17,831 research outputs found
ATS-6 engineering performance report. Volume 5: Propagation experiments
Propagation experiments at 1550 MHz to 1650 MHz are reviewed, including the Integrated L-Band Experiments system and results, and the Mobile L-Band Terminals for Satellite Communication system. Experiments at 4 GHz to 6 GHz are reported, including the Radio Frequency Interferometer Measurements system and results, and Earth station antenna evaluations. Experiments above 10 GHz are discussed, including Comsat and ATS-6 millimeter wave propagation/experiments, and communication ATS-6 version at 20 and 30 GHz
Twenty and thirty GHz millimeter wave experiments with the ATS-6 satellite
The ATS-6 millimeter wave experiment, provided the first direct measurements of 20 and 30 GHz earth-space links from an orbiting satellite. Studies at eleven locations in the continental United States were directed at an evaluation of rain attenuation effects, scintillations, depolarization, site diversity, coherence bandwidth, and analog and digital communications techniques. In addition to direct measurements on the 20 and 30 GHz links, methods of attenuation prediction with radars, rain gages, and radiometers were developed and compared with the directly measured attenuation. Initial data results of the ATS-6 millimeter wave experiment from the major participating organizations are presented
A compendium of millimeter wave propagation studies performed by NASA
Key millimeter wave propagation experiments and analytical results were summarized. The experiments were performed with the Ats-5, Ats-6 and Comstar satellites, radars, radiometers and rain gage networks. Analytic models were developed for extrapolation of experimental results to frequencies, locations, and communications systems
Spectral characteristics of earth-space paths at 2 and 30 FHz
Spectral characteristics of 2 and 30 GHz signals received from the Applications Technology Satellite-6 (ATS-6) are analyzed in detail at elevation angles ranging from 0 deg to 44 deg. The spectra of the received signals are characterized by slopes and break frequencies. Statistics of these parameters are presented as probability density functions. Dependence of the spectral characteristics on elevation angle is investigated. The 2 and 30 GHz spectral shapes are contrasted through the use of scatter diagrams. The results are compared with those predicted from turbulence theory. The average spectral slopes are in close agreement with theory, although the departure from the average value at any given elevation angle is quite large
Astrometry and geodesy with radio interferometry: experiments, models, results
Summarizes current status of radio interferometry at radio frequencies
between Earth-based receivers, for astrometric and geodetic applications.
Emphasizes theoretical models of VLBI observables that are required to extract
results at the present accuracy levels of 1 cm and 1 nanoradian. Highlights the
achievements of VLBI during the past two decades in reference frames, Earth
orientation, atmospheric effects on microwave propagation, and relativity.Comment: 83 pages, 19 Postscript figures. To be published in Rev. Mod. Phys.,
Vol. 70, Oct. 199
Concepts for 18/30 GHz satellite communication system, volume 1A: Appendix
The following are appended: (1) Propagation phenomena and attenuation models; (2) Models and measurements of rainfall patterns in the U.S.; (3) Millimeter wave propagation experiments; (4) Comparison of the theory and Millimeter wave propagation experiments; (4) Comparison of theory and experiment; (5) A practical rain attenuation model for CONUS; (6) Space diversity; (7) Values of attenuation for selected U.S. cities; and (8) Additional considerations
ETS-5, ETS-6, and COMETS projects in Japan
Three satellite communication projects now in progress in Japan are described. The first is a project to establish a telecommunication network for tele-education, TV conference, and tele-medicine in the Asia-Pacific region by using the Japan's Engineering Test Satellite-5 (ETS-5). The second is a project of the ETS-6 satellite, to be launched in 1993, for inter-satellite communication, mobile and fixed communication, and millimeter wave personal communication experiments. The third is a project of the Communications and Broadcasting Engineering Test Satellite (COMETS), to be launched in 1997, for advanced mobile satellite communication, inter-satellite link, and advanced broadcasting experiments at higher frequencies
Twenty and thirty GHz millimeter wave experiments with the ATS-6 satellite
Studies at 11 locations in the continental United States were directed at an evaluation of rain attenuation effects, scintillations, depolarization, site diversity, coherence bandwidth, and analog and digital communications techniques using the Applications Technology Satellite-6(ATS-6). In addition to direct measurements on the 20- and 30-GHz links, methods of attenuation prediction with radars, rain gages, and radiometers were developed and compared with the directly measured attenuation. Initial data results of the ATS-6 millimeter wave experiment were presented. The first section describes the experiment objectives, flight hardware, and modes of operation. The remaining six sections present papers prepared by the major participating organizations in the experiment. The papers present a comprehensive summary of the significant results of the initial 11 months of ATS-6 experiment measurements and related radiometric, radar, and radio-meteorology studies
Radio observations of active galactic nuclei with mm-VLBI
Over the past few decades, our knowledge of jets produced by active galactic
nuclei (AGN) has greatly progressed thanks to the development of
very-long-baseline interferometry (VLBI). Nevertheless, the crucial mechanisms
involved in the formation of the plasma flow, as well as those driving its
exceptional radiative output up to TeV energies, remain to be clarified. Most
likely, these physical processes take place at short separations from the
supermassive black hole, on scales which are inaccessible to VLBI observations
at centimeter wavelengths. Due to their high synchrotron opacity, the dense and
highly magnetized regions in the vicinity of the central engine can only be
penetrated when observing at shorter wavelengths, in the millimeter and
sub-millimeter regimes. While this was recognized already in the early days of
VLBI, it was not until the very recent years that sensitive VLBI imaging at
high frequencies has become possible. Ongoing technical development and wide
band observing now provide adequate imaging fidelity to carry out more detailed
analyses.
In this article we overview some open questions concerning the physics of AGN
jets, and we discuss the impact of mm-VLBI studies. Among the rich set of
results produced so far in this frequency regime, we particularly focus on
studies performed at 43 GHz (7 mm) and at 86 GHz (3 mm). Some of the first
findings at 230 GHz (1 mm) obtained with the Event Horizon Telescope are also
presented.Comment: Published in The Astronomy & Astrophysics Review. Open access:
https://link.springer.com/article/10.1007/s00159-017-0105-
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