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At least 1,387 records · Page 77
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

The Apollo 17 Surface Electrical Properties Experiment antenna performance.

The electrical properties of the lunar surface in the area of the Apollo 17 landing site were recently studied by the use of electromagnetic sounding techniques. The Apollo 17 Surface Electrical Properties Experiment was different from most other electromagnetic investigations of the lunar surface in that both the transmitting and receiving equipment was located directly on the lunar surface. The use of such inplace measurements of the electrical properties of the lunar surface is significant in that the exact structure and density of the soil contributes largely to the total electrical model of the moon. This paper will be concerned with a discussion of the transmitter antenna design problems for the Surface Electrical Properties Experiment as well as what is indicated by the returned lunar data about the transmitter antenna performance during the Apollo 17 mission.

Cubley, H. D.↗
NASA NTRS1973

The corrugated horn as an antenna range standard.

The corrugated horn is discussed as is a valuable tool for use in microwave pattern ranges. It has the properties of concentrated energy in the main beam, low backlobes, high efficiency, almost monotonic amplitude, and phase radiation patterns which make the corrugated horn useful for a source antenna in a pattern range and also as a possible standard antenna for calibration purposes.

Caldecott, R.↗
NASA NTRS1973

Microwave radiation hazards around large microwave antenna.

The microwave radiation hazards associated with the use of large antennas become increasingly more dangerous to personnel as the transmitters go to ever higher powers. The near-field area is of the greatest concern. It has spill over from subreflector and reflections from nearby objects. Centimeter waves meeting in phase will reinforce each other and create hot spots of microwave energy. This has been measured in front of and around several 26-meter antennas. Hot spots have been found and are going to be the determining factor in delineating safe areas for personnel to work. Better techniques and instruments to measure these fields are needed for the evaluation of hazard areas.

Klascius, A.↗
NASA NTRS1972

Phased array antennas for applications on spacecraft.

This is a survey paper wherein phased array antenna systems, now operating on spacecraft, are reviewed so as to reveal their basic techniques of beam formation, steering, and receive/transmit (transponder) functions. Laboratory developmental antennas, designed for ultimate spacecraft flight qualification, are assessed in terms of the needs of communications, earth resources instrumentation, and area surveillance.

Kummer, W. H.↗
NASA NTRS1975

Improved circularly polarized antenna

Antenna includes two sets of linearly polarized elements. Each set contains slots in parallel array. Sets are mutually orthogonal and are driven in phase quadrature. By changing lengths of slots or their separations, antenna beamwidth can be changed over wide range. Similar results are achieved with dipole configuration.

Van Atta, L. C.↗
NASA NTRS1975

Bidirectional zoom antenna

Antenna comprises two parabolic cylinders placed orthogoanlly to each other. One cylinder serves as main reflector, and the other as subreflector. Cylinders have telescoping sections to vary antenna beamwidth. Beamwidth can be adjusted in elevation, azimuth, or both. Design has no restriction as to choice of polarization.

Schmidt, R. F.↗
NASA NTRS1973

A study of selected radiation and propagation problems related to antennas and probes in magneto-ionic media

Research consisted of computations toward the solution of the problem of the current distribution on a cylindrical antenna in a magnetoplasma. The case of an antenna parallel to the applied magnetic field was investigated. A systematic method of asymptotic expansion was found which simplifies the solution in the general case by giving the field of a dipole even at relatively short range. Some useful properties of the dispersion surfaces in a lossy medium have also been found. A laboratory experiment was directed toward evaluating nonlinear effects, such as those due to power level, bias voltage and electron heating. The problem of reflection and transmission of waves in an electron heated plasma was treated theoretically. The profile inversion problem has been pursued. Some results are very encouraging, however, the general question of stability of the solution remains unsolved.

Source record↗
NASA NTRS1973

Dynamics of Flexible Spinning Satellites with Radial Wire Antennas

A dynamic analysis is presented for a spin stabilized spacecraft employing four radial wire antennas with tip masses, a configuration first employed in the IMP-J spacecraft. The use of wires in place of the usual booms represents the ultimate in weight reduction at the expanse of flexibility. The satellite is modelled as a 14 degree of freedom system, and the linearized equations of motion are found. The lowest order vibrational modes and natural frequencies of the gyroscopically coupled system are then determined. Because the satellite spin rate is decreased by antenna deployment, a spin-up maneuver is needed. The response of the time varying mode equations during spin-up is found, for the planar modes, in terms of Bessel functions and a Struve function of order -1/4. Because tables of the latter are not readily available, the particular solution is expressed in various forms including an infinite series of Bessel functions and a particularly useful asymptotic expansion.

Longman, R. W.↗
NASA NTRS1974

Design, fabrication, test and delivery of a K-band antenna breadboard model

The results of a research effort to develop a Ku-Band single channel monopulse antenna with significant improvements in efficiency and bandwidth are reported. A single aperture, multimode horn, utilized in a near field Cassegrainian configuration, was the technique selected for achieving the desired efficiency and bandwidth performance. In order to provide wide polarization flexibility, a wire grid, space filter polarizer was developed. A solid state switching network with appropriate driving electronics provides the receive channel sum and difference signal interface with an existing Apollo type tracking electronics subsystem. A full scale breadboard model of the antenna was fabricated and tested. Performance of the model was well within the requirements and goals of the contract.

Source record↗
NASA NTRS1974

Computer analysis of aircraft and shuttle antennas

Progress on predicting the patterns of high-frequency antennas on aircraft and shuttles is reported. Patterns are presented for an axial slot antenna on a circular cylinder partially coated with a dielectric layer. Results are shown for Omega signal disturbance by a conducting vertical pole.

Burnside, W. D.↗
NASA NTRS1974

Lightweight 3.66-meter-diameter conical mesh antenna reflector

A description is given of a 3.66 m diameter nonfurlable conical mesh antenna incorporating the line source feed principle recently developed. The weight of the mesh reflector and its support structure is 162 N. An area weighted RMS surface deviation of 0.28 mm was obtained. The RF performance measurements show a gain of 48.3 db at 8.448 GHz corresponding to an efficiency of 66%. During the design and development of this antenna, the technology for fabricating the large conical membranes of knitted mesh was developed. As part of this technology a FORTRAN computer program, COMESH, was developed which permits the user to predict the surface accuracy of a stretched conical membrane.

Moore, D. M.↗
NASA NTRS1974

Computer Program for Thin Wire Antenna over a Perfectly Conducting Ground Plane

A computer program is presented for a thin-wire antenna over a perfect ground plane. The analysis is performed in the frequency domain, and the exterior medium is free space. The antenna may have finite conductivity and lumped loads. The output data includes the current distribution, impedance, radiation efficiency, and gain. The program uses sinusoidal bases and Galerkin's method.

Richmond, J. H.↗
NASA NTRS1974

Application of an integral equation formulation to the prediction of space shuttle annular slot antenna radiation patterns

Pitch and roll plane radiation patterns computed by use of an integral equation formulation are presented for a space shuttle annular slot communications antenna. The excellent agreement between computed patterns and experimental patterns obtained from 1/35 scale models supports the use of this method as a design tool for similar spacecraft/aircraft antenna applications.

Jones, J. E.↗
NASA NTRS1974

The problem of controlling the directivity of low directivity antennas on spacecraft in flight

Interests exist in the creation of antennas allowing adjustment of the radiation pattern and directivity in flight without using complex switching and matching circuits. Results are presented of certain experimental tests performed with log-periodic conical helical antennas to determine the possibilities of regulation of their radiation patterns without changing the structure of the current-carrying elements, supply connections, etc.

Mashkov, V. I.↗
NASA NTRS1974

Analysis of strip antennas in the presence of a dielectric inhomogeneity

Moment method solutions are considered for treating the problem of wire antennas in the presence of an arbitrary dielectric inhomogeneity. In the first method, the current on the wire and the electric field intensity in the inhomogeneity are treated as independent unknowns, while in the second and third methods they are treated as dependent unknowns. The third method is applied to the problem of strip antennas in an electrically thin dielectric slab. Numerical results are presented, and are in good agreement with measurements and previous calculations.

Newman, E. H.↗
NASA NTRS1974

Design tradeoff study for reflector antenna systems for the shuttle imaging microwave system

A general tradeoff is made of the symmetric Cassegrain antenna with regard to the possibility of meeting a 90% beam efficiency. The effects of aperture taper and blockage are calculated using an adjustable sidelobe circular distribution. Numerical integration is used. For the feed spillover calculation, a low sidelobe symmetric feed pattern is used with the equivalent parabola and numerical integration. Reflector cross polarization is calculated using double numerical integration. Reflector back lobes are estimated from radiation pattern envelopes of commercial common carrier dish antennas. The curves allow a range of f/D to be determined for a specified edge taper and blockage diameter ratio, and with a table of Cassegrain parameters, a range of possible designs that meet the 90% beam efficiency is obtained. It is shown that the feed and reflector design and implementation must be carefully done.

Hansen, R. C.↗