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An antenna apparatus and method for the interception of randomly polarized electromagnetic waves utilizing a dual polarized antenna which is excited through a cross-slot aperture using two well-isolated orthogonal feeds.
An antenna apparatus and method for the interception of randomly polarized electromagnetic waves utilizing a dual polarized antenna which is excited through a cross-slot aperture using two well-isolated orthogonal feeds.
Being developed in a partnership between NASA and the Indian Space Research Organisation (ISRO), the NASA-ISRO Synthetic Aperture Radar (NISAR) satellite is planned to launch in late 2020. NISAR will measure many aspects of how Earth is changing with unprecedented accuracy on a global scale from a Low Earth Orbit (LEO) platform. With a 12-meter deployable mesh reflector, NISAR will feature one of the largest deployable mesh reflectors ever launched for a scientific mission. Two large planar phased arrays will feed the reflector, one that will operate at L-Band and be developed by the Jet Propulsion Laboratory (JPL), and an S-band array that will be developed at the ISRO Space Application Centre (SAC). This paper describes the preliminary design of the L-Band feed array.
Being developed in partnership between NASA and the Indian Space Research Organisation (ISRO), the NASA-ISRO Synthetic Aperture Radar (NISAR) satellite is planned to launch in late 2020. NISAR will measure many aspects of how Earth is changing with unprecedented accuracy on a global scale from a Low Earth Orbit (LEO) platform. With a 12m deployable mesh reflector, NISAR will feature one of the largest deployable mesh reflector ever launched for a scientific mission. Two large planar phased arrays will feed the reflector, one that will operate at L-Band and be developed by the Jet Propulsion Laboratory (JPL), and an S-band array that will be developed at the ISRO Space Application Centre (SAC). This paper describes the preliminary design of the L-Band feed array.
NISAR (NASA ISRO SAR, National Aeronautics and Space Administration, Indian Space Research Organization, Synthetic Aperture Radar) is an Earth science project currently in its final development phases at NASA Jet Propulsion Laboratory (JPL) and at ISRO. Due for launch in 2023 it will assess how our planet changes over time by measuring differences in the Earth’s solid surface due to factors like climate change, movement and melting of glaciers, earthquakes, land-slides, deforestation, agriculture and others. The enabling instrument for this mission is a dual band radar (L-Band and S-Band) that feeds a 12m deployable mesh reflector. Given the extreme accuracy needed to perform these measurements from Low Earth Orbit (LEO) some of the most stringent requirements were pushed onto the antenna subsystem to control phase and gain stability over time. In this paper we describe how environmental requirements affected the antenna design and what techniques were used to meet these requirements.
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System incorporating two or more radial feed assemblies tracks and communicates with multiple moving transmitters, receivers, or transponders. System utilizes a fixed parabolic reflector or other beam-forming device such as a lens or spherical reflector.
System has high radiation efficiency and minimal interaction between elements when inserted between a multimode, multifrequency transponder and a parabolic reflector in an airborne communications system.
System is polarization tracker and comprises variable polarizer, polarization control, and receiver servo loop. System simultaneously receives desired signal and undesired signal which are approximately orthogonal. They can be either paired as left and right circular polarizations or as cross-linear polarizations.
An account is given of the upgrading of a 12-ft-diameter single-channel monopulse tracking system, which had been relegated to slaved backup status at NASA Edwards, to support research flights for Ames Dryden Research Center and for tracking orbital passes of the Space Shuttle and Shuttle landings both at Edwards and at White Sands. The improved system is now a stand-alone telemetry tracking system. A new conical scanning feed (known as Radscan) replaces the single channel monopulse feed in the upgraded system. Where previously the system would not autotrack at elevation angles below 5 degrees, it now automatically acquires the Space Shuttle when it appears on the horizon and autotracks from approximately 2 degrees in elevation to touchdown, and does so virtually unattended.
Antenna systems and particularly compact and simple antenna feeds which can transmit and receive simultaneously in at least three frequency bands, each with high efficiency and polarization diversity are described. The feed system is applicable for frequency bands having nominal frequency bands with the ratio 1:4:6. By way of example, satellite communications telemetry bands operate in frequency bands 0.8 - 1.0 GHz, 3.7 - 4.2 GHz and 5.9 - 6.4 GHz. In addition, the antenna system of the invention has monopulse capability for reception with circular or diverse polarization at frequency band 1.
Antenna feed horn is combination of corrugated, round, and tapered waveguide configurations that are dimensioned to excite He sub 11 and He sub 12 modes to illuminate reflector antenna more uniformly than antenna horns excited only in He sub 11 mode. Horn is adaptable to both symmetrical and asymmetrical Cassagrainian antennas.
Multislot feed corrects phase errors in reflecting antennas. Variables are reduced by considering symmetry and corrective effect of each phase mode. Overall computation concerning calculation of correct phase angles while optimizing main beam efficiency is simplified by analysis used parabolic torus reflector aboard Space Shuttle.
The results are presented of a trade study designed to identify a synchronous satellite antenna system suitable for receiving and transmitting data from lower orbiting satellites at both S- and K sub u-bands simultaneously as part of the Tracking and Data Relay Satellite System. All related problems associated with maintaining a data link between two satellites with a K sub u-band half-power beamwidth of 0.4 db are considered including data link maintenance techniques, beam pointing accuracies, gimbal and servo errors, solar heating, angle tracking schemes, acquisition problems and aids, tracking accuracies versus SNR, antenna feed designs, equipment designs, weight and power budgets, and detailed candidate antenna system designs.
A simple practical method for designing antenna-feed attitude control systems for large deployable spaceborne antenna systems with long flexible booms is proposed. The basic idea is to mechanically decouple the antenna-feed from the boom so that the feed-attitude control system can be designed without taking the boom dynamics into consideration, thus avoiding a complex control problem involving an infinite-dimensional distributed parameter system. The validity of the proposed method is substantiated by analytical and numerical studies using a mathematical model for the flexible boom which could undergo both bending and torsional vibrations. This approach leads to simple antenna-feed attitude control systems which are amenable to physical implementation.