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  • 1
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    Scan performance of dual offset reflector antennas for satellite communications (1981)
    American Geophysical Union
    Details
    Publication Date: 1981-11-01
    Print ISSN: 0048-6604
    Electronic ISSN: 1944-799X
    Topics: Geosciences , Physics
    Published by American Geophysical Union
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    PAPER CURRENT
  • 2
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    Low-loss off-axis feeds for symmetric dual-reflector antennas (1986)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Circularly symmetric, dual reflector, high gain antenna systems often require feeds placed off the system's axis because of the need for multiple feeds to use the reflector antenna. Also, the constraint requiring the hyperboloid or shaped subreflector to remain circularly symmetric is sometimes added. In a Cassegrainian system, the subreflector and feed may be rotated off axis around the paraboloid focus and retain main reflector focusing. However, substantial spillover results in considerable noise with a high gain/low noise temperature system. In a shaped system, the tilt of the shaped subreflector and feed together results in substantial defocusing as well as spillover noise. If the subreflector is tilted approximately one-half the angle of the feed tilt in either the Cassegrainian or the dual shaped reflector antenna, it is found that spillover and noise are substantially reduced with tolerable defocusing. An extensive numerical analysis of these effects was conducted to determine the characteristics of a planned 70-meter, dual shaped reflector versus Cassegrainian antenna and to gain some understanding of the cause of the observed effects.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommunications and Data Acquisition Report; p 35-59
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Dual-shaped offset reflector antenna designs from solutions of the geometrical optics first-order partial differential equations (1990)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: In obtaining solutions to the first-order nonlinear partial differential equations (PDEs) for synthesizing offset dual-shaped reflectors, it is found that previously observed computational problems can be avoided if the integration of the PDEs is started from an inner projected perimeter and integrated outward rather than starting from an outer projected perimeter and integrating inward. This procedure, however, introduces a new parameter, the main reflector inner perimeter radius p(o), when given a subreflector inner angle 0(o). Furthermore, a desired outer projected perimeter (e.g., a circle) is no longer guaranteed. Stability of the integration is maintained if some of the initial parameters are determined first from an approximate solution to the PDEs. A one-, two-, or three-parameter optimization algorithm can then be used to obtain a best set of parameters yielding a close fit to the desired projected outer rim. Good low cross-polarization mapping functions are also obtained. These methods are illustrated by synthesis of a high-gain offset-shaped Cassegrainian antenna and a low-noise offset-shaped Gregorian antenna.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommunications and Data Acquisition Report; p 69-80
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    Recent advances in electromagnetic synthesis and analysis of dual-shaped reflector antennas (1982)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: Dual-shaped reflectors have been used for many years. Thus, these reflectors have been used as high gain antennas on Voyagers 1 and 2. The objectives of the geometrical optics (GO) dual shaped synthesis are considered. Concerning the synthesis of dual shaped reflectors, it has been shown for circular symmetric reflectors that an exact GO solution can be found to the problem of transforming, by two reflections, any feed pattern into any aperture distribution. This problem involves solving two simultaneous nonlinear ordinary differential equations. The same approach for offset geometry leads to two simultaneous nonlinear partial differential equations. It is shown that these equations could also be integrated numerically, except that in general these equations are not total and therefore, in general, they do not have a 'smooth' solution. It is further shown that the offset partial differentials often very nearly form a total differential in many cases of practical importance.
    Keywords: COMMUNICATIONS AND RADAR
    Format: text
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    NASA TECHNICAL REPORTS
  • 5
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    Design of a Correcting Plate for Compensating the Main Reflector Distortions of a Dual Shaped System (1993)
    In:  Other Sources
    Details
    Publication Date: 2018-06-08
    Description: We present a method of synthesizing a correcting.
    Keywords: Optics
    Format: text
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    NASA TECHNICAL REPORTS
  • 6
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    Design considerations for the beamwaveguide retrofit of a ground antenna station (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A primary requirement of the NASA Deep Space Network (DSN) is to provide for optimal reception of very low signal levels. This requirement necessitates optimizing the antenna gain to the total system operating noise level quotient. Low overall system noise levels of 16 to 20 K are achieved by using cryogenically cooled preamplifiers closely coupled with an appropriately balanced antenna gain/spillover design. Additionally, high-power transmitters (up to 400 kW CW) are required for spacecraft emergency command and planetary radar experiments. The frequency bands allocated for deep space telemetry are narrow bands near 2.1 and 2.3 GHz (Ka-band), 7.1 and 8.4 GHz (X-band), and 32 and 34.5 GHz (Ka-band). In addition, planned operations for the Search for Extraterrestrial Intelligence (SETI) program require continuous low-noise receive coverage over the 1 to 10 GHz band. To summarize, DSN antennas must operate efficiently with low receive noise and high-power uplink over the 1 to 35 GHz band.
    Keywords: COMMUNICATIONS AND RADAR
    Type: AD-P005411 , Illinois Univ., Proceedings of the Antenna Applications Symposium held in Urbana, Illinois on 17-19 September 1986, Volume 2; p 387-410
    Format: text
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    NASA TECHNICAL REPORTS
  • 7
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    Design considerations for the beam-waveguide retrofit of a ground antenna station (1986)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Retrofitting an antenna that was originally designed without a beam waveguide introduces special difficulties because it is desirable to minimize alteration of the original mechanical truss work and to image the actual feed without distortion at the focal point of the dual-shaped reflector. To obtain an acceptable image, certain Geometrical Optics (GO) design criteria are followed as closely as possible. The problems associated with applying these design criteria to a 34-meter dual-shaped DSN (Deep Space Network) antenna are discussed. The use of various diffraction analysis techniques in the design process is also discussed. GTD and FFT algorithms are particularly necessary at the higher frequencies, while Physical Optics and Spherical Wave Expansions proved necessary at the lower frequencies.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommunications and Data Acquisition Report; p 10-23
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 8
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    Interpolation Methods for GTD Analysis of Shaped Reflectors (1985)
    In:  CASI
    Details
    Publication Date: 2014-09-18
    Description: The finding of smooth analytic representations for antenna reflector surfaces which are prescribed only by discretized data obtained by various synthesis methods is examined. Frequently the data are distributed in a nonuniform grid and contain noise. The smoothness required is to C sub 1 for physical optics diffraction analysis and to C sub 2 for geometrical theory of diffraction (GTD) analysis. The GTD analysis approach requires a surface description which returns data very rapidly. Two methods of interpolation, the global and the local methods, are discussed. They each have advantages and disadvantages; characteristics are discussed and examples are presented.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommun. and Data Acquisition Rept.; p 62-67
    Format: text
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    NASA TECHNICAL REPORTS
  • 9
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    Synthesis of offset dual shaped subreflector antennas for control of Cassegrain aperture distributions (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The method presented for antenna upgrading involves a redesign of only the subreflector portion of a Cassegrain antenna or the introduction of a subreflector feed system for a paraboloid. A pair of offset subreflectors are synthesized which will produce a controllable high gain amplitude distribution in the aperture of the large paraboloid. The synthesis method is based on the approximate formulation for an offset dual shaped high gain antenna first presented by Galindo-Israel and Mittra (1977). It is pointed out that in their approximate formulation, the geometrical optics energy was scattered from a subreflector and then from a second large reflector, which reflected a uniform phase distribution. In the offset dual shaped subreflector (DSS) antenna proposed here, the second reflection is from a smaller (sub) reflector, and it scatters a spherical wave that feeds a hyperboloid or feeds a large paraboloid directly. The DSS synthesis is tested on the 210-ft-diameter Cassegrain antenna at Goldstone, California.
    Keywords: SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING
    Type: IEEE Transactions on Antennas and Propagation (ISSN 0018-926X); AP-32; 86-92
    Format: text
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    NASA TECHNICAL REPORTS
  • 10
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    Shaped reflector antenna analysis using the Jacobi-Bessel series (1980)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: A vector radiation integral is derived for an offset shaped reflector illuminated by an arbitrarily located and oriented source. A procedure for expressing the integral in terms of a series of the Fourier transforms of an effective aperture distribution is discussed. The Jacobi-Bessel series is used to evaluate the Fourier transforms. Numerical results are presented for different reflector configurations and source locations.
    Keywords: SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING
    Type: IEEE Transactions on Antennas and Propagation; AP-28; July 198
    Format: text
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