# GTD analysis of the near-field patterns of a prime-focus symmetric paraboloidal reflector antenna

TL;DR: In this article, the uniform geometrical theory of diffraction (UGTD) has been applied successfully to analyze the near-field patterns of a prime-focus paraboloid.

Abstract: The uniform geometrical theory of diffraction (UGTD) has been applied successfully to analyze the near-field patterns of a prime-focus paraboloid. In order to establish the validity of the analysis, near-field amplitude and phase patterns have been computed over the principal planes at several observation distances for a typical prime-focus paraboloid. These calculations compare very favorably with the corresponding results obtained numerically with the aid of Silver's near-field aperture integration formula.

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01 Jan 2014

TL;DR: This item cannot be reproduced or quoted extensively from without first obtaining permission in writing from the copyright holder(s).

Abstract: Copyright © and Moral Rights are retained by the author. A copy can be downloaded for personal non-commercial research or study, without prior permission or charge. This item cannot be reproduced or quoted extensively from without first obtaining permission in writing from the copyright holder(s). The content must not be changed in any way or sold commercially in any format or medium without the formal permission of the copyright holders.

1 citations

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TL;DR: In this article, an efficient approach for the analysis of surface conformed reflector antennas fed arbitrarily is presented, where the near field in a large number of sampling points in the aperture of the reflector is obtained applying the Geometrical Theory of Diffraction (GTD).

Abstract: An efficient approach for the analysis of surface conformed reflector antennas fed arbitrarily is presented. The near field in a large number of sampling points in the aperture of the reflector is obtained applying the Geometrical Theory of Diffraction (GTD). A new technique named Master Points has been developed to reduce the complexity of the ray-tracing computations. The combination of both GTD and Master Points reduces the time requirements of this kind of analysis. To validate the new approach, several reflectors and the effects on the radiation pattern caused by shifting the feed and introducing different obstacles have been considered concerning both simple and complex geometries. The results of these analyses have been compared with the Method of Moments (MoM) results.

1 citations

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##### References

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TL;DR: In this article, a compact dyadic diffraction coefficient for electromagnetic waves obliquely incident on a curved edse formed by perfectly conducting curved plane surfaces is obtained, which is based on Keller's method of the canonical problem, which in this case is the perfectly conducting wedge illuminated by cylindrical, conical, and spherical waves.

Abstract: A compact dyadic diffraction coefficient for electromagnetic waves obliquely incident on a curved edse formed by perfectly conducting curved ot plane surfaces is obtained. This diffraction coefficient remains valid in the transition regions adjacent to shadow and reflection boundaries, where the diffraction coefficients of Keller's original theory fail. Our method is based on Keller's method of the canonical problem, which in this case is the perfectly conducting wedge illuminated by plane, cylindrical, conical, and spherical waves. When the proper ray-fixed coordinate system is introduced, the dyadic diffraction coefficient for the wedge is found to be the sum of only two dyads, and it is shown that this is also true for the dyadic diffraction coefficients of higher order edges. One dyad contains the acoustic soft diffraction coefficient; the other dyad contains the acoustic hard diffraction coefficient. The expressions for the acoustic wedge diffraction coefficients contain Fresenel integrals, which ensure that the total field is continuous at shadow and reflection boundaries. The diffraction coefficients have the same form for the different types of edge illumination; only the arguments of the Fresnel integrals are different. Since diffraction is a local phenomenon, and locally the curved edge structure is wedge shaped, this result is readily extended to the curved wedge. It is interesting that even though the polarizations and the wavefront curvatures of the incident, reflected, and diffracted waves are markedly different, the total field calculated from this high-frequency solution for the curved wedge is continuous at shadow and reflection boundaries.

2,478 citations

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TL;DR: In this paper, the authors used the geometrical theory of diffraction to obtain the backscattered field for plane-wave incidence on a target with particular emphasis on those regions that are usually avoided, namely, the caustic region and its immediate vicinity.

Abstract: The fields diffracted by a body made up of finite axially symmetric cone frustums are obtained using the concepts of the geometrical theory of diffraction. The backscattered field for plane-wave incidence on such a target is obtained with particular emphasis on those regions that are usually avoided, namely, the caustic region and its immediate vicinity. The method makes use of equivalent electric and magnetic current sources which are incorporated in the geometrical theory of diffraction. This solution is such that it is readily incorporated in a general computer program, rather than requiring that a new program be written for each shape. Several results, such as the cone, the cylinder and the conically capped cylinder, are given. In addition, the method is readily applied to antenna problems. An example which is reported consists of the radiation by a stub over a circular ground plane. This present theory yields quite good agreement with experimental results reported by Lopez, whereas the original theory given by Lopez is in error by as much as 10 dB.

190 citations

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TL;DR: In this paper, the radiated far field is determined from a rapidly convergent series representation of the radiation integral, where the coefficients of the series are independent of the observation angles, and the field may be determined very rapidly at large numbers of points.

Abstract: Given the true or any approximate current on a reflector, the radiated far-field is determined from a rapidly convergent series representation of the radiation integral. The leading term is a well-shaped J_{1}(x)/x beam pointing in a desired direction. Higher order terms provide perturbations to the leading term. The coefficients of the series are independent of the observation angles. Hence, once they are computed, the field may be determined very rapidly at large numbers of points. Initially, a suitable small angle approximation is made that places the radiation integral in the form of a Fourier transform on a circular disk. The theory is then extended such that the results are valid in both the near and the wide angle regions. Application to a rotationally symmetric paraboloid is presented herein. Other applications include the offset and dual reflectors and near- to far-field integrations. A modified form of the series can also be used for Fresnel zone computations.

108 citations

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TL;DR: In this paper, a general computer program has been developed for the transverse electric case, where the computation of radiation and scattering of electromagnetic fields by electrically large convex conducting cylinders, using the geometrical theory of diffraction (GTD), is considered.

Abstract: The computation of radiation and scattering of electromagnetic fields by electrically large convex conducting cylinders, using the geometrical theory of diffraction (GTD) is considered. A general computer program has been developed for the transverse electric case. Illustrative computations are made for examples of radiation from a line source of magnetic current in the vicinity of a polygonal cylinder, scattering of plane waves, radiation from slots, and radiation from electric dipoles. Also given are examples of computations for conducting strips, grazing incidence on polygonal cylinders, and scattering from small cylinders. The computational accuracy is checked by comparing the results to corresponding ones computed by a moment solution to the H -field integral equation.

20 citations

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TL;DR: In this article, a multipole expansion technique to study radiation from aperture antennas in the form of an open-ended waveguidehorn is presented, and the far-zone fields of an axially-symmetric aperture-fed paraboloid are obtained in closed form.

Abstract: A multipole expansion technique to study radiation from aperture antennas in the form of an open-ended waveguide-horn is presented. Particular attention is paid to dual-mode and corrugated circular horns. The radiation pattern of these feeds, derived in terms of multipole moments, is in the form of an algebraic series which converges very rapidly. Further, based on the multipole-expansion technique presented, the far-zone fields of an axially-symmetric aperture-fed paraboloid are obtained in closed form. It is demonstrated that there is a drastic reduction in computer time by using this technique instead of the conventional numerical integration procedure for calculating the far-zone fields of the paraboloid.

4 citations

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