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K. Raghavan

Bio: K. Raghavan is an academic researcher from Indian Institutes of Technology. The author has contributed to research in topics: Uniform theory of diffraction & Diffraction. The author has an hindex of 3, co-authored 6 publications receiving 21 citations.

Papers
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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

Journal ArticleDOI
TL;DR: In this article, the principal plane radiation pattern of a subreflector shaped using the method enunciated by Collins has been analyzed based on the uniform geometrical theory of diffraction (UGTD).
Abstract: A technique of analyzing the principal plane radiation patterns of a subreflector shaped using the method enunciated by Collins [1] has been presented. The analysis is based on the uniform geometrical theory of diffraction (UGTD) [2], and a simplified procedure has been adopted in the determination of the principal plane radii of curvature of the subreflector. The numerical results obtained based on UGTD correlate well with those obtained using the method of physical optics (PO).

4 citations

Journal ArticleDOI
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.

4 citations

Journal ArticleDOI
TL;DR: An error in the geometrical theory of diffraction (GTD) near-field analysis of a conical horn published earlier is pointed out in this paper, and the correct expression for the near field patterns for the conical Horn is presented.
Abstract: An error in the geometrical theory of diffraction (GTD) near-field analysis of a conical horn published earlier is pointed out. This error is corrected, and the correct expression for the near-field patterns for the conical horn is presented. Computations based on the corrected formulas correlate better with results based on measurement as well as aperture integration technique [4].

3 citations

Journal ArticleDOI
TL;DR: A geometrical theory of diffraction (GTD) analysis of the principal plane far-field and near-field patterns of a Cassegrainian subreflector is presented in this article.
Abstract: A geometrical theory of diffraction (GTD) analysis of the principal plane far-field and near-field patterns of a near-field Cassegrainian subreflector is presented. The uniform geometrical theory of diffraction (UGTD) [1] that drastically reduces the computation time has been utilized to analyze the subreflector in the form of a paraboloid illuminated by a plane wave. The numerical computations of the far-field amplitude and phase patterns of a typical paraboloidal subreflector based on the above technique correlate well with the results obtained by physical optics current integration, justifying the validity of the analysis presented. The GTD near-field analysis presented here is an improvement over that published earlier [2] and removes some of its limitations.

3 citations


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DOI
01 Jun 1984
TL;DR: In this paper, various methods for the calculation of the field reflected from a subreflector in a dual reflector antenna system were presented, and it was demonstrated that the physical-optics (PO) solution agrees well with the geometrical theory of diffraction for the copolar component.
Abstract: 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.

17 citations

Journal ArticleDOI
TL;DR: In this article, a geometrical theory of diffraction/physical optics (GTD/PO) analysis technique is used to investigate the improving effects of the extended subreflector, beyond its optical rim, on the reflector efficiency and farfield patterns.
Abstract: Both offset and symmetric Cassegrain reflector antennas are used in satellite and ground communication systems. It is known that the subreflector diffraction can degrade the performance of these reflectors. A geometrical theory of diffraction/physical optics (GTD/PO) analysis technique is used to investigate the improving effects of the extended subreflector, beyond its optical rim, on the reflector efficiency and farfield patterns. Representative numerical results are shown for an offset Cassegrain reflector antenna with different feed illumination tapers and subreflector extensions. It is observed that for subreflector extensions as small as 1 \lambda noticeable improvements in the overall efficiencies can be expected. Useful design data are generated for the efficiency curves and far-field patterns.

17 citations

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

Journal ArticleDOI
TL;DR: In this paper, the energy distributions on spherical receiver centered around the focus and on a flat sectorial receiver held in a plane perpendicular to the focal line have been studied for the case of perfect tracking in hour angle and declination axes.

7 citations

Journal ArticleDOI
TL;DR: In this paper, the authors used the field correlation theorem to determine the power coupled by a prime focus feed associated with a paraboloid which is being illuminated by a uniform plane wave, and computed the front-to-back ratio of unflanged and flanged paraboloids.
Abstract: An analysis is presented which uses the uniform geometrical theory of diffraction for determining the near fields diffracted by a paraboloid either with or without a conical flange attached to its circular rim when an axially propagated plane wave is incident on the concave or convex portion of the paraboloidal reflector. The field correlation theorem is used to determine the power coupled by a prime focus feed associated with the paraboloid which is being illuminated by a uniform plane wave. Based on this analysis, the front-to-back ratio of unflanged and flanged paraboloids is computed. Computed results show satisfactory agreement with the available measured as well as computed results based on alternative procedures. The variation in the on-axis gain on a prime-focus reflector when the feed is displaced from the focus is studied. Typical computed results are presented and compared with the available measured data. Computed results on the front-to-back ratio of paraboloids (flanged or unflanged) illuminated by a PFF whose radiated field exhibits phase variation over a constant radius are also presented. >

5 citations