A simple method for measuring the attenuation constant of waveguides
Silver conductive lacquers in microwave region
Klausmann, E.↗
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Measurements of ocean surface spectrum from an aircraft using the two-frequency microwave resonance technique
The present investigation is concerned with the results of a two-frequency (Delta k) microwave radar experiment conducted from an aircraft and aimed primarily at the development of remote sensing techniques to measure ocean surface wave spectral characteristics. The experiment was conducted as part of the Maritime Remote Sensing (MARSEN) project in the North Sea during the autumn of 1979. The objective was to demonstrate the feasibility of and study the performance of the Delta k technique from a higher altitude platform, at shallower incidence angles, and at higher Doppler velocities than earlier stationary platform experiments allowed. A quantitative engineering evaluation of the results of two comprehensive flights is provided, and the qualitative significance of the results is discussed from a geophysical point of view in terms of the existing theory.
Johnson, J. W.↗
High Temperature Superconductor/Semiconductor Hybrid Microwave Devices and Circuits
Contents include following: film deposition technique; laser ablation; magnetron sputtering; sequential evaporation; microwave substrates; film characterization at microwave frequencies; complex conductivity; magnetic penetration depth; surface impedance; planar single-mode filters; small antennas; antenna arrays phase noise; tunable oscillations; hybrid superconductor/semiconductor receiver front ends; and noise modeling.
Romanofsky, Robert R.↗
Cold dark matter and degree-scale cosmic microwave background anisotropy statistics after COBE
We conduct a Monte Carlo simulation of the cosmic microwave background (CMB) anisotropy in the UCSB South Pole 1991 degree-scale experiment. We examine cold dark matter cosmology with large-scale structure seeded by the Harrison-Zel'dovich hierarchy of Gaussian-distributed primordial inhomogeneities normalized to the COBE-DMR measurement of large-angle CMB anisotropy. We find it statistically implausible (in the sense of low cumulative probability F lower than 5 percent, of not measuring a cosmological delta-T/T signal) that the degree-scale cosmological CMB anisotropy predicted in such models could have escaped a detection at the level of sensitivity achieved in the South Pole 1991 experiment.
Gorski, Krzysztof M.↗
Effects of salinity on the microwave emission of soils
Controlled plot experiments were conducted to collect L and C band passive microwave data concurrent with ground observations of salinity and soil moisture. Two dielectric mixing models were used with an emission model to predict the emissivity from a bare smooth uniform profile. The models produce nearly identical results when near zero salinity is involved and reproduce the observed data at L band extremely well. Discrepancies at C band are attributed to sampling depth problems. Comparisons of predicted emissivities at various salinities with observed values indicate that the dynamic range of the emissivities can be explained using either of the dielectric mixing models. Evaluation of the entire data set, which included four salinity levels, indicates that for general application the effects of soil salinity can be ignored in interpreting microwave data for estimating soil moisture under most agricultural conditions.
Jackson, T. J.↗
Salinity effects on the microwave emission of soils
Controlled plot experiments were conducted to collect L and C band passive microwave data concurrent with ground observations of salinity and soil moisture. Two dielectric mixing models were used with an emission model to predict the emissivity from a bare smooth uniform profile. The models produce nearly identical results when near zero salinity is involved and reproduce the observed data at L band extremely well. Discrepancies at C band are attributed to sampling depth problems. Comparisons of predicted emissivities at various salinities with observed values indicate that the dynamic range of the emissivities can be explained using either of the dielectric mixing models. Evaluation of the entire data set, which included four salinity levels, indicates that for general application the effects of soil salinity can be ignored in interpreting microwave data for estimating soil moisture under most agricultural conditions.
Jackson, Thomas J.↗
Remote sensing of ice and snow - Review and status
The interpretation of satellite data is reviewed to address the possibility of extracting geophysically useful data regarding ice and snow. The scientific and practical utility of such data is examined in terms of the required and available scales, resolutions, and data types. Satellite instrumentation for ice and snow studies includes the AVHRR, the Special Sensor Microwave Imager, and the altimeters on Geosat and the European Remote Sensing Satellite. The satellites are presently used for conducting investigations of the microwave radiometry of snow, shortwave snowcover inventories, and sensor and model validations. It is noted that these studies encompass a range of ice properties and employ approaches and scientists from a number of fields. Areas that remain to be addressed in the field include snow structure and substrate effects, fall cooling, floe flooding, and brine expulsion.
Carsey, Frank↗
Phase transition studies in barium and strontium titanates at microwave frequencies
The objectives were the following: to understand the phase transformations in barium and strontium titanates as the crystals go from one temperature to the other; and to study the dielectric behavior of barium and strontium titanate crystals at a microwave frequency of 9.12 GHz and as a function of temperature. Phase transition studies in barium and strontium titanate are conducted using a cylindrical microwave resonant cavity as a probe. The cavity technique is quite successful in establishing the phase changes in these crystals. It appears that dipole relaxation plays an important role in the behavior of the dielectric response of the medium loading the cavity as phase change takes place within the sample. The method of a loaded resonant microwave cavity as applied in this work has proven to be sensitive enough to monitor small phase changes of the cavity medium.
Dahiya, Jai N.↗
Applications of Microwaves to Remote Sensing of Terrain
A survey and study was conducted to define the role that microwaves may play in the measurement of a variety of terrain-related parameters. The survey consisted of discussions with many users and researchers in the field of remote sensing. In addition, a survey questionnaire was prepared and replies were solicited from these and other users and researchers. The results of the survey, and associated bibliography, were studied and conclusions were drawn as to the usefulness of radiometric systems for remote sensing of terrain.
Porter, R. A.↗
Passive Microwave Observation of Soil Water Infiltration
Infiltration is a time varying process of water entry into soil. Experiments were conducted here using truck based microwave radiometers to observe small plots during and following sprinkler irrigation. Experiments were conducted on a sandy loam soil in 1994 and a silt loam in 1995. Sandy loam soils typically have higher infiltration capabilities than clays. For the sandy loam the observed brightness temperature (TB) quickly reached a nominally constant value during irrigation. When the irrigation was stopped the TB began to increase as drainage took place. The irrigation rates in 1995 with the silt loam soil exceeded the saturated conductivity of the soil. During irrigation the TB values exhibited a pattern that suggests the occurrence of coherent reflection, a rarely observed phenomena under natural conditions. These results suggested the existence of a sharp dielectric boundary (wet over dry soil) that was increasing in depth with time.
Jackson, Thomas J.↗
Observed effects of soil organic matter content on the microwave intensity of soils
In order to determine the significance of organic matter content on the microwave emissivity of soils when estimating soil moisture, field experiments were conducted in which 1.4 GHz microwave emissivity data were collected over test plots of sandy loam soil with different organic matter levels (1.8, 4.0, and 6.1 percent) for a range of soil moisture values. Analyses of the observed data show only minor variation in microwave emissivity due to a change in organic matter content at a given moisture level for soils with similar texture and structure. Predictions of microwave emissivity made using a dielectric model for aggregated soils exhibit the same trends and type of response as the measured data when appropriate values for the input parameters were utilized.
Jackson, T. J.↗
Observed effects of soil organic matter content on the microwave emissivity of soils
In order to determine the significance of organic matter content on the microwave emissivity of soils when estimating soil moisture, field experiments were conducted in which 1.4 GHz microwave emissivity data were collected over test plots of sandy loam soil with different organic matter levels (1.8, 4.0, and 6.1 percent) for a range of soil moisture values. Analyses of the observed data show only minor variation in microwave emissivity due to a change in organic matter content at a given moisture level for soils with similar texture and structure. Predictions of microwave emissivity made using a dielectric model for aggregated soils exhibit the same trends and type of response as the measured data when appropriate values for the input parameters were utilized.
O'Neill, P. E.↗
Feasibility study of ferromagnetic/ferroelectric films for enhanced microwave devices
This report summarizes exploratory work conducted to assess the feasibility of ferromagnetic/ferroelectric films for next-generation microwave devices. From literature review, it is established that while an increasing number of ferroelectric/ferromagnetic composites are being investigated, a number have transition temperatures that are too low and structures that are not robust enough for low cost, room temperature antenna arrays. On the other hand, several promising systems are identified, including the multiferroic BiFeO3 and a composite system of Ba/SrTiO3 and a related perovskite manganite. It is suggested that when the NASA pulsed laser deposition chamber is fully operational, thin films of these systems be investigated. In preparation for such work, we have reconfirmed several structural features of an existing Ba/SrTiO3 film using the x-ray diffractometer at Oberlin College.
Ijiri, Yumi↗
Optimization of energy transfer in microwave electrothermal thrusters
Results are presented from preliminary tests conducted to evaluate the performance of a prototype microwave electrothermal thruster. The primary component of the device is a microwave resonant cavity. The device produces stable axial plasmas within a pressurized section of the cavity with the plasma positioned in the inlet region of the nozzle. Plasma stability is enhanced by axial power coupling, an optimal distribution of electric power density within the cavity, and a propellant gas flow which has a large vortical velocity component. The thruster has been operated with a number of propellant gases: helium, nitrogen, ammonia, and hydrogen. Plasmas can be formed in a reliable manner at cavity pressures of 1 kPa and incident power levels ranging from 50 W to 350 W, depending on the gas used, and can be operated at pressures up to 300 kPa at power levels up to 2200 W. Ideal performance results of vacuum Isp and thermal efficiency vs. specific power are presented for each gas. Representative results of this preliminary work are: He - Isp = 625 s, eta-thermal = 90 percent; N2 - Isp = 270 s, eta-thermal = 41 percent; NH3 - Isp = 475 s, eta-thermal= 55 percent; H2 - Isp = 1040 s, eta-thermal = 53 percent.
Sullivan, D. J.↗
Microwave emission from geological materials - Observations of interference effects.
Microwave radiometric field observations were conducted at wavelengths of 21, 2.8, and 0.95 cm to determine the microwave penetration depth of a number of sands and gravels as a function of particle size and moisture content. Observations of a reflecting plate covered with varying thicknesses of test material exhibit a pronounced oscillatory behavior that is consistent with established electromagnetic theory for plane-parallel layered mediums. Utilization of this interference effect is proposed as a microwave radiometric technique for determining the bulk electrical properties of geologic materials, snow, ice, and other materials readily adapted to layering experiments.
Blinn, J. C., III↗
Secondary-electron-emission properties of conducting surfaces with application to multistage depressed collectors for microwave amplifiers
To improve the efficiency of high power microwave tubes, low secondary electron yield electrode surface for use in depressed collectors are needed. The secondary emission characteristics of a number of materials were investigated. The materials studied were beryllium, carbon (soot and pyrolytic graphite), copper, titanium carbide, and tantalum. Both total secondary yield delta and relative reflected primary yield were measured. These measurements were made in conjunction with Auger spectroscopy so that the secondary emission characteristics could be determined as a function of surface contamination or purity. The results show that low atomic weight elements, such as beryllium and carbon, have the lowest reflected primary yield and that roughening the surface of an electrode can markedly decrease secondary yield both for delta and reflected primaries. All factors considered, a roughened pyrolytic graphite surface showed the greatest potential for use as an electrode surface in depressed collectors.
Forman, R.↗
Microwave radiometer measurements of the Cape Cod Canal
Microwave radiometer measurements were conducted from a railroad bridge which spans the Cape Cod Canal in Massachusetts. Data were collected as a function of viewing angle and polarization at frequencies of 1.4, 4.0, and 7.5 GHz. The results compare differences in the microwave emmissivity of a smooth vs rough water surface. Results are also given which show the effects of roughness on the bistatic scattering of sunlight.
Swift, C. T.↗
Search for extraterrestrial intelligence/High Resolution Microwave Survey team member
This final report summarizes activities conducted during the three years of the NASA High Resolution Microwave Survey (HRMS). With primary interest in the Sky Survey activity, the principal investigator attended nine Working Group meetings and traveled independently to conduct experiments or present results at other meetings. The major activity involved evaluating the effects of spaceborne radio frequency interference (RFI) on both the SETI sky survey and targeted search. The development of a database of all unclassified earth or biting and deep space transmitters, along with accompanying search software, was a key accomplishment. The software provides information about potential sources of interference and gives complete information regarding the frequencies, positions and levels of interference generated by the spacecraft. A complete description of this search system (called HRS, or HRMS RFI Search) is provided. Other accomplishments include development of a 32,000 channel Fast-Fourier-Transform Spectrum analyzer for use in studies of interference from satellites and in a 1.4 mm SETI observational study. The latest revision of HRS has now been distributed to the extended radio astronomy and SETI community.
Steffes, Paul G.↗