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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Ultrasonic simulation of MSBLS multipath fading for orbiter landing configuration

The on-shuttle antenna pattern of the MSBLS receiver, and the azimuth and elevation beamwidths were simulated by their corresponding ultrasonic transducer beams. The scanning rate for the azimuth and elevation beams was 1.75 degrees/second. The results were adjusted for full-scale maximum sinusoidal scan rates of 691 and 377 deg/sec for AZ and EL respectively. The rain drops were simulated by air bubbles, with a similar size distribution, in water. The rain volume was created along a part of the propagation path, and not on the runway, because it was found difficult to avoid an accumulation of bubbles on the runway surface and surroundings simulated by the model surface. Multipath fading from the ground, and its possible degrading effect on the orbiter received beam shape and the associated landing guidance parameters is discussed.

Hayre, H. S.↗
NASA NTRS1978

A dual polarized antenna system using a meanderline polarizer

Certain applications of synthetic aperture radars require transmitting on one linear polarization and receiving on two orthogonal linear polarizations for adequate characterization of the surface. To meet the current need at minimum cost, it was desirable to use two identical horizontally polarized shaped beam antennas and to change the polarization of one of them by a polarization conversion plate. The plate was realized as a four-layer meanderline polarizer designed to convert horizontal polarization to vertical.

Burger, H. A.↗
NASA NTRS1977

Design curves for double-heterojunction laser diodes

This paper reviews theoretical double-heterojunction laser design curves relating the structure with the transverse mode order able to propagate, the degree of radiation confinement to the active region, the maximum field intensity within the device, and the radiated beam shape. The curves presented are general and applicable to any double-heterojunction structure where the spacing of the heterojunctions and the refractive index in the relevant regions are known.

Butler, J. K.↗
NASA NTRS1977

The ESSA solution

ESSA (Electronic Switching Spherical Array) is a fixed truncated spherical antenna with its elements over the complete surface, conceived to satisfy many future antenna system requirements. Constant gain and beam shape throughout large volumetric coverage regions are the principle characteristics. In the present paper, the two existing types of ESSA are discussed. ESSA I is a simple nonphase correcting aperture approach characterized by light weight, low dc power consumption, gain between +7 and +14 dB, and 90% spherical coverage. ESSA II is a phase corrected aperture which would have very low sidelobe levels and improved gain over ESSA I (12 to 22 dB), but would be heavier and require more dc power.

Hockensmith, R. P.↗
NASA NTRS1978

A dual polarized antenna system using a meanderline polarizer

Certain applications of synthetic aperture radars (e.g., aerial crop surveying) require transmission on one linear polarization and reception on two orthogonal linear polarizations for adequate characterization of the surface. To meet this requirement at minimum cost, it was desirable to use two identically polarized shaped beam antennas and to change the polarization of one of them by a polarization conversion plate. The plate was realized as a four-layer meanderline polarizer designed to convert horizontal polarization to vertical.

Burger, H. A.↗
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 NTRS1980

High-resolution spectrometrometry/interferometer

Modified double-pass interferometer has several features that maximize its resolution. Proposed for rocket-borne probes of upper atmosphere, it includes cat's-eye retroreflectors in both arms, wedge-shaped beam splitter, and wedged optical-path compensator. Advantages are full tilt compensation, minimal spectrum "channeling," easy tunability, maximum fringe contrast, and even two-sided interferograms.

Breckinridge, J. B.↗
NASA NTRS1980

Simultaneous muscle force and displacement transducer

A myocardial transducer for simultaneously measuring force and displacement within a very small area of myocardium is disclosed. The transducer comprised of an elongated body forked at one end to form an inverted Y shaped beam with each branch of the beam constituting a low compliant tine for penetrating the myocardium to a predetermined depth. Bonded to one of the low compliance tines is a small piezoresistive element for converting a force acting on the beam into an electrical signal. A third high compliant tine of the transducer, which measures displacement of the myocardium in a direction in line with the two low compliant tines, is of a length that just pierces the surface membrane. A small piezoresistive element is bonded to the third tine at its upper end where its bending is greatest. Displacement of the myocardium causes a deformation in curvature of the third tine, and the second small piezoresistive element bonded to the surface of its curved end converts its deformation into an electrical signal.

Feldstein, C.↗
NASA NTRS1980

Wiener filtering of successive overlapping sections of an X-ray reconstruction

In this paper, a technique is developed to improve the image quality of an object in three-dimensional reconstruction by a weighted average of successive overlapping two-dimensional sections of the object. It is demonstrated that the signal-to-noise ratio of a two-dimensional picture can be improved by roughly a factor of 2 for typical X-ray beam shapes.

Reed, I. S.↗
NASA NTRS1980

SPS large array simulation

The computer programming efforts were directed primarily to beam pattern analysis. The computer programs used for simulation provide: verification of the reference design; definition of feasible departures such as quantized distributions; the study of far-out sidelobe roll-off characteristics; the analysis of errors and failures; illumination function analysis to develop beam patterns for efficient collection; and beam shaping synthesis to meet environmental constraints.

Rathjen, S.↗
NASA NTRS1982

A 1400-MHz survey of 1478 Abell clusters of galaxies

Observations of 1478 Abell clusters of galaxies with the NRAO 91-m telescope at 1400 MHz are reported. The measured beam shape was deconvolved from the measured source Gaussian fits in order to estimate the source size and position angle. All detected sources within 0.5 corrected Abell cluster radii are listed, including the cluster number, richness class, distance class, magnitude of the tenth brightest galaxy, redshift estimate, corrected cluster radius in arcmin, right ascension and error, declination and error, total flux density and error, and angular structure for each source.

Owen, F. N.↗
NASA NTRS1984

Characterization of a dual-mode horn for submillimeter wavelengths

A simple dual-mode conical horn has been developed and tested at 0.5, 1.4, 3.1, and 34.2 mm. The horn has nearly equal beam shape in the E and H plane far-field patterns, with a 3-dB half angle of 6 deg. At 34.2 mm, the waveguide reflection loss and the phase center have been determined.

Pickett, H. M.↗
NASA NTRS1985

Microwave antenna temperature of the earth from geostationary orbit

The microwave antenna temperature of the earth has been computed for the case of a communication satellite antenna viewing the earth from geostationary orbit. An earth-coverage beam is assumed and detailed computations are performed to account for varying land-ocean fractions within the field of view. Emission characteristics of the earth's atmosphere and surface are used with an accurate radiative transfer program to compute observed brightness temperatures. Values of 250 to 290 K commonly used for antenna temperature in satellite communication noise calculations are found to be over-conservative estimates, with more realistic values lying in the 60-240 K range depending on frequency and subsatellite longitude. These values also depend on assumptions concerning antenna beam coverage. Variations in atmospheric and surface conditions, and variations in antenna beam shape (as distinct from coverage), affect the computed results by less than about 10 K.

Njoku, E. G.↗
NASA NTRS1985

The microwave noise environment at a geostationary satellite caused by the brightness of the earth

The microwave antenna temperature due to the earth in the satellite antenna beam has been computed for a series of longitudes for a satellite in geostationary orbit and for frequencies of 1 to 50 GHz. An earth-coverage beam is assumed for simplicity, but the technique is applicable to arbitrary beam shapes. Detailed calculations have been performed to account for varying land-ocean fractions within the field of view. Emission characteristics of the earth's atmosphere and surface are used with an accurate radiation transfer program to compute observed brightness temperatures. The value of 290 K commonly used for antenna temperature in satellite communication noise calculations is overly conservative, with more realistic values lying in the 60 to 240 K range.

Smith, E. K.↗
NASA NTRS1986

The Large Deployable Reflector (LDR) report of the Science Coordination Group

The Large Deployable Reflector (LDR) is a telescope designed to carry out high-angular resolution, high-sensitivity observations at far-infrared and submillimeter wavelengths. The scientific rationale for the LDR is discussed in light of the recent Infrared Astronomical Satellite (IRAS) and Kuiper Airborne Observatory (KAO) results and the several new ground-based observatories planned for the late 1980s. The importance of high sensitivity and high angular resolution observations from space in the submillimeter region is stressed. The scientific and technical problems of using the LDR in a light bucket mode at approx. less than 5 microns and in designing the LDR as an unfilled aperture with subarcsecond resolution are also discussed. The need for an aperture as large as 20 m is established, along with the requirements of beam-shape stability, spatial chopping, thermal control, and surface figure stability. The instrument complement required to cover the wavelength-spectral resolution region of interest to the LDR is defined.

Source record↗
NASA NTRS1987

Engineering calculations for the Delta S method of solving the orbital allotment problem

The method of calculating single-entry separation requirements for pairs of satellites is extended to include the interference on the top link as well as on the down link. Several heuristic models for analyzing the effects of shaped-beam antenna designs on required satellite separations are introduced and demonstrated with gain contour plots. The calculation of aggregate interference is extended to include the effects of up-link interference. The relationship between the single-entry C/I requirements, used in determining satellite separation constraints for various optimization procedures, and the aggregate C/I values of the resulting solutions is discussed.

Kohnhorst, P. A.↗
NASA NTRS1988

Parametric and experimental analysis using a power flow approach

Having defined and developed a structural power flow approach for the analysis of structure-borne transmission of structural vibrations, the technique is used to perform an analysis of the influence of structural parameters on the transmitted energy. As a base for comparison, the parametric analysis is first performed using a Statistical Energy Analysis approach and the results compared with those obtained using the power flow approach. The advantages of using structural power flow are thus demonstrated by comparing the type of results obtained by the two methods. Additionally, to demonstrate the advantages of using the power flow method and to show that the power flow results represent a direct physical parameter that can be measured on a typical structure, an experimental investigation of structural power flow is also presented. Results are presented for an L-shaped beam for which an analytical solution has already been obtained. Furthermore, the various methods available to measure vibrational power flow are compared to investigate the advantages and disadvantages of each method.

Cuschieri, J. M.↗
NASA NTRS1988

Scattering of electromagnetic waves from a periodic surface with random roughness

Equations for the scattering of electromagnetic waves from a randomly perturbed periodic surface have been formulated using the extended boundary condition method and solved using the small perturbation method. Surface currents and scattered fields are solved for up to the second order. The results indicate that as the correlation length of the random roughness increases, the bistatic scattering patterns of the scattered fields show several beams associated with each Bragg diffraction direction of the periodic surface. The beam shape becomes broader with smaller correlation length. Results obtained using the Kirchhoff approximation are found to agree well with the present results for the hh and vv polarized backscattering coefficients for small angles of incidence.

Yueh, H. A.↗