Pointing Calibration of a High-resolution Millimeter-wave Antenna by Star Observations PDF Download
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Author: Melvin Burak
Publisher:
ISBN:
Category : Antennas (Electronics)
Languages : en
Pages : 76
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Book Description
An extensive pointing calibration program for the drive system and mount of the AFCRL 29-ft millimeter-wave antenna is described. The optical pointing accuracy was determined by measuring the positioning errors of the optical axis of the antenna. Since all sources of optical pointing errors produce equivalent RF errors, all RF errors except those produced by feed system and reflector asymmetry are determined. A brief description of the antenna together with the integrated IBM 1800 data aquisition and control system, tracking software, and an accurate time-synchronization method are presented. The star tracking program, which includes a method of star selection, precession correction, and refraction correction, is described. The analysis and derivation of the various pointing error parameters used to determine the best-fitting functions that characterize the positional errors are presented. Next, the star data are reduced by fitting the nightly error measurements to the best-fitting error function from which the values of the error parameters that take into account the servo, collimation, azimuth plane tilt, elevation axis skewness, and residual refraction are determined. Finally, the results of the star data analysis and statistical data are presented. The rms residual optical pointingg error, after pointin calibration, averaged about 3 percent of the antenna beamwidth, that is, 7.5 arc seconds in both azimuth and elevation. (Author).
Author: Melvin Burak
Publisher:
ISBN:
Category : Antennas (Electronics)
Languages : en
Pages : 76
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Book Description
An extensive pointing calibration program for the drive system and mount of the AFCRL 29-ft millimeter-wave antenna is described. The optical pointing accuracy was determined by measuring the positioning errors of the optical axis of the antenna. Since all sources of optical pointing errors produce equivalent RF errors, all RF errors except those produced by feed system and reflector asymmetry are determined. A brief description of the antenna together with the integrated IBM 1800 data aquisition and control system, tracking software, and an accurate time-synchronization method are presented. The star tracking program, which includes a method of star selection, precession correction, and refraction correction, is described. The analysis and derivation of the various pointing error parameters used to determine the best-fitting functions that characterize the positional errors are presented. Next, the star data are reduced by fitting the nightly error measurements to the best-fitting error function from which the values of the error parameters that take into account the servo, collimation, azimuth plane tilt, elevation axis skewness, and residual refraction are determined. Finally, the results of the star data analysis and statistical data are presented. The rms residual optical pointingg error, after pointin calibration, averaged about 3 percent of the antenna beamwidth, that is, 7.5 arc seconds in both azimuth and elevation. (Author).
Author: Michael J. Neary
Publisher:
ISBN:
Category : Antennas (Electronics)
Languages : en
Pages : 36
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Book Description
The AFCRL 29-ft millimeter wave antenna at the Prospect Hill Millimeter Wave Observatory, Waltham, Massachusetts, is used to make solar maps (spectroheliograms), at a wavelength of 8.6 mm, for solar forecasting purposes. The half-power beamwidth of the antenna, although only 4 min of arc, is not narrow enough to detect the smaller hot regions that can develop into active centers on the sun. To overcome this limitation, a data-reduction process that can effectively narrow the beamwidth of the antenna, so that finer details on the maps will be visible, is needed. A computer program that can effectively narrow the beamwidth of the scanning antenna system by restoring and enhancing the antenna output has been applied to the Prospect Hill maps. It is believed that the enhanced maps can be further improved if a quiet sun component, or mean map, is subtracted from daily maps before the restoration is attempted. This report describes the technique used on the Prospect Hill IBM 1800 computer system to center the mean and daily maps on a common heliographic reference to effect the subtraction. (Author).
Author:
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ISBN:
Category : Environmental geology
Languages : en
Pages : 304
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Author:
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ISBN:
Category : Aeronautics
Languages : en
Pages : 882
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Book Description
Lists citations with abstracts for aerospace related reports obtained from world wide sources and announces documents that have recently been entered into the NASA Scientific and Technical Information Database.
Author:
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ISBN:
Category : Aeronautics
Languages : en
Pages : 576
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Author: United States. Air Force. Office of Aerospace Research
Publisher:
ISBN:
Category : Aeronautics, Military
Languages : en
Pages : 800
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Author: Edward E. Altshuler
Publisher:
ISBN:
Category : Astronautics
Languages : en
Pages : 46
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Book Description
It is expected that with the exploration of outer space, a requirement for high data rate earth-to-space communication channels will arise. A program to investigate the feasibility of using the millimeter-wave region of the spectrum for this application is presented. The theory of atmospheric attenuation resulting from losses due to absorption, scattering and refraction processes is reviewed and used to estimate propagation losses produced by atmospheric gases, clouds and precipitation. Curves of total atmospheric attenuation and noise level as a function of meteorological parameters and antenna elevation angle are also presented. A series of experiments designed to obtain as much information as possible on the limitations imposed by the atmosphere on millimeter-wave propagation is considered. Although experiments using natural celestial bodies such as the sun, moon, planets and galaxies as radio sources are emphasized, those which would utilize aircraft, rockets and satellites are also mentioned. Finally, the characteristics of a recently installed precision 29-ft antenna designed to operate at 35 Gc (wavelength = 8.6 mm) with a traveling-wave maser as a preamplifier for the radiometer are outlined along with the specific experiments for which this antenna system will be used. (Author).
Author: United States. Air Force. Office of Aerospace Research
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ISBN:
Category : Aeronautics
Languages : en
Pages : 586
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Author: Air Force Cambridge Research Laboratories (U.S.)
Publisher:
ISBN:
Category : Aeronautics
Languages : en
Pages : 392
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Author:
Publisher:
ISBN:
Category : Science
Languages : en
Pages : 776
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