Showing papers on "Cassegrain antenna published in 1986"

Design of wide-band corrugated conical horns for Cassegrain antennas

Abstract: Design procedures based on extensive theoretical and experimental investigations are given for hybrid-mode corrugated conical horns having near-constant beamwidth, low cross-polarized sidelobes and low reflection for continuous bandwidths up to 2.1:1. The design techniques are applicable for horn flare semi-angles to about 30\deg , which includes most feed horns in dual-reflector antennas.

Reflector antenna and method of fabrication

Abstract: A parabolically-shaped reflector antenna particularly intended for space vehicle applications, can be transported into outer space in a folded state. There it is inflated by means of a gaseous agent, such as a gas compound or gaseous medium, which is transported with the space vehicle. The antenna reflector and an antenna radome form an inflatable cavity which is stabilized by a rigidizing torus. The covering material of the antenna reflector, the antenna radome and the rigidizing torus comprise a resin-impregnated layer of fabric. After inflation in outer space, the reflector antenna is aligned such that it will be substantially uniformly heated by the sun for substantially uniform polymerization of the resin impregnant. After polymerization, the reflector antenna requires no gas pressure to keep its shape.

Recent developments in the analysis of reflector antennas. A review

Abstract: The basic methods used in the analysis of reflector antennas are discussed, with emphasis on recent developments. The current integration method and its various modifications is reviewed in detail. Also, the potential of the new sampling technique is illustrated.

Subreflector extension for improved efficiencies in Cassegrain antennas--GTD/PO analysis

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.

Grasp: An improved displaced-axis, dual-reflector antenna design for EHF applications

Abstract: Research into the design of dual-reflector systems for small mobile satellite communication terminals has yielded potentially significant improvements over existing models. These new designs are similar to the dual-frequency ADE (elliptical displaced axis) reflectors' except that both reflector surfaces are shaped (Fig. 1). As a result, an arbitrary aperture illumination may be achieved; only a limited range of illumination functions can be obtained from the standard AUE configuration. This freedom in specifying the aperture illumination permits the optimization of the antenna for desired radiation characteristics, such as maximum on-axis gain or low farout sidelobes. Another important feature is that the maximum angle subtended by the feed at the subreflector can be specified as an independent parameter, which eliminates the need for a feed horn.

Electromagnetic wave spatial filter with circular polarization and a Cassegrain antenna comprising such a filter

Abstract: A spatial filter is provided for electromagnetic waves with circular polarization comprising three parallel conducting networks, the central network being totally reflecting for a rectilinear polarization of given direction and having a non zero reflection coefficient for a rectilinear polarization having a direction perpendicular to the preceding one.

Theory of imaging of Cassegrainian and Gregorian antennas

Abstract: The formation of an image by an eilipsoidal reflector under illumination from one of its foci is discussed. The transformation relating the field distributions over two conjugate surfaces \Sigma_{0} and \Sigma is determined. It is shown that the image produced by the reflected field E over \Sigma is not an exact replica of the illumination of \Sigma_{0} , but E = E_{i} + \delta E , where E_{i} is the image according to geometric optics. The distortion \delta E is primarily due to the nonzero angle of incidence i on the reflector. If i = 0 then \delta E \simeq 0 , in agreement with Fresnel's diffraction theory for an optical system of revolution. The theory applies in general to any multireflector arrangement derived from quadric surfaces of revolution and, in particular, to Cassegrainian and Gregorian antennas. As an application, a simple solution to the classical problem of illuminating efficiently the aperture of a reflector antenna is proposed. A horn of relatively small aperture is combined with an imaging reflector. The imaging reflector, an ellipsoid, transforms the horn aperture distribution into a magnified image illuminating efficiently the main reflector, with negligible spillover over a wide frequency range.

Reflector antennas for electron cyclotron resonance heating of fusion plasma

Abstract: For electron cyclotron resonance heating (ECH) of fusion plasma, transformation is required of the millimeter wave output from a gyrotron, circular TE/sub 0n/ mode, into a linearly polarized wave beam. It is easily realized by use of a parabolic cylinder reflector. Vlasov et al. proposed this type of reflector antenna which has a stair-cut aperture at an end of a circular waveguide. The authors recently proposed another type of antenna that also uses a parabolic cylinder and has an obliquely cut aperture. In this paper, the transformation efficiencies of polarization and radiation fields of the two types of antennas are calculated by means of geometrical optics and the Kirchhoff-Huygens principle. Then the authors propose a mode converter, in which the output of this type of parabolic reflector is led to a rectangular waveguide and transformed into TE/sub 10/ mode. In addition, another reflector antenna is proposed that focuses the wave beam using an elliptic cylinder reflector and a parabolic one.

Compact antenna range employing shaped reflectors

Abstract: In the preferred embodiment the compact antenna range (10) includes two shaped reflectors, a subreflector (14) and a main reflector (16) arranged in an offset configuration. Each reflector is shaped so that the reflected wave front from the main reflector is planar with a substantially uniform amplitude and phase. Substantially all of the energy emitted by the feed (12) is reflected from the subreflector onto the main reflector in such a way that the energy incident on the reflector edges is greatly reduced, thus reducing the energy diffracted therefrom significantly. Use of the shaped reflectors also allows the main reflector to be of a smaller size and thus the tolerances associated with the main reflector can be more closely controlled.

Performance of a dual-band reflector antenna incorporating a frequency selective subreflector

Abstract: The performance of a linearly polarized dual-band parabolic reflector antenna is described A frequency selective Cassegrain subreflector is used to separate the two frequency bands allowing both the prime focus and Cassegrain feeds to be used simultaneously The hyperbolic subreflectors were manufactured by directly printing frequency selective array elements onto a curved surface Two frequency selective designs were tested, gridded square and ring arrays The reflector operates at 14·5 and 23·5 GHz The gain, sidelobe and crosspolar performance of the complete antenna is assessed and compared with the performance of equivalent single-band reflectors

The equivalent paraboloid of an optimized off-set cassegrain antenna

Abstract: A. Introduction. Increasing interest is being shown in both ground-based and satellite-borne dual offset reflector systems for telecomnunication applications. A particular class of these antennas is "optimized" with respect to reduction of cross polorization by tilting the subreflector axis and cocking the boresight axis of the feed. This paper defines the parameters of an equivalent paraboloid construction for this antenna and investigates its accuracy in calculating the directivity pattern.

Microwave holographic technique for reflector antenna profile measurement

Abstract: A short-range microwave holographic technique for the measurement of reflector antenna surface profile is described. The technique uses a linearly scanned transmit/receive CW probe located on-axis at approximately two focal lengths from the reflector vertex. Rotation of the reflector provides a plane-polar data set which can be reconstructed by a fast algorithm to provide a surface profile error map. No special precautions are required with regard to the reflectivity of the environment. Practical results are provided to illustrate the performance of the system.

A Cassegrain reflector system for compact range applications

Abstract: An integral part of a compact range is the means of providing a uniform plane wave A Cassegrain reflector system is one alternative for achieving this goal Theoretically, this system offers better performance than a simple reflector system The longer pathlengths in the Cassegrain system lead to a more uniform field in the plane of interest The addition of the subreflector creates several problems, though System complexity is increased both in terms of construction and performance analysis The subreflector also leads to aperture blockage and the orientation of the feed now results in spillover illuminating the target areas as well as the rest of the range Finally, the addition of the subreflector leads to interaction between the two reflectors resulting in undesired field variations in the plane of interest These difficulties are addressed and through the concept of blending the surfaces, a Cassegrain reflector system is developed that will provide a uniform plane wave that offers superior performance over large target areas for a given size reflector system Design and analysis is implemented by considering the main reflector and subreflector separately Then the system may be put together and the final design and system analysis completed

Physical optics analysis of four-reflector antenna

Abstract: A four-reflector physical optics analysis procedure is presented. Theoretical characteristics of the National Aeronautics and Space Administration/Jet Propulsion Laboratory (NASA/JPL) 64 m antennas computed from this procedure were found to be in excellent agreement with experimental observations. The S -band horn fields will subsequently be carried through all four reflectors (resulting in a transmission viewpoint of final antenna system beams) to account fully for all nearfield, cross polarization, and higher order mode generation effects caused by various intentional asymmetries in geometry. This appears to be the first time such a complete and rigorous analysis has been performed on such a complex antenna system. The analysis techniques presented are useful in many ongoing ground station antenna research and development efforts, including high-efficiency shaped reflector and beam waveguide feed designs and microwave metrology (holography) applied to large reflector surface measurements.

A Dual Reflector High Gain Microwave Omnidirectional Antenna

Abstract: The design of a reflector system consisting of conic section reflectors rotated about an axis and fed using a biconical horn is outlined. Shaping of the main reflector to meet a required elevation radiation pattern is then described and some theoretical predictions of performance presented.

Analysis and design of radial rib reflector antennas

Abstract: The radiation characteristics of radial rib reflector antennas are studied. This type of antenna can be used as a large deployable satellite antenna. The radiation patterns of a axi-symmetric reflector are computed using both an exact physical optics analysis and a simplified approximate analysis in order to understand the behaviour of the rib-related sidelobes which have a cyclic behaviour in the azimuthal direction. A parametric study is conducted. A shaped sub-reflector is designed using diffraction profile synthesis to compensate for some of the errors introduced by the main radial rib reflector.

Fields in the focal region of paraboloid and offset paraboloid reflectors

Abstract: : While much development has been accomplished for reflector antenna technology, a need still exists in evaluating the impacts of design parameters One such area lists with the design tradeoffs associated with the beam-scanning performance of reflector designs A surface current integration analysis is derived which is exact to the order of physical optics This analysis is applied to both circular and offset reflectors for on-axis and off-axis illumination for parameters which span the cases for which both substantial and minimal degradation with beam scan occur The output of the analysis is cast in the form of contour plots defining the field structure in the focal region of the reflector The results of the analyses compare favorably with data previously obtained for specialized parameters Keywords include: Physical Optics Currents, Numerical Integration, Cassegrain Antenna, Offset Paraboloid Antenna, Contour Plots for Fields, and Angle of Scan

Synthesis and analysis of single shaped reflector antennas

Abstract: Introduction. Althou h eometrical optics (GO) is an asymptotic theory describyears constituted the foundation for synthesis of reflector antennas. While dual ing electromagnetic #e& of infinitely high frequencies only, it has for several reflectors are usually shaped to produce a certain aperture distribution leading to a pencil beam type pattern with high gain or low side lobes, etc., single reflectors field. In either of the cases, any design must necessarily be ver!fied by a diffracmay be syntheslsed to generate shaped beams by using the GO directly in the far tion analysis, because of the GO assumption made In the synthesis. In this paper we will demonstrate a numerical method for solving the synthesis problem for single reflector antennas. The technique has been found to be superior to what has reviously been applied, in particular because it returns the solution on a form wlich lends itself easily t o diffraction analysis. This is accomplished by solvin Westcott's synthesis problem usin a collocation method and an expansion of t l e reflector surface in bicubicspline?unctions. The theory will be resumed very briefly, and we wiU then present some results figuration, a reflector shaped to provide full earth coverage from a low orbitting from applying the developed synthesis and analysis programs to a particular consatellite. Formulation of the synthesis. As stated previously, the synthesis part of this study is based upon the work of Westcott (1983). To formulate the problem we of the coordinate system. The half angle subtended by the reflector at the feed is consider the reflector shown in fig. 1, illuminated by a feed located at the centre €Ic. Given the feed power densit pattern I(e,+), we require the reflector t o G(B. a) inside the far-field cone of half angle Of. Westcott showed that by using transform this pattern into a far-fie& pattern with a power density distribution an appropriate parametrization of the reflectoer surface one can derive a highly non-linear boundary value problem, the solution of which overns the reflector surface. He also showed how the non-linear problem couqd be linearized and solved by repeated solution of linear second order partial differential equations (POE'S).

Adjusting device for the exciter of a reflector antenna

Abstract: In order to change the polarisation plane and in order to change the position of the radiation centre of an exciter of a reflector antenna in a frequency-dependent manner, said antenna can be rotated about its axis of symmetry by means of a single spindle/nut drive.

Synthesis of line feeds for conical reflectors

Abstract: The matched feed concept is used to determine the electrical characteristics of a line source feed for conical reflector antennas. A linearly polarized plane wave incident on the reflector is used to determine the field distribution along and in the vicinity of the focal axis of the reflector. The co-polar, cross-polar and the axial field components are determined and their dependence on the reflector size and the radial distance is studied. The results indicate that for a line source of finite diameter its surface field distribution must contain other field components to generate a linearly polarized far field.