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NASA NTRS1986

Dc and microwave characteristics of a high current double interface GaAs/InGaAs/AlGaAs pseudomorphic modulation-doped field-effect transistor

Extremely large current double interface GaAs/In(0.15)Ga(0.85)As/Al(0.15)Ga(0.85)As pseudomorphic modulation-doped field-effect transistors (MODFET's) grown by molecular beam epitaxy were achieved. The 1-micron gate devices studied have peak current levels (430 mA/mm at 300 K and 483mA/mm at 77 K) roughly one and a half to two times that found in single interface pseudomorphic MODFET's. These devices also retain high transconductances over a broad range of gate voltage, peaking at 312 mS/mm at 300 K and 362 mS/mm at 77 K. Excellent microwave performance is also obtained with a maximum frequency of oscillation (f-max) of 37 GHz and a current gain cut-off frequency of as high as 23 GHz at 300 K. An output power level of 14 dBm (1 dB gain compression) was obtained at 6 GHz for a 290-micron gate width. This double interface single quantum well MODFET may be of great importance in millimeter wave power amplifiers.

Henderson, T.↗

NASA NTRS1977

Research in millimeter wave techniques

The following is investigated; (1) the design of a 183 GHz single ended fundamental mixer to serve as a back up mixer to the subharmonic mixer for airborne applications, (2) attainment of 6 db single sideband conversion loss with the 6 GHz subharmonic mixer model, together with initial tests to determine the feasibility of pumping the mixer at w sub s/4, (3) additional ground based radiometric measurements, and (4) derivation of equations for power transmission of wire grid interferometers, and initial tests to verify these equations.

Mcmillan, R. W.↗

NASA NTRS1975

The GSFC 20 and 30 GHz millimeter wave propagation experiment

The Goddard Space Flight Center Millimeter Wave Experiment (MWE) aboard ATS-6, designed to evaluate the propagation characteristics of earth-space communications links at 20 and 30 GHz, is outlined, and the major results to date are presented. The 20 and 30 GHz transmitters operate through spot beam or continental coverage antenna systems. The transmitted signals consist of 9 tones spaced out to 1440 MHz. A communications link 6 GHz up and 20 or 30 GHz down is provided. Attenuation ratio measurements between the 20 and 30 GHz links indicate values higher than those predicted. Clear sky scintillations have been observed with spectral components up to about 50 Hz. Observations of rain depolarization indicate that attenuation effects predominate over depolarization effects in frequency re-use communications systems in the 20 GHz region. Various methods of predicting path attenuation are under investigation.

Ippolito, L. J.↗

NASA NTRS2007

RF Performance of Membrane Aperture Shells

This paper provides an overview of recent results establishing the suitability of Membrane Aperture Shell Technology (MAST) for Radio Frequency (RF) applications. These single surface shells are capable of maintaining their figure with no preload or pressurization and minimal boundary support, yet can be compactly roll stowed and passively self deploy. As such, they are a promising technology for enabling a future generation of RF apertures. In this paper, we review recent experimental and numerical results quantifying suitable RF performance. It is shown that candidate materials possess metallic coatings with sufficiently low surface roughness and that these materials can be efficiently fabricated into RF relevant doubly curved shapes. A numerical justification for using a reflectivity metric, as opposed to the more standard RF designer metric of skin depth, is presented and the resulting ability to use relatively thin coating thickness is experimentally validated with material sample tests. The validity of these independent film sample measurements are then confirmed through experimental results measuring RF performance for reasonable sized doubly curved apertures. Currently available best results are 22 dBi gain at 3 GHz (S-Band) for a 0.5m aperture tested in prime focus mode, 28dBi gain for the same antenna in the C-Band (4 to 6 GHz), and 36.8dBi for a smaller 0.25m antenna tested at 32 GHz in the Ka-Band. RF range test results for a segmented aperture (one possible scaling approach) are shown as well. Measured antenna system actual efficiencies (relative to the unachievable) ideal for these on axis tests are generally quite good, typically ranging from 50 to 90%.

Flint, Eirc M.↗

NASA NTRS1992

SO in starburst galaxies

The use of SO and SO2 as probes of the dense interstellar medium in the nearby starburst galaxies NGC 253 and M82 is described. Emission in the 99.3 GHz 3(2) - 2(1) rotational transition of SO was detected in NGC 253 and possibly in M82, and upper limits are reported for emission in the 219.9 GHz 6(5) - 5(4) transition of SO and two lines of SO2. The column density of SO relative to carbon sulfide, CS, is more than 0.08 in NGC 253, a value not much lower than Galactic ratios and consistent with models of dense interstellar clouds with a fractional abundance of atomic oxgyen greater than about 10 exp -7. The 218.8 GHz 3(21) - 2(20) transition of para-formaldehyde, with an excitation temperature of 68 K, was also detected in NGC 253.

Petuchowski, S. J.↗

NASA NTRS1982

A tutorial assessment of atmospheric height uncertainties for high-precision satellite altimeter missions to monitor ocean currents

Information from a number of sources is synthesized, and an error budget is deduced giving the projected overall height uncertainty correction for a suggested next-generation high-precision radar altimeter. Uncertainties deriving from the wet and dry troposphere, clouds, and the ionosphere are reviewed. It is assumed that the next generation of precision altimeters will be dual-frequency (13.5 and 6 GHz) and will be designed to correct for the ionospheric error. The altimeter-carrying satellite will have a nadir pointing near coincident-beam dual-frequency microwave radiometer for mitigating the wet tropospheric uncertainty. Whereas there are a number of caveats, the combined uncertainty in the height correction due to the atmosphere for the suggested system should be nominally 3 cm rms compared with at least 6 cm associated with the Seasat-A mission. Improvements in height resolution of the kind discussed here are considered vital for future satellite missions designed to monitor ocean currents.

Goldhirsh, J.↗

NASA NTRS2021

The JAGWAR Prowls LIGO/Virgo O3 Paper I: Radio Search of a Possible Multimessenger Counterpart of the Binary Black Hole Merger Candidate S191216ap

We present a sensitive search with the Karl G. Jansky Very Large Array for the radio counterpart of the gravitational wave candidate S191216ap, which is classified as a binary black hole merger and suggested to be a possible multimessenger event, based on the detection of a high-energy neutrino and a TeV photon. We carried out a blind search at C band (4–8 GHz) over 0.3 deg2 of the gamma-ray counterpart of S191216ap reported by the High-Altitude Water Cerenkov Observatory (HAWC). Our search, spanning three epochs over 130 days of postmerger and having a mean source-detection threshold of 75 μJy beam−1 (4σ), yielded five variable sources associated with active galactic nucleus activity and no definitive counterpart of S191216ap. We find <2% (3.0% ± 1.3%) of the persistent radio sources at 6 GHz to be variable on a timescale of <1 week (week–months), consistent with previous radio variability studies. Our 4σ radio luminosity upper limit of ∼1.2 × 1028 erg s−1 Hz−1 on the afterglow of S191216ap, within the HAWC error region, is 5–10 times deeper than previous binary black hole (BBH) radio afterglow searches. Comparing this upper limit with theoretical expectations given by Perna et al. for putative jets launched by BBH mergers, for on-axis jets with energy ≃1049 erg, we can rule out jet opening angles ≲ 20° (assuming that the counterpart lies within the 1σ HAWC region that we observed).

D Bhakta↗

NASA NTRS1971

Spectrum sharing criteria for space and terrestrial systems.

The advent of artificial earth orbiting satellites has added a new dimension to electromagnetic compatibility problems. These new EMC problems arise from the necessity of sharing frequency bands between satellite and terrestrial radio systems. The first such sharing arrangement, sharing between communication satellites and line-of-sight radio relay systems in the 4 and 6 GHz bands, has proved the soundness of the sharing concept under a particular set of circumstances and has encouraged frequency management officials to apply the concept to other functional services. This paper discusses a general sharing analysis procedure and illustrates the application of the procedure by presenting an analysis of the sharing feasibility between the Meteorological Satellite and the terrestrial Meteorological Aids services in the 1670-1700 MHz band.

Friel, F. J.↗

NASA NTRS1975

High-efficiency multifrequency feed

Mutual blockage and mutual coupling are eliminated with multifrequency feed. Feed provides common aperture for 6-GHz and 4-GHz bands and crossed dipole for 1-GHz band. Design is highly efficient and has good polarization diversity.

Ajioka, J. S.↗

NASA NTRS1977

Spectrally efficient modulation

Spectrally efficient modulation, involving the maximization of the transmitted data rate through a specified bandwidth, may aid in alleviating the problem of spectral congestion in the electromagnetic spectrum. Attention is given to pulse-shaping and nonbinary modulation, and particularly to combined amplitude- and phase-modulation. Theoretical performance limits, such as Shannon's bound, are used to assess the effectiveness of the systems described. Consideration is also allotted to spectrally efficient modulation for terrestrial microwave systems, required to provide 1000 voice channels in the 4- and 6-GHz band.

Smith, J. G.↗

NASA NTRS1979

Deployable antenna reflector

The first phase in the development of a solid surface, deployable, antenna reflector is outlined and discussed. The deployment concept is described in conjunction with illustrations and photos of the fabricated reflector models. Details and results of the thermal distortion analysis are presented. Results indicate that the discussed reflector concept is an effective approach in satisfying the requirements for large deployable antennas in the 6 GHz to 100 GHz frequency regime.

Palmer, W. B.↗

NASA NTRS1981

Density measurement in air with a saturable absorbing seed gas

Resonantly enhanced scattering from the iodine molecule is studied experimentally for the purpose of developing a scheme for the measurement of density in a gas dynamic flow. A study of the spectrum of iodine, the collection of saturation data in iodine, and the development of a mathematical model for correlating saturation effects were pursued for a mixture of 0.3 torr iodine in nitrogen and for mixture pressures up to one atmosphere. For the desired pressure range, saturation effects in iodine were found to be too small to be useful in allowing density measurements to be made. The effects of quenching can be reduced by detuning the exciting laser wavelength from the absorption line center of the iodine line used (resonant Raman scattering). The signal was found to be nearly independent of pressure, for pressures up to one atmosphere, when the excitation beam was detuned 6 GHz from line center for an isolated line in iodine. The signal amplitude was found to be nearly equal to the amplitude for fluorescence at atmospheric pressure, which indicates a density measurement scheme is possible.

Baganoff, D.↗

NASA NTRS1979

The effects of geography on spectrum-orbit utilization

With over forty satellites in geostationary orbit, and many more planned, it is becoming increasingly difficult to find suitable orbit positions for new systems operating at 4 and 6 GHz. Efficient spectrum-orbit utilization can be achieved with frequency-reuse techniques - orthogonal polarization, earth-station antenna discrimination, and satellite antenna discrimination - provided that service-area geography is considered. Service arc - that portion of the orbit which affords useful service to all points in a given area - is a function of the area's climate, terrain, and location as well as its size and shape. Of the three techniques, satellite antenna discrimination is the most sensitive to these factors. According to the BSS (broadcasting-satellite service) antenna reference pattern, the maximum discrimination possible is the on-axis gain, which can be as high as 49 dB for a beamwidth of 0.6 degrees, or as low as 32 dB for a 3.5-degree beamwidth. Unlike the Fixed-Satellite Service (FSS), the BSS will normally have beams that cover no more than one or two time zones.

Sawitz, P. H.↗

NASA NTRS1982

Research in space commercialization, technology transfer, and communications

Research and internship programs in technology transfer, space commercialization, and information and communications policy are described. The intern's activities are reviewed. On-campus research involved work on the costs of conventional telephone technology in rural areas, an investigation of the lag between the start of a research and development project and the development of new technology, using NASA patent and patent waiver data, studies of the financial impact and economic prospects of a space operation center, a study of the accuracy of expert forecasts of uncertain quantities and a report on frequency coordination in the fixed and fixed satellite services at 4 and 6 GHz.

Source record↗

NASA NTRS1989

Microwave characteristics of GaAs MMIC integratable optical detectors

Interdigitated photoconductive detectors were fabricated on microwave device structures, making them easily integratable with Monolithic Microwave Integrated Circuits (MMIC). Detector responsivity as high as 2.5 A/W and an external quantum efficiency of 3.81 were measured. Response speed was nearly independent of electrode geometry, and all detectors had usable response at frequencies to 6 GHz. A small signal model of the detectors based on microwave measurements was also developed.

Claspy, Paul C.↗

NASA NTRS1992

Generating Far-Infrared Radiation By Two-Wave Mixing

Far-infrared radiation 1 to 6 GHz generated by two-wave mixing in asymmetrically grown GaAs/AlxGa1-xAs multiple-quantum-well devices. Two near-infrared semiconductor diode lasers phase-locked. Outputs amplified, then combined in semiconductor nonlinear multiple-quantum-well planar waveguide. Necessary to optimize design of device with respect to three factors: high degree of confinement of electromagnetic field in nonlinear medium to maximize power density, phase matching to extend length of zone of interaction between laser beams in non-linear medium, and nonlinear susceptibility. Devices used as tunable local oscillators in heterodyne-detection radiometers.

Borenstain, Shmuel↗

NASA NTRS1995

Radar cross-section measurements and simulation of a tethered satellite. The small expendable deployer system end-mass payload

The first Small Expendable Deployer System (SEDS-1), a tethered satellite system, was developed by NASA and launched March 29, 1993 as a secondary payload on a United State Air Force (USAF) Delta-2 launch vehicle. The SEDS-1 successfully deployed an instrumented end-mass payload (EMP) on a 20-km nonconducting tether from the second stage of the Delta 2. This paper describes the effort of NASA Langley Research Center's Antenna and Microwave Research Branch to provide assistance to the SEDS Investigators Working Group (IWG) in determining EMP dynamics by analyzing the mission radar skin track data. The radar cross section measurements taken and simulations done for this study are described and comparisons of the measured data with the simulated data for the EMP at 6 GHz are presented.

Cravey, Robin L.↗

NASA NTRS1998

Enhanced Sea Ice Concentration and Ice Temperature Algorithms for AMSR

Accurate quantification of sea ice concentration and ice temperature from satellite passive microwave data is important because they provide the only long term, spatially detailed and consistent data set needed to study the climatology of the polar regions. Sea ice concentration data are used to derive large-scale daily ice extents that are utilized in trend analysis of the global sea ice cover. They are also used to quantify the amount of open water and thin ice in polynya and divergence regions which together with ice temperatures are in turn needed to estimate vertical heat and salinity fluxes in these regions. Sea ice concentrations have been derived from the NASA Team and Bootstrap algorithms while a separate technique for deriving ice temperature has been reported. An integrated technique that will utilizes most of the channels of AMSR (Advanced Microwave Scanning Radiometer) has been developed. The technique uses data from the 6 GHz and 37 GHz channels at vertical polarization obtain an initial estimate of sea ice concentration and ice temperature. The derived ice temperature is then utilized to estimate the emissivities for the corresponding observations at all the other channels. A procedure for calculating the ice concentration similar to the Bootstrap technique is then used but with variables being emissivities instead of brightness temperatures to minimizes errors associated with spatial changes in ice temperatures within the ice pack. Comparative studies of ice concentration results with those from other algorithms, including the original Bootstrap algorithm and those from high resolution satellite visible and infrared data will be presented. Also, results from a simulation study that demonstrates the effectiveness of the technique in correcting for spatial variations in ice temperatures will be shown. The ice temperature results are likewise compared with satellite infrared and buoy data with the latter adjusted to account for the effects of the snow cover.

Comiso, Josefino C.↗