Showing papers on "Cassegrain antenna published in 1973"
Patent•
16 Jul 1973
TL;DR: In this article, a Cassegrainian antenna system has a planar array as the feed and an intermediate reflector is positioned in the near field of the array for substantially collimated illumination with all array elements operating in phase.
Abstract: A Cassegrainian antenna system has a planar array as the feed. An intermediate reflector is positioned in the near field of the array for substantially collimated illumination with all array elements operating in phase. Accordingly, an on-axis main beam is radiated from the main reflector upon illumination by energy from the intermediate reflector. By impressing a linear phase gradient across the array, the main beam is controllably tilted off-axis.
119 citations
TL;DR: In this paper, the edge currents derived from the edge diffraction theory for a halfplane were used to obtain the radiation patterns of a parabeloidal reflector antenna when illuminated by a source at the focus.
Abstract: Equivalent edge currents, derived from the edge diffraction theory for a half-plane, are used to obtain the radiation patterns of a parabeloidal reflector antenna when illuminated by a source at the focus. Cylindrical wave diffraction coefficients are used. The method avoids infinities at caustics and shadow boundaries thus giving solutions which are finite everywhere. A slope-wave equivalent current correction term is applied when the illumination is tapered towards the edge of the reflector. Comparisons are given with the physical optics approach and experimental results.
61 citations
TL;DR: Theoretical and experimental investigations on coaxial feeds excited by H 11 modes have shown that the first ring yields the highest increase in the aperture efficiency of paraboloid antennas illuminated by them as mentioned in this paper.
Abstract: Coaxial feeds produce an approximate sector-shaped pattern, an almost optimum pattern of a feed for high aperture efficiency and low spillover of paraboloid antennas. Such a coaxial feed consists of a central circular waveguide which is surrounded by one or more conductors with circular cross sections. Theoretical and experimental investigations on coaxial feeds excited by H 11 modes have shown that the first ring yields the highest increase in the aperture efficiency of paraboloid antennas illuminated by them. Measurements performed on paraboloid antennas illuminated by a coaxial feed with only one ring yielded aperture efficiencies of 68 to 75 percent for angular apertures of the paraboloidal reflector of 100\deg to 160\deg . Circularly symmetric patterns in conjunction with almost linearly polarized aperture fields can be achieved by multimode coaxial feeds. The values for the aperture efficiency, which are calculated for paraboloid antennas illuminated by multimode coaxial feeds, nearly reach the theoretical optimum. The measured values are 68 to 80 percent. In addition, the multimode feeds produce very little cross polarization.
54 citations
TL;DR: In this paper, the authors describe the experimental development of a 1:6.535 scale model line feed for the Arecibo spherical reflector, which is capable of illuminating the full 1000ft aperture of the reflector.
Abstract: The experimental development of a 1:6.535 scale model line feed for the Arecibo spherical reflector is described. The 14.7-ft long model at 2810 MHz simulates a 96.6-ft feed at 430 MHz capable of illuminating the full 1000-ft aperture of the reflector. The feed design requirements are discussed and an experimental program is outlined in which the necessary line source parameters were established using a number of leaky cylindrical test sections. Experimental measurements of both the near and far fields of the model feed are described and typical results are quoted and discussed. Finally, some results obtained after installation of a full size feed in the reflector are given and compared with predictions based on the model data.
22 citations
TL;DR: In this paper, the characteristics of the astigmatic phase error in large parabolic reflector antennas are described and a procedure for focusing an antenna and diagnosing the presence and degree of astigmatism is given.
Abstract: The characteristics of the astigmatic phase error in large parabolic reflector antennas are described. A procedure for focusing an antenna and diagnosing the presence and degree of astigmatism is given.
13 citations
TL;DR: In this paper, the authors extended the analysis to the case where the primary feed illumination is not symmetric, because real primary feeds usually have unequal E - and H -plane beamwidths.
Abstract: Gored umbrella parabolic reflectors with symmetric aperture illumination have been treated analytically in a recent paper. This communication extends the analysis to the case where the primary feed illumination is not symmetric, because real primary feeds usually have unequal E - and H -plane beamwidths. The gore loss and the shift in the defocusing curve obtained using the modified gain expression are in excellent agreement with values measured for a smooth parabolic reflector and a gore parabolic reflector of the same diameter.
11 citations
01 Jul 1973
TL;DR: In this paper, a design theory for Cassegrain antennas employing dielectric-cone feeds is presented, and a modal approach is used to describe the aperture field over the subreflector, while a ray-optics method is employed to determine the sub-reflector profile and main reflector aperture distribution.
Abstract: A design theory is presented for Cassegrain antennas employing dielectric-cone feeds. A modal approach is used to describe the aperture field over the subreflector, while a ray-optics method is employed to determine the sub-reflector profile and main-reflector aperture distribution. Experiments have been made with antennas designed for operation over bands centred near 11 and 18 GHz, and results are in generally good agreement with theory. These antennas are shown to have high efficiency, good main-beam symmetry and low mutual coupling.
10 citations
Patent•
03 Apr 1973
TL;DR: In this article, a cylindrical reflector with a plurality of feed elements located near the focal axis of the reflector is described. And each of the feed elements illuminates the reflectors with a wave energy pattern, causing a planar beam to be radiated in a direction unique to that element.
Abstract: Disclosed are antenna systems for simultaneously radiating a plurality of planar beams into a region of space. One such system includes a cylindrical reflector with a plurality of feed elements located near the focal axis of the reflector. Each of the feed elements illuminates the reflector with a wave energy pattern, causing a planar beam to be radiated in a direction which is unique to that element.
9 citations
TL;DR: The design method of and experimental results obtained from a new multiple-beam antenna for domestic communication satellites, fabricated and evaluated in the 50-GHz frequency band are described.
Abstract: This communication describes the design method of and experimental results obtained from a new multiple-beam antenna for domestic communication satellites. A seven-beam model antenna 1.98 m in diameter has been fabricated and evaluated in the 50-GHz frequency band, and the measurement data are reported here.
8 citations
Patent•
16 Apr 1973
TL;DR: A feed horn for a parabolic reflector includes a feed waveguide capable of supporting a first electromagnetic mode and a cylindrical member surrounding an open-ended radiating portion of said feed guide and located about said open end at a distance to cause a second mode to be supported.
Abstract: A feed horn for a parabolic reflector includes a feed waveguide capable of supporting a first electromagnetic mode and a cylindrical member surrounding an open-ended radiating portion of said feed guide and located about said open end at a distance to cause a second mode to be supported. Said first and second modes as propagating combine to provide a radiation pattern for illuminating said reflector to provide a high performance antenna system.
8 citations
TL;DR: In this paper, a method of obtaining the phase taper across the aperture (and hence the near-field on-axis and backscatter gains versus range) given a knowledge of the far-field ON-axis gain versus frequency, and the amplitude of the illumination over the aperture is suggested.
Abstract: In the near field of the Arecibo spherical antenna radar system, i.e., at ranges less than about 260 km, the gain is a function of range and a knowledge of gain is necessary for deducing electron-density information from the power backscattered from the ionosphere. A method of obtaining the phase taper across the aperture (and hence the near-field on-axis and backscatter gains versus range), given a knowledge of the far-field on-axis gain versus frequency, and the amplitude of the illumination over the aperture is suggested. Our studies show that measurements of on-axis far-field gain over a bandwidth of \pm7 MHz are adequate to give an accurate indication of on-axis gain versus range in the near field, while a \pm15 MHz frequency spread is needed to give accurate information on the backscatter gain versus range. The near-field correction for the antenna has also been estimated from measurements made on a model of the new line feed. Confidence in the validity of this approach has been obtained by comparing the measured far-field on-axis gain versus frequency with that calculated using the data from the model feed.
Patent•
05 Jan 1973
TL;DR: A citizens band antenna has two or more units made up of horizontal, vertical, and twin duty elements supported by a mast and a boom, at the rear of which is a triangular reflector connected to the nearest array as mentioned in this paper.
Abstract: A citizens band antenna has two or more units made up of horizontal, vertical and twin duty elements supported by a mast and a boom, at the rear of which is a triangular reflector connected at the rear of the antenna to the nearest array.
TL;DR: In this paper, a modification to the halfplane diffraction coefficients is given for a plane wave incident on a curved screen, which is used to calculate the near field of a parabolic reflector under plane-wave illumination.
Abstract: A modification to the halfplane diffraction coefficients is given for a plane wave incident on a curved screen. The result is used to calculate the near field of a parabolic reflector under plane-wave illumination. Comparison with the physical-optics method shows excellent agreement.
TL;DR: In this paper, a simple mathematical model for the vector radiation field from offset-parabolic reflector antennas is presented, which allows the primary feed to be offset from the reflector geometric focus, thus allowing the study of multiple-beam antennas.
Abstract: The development of a simple mathematical model for the vector radiation fields from offset-parabolic-reflector antennas is outlined. The model permits the primary feed to be offset from the reflector geometric focus, and thus allows the study of multiple-beam antennas. Predicted results are shown and correlated with measurements made on a 30 GHz antenna system.
TL;DR: By structurally changing the rim of reflector antennas, reduction of radiation in the shadow region is achieved in this article, where an experimental approach is used based on the concepts of edge diffraction theory.
Abstract: By structurally changing the rim of reflector antennas, reduction of radiation is achieved in the shadow region. An experimental approach is used based on the concepts of edge diffraction theory.
22 Apr 1973
TL;DR: In this article, the double-spherical Cassegrain reflector was used for multibeam scanning and multiuser operation with high gain antennas, and the effects of illumination taper, aperture blocking, and phase errors were investigated.
Abstract: There is a need for high gain antennas that are capable of rapid scanning and multibeam operations. This paper presents a study of the double-spherical Cassegrain reflector to ascertain whether this antenna is practical for these purposes. Aperture blocking, spread of the field, and phase and amplitude distributions are examined using geometric optical techniques. Some radiation patterns are calculated to show the effects of illumination taper, aperture blocking, and phase errors.
01 Oct 1973
TL;DR: In this article, the superior off-axis crosspolarization performance of Cassegrain antennas compared with that of front-fed antennas is emphasised for conventional primary feeds, supported by theory and by measurements on both configurations.
Abstract: The superior off-axis crosspolarisation performance of Cassegrain antennas, compared with that of front-fed antennas, is emphasised for conventional primary feeds. This statement is supported by theory and by measurements on both configurations.
01 Oct 1973
TL;DR: The approximate log normal distribution of normalized power antenna patterns within the \pm1 rad near-in region is presented for several families of illumination functions as an aid to system designers concerned with interacting radar type systems.
Abstract: The approximate log normal distribution of normalized power antenna patterns within the \pm1 rad near-in region is presented for several families of illumination functions as an aid to system designers concerned with interacting radar type systems. The means agree well with experimental data on similar patterns, but the standard deviations are considerably greater. An empirical expression relating the first sidelobe level and antenna size to the 0.5 probability level has been extracted to aid system applications of the results. For 360\deg coverage, a synthetic pattern is presented which gives a distribution close to the measured data.
TL;DR: In this paper, a computer program is described for the calculation of the near-axis secondary-radiation pattern of a parabolic reflector for laterally or axially displaced feed, in particular a log-periodic dipole array.
Abstract: A computer program is described for the calculation of the near-axis secondary-radiation pattern of a parabolic reflector. The program has been devised for a laterally or axially displaced feed, in particular a log-periodic dipole array. The illumination-function data are input in the form of radiation-pattern co-ordinates of the feed aerial.
TL;DR: In this article, the design of a dual-reflector antenna that focuses an inclined incident plane wave to a point away from the axis of symmetry of the reflector is discussed.
Abstract: The design of a dual-reflector antenna that focuses an inclined incident plane wave to a point away from the axis of symmetry of the reflector is discussed A useful application of such a system would be as a multibeam antenna for use in communication via satellites Curves of path-length errors are presented for the feed positioned on the axis of symmetry, and the effects of refocusing are shown
01 Jan 1973
TL;DR: In this article, the electric field in the aperture of offset front-fed paraboloid antennas and open cassegrain antennas, excited by an elec'tric dipole or Huygens source in the focus, is compared with the fields of front-feed circularly symmetrical Paraboloid reflector antennas and classical casse grain antennas.
Abstract: The electric field in the aperture of offset front-fed paraboloid antennas and open cassegrain antennas, excited by an elec'tric dipole or Huygens source in the focus, is compared with the fields of front-fed circularly symmetrical paraboloid reflector antennas and classical cassegrain antennas. The aperture field forms the basis of expressions to calculate the polarization efficiency of all four types of antenna. Computed results are given, showing that offset antennas can compete with front-fed paraboloids if they are excited by an electric dipole; the classical cassegrain antenna, however, shows better results. If offset antennas are excited by a Huygens source, they are very unfavourable compared with the symmetrical antennas which show no cross-polarization. Mr. Dijk, Mr. Maanders and Mr. Thurlings are with Eindhoven University of Technology, Netherlands. Mr. Van Diepenbeek is with Max Planck-Institut fur Radioastronomie, Bonn, Germany.
TL;DR: A simple method for accurately predicting the tracking sensitivity of a Cassegrain antenna having four peripheral horns grouped around a central `communication´ feed is described.
Abstract: A simple method for accurately predicting the tracking sensitivity of a Cassegrain antenna having four peripheral horns grouped around a central `communication´ feed is described. The technique utilises an analysis based on circular symmetry, similar to that ordinarily used to predict the antenna communication performance.
01 Oct 1973
01 Oct 1973
01 Jun 1973
TL;DR: The analysis of the reflector antenna is a monograph which documents the recent advances in the theory of reflectors developed during the space program and particularly of the work at the Jet Propulsion Laboratory.
Abstract: The Analysis of the Reflector Antenna is a monograph which documents the recent advances in the theory of reflectors developed during the space program and particularly of the work at the Jet Propulsion Laboratory. It is written for the engineer who needs to understand the design and performance limitations of reflector antennas. While it is not a text book, it may also prove useful in engineering introduction courses on diffraction. The book is divided into three sections: 1) the mathematical theory of diffraction, 2) the definition and calculation of antenna parameters, and 3) the use of digital computers in the analysis and design of reflector antennas and feed systems.