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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Aircraft-based radiometric imaging of tropospheric temperature and precipitation using the 118.75-GHz oxygen resonance

Passive microwave imaging of O2 emissions using the 118.75-GHz resonance has been investigated for tropospheric and stratospheric remote sensing of atmospheric temperature and precipitation. An imaging millimeter-wave spectrometer (MTS) using eight double-sideband channels centered around the 118.75-GHz resonance, and including a fixed-beam 53.65-GHz radiometer and video camera was constructed. The MTS collected data during 33 flights of the NASA-ER-2 high-altitude aircraft in 1986 during GALE and Cohmex, yielding the first high-spatial-resolution microwave images of atmospheric O2 brightness. The isolated 118-GHz line offers higher spatial resolution and precipitation sensitivity than O2 lines in the 5-mm band near 60 GHz. The brightness temperature perturbations of clouds in nonprecipitating regions are typically twice as large in the 118-GHz channels. However, observations over cirrus anvils show that the 118-GHz brightnesses are not adversely sensitive to some optically opaque cloud cover. Thus these channels are expected to be useful for temperature sounding in the presence of clouds, although retrieval ambiguities can result from variations in the water-vapor profile and surface emissivity.

Gasiewski, A. J.↗
NASA NTRS1990

The molecular spiral arms of NGC 6946

High resolution observations of molecules in external galaxies are essential to understanding physical processes leading to the formation of stars. One question is whether there is a spiral structure in the molecular gas, but it was not possible to resolve the spiral arms of external galaxies until the advent of large millimeter-wave telescopes. With the Institute for Radio Astronomy in the Millimeter Range (IRAM) 30 m telescope, researchers are carrying through the mapping of NGC 6946 in the CO-12(1-0) and (2-1) lines. This galaxy is a large, gas-rich Scd spiral with a strong star formation activity. NGC 6946 is well studied at radio and optical wavelengths, so that it is possible to compare the location of the spiral arms tracers: HI ridge, HII regions and molecular clouds. The disk CO emission is very contrasted (no lines for some positions, 1 K in CO(1-0) for some others) and correlated with the optical spiral arms: this clearly shows up in a figure which presents superimposed contours of CO(2-1) integrated emissivity and of H alpha line emission. The agreement is very good, and there is no displacement across the arm between the CO, HI and H alpha ridges of emission. The arms are barely resolved by the 23 inch beam and the molecular contrast averaged over the map is about 4. The CO(2-1) maxima are closer to the position of the HII regions than those of CO(1-0), which could be due to variations of excitation conditions. The CO excitation in the disk of NGC 6946 is low: when all data are convolved to the same resolution of 23 inches the CO(2-1) lines are about 0.45 times fainter than the CO(1-0) ones, while in the nucleus they have roughly the same intensity. This suggests that in the disk of NGC 6946 most of the CO emission comes from cold optically thick gas located in cloud envelopes rather than from cloud cores. The molecular and atomic component in the observed regions of NGC 6946 seems to be organized in large gaseous complexes.

Casoli, F.↗
NASA NTRS1991

Comparative study of bolometric and non-bolometric switching elements for microwave phase shifters

The performance of semiconductor and high critical temperature superconductor switches is compared as they are used in delay-line-type microwave and millimeter-wave phase shifters. Such factors as their ratios of the off-to-on resistances, parasitic reactances, power consumption, speed, input-to-output isolation, ease of fabrication, and physical dimensions are compared. Owing to their almost infinite off-to-on resistance ratio and excellent input-to-output isolation, bolometric superconducting switches appear to be quite suitable for use in microwave phase shifters; their only drawbacks are their speed and size. The SUPERFET, a novel device whose operation is based on the electric field effect in high critical temperature ceramic superconductors is also discussed. Preliminary results indicate that the SUPERFET is fast and that it can be scaled; therefore, it can be fabricated with dimensions comparable to semiconductor field-effect transistors.

Tabib-Azar, Massood↗
NASA NTRS1991

Integrated 222-GHz corner-reflector antennas

A high-gain monolithic millimeter-wave antenna has been designed, fabricated, and tested at 222 GHz. 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 new traveling-wave antenna design yields a wideband input impedance and a low cross-polarization component in the E- and quasi-H-plane patterns. A directivity of 17.7 dB and a main-beam efficiency of 88.5 percent are calculated from the 222-GHz pattern measurements. The integrated corner-reflector antenna is well suited for millimeter- and submillimeter-wave imaging applications in large f-number systems.

Gearhart, Steven S.↗
NASA NTRS1991

Electron densities and the excitation of CN in molecular clouds

In molecular clouds of modest density and relatively high fractional ionization, the rotational excitation of CN is controlled by a competition among electron impact, neutral impact and the interaction with the cosmic background radiation. The degree of excitation can be measured through optical absorption lines and millimeter-wave emission lines. The available, accurate data on CN in diffuse and translucent molecular clouds are assembled and used to determine electron densities. The derived values, n(e) = roughly 0.02 - 0.5/cu cm, imply modest neutral densities, which generally agree well with determinations by other techniques. The absorption- and emission-line measurements of CN both exclude densities higher than n(H2) = roughly 10 exp 3.5/cu cm on scales varying from 0.001 to 60 arcsec in these clouds.

Black, John H.↗
NASA NTRS1991

Thin-film power-density meter for millimeter wavelengths

A quasi-optical power density meter for millimeter and submillimeter wavelengths has been developed. The device is a 2-cm2 thin-film bismuth bolometer deposited on a mylar membrane. The resistance responsivity is 150 Ohms/W, and the time constant is 1 min. The meter is calibrated at DC. The bolometer is much thinner than a wavelength, and can thus be modeled as a lumped resistance in a transmission-line equivalent circuit. The absorption coefficient is 0.5 for 189-Ohms/square film. The power-density meter has been used to measure absolute power densities for millimeter-wave antenna efficiency measurements. Absolute power densities of 0.5 mW/sq cm have been measured to an estimated accuracy of 5 percent.

Lee, Karen A.↗
NASA NTRS1991

High temperature superconductivity space experiment (HTSSE)

An experiment dealing with high-temperature superconducting devices and components in space is discussed. A variety of devices (primarily passive microwave and millimeter-wave components) has been procured and will be integrated with a cryogenic refrigerating and data acquisition system to form the space package, which will be launched in late 1992. This space experiment is expected to demonstrate that this technology is sufficiently robust to survive the space environment and that the technology has the potential to improve the operation of space systems significantly. The devices for the initial launch have been evaluated electrically, thermally, and mechanically, and will be integrated into the final space package early in 1991. The performance of the devices is summarized, and some potential applications of this technology in space systems are outlined.

Ritter, J. C.↗
NASA NTRS1991

Performance of NbN superconductive tunnel junctions as SIS mixers at 205 GHz

Small area (less than 1 sq micron), high-current-density NbN/MgO/NbN tunnel junctions with I-V characteristics suitable for high-frequency mixers have been fabricated. Mesa-geometry junctions with an area of about 1 sq micron and critical current density of 5-10 kA/sq cm are integrated with superconducting microstrip lines designed to resonate out the junction capacitance. A study was made of the mixer gain and noise performance near 205 GHz as a function of the inductance provided by the microstrip line. This has confirmed, at a high millimeter-wave frequency, values of junction capacitance of 85 fF/sq micron and recently measured values of a magnetic penetration depth of 380 nm. Mixer noise temperatures as low as 134 K at 1.5 K have been obtained for properly tuned junctions. A significant improvement in mixer performance on cooling from 4.2 K to 1.5 K was observed. Edge-geometry junctions with an area of 0.3 sq microns and critical current density of 18-25 kA/sq cm have also been fabricated. These junctions give a mixer noise temperature of 145 K at 4.2 K without the use of integrated tuning elements. These are the best results ever achieved for NbN-based SIS mixers.

Mcgrath, W. R.↗
NASA NTRS1991

Measurement of self-broadening of the ozone nu(3) transitions

Self-broadening coefficients have been measured for a number of rovibrational lines in the nu(3) band of ozone, in the frequency range 1015-1058/cm, with J values between 0 and 27, and over a range of K(a) values. A multiparameter nonlinear least-squares fitting procedure is used to reduce the data, and the sensitivity of the procedure to instrument line width, weak satellite features, and absolute intensity has been examined. The retrieved coefficients are compared with millimeter-wave broadening coefficients, direclty measured rotational relaxation times, and recently suggested empirical representations.

Flannery, C.↗
NASA NTRS1991

Integrated 119-micron linear corner-cube array

An integrated corner-cube antenna has been designed, fabricated, and measured at 119 microns. The structure consists of a traveling-wave antenna integrated on a 1-micron dielectric membrane and suspended in a longitudinal cavity etched in silicon wafers. The patterns at 119 microns agree well with millimeter-wave patterns measured on a scaled antenna at 222 GHz. A directivity of 18 +/- 0.5 dB is calculated from E- and H-plane measurements. This work demonstrates that high-efficiency integrated corner-cube antennas are easily scalable to terahertz frequencies and could be used for radio-astronomical and plasma-diagnostic applications.

Gearhart, Steven S.↗
NASA NTRS1991

A 29.3-GHz cavity-enclosed aperture-coupled circular-patch antenna for microwave circuit integration

A circular patch antenna fed by an aperture-coupled microstrip line has been demonstrated at 29.3 GHz. The patch was enclosed by a cavity to reduce surface-wave interactions in an array environment and to improve heat dissipation when using active devices. The antenna exhibited a 2:1 input VSWR (voltage standing wave ratio) over a bandwidth of 12 percent from 27.52 to 30.95 GHz. The antenna should have applications in conformal phased arrays at millimeter-wave frequencies.

Navarro, Julio A.↗
NASA NTRS1991

An infrared companion to Z Canis Majoris

New near-infrared speckle observations of Z CMa reveal it to be a double star with a separation 0.1 arcsec at P.A. 120 deg. The northwest component is an infrared object whose broadband spectrum is reminiscent of the infrared companions to several T Tauri stars. The southeast component has the spectral energy distribution expected for a circumstellar disk whose luminosity is dominated by gravitational accretion. The far-infrared and millimeter-wave photometric fluxes suggest the presence of a massive second disk large enough to surround both components; this may be the reservoir from which the material accreted by the first disk is drawn.

Koresko, Chris D.↗
NASA NTRS1991

Demonstration of microwave power transmission in space

Three experiments are proposed to demonstrate the feasibility of converting dc power into microwave or millimeter-wave beam and transmitting it to users through free space. The generator could be located on earth or on a utility power satellite. The received power would be converted back into dc or ac power. The success of the experiments could lead to the commercial use of this technology.

Chang, K.↗
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 NTRS1990

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

Measurements are reported of the millimeter-wave surface resistance of grain-aligned YBa2Cu3O(x) bulk material grown by a liquid-phase process. The measurements were performed by replacing the endplate of a TE(011) 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. For the parallel configuration, the surface resistance at 77 K and 80 GHz is given. 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 derived at 88 K. The effect of microstructure on surface resistance is discussed.

Wosik, J.↗
NASA NTRS1991

Mixed application MMIC technologies - Progress in combining RF, digital and photonic circuits

Approaches for future 'mixed application' monolithic integrated circuits (ICs) employing optical receive/transmit, RF amplification and modulation and digital control functions are discussed. We focus on compatibility of the photonic component fabrication with conventional RF and digital IC technologies. Recent progress at Honeywell in integrating several parts of the desired RF/digital/photonic circuit integration suite required for construction of a future millimeter-wave optically-controlled phased-array element are illustrated.

Swirhun, S.↗
NASA NTRS1991

Phase shifter technology assessment - Prospects and applications

Capabilities and limitations of MMIC phase shifter technology at microwave and millimeter wave frequencies are reviewed. MMIC-based phase arrays make it possible to integrate active elements at the array face, i.e., to incorporate transmit power amplifiers and/or low noise amplifiers at each antenna element. Active elements make it possible to increase power efficiency and reliability and provide graceful degradation. Monolithic integration of the various transmit/receive functions including phase shifting is considered to be feasible through at least the lower millimeter-wave frequency range (about 30-100 GHz). MMIC integration also allows more flexibility in array design including those that are intended for airborne conformal applications.

Sokolov, Vladimir↗
NASA NTRS1991

Comparative study of bolometric and non-bolometric switching elements for microwave phase shifters

The performance of semiconductor and high critical temperature superconductor switches is compared as they are used in delay-line-type microwave and millimeter-wave phase shifters. Such factors as their ratios of the off-to-on resistances, parasitic reactances, power consumption, speed, input-to-output isolation, ease of fabrication, and physical dimensions are compared. Owing to their almost infinite off-to-on resistance ratio and excellent input-to-output isolation, bolometric superconducting switches appear to be quite suitable for use in microwave phase shifters; their only drawbacks are their speed and size. The SUPERFET, a novel device whose operation is based on the electric field effect in high critical temperature ceramic superconductors is also discussed. Preliminary results indicate that the SUPERFET is fast and that it can be scaled; therefore, it can be fabricated with dimensions comparable to semiconductor field-effect transistors.

Tabib-Azar, Massood↗