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  • Other Sources  (350)
  • COMMUNICATIONS AND RADAR  (350)
  • 1990-1994  (350)
  • 1945-1949
  • 1990  (350)
  • 1
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    Research into command, control, and communications in space construction (1990)
    In:  CASI
    Details
    Publication Date: 2004-10-02
    Description: Coordinating and controlling large numbers of autonomous or semi-autonomous robot elements in a space construction activity will present problems that are very different from most command and control problems encountered in the space business. As part of our research into the feasibility of robot constructors in space, the CSC Operations Group is examining a variety of command, control, and communications (C3) issues. Two major questions being asked are: can we apply C3 techniques and technologies already developed for use in space; and are there suitable terrestrial solutions for extraterrestrial C3 problems? An overview of the control architectures, command strategies, and communications technologies that we are examining is provided and plans for simulations and demonstrations of our concepts are described.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Second Annual Symposium; p 248-254
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  • 2
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    Dutch X-band SLAR calibration (1990)
    In:  CASI
    Details
    Publication Date: 2005-08-04
    Description: In August 1989 the NASA/JPL airborne P/L/C-band DC-8 SAR participated in several remote sensing campaigns in Europe. Amongst other test sites, data were obtained of the Flevopolder test site in the Netherlands on August the 16th. The Dutch X-band SLAR was flown on the same date and imaged parts of the same area as the SAR. To calibrate the two imaging radars a set of 33 calibration devices was deployed. 16 trihedrals were used to calibrate a part of the SLAR data. This short paper outlines the X-band SLAR characteristics, the experimental set-up and the calibration method used to calibrate the SLAR data. Finally some preliminary results are given.
    Keywords: COMMUNICATIONS AND RADAR
    Type: JPL, Proceedings of the Second Airborne Synthetic Aperture Radar (AIRSAR) Workshop; p 14-20
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  • 3
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    Calibration experiments with DC-8 SAR data (1990)
    In:  CASI
    Details
    Publication Date: 2005-08-04
    Description: This paper is a summary of some research activities in calibrating DC-8 SAR data conducted in 1989/90 by the author and others. Firstly, by examining the process of 'symmetrization' in the production of DC-8 Stokes' matrix data, it is shown that an exact solution to the problem of calibrating this data exists, given certain assumptions. Secondly a new, more general, system model for radar polarimeters is proposed, together with a simple approach for verifying the model's validity. The importance of the orientation angle about the radar line of sight for some types of calibration devices is discussed and some results of an experiment to cross-calibrate the C-Band VV data from the DC-8 and DLR E-SAR sensors are presented.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Proceedings of the Second Airborne Synthetic Aperture Radar (AIRSAR) Workshop; p 1-7
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  • 4
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    The performance of trellis-coded MDPSK with multiple symbol detection (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The idea of using a multiple (more than two) symbol observation interval to improve error probability performance is applied to differential detection of trellis-coded multiple phase-shift keying (MPSK) over an additive white Gaussian noise (AWGN) channel. An equivalent Euclidean distance measure per trellis branch is determined for this detection scheme. This is used to define an augmented (larger multiplicity) trellis code whose distance measure is the conventional squared Euclidean distance typical of conventional trellis-coded modulation on the AWGN. Such an augmented multiple trellis code is a convenient mathematical tool for simplifying the analysis. Results are obtained by a combination of analysis (upper Chernoff bounds and asymptotic large-SNR approximations) and computer simulation. It is shown that only a slight increase (e.g., one symbol) in the length of the observation interval will provide a significant improvement in bit error probability performance.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Communications (ISSN 0090-6778); 38; 1391-140
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  • 5
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    The use of interleaving for reducing noisy reference loss in trellis-coded modulation systems (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The use of interleaving/deinterleaving in trellis-coded modulation systems to reduce the SNR loss due to imperfect carrier demodulation references is demonstrated. Both the discrete carrier (phase-locked loop) and the suppressed carrier (Costas loop) cases are considered, and the differences between the two are clearly demonstrated by numerical results. The special case of convolutional codes is also treated and illustrated with an example of practical interest.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Communications (ISSN 0090-6778); 38; 1190-119
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  • 6
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    Communication protocol standards for space data systems (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The main elements and requirements of advanced space data networks are identified. The communication protocol standards for use on space missions during the coming decades are described. In particular, the blending of high-performance space-unique data transmission techniques with off-the-shelf open systems interconnection (OSI) protocols is described.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE, Proceedings (ISSN 0018-9219); 78; 1295-130
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  • 7
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    Experimental study of the two-layer electromagnetically coupled rectangular patch antenna (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Experimental results on the characteristics of two-layer electromagnetically coupled rectangular patch antennas are presented. In addition to the relatively large bandwidth region that occurs when the separation between the two layers is less than 0.15 wavelength, a high-gain region is found when the separation exceeds 0.3 wavelength. The relative sizes of the parasitic and fed patches are found to have significant effects on the resonant input resistance and bandwidth.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Antennas and Propagation (ISSN 0018-926X); 38; 1298-130
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  • 8
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    Analysis of near-field Cassegrain reflector - Plane wave versus element-by-element approach (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: A near-field Cassegrain reflector (NFCR) is an effective way to magnify a small phased array into a much larger-aperture antenna for limited scan applications. Traditionally the pattern analysis of NFCR is based on a plane wave approach, which simplifies the computation tremendously, but fails to provide design information about the most critical component of the whole antenna system, the feed array. Currently available computers make it possible to calculate the pattern of an NFCR by a more exact element-by-element approach. Each element in the feed array is considered individually, and the diffraction pattern from the subreflector is calculated by the geometrical theory of diffraction (including uniform theories at the shadow boundaries). The field contributions from all elements are superimposed at the curved main reflector surface, and a physical-optics integration is performed to obtain the secondary pattern.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Antennas and Propagation (ISSN 0018-926X); 38; 1010-101
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  • 9
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    Wideband arrays with variable element sizes (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: A new planar array architecture based on adding half-sized elements in between the other elements in order to extend the frequency by one octave is proposed and validated. This wideband array with variable element sizes (WAVES) antenna is shown by calculations and by measurements using Archimedean spirals to be the elements necessary to maintain a simple clean mainbeam and principal plane sidelobes below about -10 dB over two octaves. In spite of using a test antenna with a simple parallel feed and no impedance matching or isolation, the agreement between predicted and measured results is good.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEE Proceedings, Part H - Microwaves, Antennas and Propagation (ISSN 0950-107X); 137; 4, Au
    Format: text
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  • 10
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    Stochastic estimation of tropospheric path delays in global positioning system geodetic measurements (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Water vapor radiometric and surface meteorological measurements taken during three GPS geodetic experiments are used to calculate process noise levels for random walk and first-order Gauss-Markov temporal models of tropospheric path delays. Entire wet and combined wet and dry zenith delays at each network site are estimated simultaneously with the geodetic parameters without prior calibration. The path delays and corresponding baseline estimates are compared to those obtained with calibrated data and stochastic residual delays. In this manner, the marginal utility of a priori tropospheric calibration is assessed given the ability to estimate the path delays directly using only the GPS data. Estimation of total zenith path delays with appropriate random walk or Gauss-Markov models yields baseline repeatabilities of a few parts in 100 million. Results suggest that GPS data alone have sufficient strength to resolve centimeter-level zenith path delay fluctuations over periods of a few minutes.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Bulletin Geodesique (ISSN 0007-4632); 64; 2, 19
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