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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Research in millimeter wave techniques

During the past six months, efforts on this project have been devoted to: (1) continuation of construction and testing of a 6 GHz subharmonic mixer model with extension of the pumping frequency of this mixer to omega sub s/4, (2) construction of a 183 GHz subharmonic mixer based on the results of tests on this 6 GHz model, (3) ground-based radiometric measurements at 183 GHz, (4) fabrication and testing of wire grid interferometers, (5) calculations of reflected and lost power in these interferometers, and (6) calculations of the antenna temperature due to water vapor to be expected in down-looking radiometry as a function of frequency. Significant events during the past six months include: (1) Receipt of a 183 GHz single-ended fundamental mixer, (2) attainment of 6 db single sideband conversion loss with the 6 GHz subharmonic mixer model by using a 1.5 GHz (omega sub s/4) pump frequency, (3) additional ground-based radiometric measurements and (4) derivation of equations for reflection and loss for wire grid interferometers.

Mcmillan, R. W.↗
NASA NTRS1978

Millimeter wave propagation modeling of inhomogeneous rain media for satellite communications systems

A theoretical propagation model that represents the scattering properties of an inhomogeneous rain often found on a satellite communications link is presented. The model includes the scattering effects of an arbitrary distribution of particle type (rain or ice), particle shape, particle size, and particle orientation within a given rain cell. An associated rain propagation prediction program predicts attenuation, isolation and phase shift as a function of ground rain rate. A frequency independent synthetic storm algorithm is presented that models nonuniform rain rates present on a satellite link. Antenna effects are included along with a discussion of rain reciprocity. The model is verified using the latest available multiple frequency data from the CTS and COMSTAR satellites. The data covers a wide range of frequencies, elevation angles, and ground site locations.

Persinger, R. R.↗
NASA NTRS1978

The phase of the crosspolarized signal generated by millimeter wave propagation through rain

Proposed schemes for cancelling rain-induced crosstalk in dual-polarized communications systems depend upon the phase relationships between the wanted and unwanted signals. This report investigates the phase relationship of the rain-generated crosspolarized signal relative to the copolarized signal. Theoretical results obtained from a commonly accepted propagation model are presented. Experimental data from the Communications Technology Satellite beacon and from the Comstar beacon are presented and the correlation between theory and data is discussed. An inexpensive semi-adaptive cancellation system is proposed and its performance expectations are presented. The implications of phase variations on a cancellation system are also discussed.

Overstreet, W. P.↗
NASA NTRS1977

Infrared and millimeter wave techniques for the Cosmic Background Explorer Satellite

The Cosmic Background Explorer Satellite will employ infrared and microwave techniques to gain information about the very early universe. Three instruments will cover the spectral range from 8 microns to 13 mm, determining both the spectrum and angular distribution of the large scale background radiation fields. A cryogenic polarizing Michelson interferometric spectrometer will measure the spectrum of the 3 deg K relic radiation from the big bang with precision. Four differential microwave radiometers will map the sky from 23 to 90 GHz in a search for anisotropy of the universe. A broadband cryogenic IR photometer will map zodiacal dust emission, galactic dust, and an extragalactic residual component.

Mather, J. C.↗
NASA NTRS1979

Research in millimeter wave techniques

The following technical developments are described: (1) a reliable 183 GHz subharmonic mixer, (2) a precision noise figure test setup, (3) the successful deposition of SiO2 on a noncontacting backshort, and (4) sturdier whisker points used for diode contacting.

Forsythe, R. E.↗
NASA NTRS1978

Progress on millimeter wave Josephson junction mixers

Preset, recyclable Nb point contacts are tested as low-noise Josephson mixers at a signal frequency of 115 GHz. The best result achieved is a mixer noise temperature (single sideband) of 120 K with unity conversion efficiency (SSB) for a junction at 6 K. Variation of mixer properties with temperature and other parameters is presented.

Taur, Y.↗
NASA NTRS1981

Ice/frost detection using millimeter wave radiometry

A series of ice detection tests was performed on the shuttle external tank (ET) and on ET target samples using a 35/95 GHz instrumentation radiometer. Ice was formed using liquid nitrogen and water spray inside a test enclosure containing ET spray on foam insulation samples. During cryogenic fueling operations prior to the shuttle orbiter engine firing tests, ice was formed with freon and water over a one meter square section of the ET LOX tank. Data analysis was performed on the ice signatures, collected by the radiometer, using Georgia Tech computing facilities. Data analysis technique developed include: ice signature images of scanned ET target; pixel temperature contour plots; time correlation of target data with ice present versus no ice formation; and ice signature radiometric temperature statistical data, i.e., mean, variance, and standard deviation.

Gagliano, J. A.↗
NASA NTRS1981

Near millimeter wave bandpass filters

The properties of bandpass filters for broadband photometry are reported in the 3-12/cm frequency range. The filters are based on a combination of capacitive grids deposited on thick Mylar substrates and are designed to have very high out-of-band rejection. Low frequencies are blocked by a thick grill that consists of a hexagonal grid of circular holes in a thick metal plate.

Timusk, T.↗
NASA NTRS1980

Advanced millimeter wave imaging systems

Unique techniques are being utilized to develop self-contained imaging radiometers operating at single and multiple frequencies near 35, 95 and 183 GHz. These techniques include medium to large antennas for high spatial resolution, lowloss open structures for RF confinemnt and calibration, wide bandwidths for good sensitivity plus total automation of the unit operation and data collection. Applications include: detection of severe storms, imaging of motor vehicles, and the remote sensing of changes in material properties.

Schuchardt, J. M.↗
NASA NTRS1982

Research in millimeter wave techniques

Subharmonically pumped mixers were ascended and tested. A computerized version of the automatic noise figure measurement system was developed. Impedance matching techniques suitable for these types of mixers were investigated. Narrow and broadband (one octave) matching networks for the subharmonic mixers were designed. The automatic mixer noise figure test facility was completed. Subharmonic mixers and the systems that use them at 183 and 220 GHz were evaluated and characterized.

Forsythe, R. E.↗
NASA NTRS1983

Millimeter-wave studies of the surfaces of Mercury and Mars and the atmosphere of Venus

Disk average brightness temperatures of Mercury were obtained using a 4.6 m radio telescopes. The data was searched for periodicities which correlate with phase angle, hermocentric longitude and beat frequencies produced by modulations of various celestial mechanical parameters. Spectral line observations were made of Venus with the NRAO 11 m radio telescope. The total CO content and the CO vertical profile, and their variability were observed. Large scale thermophysical properties of the surface of Mars were studied.

Epstein, E. E.↗
NASA NTRS1982

Centimeter and millimeter wave attenuation and brightness temperature due to atmospheric oxygen and water vapor

Calculations are presented for atmospheric absorption and radiation emission for several atmospheric conditions and elevation angles. The calculations are for frequencies in the 1 to 340 GHz frequency range. The calculations are compared to those from other models. Agreement is found to within 15% for absorption coefficient (7.5 g/m/cubed water vapor at 290 K) and approximately the same for total zenithal attenuation. The attenuation and gaseous emission noise curves defined by the International Radio Consultative Committee are found to have minor inconsistencies.

Smith, E. K.↗