Front-to-back ratio of paraboloidal reflectors
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. >
...read more
Citations
More filters
TL;DR: In this article, the problem is first formulated in terms of the dual series equations and then is regularized by the Riemann-Hilbert problem technique, and the resulting matrix equation is solved numerically with a guaranteed accuracy.
Abstract: The radiation from circular cylindrical reflector antennas is treated in an accurate manner for both polarizations. The problem is first formulated in terms of the dual series equations and then is regularized by the Riemann-Hilbert problem technique. The resulting matrix equation is solved numerically with a guaranteed accuracy, and remarkably little CPU time is needed. The feed directivity is included in the analysis by the complex source point method. Various characteristic patterns are obtained for the front and offset-fed reflector antenna geometries with this analysis, and some comparisons are made with the high frequency techniques. The directivity and radiated power properties are also studied. >
51 citations
30 Jan 2011
TL;DR: In this paper, Rahmat-Samii et al. presented a mathematical model of the single-reflector paraboloid antenna and double-reflectors Paraboloid Cassegrain antenna based on physical optics method.
Abstract: The numerical modeling of reflector antennas is a necessary stage of their design Due to numerical modeling dimensions of all antenna elements are defined The more factors are accounted during antenna numerical modeling the more accurately the antenna elements dimensions are defined There are many methods used in the programs of antenna numerical modeling: geometric optics method; aperture method; geometric theory method of diffraction; physical optics method, integral equations method; finite elements method By now there are many papers in which the different aspects of reflector antenna numerical modeling are discussed For determination of the field antenna reflector in regions of main lobe and first side lobes in front semi-space the aperture method is used; for determination of the field in full semi-space the physical optics method is used (Chen & Xu, 1990; Charles, 1975; Rusch, 1974) The geometric theory of diffraction (Narasimhan & Govind, 1991; Rahmat-Samii, 1986; Narasimhan et al, 1981) and moment method (Khayatian & RahmatSamii, 1999) are used for determination of the field in back semi-space, for determination of field features in front semi-space related with diffraction of the field on the edge of paraboloid and hyperboloid surfaces and for modeling the feed-horn In a number of papers different approaches are used for simplification of analytical expressions for calculation of antenna fields to reduce a mathematical model of antenna and to simplify modeling program (Rahmat-Samii, 1987) A number of works deal with research into the field in nearfield zone (Narasimhan & Christopher, 1984; Fitzgerald, 1972; Houshmand et al, 1988; Watson, 1964) But the results are not reduced to numerical data in that volume which is necessary for antenna design The field distribution in near-field zone is described in detail for plane aperture at uniform its excitation (Laybros et al, 2005), but for reflector antennas such research was not provided The reflector antenna in receiving mode is not discussed in literature, however at designing antenna for radioimaging systems it is necessary to know of field distribution in the focal region at receiving of the wave from near-field zone points The issue of isolation of channels in multi-beam reflector antenna at receiving of the wave from near-field zone is not analyzed too Without analysis of the isolation between channels it is impossible to analyze the quality of imaging in radioimaging systems In literature a number of works deal with describing the feed-horns in monopulse reflector antennas (Hannan, 1961; Scolnic, 1970) There is a little information on numerical characteristics description the regularity in monopulse reflector antenna In the present chapter the mathematical model of the single-reflector paraboloid antenna and double-reflector paraboloid Cassegrain antenna is based on physical optics method
3 citations
Cites methods from "Front-to-back ratio of paraboloidal..."
...The geometric theory of diffraction (Narasimhan & Govind, 1991; Rahmat-Samii, 1986; Narasimhan et al, 1981) and moment method (Khayatian & RahmatSamii, 1999) are used for determination of the field in back semi-space, for determination of field features in front semi-space related with diffraction…...
[...]
TL;DR: In this paper, a two-and-a-half dimensional analytical regularization method (2.5D ARM) was proposed to analyze reflector antennas for microwave, millimeter wave or ultra wide band applications.
Abstract: A novel and efficient approach, which is called two-and-a-half dimensional Analytical Regularization Method (2.5D ARM), is proposed to analyse reflector antennas for microwave, millimeter wave or ultra-wide band applications. To present computational performance of the proposed method, its results are compared with well known Physical Optics (PO) and Method of Moments (MoM) solutions for a PEC hollow cylinder and an open-ended corner reflector. Moreover, radiation pattern of a ridged horn fed parabolic reflector antenna is measured to validate the method experimentally. It is observed that either the simulated or the measured data and the 2.5D ARM results are in close agreement with each other.
2 citations
28 Oct 2010
TL;DR: In this article, the authors proposed the method of analytical regularization (MAR) for 3D and 2D reflector antennas in both polarizations, which can provide finer accuracy within a reasonable computation time.
Abstract: The parabolic reflector antennas are widely used in the telecommunication systems and generally have large aperture sizes like 50λ to 80λ and larger Their reliable full-wave analysis with the conventional Method of Moments (MoM) or with the other numerical methods is difficult because of inaccessible speed and accuracy This statement is valid both for 3D and 2D reflector antennas in both polarizations The Method of Analytical Regularization (MAR) constitutes an alternative solution compared to the ordinary MoM, which can provide only 1–2 digit accuracy It provides finer accuracy within a reasonable computation time because the computational error can be decreased simply by increasing the matrix size in MAR We have previously developed this method for the accurate simulation of the arbitrary conical section profile 2D reflector antennas, and the corresponding codes have provided us with accurate benchmark data Here we study a similar problem however with the feed simulated by Complex Source Point (CSP) source located at an off-focus point on the symmetry axis of a front-fed reflector antenna The numerical results are presented for the radiation characteristics including the forward and backward directivities and the radiation patterns in all directions
References
More filters
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.
2,478 citations
TL;DR: In this article, a uniform geometrical theory of diffraction (GTD) solution for the diffraction of an arbitrary ray optical electromagnetic field by a smooth perfectly conducting convex surface is proposed.
Abstract: The problem of the diffraction of an arbitrary ray optical electromagnetic field by a smooth perfectly conducting convex surface is investigated. A pure ray optical solution to this problem has been developed by Keller within the framework of his geometrical theory of diffraction (GTD). However, the original GTD solution fails in the transition region adjacent to the shadow boundary where the diffracted field plays a significant role. A uniform GTD solution is developed which remains valid within the shadow boundary transition region, and which reduces to the GTD solution outside this transition region where the latter solution is valid. The construction of this uniform solution is based on an asymptotic solution obtained previously for a simpler canonical problem. The present uniform GTD solution can be conveniently and efficiently applied to many practical problems. Numerical results based on this uniform GTD solution are shown to agree very well with experiments.
249 citations
01 May 1978
TL;DR: Rahmat-Samii, Mittra, and Galindo-Israel as discussed by the authors studied the high-frequency asymptotic solution of diffraction by a conducting subreflector using Keller's geometrical theory.
Abstract: The high-frequency asymptotic solution of diffraction by a conducting subreflector is studied. By using Keller's geometrical theory of diffraction and the newly developed uniform asymptotic theory of diffraction, the scattered field is determined up to an including terms of order k^{-1/2} relative to the incident field. The key feature of the present work is that the surface of the subreflector is completely arbitrary. In fact, it is only necessary to specify the surface at a set of discrete points over a random net. Our computer program will fit those points by cubic spline functions and calculate the necessary geometrical parameters of the subreflector. In a companion paper by Y. Rahmat-Samii, R. Mittra, and V. Galindo-Israel, the scattered field from the submflector is used to calculate the secondary pattern of an arbitrarily shaped reflector by a series expansion method. Thus, in these two papers, it is hoped that we have developed a "universal" computer program that can analyze most dual-reflector antennas currently conceivable. It should also be added that our method of calculation is extremely numerically efficient. In many cases, it is one order of magnitude faster than the conventional integration method based on physical optics.
57 citations
TL;DR: In this paper, the radiation patterns of a parabolic reflector with large lateral-feed displacements are computed utilizing both the vector current method and scalar aperture theory, and compared to experimental results.
Abstract: The radiation patterns of a parabolic reflector with large lateral-feed displacements are computed utilizing both the vector current method and scalar aperture theory, and compared to experimental results. The theory is general enough to include asymmetric primary pattern illumination. The scalar and vector solutions are derived from the same initial equation so that the approximations used in obtaining the scalar solution are clearly displayed. Results from the vector and scalar theories are compared and the range of validity of the approximate analysis is indicated.
54 citations
TL;DR: In this paper, the scan-plane fields in the focal region of a beam-scanning paraboloid are determined from physical optics and the contours for maximum scan-gain are determined as a function of F/D and illumination taper and compared with the Petzval surface.
Abstract: The scan-plane fields in the focal region of a beam-scanning paraboloid are determined from physical optics. Amplitude and phase contours are presented, and comparisons are made with the geometrical-optics results. Contours for maximum scan-gain are determined as a function of F/D and illumination taper and compared with the Petzval surface. Unless the F/D is very large or spillover is excessive, a higher scan gain is achieved when the axis of a directional feed is parallel to the axis of the reflector than when the feed is directed toward the vertex. The contour of maximum scan-gain is a function of both illumination taper and F/D . In general, larger F/D values tend to have a maximum-gain contour close to the focal plane, while the smaller F/D values tend to have a maximum-gain contour closer to the Petzval surface. Increasing the illumination taper moves the maximum-gain contour closer to the Petzval surface. Normalized maximum-gain contours are presented as a function of beamwidths of scan. The frequency dependence of these results is discussed.
36 citations