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At least 415 records · Page 23

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NASA NTRS1978

Deployable antenna demonstration study

A demonstration system and shuttle flight program was defined to demonstrate packaging, transportation, erection, and structural integrity of a large deployable antenna concept. An analysis of deployable antenna requirements indicates that (1) erectable structures are clearly applicable to very high precision (above 50 GHz) antennas (10 to 30 m); (2) deployable structures are light weight, applicable to moderate precision (below 14 GHz) large antennas (up to 300 m); and (3) both deployable and erectable apply to small and large antenna platforms with common utilities.

Thompson, W.↗

NASA NTRS1978

A review of the state of the art in large spaceborne antenna technology

Three classes of antennas (reflectors, lenses, and arrays) are studied with a view toward their use as extremely large space antennas. RF performance characteristics, weight, manufacturing complexity, and cost are discussed for each class. Examples of antennas of each class which were built or analyzed are described to give an appreciation of current and expected industry capability. Multibeam antennas are discussed. General guidelines are given for use of the appropriate class of antenna to meet certain performance requirements, and recommendations are made for future study. The reflector emerges as the optimum choice for most very large aperture applications, though the lens and array appear ideally suited for use as feeds for multibeam near-field Cassegrain or Gregorian designs.

Smith, C. A.↗

NASA NTRS1978

Antenna evaluation study for the shuttle multispectral radar, phase 3

The principal objectives of Phase III were: (1) to continue simulations of the effects of excitation errors in the performance of a planar array antenna, (2) to apply this model specifically, to the SIR-A antenna, (3) to support measurements of the SIR-A antenna at JPL by quick-turnaround analyses of the SIR-A antenna under a variety of conditions encountered at the JPL West Mesa Antenna Range, and (4) to document fully all software developed for NASA Johnson Space Center (JSC) during Phases I, II, and III.

Coffey, E. L., III↗

NASA NTRS1978

Antenna development for the Space Shuttle Orbiter vehicle

A number of difficulties have to be overcome in connection with the design and the mounting of the antennas of the Space Shuttle Orbiter. These difficulties, in combination with a service life goal of 100,000 h, made it necessary to develop antennas with special design features. The particular problems associated with developing antennas for the Shuttle Orbiter are discussed. It is pointed out that this vehicle must function as both a spacecraft and as an aircraft. This feature imposes some rather severe design constraints on the Shuttle antennas. The various structural, operational, and environmental design requirements are considered and design techniques which are used to meet these requirements are examined. A description is presented of the methods employed for testing the various antennas, both with and without the thermal protection system.

Cubley, H. D.↗

NASA NTRS1979

Surface accuracy measurement system deployable reflector antennas

Conceptual optical sensor configurations for measuring the surface deformations of large, deployable space antennas are described. These antennas include precision deployable reflectors up to 30 meters diameter and 1000 GHz frequency and mesh deployable reflectors up to 100 meters diameter and 30 GHz frequency. For each representative antenna configuration, the surface deformation sensor provides continuous, real-time measurements at a sufficient number of sample points to be compatible with active surface control. Moreover, the sensor system does not interfere with the mechanical or microwave characteristics of either the antenna surface or the feed. For the applications considered, the sensor system consists of a central receiver ring containing six to ten long focal length, angle measuring instruments, each viewing a dedicated set of bright point targets at the antenna. The targets, either light emitting diodes or illuminated retroreflectors, are modulated to eliminate errors from spurious backgrounds. Very preliminary performance estimates indicate that the sensor system, using commerical grade components, can produce a 20th to a 30th wavelength accuracy (3 sigma).

Neiswander, R. S.↗

NASA NTRS1979

Voyager high gain antenna calibration and pointing

A mathematical description of the data reduction technique used in analyzing Voyager calibration data is presented. To achieve the required telecommunication link performance, highly accurate pointing of the Voyager high gain antenna boresight relative to earth is necessary. To provide the optimum pointing, in-flight calibrations of the high gain antenna pointing mechanism are regularly made, and the design of the calibration and the antenna error models is delineated. It is shown that due to the use of wide angle sun sensors for celestial attitude control, the Voyager antenna error model differs from those of previous missions. Results of the in-flight calibrations and their implementation in improving the antenna pointing are also presented.

Jahanshahi, M. H.↗

NASA NTRS1979

On attaining lower sidelobes and new antenna envelopes for better orbit spectrum utilization in satellite broadcasting

The concept of using beam-shaping techniques to reduce sidelobe levels at the expense of efficiency is introduced and analyzed with respect to the potential for improving orbit-spectrum utilization. Emphasis is placed on a simple method: improving the antenna patterns used in satellite systems, for both the satellite antennas and the ground station antennas. Only broadcasting applications are considered. The discussion includes how the antenna envelope can be improved, how this improvement can be interpreted in terms of orbit spectrum utilization efficiency, and whether this improved envelope is actually realizable and feasible. It is noted that the magnitude of the improvement with a better spacecraft antenna increases rapidly as the coverage area decreases.

Janky, J. M.↗

NASA NTRS1979

Antenna of the space radiotelescope KRT-3

The questions of antenna design with a diameter of 3 m for space radio-interferometry are examined. The basic characteristics of the antenna are determined, on the basis of which a model of the antenna of a space radiotelescope of 3.1 m KRT-3 is developed and prepared. The technological peculiarities of the antenna preparation are examined. The results of measurement of the reflecting surfaces of the telescope are cited, which point to the fact that the antenna may operate to wave lengths in the order of 2 mm.

Kostenko, V. I.↗

NASA NTRS1980

A parametric analysis of performance characteristics of satellite-borne multiple-beam antennas

An analytical and empirical model is presented for parametric study of multiple beam antenna frequency reuse capacity and interbeam isolation. Two types of reflector antennas, the axisymmetric parabolic and the offset-parabolic reflectors, are utilized to demonstrate the model. The parameters of the model are introduced and their limitations are discussed in the context of parabolic reflector antennas. The model, however, is not restricted to analysis of reflector antenna performance. Results of the analyses are covered in two tables. The model parameters, objectives, and descriptions are given, multiple-beam antenna frequency reuse capacity and interbeam isolation analysis of the two types of reflectors are discussed as well as future developments of the program model.

Salmasi, A. B.↗

NASA NTRS1979

UHF coplanar-slot antenna for aircraft-to-satellite data communications

The initiative for starting the Aircraft-to-Satellite Data Relay (ASDAR) Program came from a recognition that much of the world's weather originates in the data sparse area of the tropics which are primarily ocean. The ASDAR system consists of (1) a data acquisition and control unit to acquire, store and format these data; (2) a clock to time the data sampling and transmission periods; and (3) a transmitter and low-profile upper hemisphere coverage antenna to relay the formatted data via satellite to the National Weather Service ground stations, as shown schematically. The low-profile antenna is a conformal antenna based on the coplanar-slot approach. The antenna is circular polarized and has an on-axis gain of nearly 2.5 dB and a HPBW greater than 90 deg. The discussion covers antenna design, radiation characteristics, flight testing, and system performance.

Myhre, R. W.↗

NASA NTRS1980

The Seasat scanning multichannel microwave radiometer /SMMR/: Antenna pattern corrections - Development and implementation

The antenna temperatures measured by the Seasat scanning multichannel microwave radiometer (SMMR) differ from the true brightness temperatures of the observed scene due to antenna pattern effects, principally from antenna sidelobe contributions and cross-polarization coupling. To provide accurate brightness temperatures convenient for geophysical parameter retrievals the antenna temperatures are processed through a series of stages, collectively known as the antenna pattern correction (APC) algorithm. A description of the development and implementation of the APC algorithm is given, along with an error analysis of the resulting brightness temperatures.

Njoku, E. G.↗

NASA NTRS1980

Ku-band multiple beam antenna

The frequency reuse capability is demonstrated for a Ku-band multiple beam antenna which provides contiguous low sidelobe spot beams for point-to-point communications between any two points within the continental United States (CONUS), or regional coverage beams for direct broadcast systems. A spot beam antenna in the 14/21 GHz band which provides contiguous overlapping beams covering CONUS and two discrete beams covering Hawaii and Alaska were designed, developed, and tested. Two reflector antennas are required for providing contiguous coverage of CONUS. Each is comprised of one offset parabolic reflector, one flat polarization diplexer, and two separate planar array feeds. This antenna system provides contiguous spot beam coverage of CONUS, utilizing 15 beams. Also designed, developed and demonstrated was a shaped contoured beam antenna system which provides contiguous four time zone coverage of CONUS from a single offset parabolic reflector incorporating one flat polarization diplexer and two separate planar array feeds. The beams which illuminate the eastern time zone and the mountain time zone are horizontally polarized, while the beams which illuminate the central time zone and the pacific time zone are vertically polarized. Frequency reuse is achieved by amplitude and polarization isolation.

Chen, C. C.↗

NASA NTRS1981

The 34-meter antenna drive control system

Detailed definitions of the baseline antenna drive and control/instrumentation equipment for 34 meter antennas included in Network Consolidation Program of the Deep Space Network are presented. The overall antenna control and monitor system and its interfaces with other higher level control and monitor equipment is described. Explicit descriptions of the antenna axis drive motors and motor controllers, the axis angle encoding systems, and miscellaneous antenna located components are presented, and related to system functional and performance requirements. Some potential alternates to the baseline system configuration are described and discussed.

Source record↗

NASA NTRS1981

The design of a microstrip antenna array for a UHF space telemetry link

An array of microstrip antenna panels was designed for use on a small instrumented satellite as part of a 400-MHz telemetry link between that satellite and NASA's shuttle spacecraft. A roughly omnidirectional phi-plane pattern was desired. The 1.4-wavelength diameter of the satellite and the various ports and structures on its surface presented strong constraints on the antenna array design. Eight antennas, each one a quarter-wavelength panel with one radiating and one shorted edge, were chosen. A phi-plane pattern ripple of 4.4 dB and a gain of at least 0.1 dB relative to a half-wavelength dipole were realized. The design technique used for the individual antenna panels included the study of feed-point location for impedance matching and the effect of losses in the dielectric. A superposition method was used to synthesize the radiation patterns for different numbers and different excitations of antennas on the satellite.

Post, R. E.↗

NASA NTRS1982

Dipole-Excited Ring Antenna

Dipole radiator drives ring radiator in compact C-band antenna. Antenna can be mounted flush with surface. Compared with horn or parabolic dish with same aperature, new ring antenna has greater gain, lower side lobes, and narrower beam width. Used on vehicles requiring flush-mounted antennas with very directive signals. Used as radar altimeter antenna for aircraft.

Ellis, H., Jr↗

NASA NTRS1982

Imaging antenna arrays

Many millimeter and far-infrared imaging systems are limited in sensitivity and speed because they depend on a single scanned element. Because of recent advances in planar detectors such as Schottky diodes, superconducting tunnel junctions, and microbolometers, an attractive approach to this problem is a planar antenna array with integrated detectors. A planar line antenna array and optical system for imaging has been developed. The significant advances are a 'reverse-microscope' optical configuration and a modified bow-tie antenna design. In the 'reverse-microscope' configuration, a lens is attached to the bottom of the substrate containing the antennas. Imaging is done through the substrate. This configuration eliminates the troublesome effects of substrate surface waves. The substrate lens has only a single refracting surface, making possible a virtually aplanatic system, with little spherical aberration or coma. The array is characterized by an optical transfer function that is easily measured. An array with 19 dB crosstalk levels between adjacent antennas has been tested and it was found that the array captured 50 percent of the available power. This imaging system was diffraction limited.

Rutledge, D. B.↗

NASA NTRS1983

Survey of deployable antenna concepts

Deployable space antenna concepts are surveyed. Precision reflector antennas, stiffened membrane antennas, truss antennas, infrared antennas, and electrostatically figured membrane reflectors are described.

Freeland, R. E.↗

NASA NTRS1982

Low gain and steerable vehicle antennas for communications with land mobile satellite

Current development activities at JPL for ground mobile vehicle antennas to be used with the Land Mobile Satellite Service (LMSS) system are described. Both low gain and electronically steerable high gain type antennas are discussed in terms of their design concept and RF performance. For the low gain type, three classes of antennas are under various stages of development. These are the crossed-drooping dipole, quadrifilar helix, and microstrip patch designs. The antennas are intended to provide circularly-polarized radiation with a minimum of 3-dB gain in the angular region from 19 degrees to 60 deg from the horizon in elevation plane and with an omnidirectional pattern in azimuthal plane. For the electronically steerable high gain type, circularly-polarized microstrip patch phased arrays formed on a planar surface and on the surface of a truncated cone are under study. The arrays are intended to provide a minimum of 12 dB gain in the same angular region in elevation plane at all azimuthal angles. This coverage is accomplished by scanning the high gain pencil beam in both elevation and azimuthal directions. Both types of antennas are to transmit at 821-831 MHz band and to receive at 866-876 MHz band. They must be of low cost design and reasonably conformal to the vehicle.

Woo, K.↗