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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 775 records · Page 43
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

A class of optically controlled millimeter wave devices

Three specific devices were investigated: the sheet resistance device, the Schottky-barrier diode and the PIN diode. Several sheet resistance devices were fabricated and tested. Based on the encouraging results from these devices, a mask was designed and sent to a vendor and is expected to be received very soon. A set of masks for fabricating transparent cathode Schottky-barrier diodes was designed. These masks were given to NASA Goddard Space Flight Center for fabrication of the diodes. A mask set was designed to fabricate PIN diodes with transparent electrodes. With slight modifications, the same mask set also can be used to fabricate other devices, such as MESFET and the IMPATT diode.

Chowdhary, R.↗
NASA NTRS1985

A map of the cosmic background radiation at 3 millimeters

Data from a series of balloon flights covering both the Northern and Southern Hemispheres, measuring the large angular scale anisotropy in the cosmic background radiation at 3.3 mm wavelength are presented. The data cover 85 percent of the sky to a limiting sensitivity of 0.7 mK per 7 deg field of view. The data show a 50-sigma (statistical error only) dipole anisotropy with an amplitude of 3.44 + or - 0.17 mK and a direction of alpha = 11.2 h + or - 0.1 h, and delta = -6.0 deg + or - 1.5 deg. A 90 percent confidence level upper limit of 0.00007 is obtained for the rms quadrupole amplitude. Flights separated by 6 months show the motion of earth around the sun. Galactic contamination is very small, with less than 0.1 mK contribution to the dipole quadrupole terms. A map of the sky has been generated from the data.

Lubin, P.↗
NASA NTRS1985

Submillimeter and millimeter wave characterization of absorbing materials

Several microwave absorbers have been characterized in terms of transmittance and reflectance at frequencies between 35 GHz and 3 THz. The materials studied were a series of iron-loaded cast epoxy absorbers known as Eccosorb. Measurements show that reflectance and absorption coefficient increase with the iron density. A dramatic decrease, by as much as a factor of 2, in absorption coefficient was observed when the samples were cooled from ambient to cryogenic temperatures. A blackbody calibrator to be operated at liquid helium temperature was constructed using the measured optical constants for these absorbers. The measured absorption coefficient for cold Eccosorb CR-110 is within 20 percent of that reported recently by Peterson and Richards.

Hemmati, H.↗
NASA NTRS1986

Submillimeter and millimeter observations of Jupiter

Using absolute calibrations referenced to Mars, narrowband photometry has been obtained for the Jovian disk in ten passbands covering the 0.35-3.3 mm wavelength range. Existing atmospheric temperature structure and composition constraints are taken as the context for an analysis of the derived brightness temperature spectrum. Results obtained for the 0.35-0.45 mm range are noted to suggest that radiances can be matched by models which include NH3 ice particles of 30-100 micron size. A 5-percent increase of the absolute calibration scale would yield results well fitted by a clear atmosphere model, obviating the supposition of additional Jovian atmosphere absorption.

Griffin, M. J.↗
NASA NTRS1985

Design, fabrication, and performance of a whiskerless Schottky diode for millimeter and submillimeter wave applications

Design considerations, fabrication techniques, and performance predictions are presented for a planar whiskerless Schottky diode to be used (in radio astronomy applications) at 100-300 GHz. The anode and ohmic contacts are on the same side of the device, and proton bombardment is used to establish the divided surface (by making some regions of the GaAs wafer semiinsulating) prior to definition of a B-doped SiO2 finger, ohmic contacting, anode formation, and anode contact metallization (all using photolithographic techniques). The contributions of parasitic elements are calculated for a device with a 3.5-micron-deep n(+) layer doped at 2 x 10 to the 18th/cu cm, a 250-nm-thick epitaxial layer doped at 5 x 10 to the 16th/cu cm, and a 1-micron-radius anode (providing zero-bias junction capacitance 7 fE). It is predicted that such a device would have total series resistance 12.58 ohm and total shunt capacitance 1.37 fF, compared with 14.27 ohm and 0.93 fF for the corresponding whiskered device.

Mckinney, K.↗
NASA NTRS1985

An upward looking airborne millimeter wave radiometer for atmospheric water vapor sounding and rain detection

A 90/180 GHz multichannel radiometer is currently under development for NASA's 1985 Hurricane Mission onboard the Convair 990 research aircraft. The radiometer will be a fixed beam instrument with dual corrugated horns and a common lens antenna designed to operate simultaneously at 90 and 180 GHz. The all solid state front-end will contain three double side band data channels at 90 + or - 3 GHz, 180 + or - 3 GHz, and 180 + or - 7 GHz. The airborne radiometer will mount in a window port on the CV-990 and will maintain a fixed beam view approximately 14 degrees off zenith. The radiometer design is a Dicke chopper arrangement selected to achieve maximum absolute temperature accuracy and minimum brightness temperature sensitivity. Analog outputs of the three data channels will be calibrated dc voltages representing the observed radiometric brightness temperatures over the selected integration time.

Gagliano, J. A.↗
NASA NTRS1987

Millimeter-wave imaging sensor data evaluation

A passive 3-mm radiometer system with a mechanically scanned antenna was built for use on a small aircraft or an Unmanned Aerial Vehicle to produce real near-real-time, moderate-resolution (0.5) images of the ground. One of the main advantages of this passive imaging sensor is that it is able to provide surveillance information through dust, smoke, fog and clouds when visual and IR systems are unusable. It can also be used for a variety of remote sensing applications, such as measurements of surface moisture, surface temperature, vegetation extent and snow cover. It is also possible to detect reflective objects under vegetation cover.

Wilson, William J.↗
NASA NTRS1986

Complex dielectric constants for selected near-millimeter-wave materials at 245 GHz

A double-beam instrument developed in this laboratory has been used to measure the complex dielectric constant of selected materials at 245 GHz. It is reported here the results for crystalline quartz, fused silica (Spectrosil WF and Dynasil 4000), beryllia (iso-pressed), boron nitride (hot-pressed), and a nickel ferrite (Trans-Tech 2-111). Results are compared with the data obtained by other researchers.

Dutta, J. M.↗
NASA NTRS1986

A search for the millimeter-wave transitions of CO(+) in Comet P/Halley

Although no detection was obtained in the present search for the N = 2-1, J = 5/2-3/2, and J = 3/2-1/2 mm-wave transitions of CO(+) in Comet P/Halley, a 2-sigma upper limit of 8 x 10 to the 11th/sq cm was determined for the beam-averaged column density of this specie. Upon comparison of this upper limit estimate with model predictions involving the variation of such parameters as the chemical composition and ionization mechanisms, it appears that H2O may be the main nucleus constituent of the comet. If, in addition, photodissociation ionization is active in the coma, then the origin of the CO(+) is more likely to be in CO2 than in CO.

Baum, S.↗
NASA NTRS1987

Millimeter-band oscillations based on resonant tunneling in a double-barrier diode at room temperature

A double-barrier diode at room temperature has yielded oscillations with fundamental frequencies up to 56 GHz and second harmonics up to 87 GHz. The output powers at these frequencies were about 60 and 18 microW, respectively. These results are attributed to a recent improvement in the material parameters of the device and to the integration of the device into a waveguide resonator. The most successful diode to date has thin (about 1.5 nm) AlAs barriers, a 4.5-nm-wide GaAs quantum well, and 2 x 10 to the 17th/cu cm doping concentration in the n-GaAs outside the barriers. This particular diode is expected to oscillate at frequencies higher than those achieved by any reported p-n tunnel diode.

Brown, E. R.↗
NASA NTRS1987

Observation of millimeter-wave oscillations from resonant tunneling diodes and some theoretical considerations of ultimate frequency limits

Recent observations of oscillation frequencies up to 56 GHz in resonant tunneling structures are discussed in relation to calculations by several authors of the ultimate frequency limits of these devices. It is found that calculations relying on the Wentzel-Kramers-Brillouin (WKB) approximation give limits well below the observed oscillation frequencies. Two other techniques for calculating the upper frequency limit were found to give more reasonable results. One method employs the solution of the time-dependent Schroedinger equation obtained by Kundrotas and Dargys (1986); the other uses the energy width of the transmission function for electrons through the double-barrier structure. This last technique is believed to be the most accurate since it is based on general results for the lifetime of any resonant state. It gives frequency limits on the order of 1 THz for two recently fabricated structures. It appears that the primary limitation of the oscillation frequency for double-barrier resonant-tunneling diodes is imposed by intrinsic device circuit parameters and by the transit time of the depletion layer rather than by time delays encountered in the double-barrier region.

Sollner, T. C. L. G.↗
NASA NTRS1988

Millimeter-Wave Radiometer Imager

A 3-mm radiometer system with mechanically scanned antenna built for use on small aircraft or helicopter to produce near-real-time moderate-resolution images of ground. Main advantage of passive imaging sensor able to provide information through clouds, smoke, and dust when visual and infrared (IR) systems unusable. Used also for variety of remote-sensing applications such as measurements of surface moisture, snow cover, vegetation type and extent, mineral type and extent, surface temperature, and thermal inertia. Possible to map fires and volcanic lava flows through obscuring clouds and smoke.

Wilson, W. J.↗
NASA NTRS1987

Broad-band properties of the CfA Seyfert Galaxies. II - Infrared to millimeter properties

IR and mm observations of the 48 Seyfert 1 and 2 galaxies (SG1s and SG2s) of the CfA sample (Huchra and Berg, 1987) are reported. Data obtained (1) in the NIR using the 1.55-m reflector at Stewart Observatory and the 3-m IRTF during 1984-1986, (2) in the FIR with IRAS, and (3) at 1.3 mm using the 12-m NRAO telescope at KPNO in June 1984 are presented in extensive tables and graphs and characterized in detail. None of the objects was detected at 1.3 mm, and the IR spectra of the SG2s are found to be significantly steeper (indicating thermal emission) than those of SG1s and QSOs (nonthermal emission). Turnover in the IR emission below 100 microns (in half of the objects detected at three or more IRAS wavelengths) is shown to be consistent with an accretion disk in dust-free SG1s and with unusually warm (35-65 K) dust in SG2s. It is inferred that a 60-100-micron cool excess is masking turnover in the other SGs, so that a general association of SG nuclei with strong star formation can be confirmed.

Edelson, R. A.↗
NASA NTRS1988

Millimeter-wave diode-grid phase shifters

Monolithic diode grids have been fabricated on 2-cm square gallium-arsenide wafers with 1600 Schottky-barrier varactor diodes. Shorted diodes are detected with a liquid-crystal technique, and the bad diodes are removed with an ultrasonic probe. A small-aperture reflectometer that uses wavefront division interference was developed to measure the reflection coefficient of the grids. A phase shift of 70 deg with a 7-dB loss was obtained at 93 GHz when the bias on the diode grid was changed from -3 V to 1 V. A simple transmission-line grid model, together with the measured low-frequency parameters for the diodes, was shown to predict the measured performance over the entire capacitive bias range of the diodes, as well as over the complete reactive tuning range provided by a reflector behind the grid, and over a wide range of frequencies from 33 GHz to 141 GHz. This shows that the transmission-line model and the measured low-frequency diode parameters can be used to design an electronic beam-steering array and to predict its performance. An electronic beam-steering array made of a pair of grids using state-of-the-art diodes with 5-ohm series resistances would have a loss of 1.4 dB at 90 GHz.

Lam, Wayne W.↗
NASA NTRS1988

Noise tube sources for the far IR and millimeter region

The radiant output of a noise tube designed for the 90-140-GHz (3.3-2.1-mm) frequency range has been compared with that from mercury lamps over the wavelength region from 0.4 to about 6 mm. Lamellar grating and Michelson Fourier transform spectrometers were used in conjunction with He cooled bolometers of NEP from 10 to the -12th to 10 to the -14th W/sq rt H2 to measure relative spectral irradiance. With this instrumental arrangement, the radiant power emitted by the noise tube was observed to be less than that from a mercury lamp, at least to a 3-mm wavelength, but it produced less source noise than an ac operated mercury lamp. When the noise tube operating current was reduced, the spectral irradiance peak shifted to longer wavelengths.

Moller, K. D.↗
NASA NTRS1988

Microwave and millimeter-wave power generation in silicon carbide avalanche devices

Numerical simulations were performed to investigate the typical power-generating capabilities of SiC IMPATT diodes. Using available material parameters, SiC double-drift IMPATT diodes were simulated at 10, 35, 60, and 94 GHz, and the operating characteristics of these devices were compared to those of Si and GaAs devices. Compared to the Si and GaAs IMPATT performances in the pulsed mode, the SiC IMPATT performance was found to be far superior. The performance of SiC devices in the CW mode was also superior to that of GaAs devices, especially at lower frequencies. At a high frequency (94 GHz), the performance of the SiC device was found to be comparable to that of Si devices.

Mehdi, I.↗
NASA NTRS1988

Microwave and millimeter-wave resonant-tunneling devices

Resonant-tunneling devices in microelectronic component form, whose structure is the electron analog of a Fabry-Perot resonator, encompass oscillators, self-oscillating mixers, and harmonic multipliers. The negative differential resistance characteristic of these devices has been obtained at room temperature, and resonant-tunneling transistors capable of operation in the THz-frequency range appear to be feasible. Three-terminal resonant-tunneling device development is in its infancy, as is that of devices for digital applications.

Sollner, T. C. L. Gerhard↗