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At least 919 records · Page 51

All sources NASA NTRS DOE OSTI

NASA NTRS1972

Optimization in the design of a 12 gigahertz low cost ground receiving system for broadcast satellites. Volume 2: Antenna system and interference

The antenna characteristics are analyzed of a low cost mass-producible ground station to be used in broadcast satellite systems. It is found that a prime focus antenna is sufficient for a low-cost but not a low noise system. For the antenna feed waveguide systems are the best choice for the 12 GHz band, while printed-element systems are recommended for the 2.6 GHz band. Zoned reflectors are analyzed and appear to be attractive from the standpoint of cost. However, these reflectors suffer a gain reduction of about one db and a possible increase in sidelobe levels. The off-axis gain of a non-auto-tracking station can be optimized by establishing a special illumination function at the reflector aperture. A step-feed tracking system is proposed to provide automatic procedures for searching for peak signal from a geostationary satellite. This system uses integrated circuitry and therefore results in cost saving under mass production. It is estimated that a complete step-track system would cost only $512 for a production quantity of 1000 units per year.

Ohkubo, K.↗

NASA NTRS1973

Extendible-retractable electric field measurement antenna for IMP J

An antenna dispenser mechanism for the IMP J spacecraft was designed, fabricated, and tested. Upon command the mechanism deploys or retracts a conductor for use as a receiving antenna for an electric field measurement experiment. Five identical units were fabricated and tested to the IMP H & J environmental test specification. Of these, four are designated for flight on the IMP J spacecraft and one as a prototype flight spare. The testing program was successfully completed although certain design modifications were required as problems were uncovered by the testing; particularly thermal vacuum operation. The antenna mechanism functions well under the expected environmental and loading conditions. The wear life and load capability of the dry molybdenum disulphide lubricant originally used on the heavily loaded worm and gear pair were disappointing and a substitute material was applied. The lubricant finally applied performed well; although other problems were generated.

Larrick, W.↗

NASA NTRS1974

Roll plane analysis of on-aircraft antennas

Roll plane radiation patterns of on-aircraft antennas are analyzed using high frequency solutions. Aircraft-antenna pattern performance in which the aircraft is modelled in its most basic form is presented. The fuselage is assumed to be a perfectly conducting elliptic cylinder with the antennas mounted near the top or bottom. The wings are simulated by arbitrarily many sided flat plates and the engines by circular cylinders. The patterns in each case are verified by measured results taken on simple models as well as scale models of actual aircraft.

Burnside, W. D.↗

NASA NTRS1974

A study of KC-135 aircraft antenna patterns

Numerical solutions for the radiation patterns of aircraft antennas are evaluated. Designing and locating antennas in order to achieve the desired performance is discussed. The high frequency solutions presented in this report are based on fuselage antennas mounted on a general-type aircraft but applied specifically to the KC-135 aircraft. The roll and elevation plane patterns are computed for a monopole, axial slot, and circumferential slot mounted both over and forward of the wings. In each case the calculated patterns compare very favorably with the measured patterns. The precision pattern measurements were taken on a 1/25 scale model of the KC-135 aircraft at NASA (Langley, Virginia) with special emphasis on reducing the mount and background effects.

Burnside, W. D.↗

NASA NTRS1974

Flush-mounted antennas radiating on aircraft type surfaces

The roll plane radiation patterns of on-aircraft antennas are analyzed using high frequency solutions. This is a basic study of aircraft-antenna pattern performance in which the aircraft is modelled in its most basic form. The fuselage is assumed to be a perfectly conducting elliptic cylinder with the antennas mounted near the top or bottom. The wings are simulated by arbitrarily many sided flat plates.

Burnside, W. D.↗

NASA NTRS1974

Roll plane analysis of on-aircraft antennas

Burnside, W. D.↗

NASA NTRS1974

High temperature antenna development for space shuttle, volume 2

An S-band antenna system and a group of off-the-shelf aircraft antenna were exposed to temperatures simulating shuttle orbital cold soak and entry heating. Radiation pattern and impedance measurements before and after exposure to the thermal environments were used to evaluate the electrical performance. The results of the electrical and thermal testing are given. Test data showed minor changes in electrical performance and established the capability of these antenna to withstand both the low temperatures of space flight and the high temperatures of entry.

Kuhlman, E. A.↗

NASA NTRS1974

A study program on large aperture electronic scanning phased array antennas for the shuttle imaging microwave system

Fundamental phased array theory and performance parameters are discussed in terms of their application to microwave radiometry, and four scanning phased arrays representing current examples of state-of-the-art phased array technology are evaluated for potential use as components of the multispectral antenna system for the space shuttle imaging microwave system (SIMS). A discussion of problem areas, both in performance and fabrication is included, with extrapolations of performance characteristics for phased array antennas of increased sizes up to 20 m by 20 m. The possibility of interlacing two or more phased arrays to achieve a multifrequency aperture is considered, and, finally, a specific antenna system is recommended for use with SIMS.

Source record↗

NASA NTRS1974

Developments of a unique graphite/epoxy antenna subreflector

Advanced concepts for large, furlable space antennas have led to an extensive development program at the Jet Propulsion Laboratory (JPL) with configurations utilizing conical main reflectors. The antenna subreflectors for these conical configurations have unusual geometries and new structural requirements. Structural efficiency of the conical antennas is improved through the use of fiber composites. A subreflector was designed and fabricated with graphite/epoxy material. The subreflector is a cylindrical paraboloid with demanding criteria for contour surface precision, high thermal stability, and sufficient structural capacity for inertial launch loads in axial and transverse directions. The paper describes the design, analysis, and fabrication of the subreflector.

Robinson, E. Y.↗

NASA NTRS1974

Fabrication of a graphite/epoxy antenna for the Viking Orbiter spacecraft

A graphite/epoxy composite high-gain antenna has been developed for the Viking Orbiter 1975 spacecraft. A thin-skin honeycomb sandwich construction was used for the reflector structure. The antenna has been designed, and several have been fabricated and successfully tested and qualified under simulated launch and space environments. The graphite/epoxy material was used primarily because of the weight saving over a more conventional aluminum honeycomb construction and because of its low expansion characteristics. The low coefficient of thermal expansion of the graphite composite results in a dimensionally stable antenna structure under the extreme thermal environment to be encountered in this Mars mission.

Stonier, R. A.↗

NASA NTRS1974

Dual S and Ku-band tracking feed for a TDRS reflector antenna

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.

Pullara, J. C.↗

NASA NTRS1974

Selection of an optimal plan for construction of a spacecraft antenna system

An attempt is made to summarize the experience of the design of antennas for various types of spacecraft: fully oriented, partially oriented, and with arbitrary orientation. Several examples of the construction of antenna systems and their characteristics are given. The optimal relationship between weight, dimension and power characteristics of on-board devices allows selection of the most acceptable versions. Questions are presented for consideration in design of optimal spacecraft antenna-feeder systems.

Prigoda, B. A.↗

NASA NTRS1974

Circularly polarized antennas with controlled radiation patterns

Log-helix conical antennas were examined as a way to satisfy the requirement for circular polarization of antennas for spacecraft use. It was concluded that a multiple-helix antenna which allows the helix lead angle to be changed can be used when the radiation and directivity in the direction of the reception point must be changed during flight.

Prigoda, B. A.↗

NASA NTRS1974

Antenna performance and resolution

The performance of the antenna throughout SL-2, SL-3, and SL-4 was investigated along with the antenna resolution of brightness temperature during flight. The target area selected for the test flights was the Gulf of California, as it offered land/water interface. The coordinate transformations and antenna orientation, flight path simulation, and integration over the radiometric target are discussed.

Carney, J. J.↗

NASA NTRS1975

S-band antenna phased array communications system

The development of an S-band antenna phased array for spacecraft to spacecraft communication is discussed. The system requirements, antenna array subsystem design, and hardware implementation are examined. It is stated that the phased array approach offers the greatest simplicity and lowest cost. The objectives of the development contract are defined as: (1) design of a medium gain active phased array S-band communications antenna, (2) development and test of a model of a seven element planar array of radiating elements mounted in the appropriate cavity matrix, and (3) development and test of a breadboard transmit/receive microelectronics module.

Delzer, D. R.↗

NASA NTRS1975

Electronically steerable millimeter wave antenna techniques for space shuttle applications

A large multi-function antenna aperture and related components are described which will perform electronic steering of one or more beams for two of the three applications envisioned: (1) communications, (2) radar, and (3) radiometry. The array consists of a 6-meter folded antenna that fits into two pallets. The communications frequencies are 20 and 30 GHz, while the radar is to operate at 13.9 GHz. Weight, prime power, and volumes are given parametrically; antenna designs, electronics configurations, and mechanical design were studied.

Kummer, W. H.↗

NASA NTRS1975

Study of the performance of antennas in magnetized plasmas

The antenna studies were performed in a large magnetized plasma source, a schematic drawing of which is shown. The plasma diagnostics consist of a 70 GHz (4 mm) microwave interferometer for density measurements and of various Langmuir probes for spatially resolved measurements of t sub e, n sub e and the shape of the electron distribution function. All diagnostic data are time-resolved by sample-and-hold techniques so as to yield information about the plasma build-up, the steady-state discharge, and the plasma decay in the afterglow. Whistler waves are excited and detected with various antennas which are inserted into the center of the plasma column through one axial and two orthogonal radial ports. The antennas were tested for their proper dipole response and then calibrated in a known field geometry in air. For the electric dipole, a parallel plate capacitor field was used; the magnetic loop is calibrated in the near-zone field of a long linear conductor of known radio frequency current distribution. Results are presented and discussed.

Stenzel, R. L.↗

NASA NTRS1975

L-band, 1.2 m parabolic antenna-noise temperature measurement

Extensive antenna-noise temperature measurements at 1.6 GHz (L-band) were made using a 1.2 m (4 ft. diameter) parabolic dish antenna mounted on the flying bridge of a modern 15,690-ton, commercial-container ship. Both in-harbor and at-sea radiometer measurements were made that indicated a steady background, antenna-noise temperature value slightly less than 70 degrees Kelvin (K) at elevation angles of 5 percent, and greater, at 1.6 GHz. A comparison of theoretical and measured values indicate excellent agreement within about 5K for at-sea data. These measurements are helpful to RF equipment designers of maritime, L-band shipboard terminals for operation with the two, geostationary, maritime satellites, Marisat-A and -B.

Taylor, R. E.↗