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Journal ArticleDOI

GTD analysis of the radiation patterns of a prime focus paraboloid with shroud

TL;DR: In this paper, the uniform geometrical theory of diffraction (UGTD) is employed to analyze the far-field radiation patterns of a prime focus paraboloid with a cylindrical shroud.
Abstract: The uniform geometrical theory of diffraction (UGTD) is employed to analyze the far-field radiation patterns of a prime focus paraboloid with a cylindrical shroud. The blockage of the aperture illumination of the dish by the gooseneck and the primary feed is also taken into account in the analysis. Far-field radiation patterns (for 0\deg\leq\Theta \leq 180\deg ), calculated for a typical prime focus paraboloid with 2 m aperture diameter, designed and fabricated, are compared with the experimentally derived patterns at 8.8 GHz in the E - and H -planes. There is a satisfactory agreement between the two results.
Citations
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Journal ArticleDOI
TL;DR: In this article, the radiation characteristics of a parabolic dish with a loaded peripheral flange are examined in detail in order to assess the effectiveness of such a loading in further reducing the backward scattered field.
Abstract: The radiation characteristics of a parabolic dish with a loaded peripheral flange are examined in detail in order to assess the effectiveness of such a loading in further reducing the backward scattered field. Uniformly valid diffraction coefficients are developed to deal with both isotropic and anisotropic surface impedances. It is shown that substantial improvement of the antenna performance can be obtained in a wide rear angular sector, and the optimal loading conditions are determined.

11 citations

Proceedings ArticleDOI
20 Oct 2011
TL;DR: This paper proposes two analysis for increasing the performance of a prime fed reflector antenna, the first analysis is choosing the true feedline mechanism and the second one is the effect of shroud usage.
Abstract: High gain, low sidelobe and backlobe levels are important parameters in the reflector antenna design These parameters are being vital important for the antennas used in radar systems, especially in military applications If the design of the reflector is made without considering the implemantation stage, the characteristics mentioned above can not be provided To manage this performance reduction, some improvements should be added to the design in the theoretical design stage This paper propose two analysis for increasing the performance of a prime fed reflector antenna The first analysis is choosing the true feedline mechanism and the second one is the effect of shroud usage These analysis are made for an X-band waveguide fed prime focus reflector antenna Numerical results and chosen design configuration are also presented in the numerical results section

1 citations


Cites methods from "GTD analysis of the radiation patte..."

  • ...In addition the diffraction effects and the pattern calculations with and without shroud are shown in [3]....

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  • ...Narasimhan talks about feed line effect as blocked area and blocking of the primary feed by the goose neck in [3] and also feed line effect is shown by calculating of antenna pattern with and without aperture blocking using GTD method....

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  • ...It has been mentioned as absorber-lined tunnels in [1] and analysed with GTD in [3] and [4]....

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Proceedings ArticleDOI
29 Jul 2008
TL;DR: In this article, a technique for calculating radiation patterns of reflector antennas with curvilinear impedance peripheral flanges is presented, based on the uniform asymptotic theory with numerical diffraction coefficients and on the equivalent edge currents method.
Abstract: A technique for calculating radiation patterns of reflector antennas with curvilinear impedance peripheral flanges is presented. It is based on the uniform asymptotic theory with numerical diffraction coefficients and on the equivalent edge currents method. The use of numerical diffraction coefficients allows to account near-field terms in the incident field and nonuniform impedance distributions on the flange, provided that dimensions of the flange do not exceed several wavelengths.

1 citations

Journal ArticleDOI
TL;DR: In this article, a cylindrical and conical shroud was used to reduce the spillover noise of a reflector antenna and reduce the conical sidelobe level in the front hemisphere.
Abstract: The spillover noise of a reflector antenna can be reduced by attaching a shroud extending forward from the edge of the reflector; the shroud prevents ground radiation from entering the feed. Symmetrical paraboloidal antennas of diameter 40 wavelengths, equipped with cylindrical and conical shrouds, are analyzed using the method of moments. A cylindrical shroud, parallel to the reflector axis, may reduce antenna noise, but it raises the sidelobe level in the front hemisphere substantially and can also reduce antenna gain. These drawbacks can be overcome by using a conical shroud, flared outward. Such a shroud reduces the spillover lobes in the back hemisphere, thus lowering the antenna noise temperature, but generates a conical sidelobe in the front hemisphere. The peak level of this sidelobe can be reduced by building the shroud using two cones of different flare angles or by curving its cross section. The decrease in noise temperature, as well as the location and level of the conical sidelobes in the front hemisphere, can be predicted to useful accuracy using geometrical optics. The addition of a shroud increases the level of cross polarization near the main beam. However, this effect is reduced if the sharp corner where the shroud joins the reflector rim is replaced by a smooth transition. The level of cross polarization is then at a level comparable to that produced by scattering from feed-support struts.
References
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Journal ArticleDOI
01 Nov 1974
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.

2,582 citations

Journal ArticleDOI
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.

191 citations

Journal ArticleDOI
C. Knop1
TL;DR: In this article, an explicit expression for the radiation field in the back zone of a typical parabolic dish antenna was obtained for both the ideal 100 percent aperture efficiency feed and for an arbitrary, feed.
Abstract: Adopting the earlier work of Kouyoumjian's Ohio State group, as recently reviewed and extended by Rusch, an explicit expression for the radiation field in the back zone of a typical parabolic dish antenna is obtained. Evaluation of this expression directly in the back for both the ideal 100 percent aperture efficiency feed and for an arbitrary, feed gives (in conjunction with the known front field for the 100 percent case) the front to back ( f/b ) ratio for the arbitrary feed case of (f/b) = G + T + K - G horn . Here G is the gain of the dish with the arbitrary feed, G horn is the on axis gain of the feed, T is the feed's average pattern edge taper relative to on axis, K = 20 \log_{10}{\sqrt{1 + 16(F/D)^{2}}/4(F/D)} (all being in decibels), and F/D is the ratio of the focal length to the dish diameter. Comparison of this result with measured values for dishes ranging from 6 to 15 ft in diameter operating over a 920 MHz to 14 GHz range gives an agreement within several decibels in most cases.

22 citations

Journal ArticleDOI
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.

13 citations

Journal ArticleDOI
TL;DR: A geometrical theory of diffraction analysis of the principal plane far-field radiation patterns of a hyperboloidal subreflector with a conical flange attachment (HWF) fed by a primary feed located at its focus is presented in this article.
Abstract: A geometrical theory of diffraction (GTD) analysis of the principal plane far-field radiation patterns of a hyperboloidal subreflector with a conical flange attachment (HWF) fed by a primary feed located at its focus is presented. While using the uniform geometrical theory of diffraction (UGTD) for evaluating the nonaxial fields, the method of equivalent currents is used in the axial region. In this paper, both the diffraction by the wedge formed between the hyperboloid and the conical flange and the diffraction by the edge of the flange are considered. While considering the diffraction by the edge due to the diffracted ray from the wedge in the H -plane, the slope diffraction technique has been used. The computed diffracted farfields of a typical HWF illuminated by a high performance primary feed shows good agreement with the available measured data and with the results based on the method of physical optics (PO). The sharp cutoff and the low spillover characteristics of the HWF are highlighted by comparing its radiation pattern with that of a hyperboloid without a flange. Further, the effects of the different parameters of the HWF on its radiation pattern are also studied and plotted, so that these results can be utilized in the design of the HWF for a specific requirement.

5 citations