Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Faraday rotator”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Radio wave propagation experiments to probe the ionosphere

Ionospheric bias corrections associated with radio tracking of spacecraft depend on the following measuring techniques for integrated electron content: (1) Faraday rotation measurements from an earth synchronous satellite; (2) ranging measurements at two frequencies; and (3) group and phase velocity measurements obtained from tracking data. The extraction of the integrated electron content directly from tracking data is achieved by comparison of range-rate measurements based on Doppler shift with differentiated range measurements based on tone delay. This method is most desirable because the measured corrections pertain directly to the spacecraft whose orbit is being determined and can be used in near earth as well as deep space tracking data.

Schmid, P. E.↗
NASA NTRS1972

VHF/UHF technique for the determination of the columnar electron contents of the plasmasphere and of the protonosphere using geostationary satellite transmission: Observations during magnetic storms

Measurements of the total electron content of the plasmasphere up to geostationary heights were made using the beacon transmitters aboard the satellite ATS-3. The technique employed is a combination of the phase-path length difference and the Faraday rotation angle methods. Such a combination permits very accurate determination of the integration constant necessary to convert phase-path length difference data into information about the absolute value of the columnar content.

Almeida, O. G.↗
NASA NTRS1971

The magnetic field structure in the active solar corona.

The structure of the magnetic field of the active solar corona is discussed with reference to optical and radio observations of the solar atmosphere. Eclipse observations provide evidence of fine scale structures in the solar atmosphere that appear to relate to the coronal magnetic field. The coronal magnetic field used for comparison is calculated from potential theory; the influence of solar activity upon the potential theory field is discussed with reference to observations of the Faraday rotation of a microwave signal from Pioneer 6 as it was occulted by the solar atmosphere. Evidence has been found suggesting the existence of expanding magnetic bottles located at 10 solar radii above flaring active regions. The dynamics of these events is discussed. It is further suggested that these magnetic bottles are an important component in the solar corona.

Schatten, K. H.↗
NASA NTRS1971

The use of semiconductors in nonreciprocal devices for submillimeter wavelengths.

This paper reviews the use of anisotropic effects in a passive semiconductor magnetoplasma for the development of submillimeter isolators and circulators. The emphasis is on two schemes that are applicable over the far infrared portion of the spectrum. The theory of transmission devices depending on Faraday rotation is described, and experiments are discussed. At far infrared wavelengths it is not necessary to cool the semiconductor in order to achieve low forward loss. Some experimental results are available in this frequency range, and a theoretical evaluation of device performance is given. Reflection devices in which the desired signal does not propagate through the semiconductor, but is reflected off of its surface, are also discussed. Experimental results show that these devices can have a low forward loss; a variety of novel geometrical arrangements are able to improve isolator performance. Theoretical results indicating satisfactory performance for a far infrared isolator using InSb at room temperature are presented.

Hayes, R. E.↗
NASA NTRS1972

On the semiannual change in exospheric temperature.

Discussion of some uncertainties about the semiannual density variations of the neutral atmosphere at heights above 100 km ascribed by Jacchia (1965), on the basis of long observations of the decay of satellite orbits, to changes in exosphere temperature, but later, because of some difficulties, attributed by Jacchia (1971) to semiannual density variations that may not be produced primarily by changes in temperature. Temperature values derived from ionosphere electron content data recorded since 1965 at several sites in New Zealand using the Faraday rotation of geostationary satellite signals and from their comparison with ionosonde measurements are shown to suggest that the semiannual variations represent primarily changes in temperature and only secondarily in density.

Titheridge, J. E.↗
NASA NTRS1972

Polarization tracking system for satellites.

The basic problem is to develop a 4 GHz polarization follower which tracks a linear vector transmitted by the satellite, with high precision. Applications include spacecraft attitude control, polarization following for linearly polarized communication receiving antennas, and Faraday rotation measurements. Considered primary information, an angular precision of better than 0.5 deg has been demonstrated at 4 GHz. Both theoretical and experimental aspects are discussed.

Taylor, R. E.↗
NASA NTRS1973

Propagation studies using a theoretical ionosphere model

The mid-latitude ionospheric and neutral atmospheric models are coupled with an advanced three dimensional ray tracing program to see what success would be obtained in predicting the wave propagation conditions and to study to what extent the use of theoretical ionospheric models is practical. The Penn State MK 1 ionospheric model, the Mitra-Rowe D region model, and the Groves' neutral atmospheric model are used throughout this work to represent the real electron densities and collision frequencies. The Faraday rotation and differential Doppler velocities from satellites, the propagation modes for long distance high frequency propagation, the group delays for each mode, the ionospheric absorption, and the spatial loss are all predicted.

Lee, M.↗
NASA NTRS1972

A receiver design for the ATS-F radio beacon experiment.

The basic design of the overall receiving system is determined by the received power density from the satellite and the desired compromise between ground antenna aperture, system response times, and measurement signal-to-noise ratio. The measurement of Faraday rotation is discussed together with the measurement of modulation phase, aspects of system calibration, and overall system concepts.

Grubb, R. N.↗
NASA NTRS1973

Corrections of satellite positions in near-real time.

The influence of sudden increases of electron content on the accurate determination of the position of a satellite is investigated based on a spherically stratified ionospheric model. Using the total electron content information from Faraday rotation measurements, a procedure is presented whereby the corrections of satellite position due to the unpredicted electron increase can be accounted for without the need to know the spatial distribution of the additional electrons.

Poularikas, A. D.↗
NASA NTRS1973

The slab thickness of the mid-latitude ionosphere.

The thickness of the peak of the ionosphere depends primarily on the temperature T sub n of the neutral gas, and corresponds approximately to an alpha-Chapman layer at a temperature of 0.87T sub n. The overall slab thickness, as given by Faraday rotation measurements, is then tau = 0.22T sub n + 7 km. Expansion of the topside ionosphere, and changes in the E- and F1-regions increase tau by about 20 km during the day in summer. Near solar minimum, tau is increased by a lowering of the O(+)/H(+) transition height; if the neutral temperature T sub n is estimated, this height can be obtained from observed values of tau. Hourly values of slab thickness were determined over a period of 6 yr at 34 and 42 S. Near solar maximum the nighttime values were about 260 km in all seasons. The corresponding neutral temperatures agree with satellite drag values; they show a semiannual variation of 14% and a seasonal change of 5%. Daytime values of tau were about 230 km in winter and 320 km in summer, implying a seasonal change of 30% in T sub n.

Titheridge, J. E.↗
NASA NTRS1974

Comparisons of techniques for measurement of D-region electron densities

This paper reviews the ground-based and rocket techniques that are presently being used to determine electron density profiles in the ionospheric D region. Ground-based techniques include VLF, LF, and MF sounding; differential absorption and differential phase measurements using partial reflections; wave interaction; and incoherent scatter. Rocket techniques include differential absorption and Faraday rotation in association with high-resolution dc probes calibrated by means of the radio measurements. The characteristics of the aforementioned techniques are presented, including time and height resolution, accuracy estimates, preferred height ranges, and problems encountered. Electron density profiles obtained with these techniques are presented for comparable solar zenith angles and undisturbed solar and geophysical conditions.

Sechrist, C. F., Jr.↗
NASA NTRS1974

Accuracy of rocket measurements of lower ionosphere electron concentrations

Measurements of electron concentration taken at the same time and at the same place in the lower ionosphere by independent instrumentation mounted on the same rocket are described. The technique utilizes Faraday rotation and differential absorption of radio waves propagating from the ground to the rocket at two different frequencies. Agreement near 90 km within 7%, 6%, 8%, and 3% is demonstrated by the four available cases of coincidence in time and altitude. Maximum dispersion at other altitudes is calculated from known random errors. Stronger variation of electron collision frequency with altitude than with season is indicated by 34 measurements between 75 and 100 km. Insensitivity of electron concentration determinations at 72 km to errors in extrapolated collision frequency models is demonstrated.

Mechtly, E. A.↗
NASA NTRS1974

Propagation of transverse waves in a radially expanding plasma

Investigation of the properties of low-frequency transverse waves in an expanding plasma. The wave vector, the background magnetic field, and the streaming velocity of the plasma are all assumed to lie along the radial direction. Expressions are presented for the radial dependence of the amplitude and phase of left and right circularly polarized waves, correct to first order in the wave frequency divided by the proton cyclotron frequency. Differences in the phase velocities of these two circular polarizations result in a Faraday rotation that can be substantial for typical interplanetary conditions near 1 AU. The implications of these results for a realistic solar wind model with the interplanetary magnetic field along the spiral direction are also considered.

Solodyna, C. V.↗
NASA NTRS1974

A novel method for measuring the polarization angle of satellite radio waves

One of the most important parameters for the study of the physics of the ionosphere is the columnar electron content. This can be obtained indirectly by measuring the Faraday rotation of signals emitted from satellites. Many different types of polarimeters have been developed for this purpose. Efforts to develop a new type of polarimeter, suitable for extensive network operation, led to a novel technique for measuring the polarization angle.

Antoniadis, D. A.↗
NASA NTRS1975

Study of the brightness and polarization structure of extragalactic radio sources

The brightness and linear-polarization structure of 19 extended extragalactic radio sources are determined at a frequency of 10.7 GHz. Compact components with self-absorption spectra coincident with the nucleus of an associated galaxy are fairly common, while many sources display regions of high-percentage polarization, sometimes greater than 40%. Comparison of our results with other studies, all at lower frequencies (generally not exceeding 5 GHz), has yielded information on spectra, depolarization rates, and Faraday rotation of the polarization plane in various source regions. At least four distinct classes of extragalactic radio sources are identified. These classes form a sequence along which the prominence of the compact central component declines relative to that of the extended outer regions, while those outer regions become more ordered in their structure and assume specific polarization characteristics. It is suggested that this sequence is in fact an evolutionary sequence.

Stull, M. A.↗
NASA NTRS1975

Some early results from the ATS-6 radio beacon experiment

The multifrequency satellite radio beacon enables the measurement of the columnar electron content of the ionosphere and plasmasphere along the ray path and its spatial and temporal structure. Measurements include modulation phase, Faraday rotation, and amplitude. The characteristics of the beacon transmitter and its design are presented together with the design of the Boulder receiver and antennas and the calibration procedures. A shape factor F is defined which depends on the electron density and geomagnetic field distributions. It is found that F varies by about 30% from day to night. It is shown that the ratio of the plasmaspheric content to total content varies from about 0.08 during the day to about 0.35 at night. Other examples which are presented to illustrate the uses of the radio beacon include sunrise effects, solar flare enhancements of total content, and the ionospheric storms of early July 1974.

Davies, K.↗
NASA NTRS1976

DSN research and technology support

Continuing testing and refinement of the remote controlled, unattended automated pulsar observing station is noted, along with routine pulsar observations of 22 pulsars. Radar observations of geostationary satellite are discussed. Current status of the 400-kW X-band radar is reported along with routine automatic testing of the stability-reliability of the DSS 13 maser-receiver noise adding radiometer combination. A failure in the Faraday rotation receiving system is noted along with discussion in some detail of the activities of the high power transmitter maintenance facility. Continuation of receiver phase stability testing, specifically the effects of temperature on coaxial cables, is discussed and results reported. A demonstration at full power of the microwave power transmission facility is noted and routine support of the planetary radio astronomy experiment is discussed. Transmission of master clock synchronization signals to overseas DSN stations is also reported.

Jackson, E. B.↗