable objects with an adequate degree of accuracy. Numerical results concerning the scattering from solid and hollow penetrable wedges show the suitability of the proposed diffraction coefficient to analyze complex structures of large practical interest. A good agreement with exact numerical results already available in the literature has been found.

Errata to "A new heuristic diffraction coefficient for lossy dielectric wedges at normal incidence"

For the above-named work [ibid., vol. 1, pp. 165?168, 2002] in (1, Sec. III), there are two corrections to the text that are presented here.

High-frequency scattering by the edge of a thin dielectric slab loaded by a metallic strip grating

A heuristic diffraction coefficient is presented that is suitable to describe the scattering from the edge of a thin dielectric half-plane, loaded by a metallic strip grating on one of its faces, when the grating period is much smaller than the free-space wavelength. The most general case of oblique incidence is analysed, with the incident plane wave arbitrarily polarised. The direction of the strips can be arbitrarily oriented with respect to the edge of the half-plane. Extensive numerical tests have been performed to verify the effectiveness of the heuristic solution and to check its accuracy through comparisons with reference data.

Scattering by a right-angled lossy dielectric wedge

Electromagnetic scattering by a right-angled lossy dielectric wedge at normal incidence is considered in detail. The lossy dielectric material of the wedge is simulated using second-order impedance boundary conditions on its faces. The Maliuzhinets method is employed to obtain the total exterior field. A high-frequency asymptotic approximation of the Sommerfeld integral is carried out to obtain a UTD expression for the total field. The predictions are validated against experimental measurements taken in a controlled laboratory environment. A comparison with the widely used heuristic UTD diffraction coefficient of Luebbers is presented and the validity of the latter coefficient is discussed.

Heuristic diffraction coefficient for plane-wave scattering from edges in periodic planar surfaces

A uniform heuristic high-frequency solution is obtained for plane-wave scattering from edges in periodic planar surfaces. The case of a wedge with periodic impedance boundary conditions on its faces and that of a truncated strip grating are analyzed. Numerical results are presented and compared with reference solutions to validate the heuristic expressions proposed.