Exploring the Validity of Plane and Spherical Millimeter-Wave Incidences for Multiple-Diffraction Calculations in Wireless Communication Systems

Rays and modes for plane wave coupling into a large open-ended circular waveguide

A comparison of the presence of cylindrical against rectangular obstacles in radio wave multiple-diffraction analysis is performed both theoretically - through hybrid formulations based on the uniform theory of diffraction (UTD) and physical optics (PO) - and experimentally - through measurements performed at 60 GHz. The results can be applied to the analysis of multiple diffraction in the mm-wave band when propagation over periodic obstacle patterns - either rounded or flat - has to be considered.

The problem of scattering from a perfectly conducting cylindrical reflector is examined with the method of the modified theory of physical optics. In this technique the physical optics currents are modified by using a variable unit vector on the scatterer's surface. These current components are obtained for the reflector, which is fed by an offset electric line source. The scattering integral is expressed by using these currents and evaluated asymptotically with the stationary phase method. The results are compared numerically by using physical optics theory, geometrical optics diffraction theory, and the exact solution of the Helmholtz equation. It is found that the modified theory of physical optics scattering field equations agrees with the geometrical optics diffraction theory and the exact solution of the Helmholtz equation.

In order to control its attitude, there usually have wings or other structures on the midcourse target. It is the foundation to simulate the radar echo of this kind of rotationally asymmetric target to get it recognized correctly. Firstly, the position variation of each scattering center on both the body and the wing is analyzed. After that, according to the high frequency method and local field theory, the RCS calculation formulas of body and wings of the target are derived with the Geometrical Theory of Diffraction(GTD) and Physical Optics(PO) method respectively. Then, a simple method is put forward to judge whether the wing is shielded with the target's movement according to the PO method. Finally, the wideband radar echo is simulated and the impacts of non-idealization of the scattering centers and rotationally asymmetry of the target on the echo are also analyzed.

This paper illustrates the influence of pre-stress and finite strain on the reflection of homogeneous plane waves from a plane boundary in an incompressible isotropic elastic solid. For a special class of constitutive laws it is shown that an incident SV wave propagating in a principal plane of the finite deformation gives rise to a surface wave in addition to a reflected SV wave for every angle of incidence (except discrete angles for which the surface wave amplitude vanishes). For materials not in this special class and for certain states of deformation and stress, on the other hand, two SV waves are in general reflected when the angle of incidence (measured from parallel to the plane boundary) is less than a critical value. One reflected wave has angle of reflection equal to the angle of incidence. The angle of reflection of the second reflected wave may be greater than, equal to or less than the angle of incidence, but for the second reflected wave to have time-averaged energy flux directed into the material away from the boundary its wave normal is, for certain angles of incidence, necessarily directed out of the material. For angles of incidence greater than the critical angle the situation is similar to that for the special class of materials. This contrasts with the situation in the (compressible) classical theory in which an incident SV wave leads to a surface wave for angles of incidence less than some critical value. The dependence of the reflection coefficients on the angle of incidence depends markedly on the state of deformation and stress, and the range of behaviour is illustrated graphically for a specific material model. The surface wave speed increases indefinitely as the angle of incidence approaches normal incidence while its amplitude approaches zero. This is a consequence of the degeneracy associated with the incompressibility constraint that the P-wave speed is infinite.

The paper presents various methods for the calculation of the field reflected from a subreflector in a dual reflector antenna system. It is demonstrated that the physical-optics (PO) solution agrees well with the geometrical theory of diffraction (GTD) for the copolar component. Significant discrepancies may appear for the crosspolar component, and it is necessary to introduce additional fringe currents in the PO solution. If the subreflector is located in the near field of the feed, special precautions must be taken. One can either subdivide the feed aperture into a number of smaller subapertures for each of which standard GTD can be applied or an alternative and more efficient method is to use complex ray analysis (CRA), where the directive feed is represented by a point source located in the complex co-ordinate space. Both methods are compared with PO solutions taking the near-field effects into account. The theoretical results are verified experimentally for a near-field illuminated offset hyperboloidal subreflector.

In this paper geometrical theory of diffraction (GTD), geometrical optics (GO) and physical optics (PO) are used to calculate the back scattering field of a cylinder-rotating parabolic body. The calculated result is in accordance with the measured result given by the references. It is concluded that, when target's electric size in excess of twice the wavelength, higher diffraction fields can be ignored.

For the electromagnetic modeling of scattered fields from large and complex objects, a very efficient simulation tool based on the well-known Shooting-and-Bouncing-Rays (SBR) technique has been developed [1]. This algorithm uses field-based high-frequency approaches for finding the relevant propagation paths, i.e. rays are traced through the scenario according to the laws of Geometrical Optics (GO) and diffracted rays are generated according to the laws of the Uniform Theory of Diffraction (UTD). This GO/UTD part is combined with a source-based approach, where each ray generates an equivalent surface current at each interaction with the object. These currents are calculated using Physical Optics (PO) and Physical Theory of Diffraction (PTD), and the superposition of all these contributions leads to the total scattered field strengths. Further technical details about the ray tracing approach can be found in [1, 2, 4]. With this simulation tool, large and complex objects can be modeled, which are still too costly for numerically exact methods. Generally, both metallic and dielectric objects [2], and also combined metallic-dielectric objects, can be modeled.

Airborne Laser Scanning (ALS) has been established as a valuable tool for the estimation of biophysical vegetation properties such as tree height, crown width, fractional cover and leaf area index (LAI). It is expected that the conditions of data acquisition, such as viewing geometry and sensor configuration influence the value of these parameters. In order to gain knowledge about these different conditions, we test for the sensitivity of vegetation products for viewing geometry, namely flying altitude and scanning (incidence) angle. Based on two methodologies for single tree extraction and derivation of fractional cover and LAI previously developed and published by our group, we evaluate how these variables change with either flying altitude or scanning angle. These are the two parameters which often need to be optimized towards the best compromise between point density and area covered with a single flight line, in order to reduce acquisition costs. Our test‐site in the Swiss National Park was sampled with two nominal flying altitudes, 500 and 900 m above ground. Incidence angle and local incidence angle were computed based on the digital terrain model using a simple backward geocoding procedure. We divided the raw laser returns into several different incident angle classes based on the flight path data; the TopoSys Falcon II system used in this study has a maximum scan angle of ±7.15°. We compared the derived biophysical properties from each of these classes with field measurements based on tachymeter measurements and hemispherical photographs, which were geolocated using differential GPS. It was found that with increasing flying height the well‐known underestimation of tree height increases. A similar behaviour can be observed for fractional cover; its respective values decrease with higher flying height. The minimum distance between first and last echo increases from 1.2 metres for 500 m AGL to more than 3 metres for 900 m AGL, which does alter return statistics. The behaviour for incidence angles is not so evident, probably due to the small scanning angle of the system used. fCover seems to be most affected by incidence angles, with significantly higher differences for locations further away from nadir. As expected, incidence angle appears to be of higher importance for vegetation density parameters than local incidence angle.

The usefulness of the geometrical theory of diffraction (GTD) in computing the surface current and charge density induced on aircraft is illustrated. This is a high-frequency solution for an arbitrary incident plane wave and fuselage observation points. A pattern is presented for an arbitrary incident plane wave as well as a series of frequency and time domain plots for roll plane incidence. A 3-dimensional pattern is presented for plane wave incidence (as a function of incidence angle) as well as examples of roll plane results in both the frequency and time domain.

A new and simple method of interpreting the of the backscatter radar cross section (RCS) from ocean waves of individual wavelength is presented. Using the Kirchhoff scattering (Physical Optics) theory, the RCS from the ambient waveheight spectrum is first computed as a function of the wavenumber. Differentiating this cumulative RCS yields the distribution function of the RCS from ocean waves of different wavenumbers. The present study shows, as a general feature, that the maximum RCS contribution tends to come from the ocean waves of wavenumbers closer to the Bragg wavenumber as the radar incidence angle increases. Under low wind speeds (/spl sim/2 m/s) and at incidence angles between 200 and 45/spl deg/, the dominant RCS contribution at both C-band and L-band comes from ocean waves of wavenumbers close to the Bragg wavenumber. Under intermediate to high wind speeds (/spl sim/10-15 m/s) and at the small incidence angle of 200, the radar backscatter is dominated by long ocean waves with little contribution from the Bragg waves at both bands. At the intermediate incidence angles (/spl sim/35/spl deg/ to 45/spl deg/), the RCS distribution is centered at wavenumbers near the Bragg wavenumber at all wind speeds from 2 m/s to 15 m/s. These features are more pronounced at C-band than at L-band. The present theory is based on the Kirchhoff scattering model, and as such, its validity may also be limited to a range of small to intermediate incidence angles where the polarization effect is not very significant. The RCS distribution is evaluated for the ambient sea surface and the surface perturbed by varying currents induced by the interaction between the current and bottom topography.

This paper concerns the analysis and measurement of the RCS of missile-shaped targets. Physical optics and the uniform theory of diffraction are used to determine the frequency-domain RCS at various incident and roll angles. A discrete inverse Fourier transform with a Kaiser-Bessel window then gives the corresponding time-domain response. This determines the magnitude and location of the major target scattering centres. The resulting target scattering centre parameters are used in a simulation to predict the performance of an HRR (high range resolution) radar. The input to the simulation includes, in addition to the magnitude and location of the individual scattering centres of the missile, the clutter level, the speed of the target and radar parameters such as number of frequencies, starting frequency, frequency step, and percentage phase noise. Conclusions are drawn on the feasibility of recognising targets with the proposed HRR radar.

Reflection and transmission of elastic waves at an interface between two micropolar piezoelectric half-spaces

A ray-based method is presented for evaluating multiple acoustic diffraction by separate rigid and parallel wide barriers, where two or more neighboring ones are of equal height. Based on the geometrical theory of diffraction and extended from the exact boundary solution for a rigid wedge, the proposed method is able to determine the multiple diffraction along arbitrary directions or at arbitrary receiver locations around the diffracting edges, including the positions along the shadow or reflection boundaries or very close to the edges. Comparisons between the results of the numerical simulations and the boundary element method show validity of the proposed method.

A new method termed Directive Line Source Model (DLSM) is presented for predicting the diffracted field produced by a sound wave incident on a rigid or pressure release half plane. In the new method the edge of the half plane is modeled as an infinite set of directive point sources continuously distributed along the edge. Because DLSM is fast, simple and intuitive, it is a promising tool for the study of diffraction. It can be applied for several types of incident radiation: omnidirectional cylindrical and spherical waves, plane waves, as well as waves from directional sources. Wedges may also be treated. Finally, DLSM can handle diffraction by an arbitrarily shaped edge profile, for example, a half plane having an edge that is jagged instead of straight. Results for plane, cylindrical and spherical incident waves, as well as for arrays of line and point sources, are presented and their agreement with known analytical solutions is demonstrated. Predictions based on DLSM compare favorably with experimental data.