Physical optics

About: Physical optics is a research topic. Over the lifetime, 5342 publications have been published within this topic receiving 101388 citations. The topic is also known as: wave optics.

Modified theory of physical optics.

Abstract: A new procedure for calculating the scattered fields from a perfectly conducting body is introduced. The method is defined by considering three assumptions. The reflection angle is taken as a function of integral variables, a new unit vector, dividing the angle between incident and reflected rays into two equal parts is evaluated and the perfectly conducting (PEC) surface is considered with the aperture part, together. This integral is named as Modified Theory of Physical Optics (MTPO) integral. The method is applied to the reflection and edge diffraction from a perfectly conducting half plane problem. The reflected, reflected diffracted, incident and incident diffracted fields are evaluated by stationary phase method and edge point technique, asymptotically. MTPO integral is compared with the exact solution and PO integral for the problem of scattering from a perfectly conducting half plane, numerically. It is observed that MTPO integral gives the total field that agrees with the exact solution and the result is more reliable than that of classical PO integral.

Wave analysis of Airy beams.

Abstract: The Airy beams are analyzed in order to provide a cogent physical explanation to their intriguing features which include weak diffraction, curved propagation trajectories in free-space, and self healing. The asymptotically exact analysis utilizes the method of uniform geometrical optics (UGO), and it is also verified via a uniform asymptotic evaluation of the Kirchhoff-Huygens integral. Both formulations are shown to fully agree with the exact Airy beam solution in the paraxial zone where the latter is valid, but they are also valid outside this zone. Specifically it is shown that the beam along the curved propagation trajectory is not generated by contributions from the main lobe in the aperture, i.e., it is not described by a local wave-dynamics along this trajectory. Actually, this beam is identified as a caustic of rays that emerge sideways from points in the initial aperture that are located far away from the main lobe. The field of these focusing rays, described here by the UGO, fully agrees with the Airy beam solution. These observations explain that the “weak-diffraction” and the “self healing” properties are generated, in fact, by a continuum of sideways contributions to the field, and not by local self-curving dynamics. The uniform ray representation provides a systematic framework to synthesize aperture sources for other beam solutions with similar properties in uniform or in non-uniform media.

Diffraction of cylindrical and plane waves by an array of absorbing half-screens

Abstract: Multiple forward diffraction past an array of many absorbing half-screens whose separation is large compared to wavelength is examined. Starting with the physical optics approximation for half-planes that are equally spaced and of equal height, the field incident on successive edges is represented by a multidimensional Fresnel integral, which is then expanded into a series of functions studied by Boersma (1978). When the angle of incidence with respect to the plane containing the edges is small, each edge is in the transition region of the previous edge, which precludes the use of the geometrical theory of diffraction and related asymptotic theories. The solution obtained applies for incidence either from above or below the plane containing the edges, and is especially suited to the case of near-grazing incidence. This method of solution allows for numerical evaluation of a large number of half-screens and shows how the multiple diffracted fields are influenced by the physical parameters. Both incident plane waves and incident cylindrical waves can be treated. >

A progression of high-frequency RCS prediction techniques

Abstract: Since the widespread use of radar in World War II, engineers have grappled with the problem of calculating the radar echo characteristics of a wide variety of bodies, and over the years methods have steadily improved. This paper surveys a progression of methods, not necessarily in chronological order, each of which offers its own peculiar advantage. We begin with the caveat that large, complex targets are of prime current interest, hence the scattering calculations are for the "high-frequency" regime. As such, the method of moments, although an extremely powerful tool, is not suitable for routine computations for large bodies. Geometric optics, perhaps the oldest method in use, is a simple prescription, but gives the wrong answer for flat and singly curved surfaces, and no answer at all if the specular point is not on the surface. Physical optics does yield results in those cases, but fails by progressively wider margins as the scattering direction swings farther from the specular direction. The theories of Keller and Ufimtsev introduce edge-diffraction terms that improve the prescription, but the diffraction coefficients are poorly behaved in the transition regions of the shadow and reflection boundaries. The uniform theory of Kouyoumjian and Pathak provides the proper behavior of the transition regions, but the scattering direction is constrained to lie on the Keller cone. A method of equivalent currents suggested by Ryan and Peters, extended by Knott and Senior, and refined by Michaeli allows the scattering direction to be arbitrary, but the equivalent currents are nonphysical because they depend on the direction of the observation. Mitzner developed an "incremental length diffraction coefficient" which extends Ufimtsev's theory much as Michaeli's equivalent currents extend Keller's theory. None of these methods can handle the surface traveling wave, a significant echo mechanism for long, smooth bodies, because the methods treat localized scattering phenomena, while the surface traveling wave involves the entire surface. However, as demonstrated by Ross, the repeated application of edge-diffraction theory to account for multiple interactions between pairs of parallel edges comes close to giving the correct result. Unfortunately, there has been no extension of this application to the routine calculation of the surface traveling wave contribution for arbitrary surface geometries. Moreover, practical schemes developed for re-entrant structures and for the interaction between scattering elements consume a great deal of computer time. Thus while our repertory of useful computation methods has greatly expanded in the last 40 years, there remain some scattering mechanisms we still cannot treat in a routine fashion.

High frequency scattering from trihedral corner reflectors and other benchmark targets: SBR versus experiment

Abstract: A general method for calculating the radar cross section (RCS) from a three-dimensional target is described. The target is first constructed by using a solid-geometry-modeling computer-aided design (CAD) package. Following the shooting and bouncing ray (SBR) method, a very dense grid of rays is launched from the incident direction toward the target. Each ray is traced according to the geometrical optics theory including the effect of ray tube divergence, polarization, and material reflection coefficient. At the point where the ray exits the target, a physical optics-type integration is performed to obtain the scattered far fields. This method is tested using several simple examples involving interaction among plates, cylinders, and spheres. The theoretical results are generally in good agreement with measured data. >