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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Millimeter wave space communications - Recent experimental results and present development programs.

Major results of millimeter wave propagation measurements conducted with the ATS-5 satellite are reviewed, and their impact on the design of operational millimeter wave communications systems is evaluated. Statistical results show attenuation probabilities in different localities at various intervals of observation in an attempt at correlation with precipitation conditions. Advanced millimeter wave propagation experiments currently under development for the ATS-F satellite are also discussed.

Ippolito, L. J.↗
NASA NTRS1990

Millimeter wave near-field study

The possibility is evaluated of current technology measuring large aperture millimeter wave antennas. Included are a mathematical modeling of system errors, experimental data supporting error model, predictions of system accuracy at millimeter wavelengths, advantage of near-field measurements, and a cost estimate for a facility upgrade. The use is emphasized of software compensation and other inexpensive alternatives to develop a near optimum solution to near-field measurement problems at millimeter wavelengths.

Kefauver, Neill↗
NASA NTRS1991

Millimeter wave surface resistance of grain-aligned Y1Ba2Cu3O(x) bulk material

Measurements of the millimeter wave surface resistance of grain-aligned YBa2Cu3O(x) bulk material grown by a liquid phase process are reported. The measurements were performed by replacing the endplate of a TE011 cylindrical copper cavity with the superconducting sample. Surface resistance was measured for samples with surfaces oriented perpendicular and parallel to the c-axis of the grains. It is shown that, for the parallel configuration, the surface resistance at 77 K and 80 GHz is typically near 100 milliohms. For a very well-aligned sample with a very low density of Y2BaCuO(y) precipitates, measured in the perpendicular configuration, the transition width (10-90 percent) is about 2 K, and the surface resistance is less than 50 milliohms at 88 K. The effect of microstructure on surface resistance is discussed.

Wosik, J.↗
NASA NTRS2014

Challenges and Techniques in Measurements of Noise, Cryogenic Noise and Power in Millimeter-Wave and Submillimeter-Wave Amplifiers

We will present the topic of noise measurements, including cryogenic noise measurements, of Monolithic Microwave Integrated Circuit (MMIC) and Sub-Millimeter-Wave Monolithic Microwave Integrated Circuit (S-MMIC) amplifiers, both on-wafer, and interfaced to waveguide modules via coupling probes. We will also present an overview of the state-of-the-art in waveguide probe techniques for packaging amplifier chips, and discuss methods to obtain the lowest loss packaging techniques available to date. Linearity in noise measurements will be discussed, and experimental methods for room temperature and cryogenic noise measurements will be presented. We will also present a discussion of power amplifier measurements for millimeter-wave and submillimeter-wave amplifiers, and the tools and hardware needed for this characterization.

Samoska, Lorene↗
DOE OSTI2025

Real-time steerable frequency-stepped Doppler backscattering (DBS) system for local helicon wave electric field measurements on the DIII-D tokamak

A new frequency-stepped Doppler backscattering (DBS) system has been integrated into a real-time steerable electron cyclotron heating launcher system to simultaneously probe local background turbulence (f < 10 MHz) and high-frequency (20–550 MHz) density fluctuations in the DIII-D tokamak. The launcher allows for 2D steering (horizontally and vertically) over wide angular ranges to optimize probe location and wavenumber response. The vertical steering can be optimized during a discharge in real time. The new DBS system employs a programmable frequency synthesizer with adjustable dwell time as a source to launch either O or X-mode polarized millimeter waves. This system can step in real-time over the entire E-band frequency range (60–90 GHz). This combination of capabilities allows for the diagnosis of the complex internal spatial structure of high power (>200 kW) helicon waves (476 MHz) injected from an external antenna during helicon current drive experiments in DIII-D. Broadband density fluctuations around the helicon frequency are observed during real-time scans of measurement location and wavenumber during these experiments. Analysis indicates that these broadband high-frequency fluctuations are a result of backscattering of the DBS millimeter-wave probe beam from plasma turbulence modulated by the helicon wave. It is observed that background turbulence is effectively locally “tagged” with the helicon wave electric field, forming images of the turbulent spectrum in the overall density fluctuation spectrum that appear as high-frequency sidebands of the turbulence. These observations of background turbulence and high-frequency fluctuations open up the possibility of monitoring local helicon wave amplitude by comparing the high-frequency signal amplitude to the simultaneously measured background turbulence. In combination with the real-time measurement location and wavenumber scanning capabilities (offered by real-time frequency-stepping and steering), this allows rapid determination of the spatial distribution of the helicon wave power during steady-state plasma operation.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1975

ATS-6 - Millimeter Wave Propagation and Communications Experiments at 20 and 30 GHz

The Applications Technology Satellite (ATS-6) Millimeter Wave Experiment, developed and implemented by the NASA Goddard Space Flight Center, has provided the first direct measurements of 20- and 30-GHz earth-space links from an orbiting satellite. Studies at eleven locations in the continental United States were directed at an evaluation of rain attenuation effects, scintillations, depolarization, site diversity, coherence bandwidth, and analog and digital communications techniques. In addition to direct measurements on the 20- and 30-GHz links, methods of attenuation prediction with radars, rain gauges, and radiometers were developed and compared with the directly measured attenuation. This paper presents a review of the major results of the first year of measurements with ATS-6, with emphasis on the impact of the measurements on millimeter wave space systems design.

Ippolito, L. J.↗
NASA NTRS1989

Laboratory measurements of microwave and millimeter-wave properties of planetary atmospheric constituents

Accurate data on microwave and millimeter-wave properties of potential planetary atmospheric constituents is critical for the proper interpretation of radio occultation measurements, and of radio astronomical observations of both continuum and spectral line emissions. Such data is also needed to correct for atmospheric effects on radar studies of surface reflectivity. Since the refractive and absorptive properties of atmospheric constituents often vary drastically from theoretically-predicted profiles, especially under the extreme conditions characteristic of the planetary atmosphere, laboratory measurements under simulated planetary conditions are required. This paper reviews the instrumentation and techniques used for laboratory measurement of the refractivity and absorptivity of atmospheric constituents at wavelengths longward of 1 mm, under simulated planetary conditions (temperature, pressure, and broadening gases). Techniques for measuring both gases and condensates are considered. Also reviewed are the relative accuracies of the various techniques. Laboratory measurements are reviewed which have already been made, and additional measurements which are needed for interpretation of data from Venus and the outer planets, are highlighted.

Steffes, Paul G.↗
NASA NTRS1990

Laboratory measurements of microwave and millimeter-wave properties of planetary constituents

Accurate data on microwave and millimeter-wave properties of potential planetary atmospheric constituents is critical for the proper interpretation of radio occultation measurements, and of radio astronomical observations of both continuum and spectral line emissions. Such data is also needed to correct for atmospheric effects on radar studies of surface reflectivity. Since the refractive and absorptive properties of atmospheric constituents often vary drastically from theoretically predicted profiles, especially under the extreme conditions characteristic of the planetary atmosphere, laboratory measurements under simulated planetary conditions are required. The instrumentation and techniques used for laboratory measurement of the refractivity and absorptivity of atmospheric constituents at wavelengths longward of 1 mm, under simulated planetary conditions (temperature, pressure, and broadening gases) are reviewed. Techniques for measuring both gases and condensates are considered. Also reviewed are the relative accuracies of the various techniques. Laboratory measurements are reviewed which have already been made, and additional measurements which are needed for interpretation of data from Venus and the outer planets, are highlighted.

Steffes, Paul G.↗
NASA NTRS1984

A measurement of stratospheric HO2 by ground-based millimeter-wave spectroscopy

Stratospheric perhydroxyl (HO2) was measured by using a sensitive mm-wave receiver to obtain spectroscopic line profiles of three rotational emission lines in the vicinity of 265.8 GHz. The observations were carried out over four days in September-October 1982 at Mauna Kea, Hawaii and yield good agreement with the column density and vertical distribution predicted above 35 km by three representative two-dimensional photochemical models employing JPL 82-57 reaction rates and chemistry. Contrasts between current theoretical predictions and previous observations by Anderson et al. (1981) are pointed out for HO2 in the 28 to 37-km range, along with the difficulty of joining the latter with the present measurements through a monotonically varying vertical profile for HO2. A possible explanation involving strong temporal and spatial variation in stratospheric water vapor content is suggested.

De Zafra, R. L.↗
NASA NTRS1991

Variable temperature pressure broadening of HNO3 in the millimeter wave spectral region

Measurements were performed for both O2 and N2 broadening in the 100-380 K temperature range by using a heated equilibrium cell for elevated temperatures and the utilization of a collisionally cooled cell at the lower temperatures where HNO3 has a small vapor pressure. Observed pressure-broadening data can be fit to the normal empirical law, giving n values between 0.62 and 0.84.

Goyette, Thomas M.↗
NASA NTRS1992

Error analysis applied to several inversion techniques used for the retrieval of middle atmospheric constituents from limb-scanning MM-wave spectroscopic measurements

The formal retrieval error analysis of Rodgers (1990) allows the quantitative determination of such retrieval properties as measurement error sensitivity, resolution, and inversion bias. This technique was applied to five numerical inversion techniques and two nonlinear iterative techniques used for the retrieval of middle atmospheric constituent concentrations from limb-scanning millimeter-wave spectroscopic measurements. It is found that the iterative methods have better vertical resolution, but are slightly more sensitive to measurement error than constrained matrix methods. The iterative methods converge to the exact solution, whereas two of the matrix methods under consideration have an explicit constraint, the sensitivity of the solution to the a priori profile. Tradeoffs of these retrieval characteristics are presented.

Puliafito, E.↗
NASA NTRS2005

Infrared Extinction and the Initial Conditions for Star and Planet Formation

This grant funded a research program to use infrared extinction measurements to probe the detailed structure of dark molecular clouds and investigate the physical conditions which give rise to star and planet formation. The goals of the this program were to: 1) acquire deep infrared and molecular-line observations of a carefully selected sample of nearby dark clouds, 2) reduce and analyze the data obtained in order to produce detailed extinction maps of the clouds, 3) use the results to measure and quantitatively describe the physical conditions of the dense gas and dust that produce stars and their accompanying planetary systems in molecular clouds. The goals of this project were met and exceeded as described below. 1) The infrared data for the project were obtained in a number of observing runs using the 3.5-meter NTT and 8-meter VLT telescopes of the European Southern Observatory in Chile and the 1.2-meter telescope of the Smithsonian Astrophysical Observatory in Arizona, the 1 0-meter Keck telescope in Hawaii, the 6.5-meter MMT of the Smithsonian Astrophysical Observatory in Arizona, and the NASA Hubble Space Telescope. The molecular-line data was obtained in three runs using the IRAM 30-meter telescope in Spain and one run with the ESO-15 meter millimeter-wave telescope in Chile. Millimeter-wave continuum measurements were obtained with the 15-meter JCMT in Hawaii. 2) Considerable effort was expended to reduce the infrared imaging observations including the development of custom software to produce high quality photometry and source astrometry. All the millimeter-line data was reduced using standard reduction routines. The highlights of the infrared analysis were the production of detailed extinction maps and the construction of profiles of the density structure of the B68, Coalsack, B335 and Lupus clouds. 3) The principal scientific accomplishments of this research program include the following: We were able to use our infrared observations to determine the density structure of the B68 cloud to an unprecedented level of precision. This lead to a major breakthrough in the study of molecular cloud structure. For the first time we have been able to characterize the structure of a dark cloud in a detail only exceeded by that known for a star. We determined that the cloud's structure is exquisitely well described by the equations of a Bonner-Ebert sphere (a pressure confined isothermal sphere). We were able to show that the cloud is very nearly in equilibrium with the internal thermal pressure of the cloud balancing gravity and the external pressure of the surrounding interstellar medium. We were able to determine for the first time the gas-to-dust ratio in a dense cloud core. We also demonstrated a new method to determine extremely precise distances to such clouds by combining knowledge of the properties of Bonner-Ebert Spheres with our infrared and millimeter-wave observations.

Lada, Charles J.↗
NASA NTRS1990

Dependence of millimeter wave surface resistance on the deposition parameters of laser ablated YBa2Cu3O(x) thin films

Measurements of millimeter-wave surface resistance versus temperature have been performed for YBa2Cu3O(x) thin films on 100 line-type SrTiO(3) substrates using a TE(011) cylindrical copper cavity at 80 GHz. The 0.6-micron thick films were grown at several deposition temperatures in the range 690 C to 810 C by means of a pulsed excimer laser ablation technique. A surface resistance minimum (60 milliohm at 77 K) near 770 C is shown to correlate with a minimum in c-axis lattice parameter (11.72 A). The highest value of Tc also occurs near this temperature. The surface resistance of films deposited at 790 C on 110 line-type LaAlO3 subtrates is lower, reaching 8 milliohm at 98 GHz and 80 K, demonstrating the influence of substate material on film quality.

Wosik, J.↗
NASA NTRS1991

Integrated millimeter-wave corner-cube antennas

An integrated corner-reflector antennas has been designed, fabricated, and measured at millimeter-wave frequencies. The structure consists of a traveling-wave antenna integrated on a 1.2-micron dielectric membrane, and suspended in a longitudinal cavity etched in a silicon wafer. A novel traveling wave antenna design, the modified-bend antenna, with an antenna length of 1.2 lambda and spacing 0.96 lambda from the apex, results in a wideband input impedance centered at 140 Ohm and low cross-polarization levels. Measurements at 180-270 GHz show a well-defined pattern with low sidelobe levels, and a main-beam efficiency of 93 percent and 83 percent at 180 and 222 GHz, respectively. The monolithic approach allows the integration of a matching network and a Schottky-diode or SIS detector at the base of the antenna to yield a low-noise monolithic millimeter-wave receiver.

Gearhart, Steven S.↗
NASA NTRS1972

Electron density measurements of an inhomogeneous plasma using millimeter wave Fabry-Perot interferometers.

The electron density of a laboratory generated inhomogeneous plasma was measured using 60-90, GHz flat-plate and 150 GHz semi-confocal Fabry-Perot interferometers. The plasma was a negative glow-type and had a measured parabolic electron density profile. An analytical comparison between the derived equations of electron density for an assumed homogeneous plasma slab and an inhomogeneous plasma with parabolic distribution showed that the slab approximation was valid for such a profile. Comparison of measured values of electron density with those using X-band and K-band interferometers for the same plasma indicated good agreement.

Kendall, B. M.↗
NASA NTRS1992

Laboratory measurements of the microwave and millimeter-wave opacity of gaseous sulfur dioxide (SO2) under simulated conditions for the Venus atmosphere

Laboratory measurements have been conducted of the opacity of gaseous SO2 in a CO2 atmosphere at 12.3 cm, 1.32 cm, and 0.32 cm, with a view to the effects of this gas on the mm-wave emission of the Venus atmosphere. Close agreement is noted between the results obtained and the absorptivity predicted from a Van Vleck-Weisskopf formalism at the two shortest wavelengths, but not at the longest. These results have been incorporated into a radiative transfer model in order to infer an abundance profile for gaseous SO2 in Venus' middle atmosphere, and are also used to ascertain the effects of a SO2/CO2 gaseous mixture on the mm-wavelength spectrum of Venus.

Fahd, Antoine K.↗