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Two omni-directional and circularly polarized low gain antennas (the crossed drooping dipole and the TM(sub 21) mode circular patch antenna)are developed for direct broadcast satellite radio (DBSR) outdoor mobile terminal applications.
Ground antennas are the major visible components of NASA's Deep Space Network (DSN). The role, key characteristics, and performance of these antennas in deep space telecommunications are described.
The IN-STEP Inflatable Antenna Experiment was intended to demonstrate high payoff technology for large, inflatable space antenna structures, in a realistic operational environment.
Here, this paper presents a dedicated study of plasma-antenna (PA) coupling with the Alfvén Eigenmode Active Diagnostic (AEAD) in JET. Stable AEs and their resonant frequencies f, damping rates γ < 0, and toroidal mode numbers n are measured for various PA separations and limiter versus X-point magnetic configurations. Two stable AEs are observed to be resonantly excited at distinct low and high frequencies in limiter plasmas. The values of f and n do not vary with PA separation. However, |γ| increases with PA separation for the low-f, but not high-f, mode, yet this may be due to slightly different edge conditions. The high-f AE is detected throughout the transition from limiter to X-point configuration, though its damping rate increases; the low-f mode, on the other hand, becomes unidentifiable. The linear, resistive MHD code CASTOR is used to simulate the frequency scan of an AEAD-like external antenna. For the limiter pulses, the high-f mode is determined to be an n = 0 GAE, while the low-f mode is likely an n = 2 TAE. During the transition from limiter to X-point configuration, CASTOR indicates that n = 1 and 2 EAEs are excited in the edge gap. These results extend previous experimental studies in JET and Alcator C-Mod; validate the computational work performed by Dvornova et al; and provide guidance for the optimization of PA coupling in upcoming JET energetic particle experiments, for which the AEAD will aim to identify the contribution of alpha particles to AE drive during the DT campaign.
The Photosynthetic Antenna Research Center (PARC) was funded for five years (2009-2014) with the initial group of Energy Frontier Research Centers (EFRCs) by the U.S. Department of Energy. The PARC grant was then renewed for four more years (2014-2018). PARC was focused on basic scientific research aimed at elucidating the fundamental principles that underlie light harvesting and energy funneling in natural photosynthetic antennas and translating those principles into construction of biohybrid and bioinspired architectures to form the basis for next-generation systems for solar-energy conversion. PARC carried out high quality fundamental science on the path towards ambitious, visionary goals. The resources, infrastructure, and melding of scientific subdisciplines, techniques, and experiences made possible in PARC resulted in high risk but high reward and high impact research, enabling conceptual breakthroughs in light harvesting. PARC’s broad global vision was addressed through specific research and educational activities, and the legacy of intellectual and technical capacity that it built.
A simple beamshaping modification for Cassegrainian systems is described. A qualitative analysis is used to describe this device as well as to explain the poor performance observed with an unmodified Cassegrainian system. Experimental data are presented on both the modified and unmodified systems. The modification reduces spillover by a factor of 2 to a value of only 1. 3%. Simultaneously, the aperture efficiency is increased from 50% for the unmodified system to 60% for the modified system. Field measurements on an 85- ft modified Cassegrainian system are described which experimentally verify the applicability of the modified subreflector to low-noise antenna design. The measured zenith antenna temperature for this system is 9. 5° K; measured aperture efficiency is 50%.
Antenna impedance behavior in plasma, related to radio astronomy, emphasizing electrically small antennas used in space vehicles
Antenna impedance behavior in plasma related to radio astronomy, emphasizing electrically small antennas used in space vehicles
Antenna systems for deep space communication emphasizing ground station, balancing of ground antenna aperture with spacecraft performance, arrays, etc
Two degree of freedom spacecraft antenna pointing system evaluation based on geometry, attitude drift errors, and sensor error signal methods of correcting antenna position for attitude drift
Combination resonant V-antenna and traveling-wave dipole antenna
Radiation patterns and gains measured for short backfire antenna as function of antenna dimensions
Optimum antenna weight distribution curves for six techniques to erect large aperture antennas
Large antenna radiation from radio astronomy Explorer satellite determined on basis of antenna current distribution
NASA STADAN and Apollo network antenna systems, analyzing tracking antenna systems, command systems and operational problems
Gemini spacecraft antennas performance during reentry into ionized medium, discussing electron concentration profiles, nonearth atmosphere extrapolation and antenna breakdown effect
This publication is a compilation of the unclassified papers presented at the NASA Conference on Large Space Antenna Systems Technology, which was held at the Langley Research Center, Hampton, Virginia, November 30 - December 3, 1982. The conference, which was sponsored jointly by the NASA Office of Aeronautics and Space Technology (OAST) and the NASA Langley Research Center, was organized into five sessions: Systems, Structures Technology, Control Technology, electromagnetics, and Space Flight Test and Evaluation. All speakers and topics were selected by the session cochairmen and included representation from industry, universities, and government. The program was organized to provide a comprehensive review of space missions requiring large antenna systems and of the status of key technologies required to enable these missions.
Simple models for the patterns as well as their cumulative gain probability and probability density functions of the Deep Space Network antennas are developed. These are needed for the study and evaluation of interference from unwanted sources such as the emerging terrestrial system, High Density Fixed Service, with the Ka-band receiving antenna systems in Goldstone Station of the Deep Space Network.