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At least 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Multifrequency broadband polarized horn antenna

A corrugated conical horn antenna is simultaneously fed a multiplicity of signals, two for each of five frequencies, with each of a pair of signals fed in each of two orthogonal planes for excitation of a desired spherical hybrid mode. The lowest frequency is fed into the horn through orthogonal pairs of colinear slots, each pair being fed by coaxial tee power dividers. Other signals are fed through a circular waveguide connected to the vertex. The highest frequency signals are fed through orthogonal ports near the far end of the circular waveguide. The intermediate frequency signals are fed through orthogonal ports spaced along the waveguide. Filtering is incorporated for each to maintain isolation and low insertion loss.

Green, K. A.↗
NASA NTRS1981

Broadband electrostatic noise and field-aligned currents in Jupiter's middle magnetosphere

Voyager 1 plasma wave observations have revealed the presence of an impulsive electrostatic emission localized to the Jovian middle magnetosphere that appears on the edges of the plasma sheet. This plasma mode has the same spectral and morphological characteristics of an emission that has been extensively studied in the earth's magnetosphere and has been associated with the presence of field-aligned currents. The results of a detailed study of the properties of this Jovian emission are presented by using comparisons with terrestrial observations as a basis for mode identification. The occurrence regions of the waves are compared with the measured magnetic field configuration to establish a correspondence with the plasma sheet. It is argued that this is a quasi-permanent global system of field-aligned currents linking the ionosphere of Jupiter to the middle magnetosphere, which powers energetic plasma heating processes occurring there. On the basis of knowledge of the consequences of field-aligned currents in the terrestrial magnetosphere, a scenario for acceleration/precipitation of inverted V electrons, concomitant aurorae, and energetic (approximately 10 keV) proton deposition into the middle magnetosphere resulting from field-aligned potential drops associated with this current system is suggested.

Barbosa, D. D.↗
NASA NTRS1982

Generation of Alfven waves by deceleration of magnetospheric convection and broadband Pi pulsations

The generation of Alfven waves by the deceleration of magnetospheric convection caused by ionospheric loading effects in the magnetospheric dynamo is considered. A one-dimensional model of that region of the plasma sheet where convection is decelerated due to the dynamo process in the magnetosphere-ionosphere coupling is formulated, and the stability of the region is analyzed in order to derive the growth rate of unstable Alfven waves. The effects of ionospheric damping on unstable Alfven wave packets bounding between hemispheres are estimated. It is found that the overall growth rate is proportional to the height-integrated Pedersen conductivity and the convection speed in the dynamic region, but changes into a damping rate when the Pedersen conductivity is reduced below a specific threshold. The unstable Alfven waves thus generated are also found to contribute to both burstlike and relatively continuous Pi pulsations observed during substorms.

Kan, J. R.↗
NASA NTRS1981

Broadband optical radiation detector

A method and apparatus for detecting optical radiation by optically monitoring temperature changes in a microvolume caused by absorption of the optical radiation to be detected is described. More specifically, a thermal lens forming material is provided which has first and second opposite, substantially parallel surfaces. A reflective coating is formed on the first surface, and a radiation absorbing coating is formed on the reflective coating. Chopped, incoming optical radiation to be detected is directed to irradiate a small portion of the radiation absorbing coating. Heat generated in this small area is conducted to the lens forming material through the reflective coating, thereby raising the temperature of a small portion of the lens forming material and causing a thermal lens to be formed therein.

Gupta, A.↗
NASA NTRS1984

Broadband water vapor transmission functions for atmospheric IR flux computations

Transmission functions associated with water vapor molecular line and e-type absorption in the IR spectra regions are presented in the form of simple analytical functions and small tables, from which atmospheric IR fluxes and cooling rates can be easily computed. For typical clear atmospheres ranging from the tropics to the subarctic region, the difference with respect to line-by-line calculations is less than 0.15 C/day in the cooling rate and approximately equal to or less than 1 percent in fluxes.

Chou, M.-D.↗
NASA NTRS1983

Broadband transmission functions for atmospheric IR flux computations and climate studies

In order to reduce the size of precomputed tables which are used in the emissivity approach to computing IR radiation in a climate model, the three-dimensional transmission function in the water vapor bands is defined in this study by a simple regression equation consisting of three two-dimensional parameters. The transmittances in the 9.6 and 15 micron bands are individually parameterized as functions of the amount of scaled absorber. This approach can thus be applied to atmospheres with a variable CO2 concentration.

Chou, M.-D.↗
NASA NTRS1986

Broadband Ultrasonic Transducers

New geometry spreads out resonance region of piezoelectric crystal. In new transducer, crystal surfaces made nonparallel. One surface planar; other, concave. Geometry designed to produce nearly uniform response over a predetermined band of frequencies and to attenuate strongly frequencies outside band. Greater bandwidth improves accuracy of sonar and ultrasonic imaging equipment.

Heyser, R. C.↗
NASA NTRS1986

A new model for broadband waveguide to microstrip transition design

A new model is presented which permits the prediction of the resonant frequencies created by antipodal finline waveguide to microstrip transitions. The transition is modeled as a tapered transmission line in series with an infinite set of coupled resonant circuits. The resonant circuits are modeled as simple microwave resonant cavities of which the resonant frequencies are easily determined. The model is developed and the resonant frequencies determined for several different transitions. Experimental results are given to confirm the models.

Ponchak, George E.↗
NASA NTRS1987

Broadband reflectance coatings for vacuum ultraviolet application

An experimental investigation has obtained results indicating that neither LaF3 nor LiYF4 are acceptable alternatives to MgF2 as coatings for vacuum-deposited aluminum mirrors from which high UV reflectance down to 1150 A is required. Nevertheless, LaF3 may prove useful in those specialized applications in which the suppression of lower wavelength emissions, such as the 1216-A hydrogen line, is desirable.

Herzig, Howard↗
NASA NTRS1988

A new model for broadband waveguide-to-microstrip transition design

A new model is presented which permits the prediction of the resonant frequencies created by antipodal finline waveguide to microstrip transitions. The transition is modeled as a tapered transmission line in series with an infinite set of coupled resonant circuits. The resonant circuits are modeled as simple microwave resonant cavities of which the resonant frequencies are easily determined. The model is developed and the resonant frequencies determined for several different transitions. Experimental results are given to confirm the models.

Ponchak, George E.↗
NASA NTRS1987

Generation of broadband noise in the magnetotail

The generation of electrostatic noise in the geomagnetic tail by ion beams is evaluated, assuming a stationary plasma-sheet electron distribution and streaming-ion distributions. Both warm ion streams, as observed within the plasma-sheet boundary layer, and cold ion streams, as expected from upward flowing ionospheric ions, are considered. Warm ion streams by themselves are found to be stable, whereas a cold ion stream by itself is unstable to the beam acoustic mode. However, wave growth is increased if both cold and warm streams are simultaneously present. These results suggest that the interaction between the warm and cold ion streams is responsible for the peak in electrostatic-wave intensities observed within the plasma-sheet boundary layer. For cold and warm ions streaming in the same direction, wave-growth peaks are found for wave normal angles theta = 0 deg and wave frequencies about 0.1 times the electron plasma frequency. However, for antiparallel streaming cold and warm ions, wave growth peaks near theta = 90 deg and wave frequencies are an order of magnitude smaller.

Dusenbery, P. B.↗
NASA NTRS1989

Broadband electrostatic waves as a consequence of magnetotail reconnection

One and two-dimensional particle stimulations are used to study ion beam driven instabilities within the plasma sheet boundary layer (PSBL) and the consequences these instabilities have in terms of plasma heating. It shown that when cold lobe plasma convects into the PSBL and interacts with the ion beams, two wave modes can be driven unstable, the electron acoustic and ion-ion two stream instabilities; these waves heat the cold electrons and cold ions close to plasma sheet temperatures.

Ashour-Abdalla, Maha↗
NASA NTRS1989

The source location and beaming of broadband bursty radio emissions from Uranus

A rotationally-dependent occurrence pattern is identified for the b-bursty emissions observed with Voyager 2 during its 1986 encounter with Uranus. Certain features of this pattern, such as its extension to the highest frequencies and a 40-min signal gap, were sometimes recognizable on individual rotations despite the bursty character of the signals. This pattern is interpreted in terms of Voyager's passing from the inside of a broad, hollow emission cone coming from the southern hemisphere to the outside, and then back in, as a result of planetary rotation. The emission gap then corresponds to the times when Voyager was outside the cone.

Farrell, W. M.↗