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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Finding the Focal Axes of Offset Antennas

Focal axis of offset paraboloidal reflector antennas determined by direct measurement instead of trial and error. Two feed horns transmit sum or difference pattern to antenna under test, which reflects energy to far-field detector. When axis of feed horns coincides with focal axis of antenna reflector, far-field detector records minimum in amplitude difference and maximum in absolute-magnitude phase difference between sum and difference signals.

Schmidt, R. F.↗
NASA NTRS1981

Realizable feed-element patterns for multibeam reflector antenna analysis

The radiation pattern of a feed element is approximately described by a simple function (cos theta) to the q power. For a given element spacing of the feed array, simple formulas for estimating the practical value of q when the element is an open-ended rectangular waveguide, an open-ended circular waveguide, a pyramidal horn, or a cigar antenna are given.

Rahmat-Samii, Y.↗
NASA NTRS1996

On the Accurate Calibration of the SeaWinds Radar Antenna: A Cylindrical Near-Field Measurement Approach

This paper demonstrates the utility of a cylindrical near-field measurement approach for the SeaWinds radar antenna calibration. Both generalized measurement error models and measured tests on a standard gain horn and NASA Scatterometer instrument antenna have been performed to achieve and verify the desired calibration accuracy. A comparison between far-field measured data and those obtained from cylindrical near-field measurements was found in excellent agreement.

spaceborne↗
NASA NTRS1980

Dual-frequency microwave antenna

Single antenna using two feed horns (one for receiving and radiation X-band signals, and one for S-band signals), in conjunction with ellipsoid reflector and dichronic plate, can accommodate two different frequencies simultaneously.

Bathker, D. A.↗
NASA NTRS1983

Calibration of the Nimbus-7 SMMR. 2: Polarization mixing corrections

Averaged radiance data obtained over the oceans from the Nimbus-7 Scanning Multichannel Microwave Radiometer (SMMR) are used to produce an empirical correction algorithm for the polarization mixing which is inherent to the SMMR because of its fixed multichannel receiving horn and its scanning antenna dish. The algorithm, developed without the use of an ocean/atmosphere radiance model, also properly accounts for off center and scan independent polarization mixing, which were discovered after launch as a result of analyzing the aforementioned data. The radiance averaging consisted of collecting data for each beam position of each of the ten radiance channels of SMMR (nominal horizontal and vertical polarizations of the five SMMR wavelengths, 0.81, 1.4, 1.7, 2.8, and 4.6 cm) for about 300 orbits, subdividing the global ocean radiance data into 10 deg latitude bands and ascending (daytime) and descending (nighttime) orbits. This served to smooth out atmospheric and ocean surface variations in order to perform the polarization mixing analysis.

Gloersen, P.↗
NASA NTRS2012

A Dual-Polarized, Dual-Frequency, Corrugated Feed Horn for SMAP

SMAP will be the first Earth science mission to use a deployable 6m mesh reflector for both radar and radiometric measurements from low Earth orbit. The instrument antenna will spin at about 14 rpm, making the design of both reflector and feed more challenging. While the performance requirements imposed by the radar instrument are relatively benign, those pertinent to the radiometer are more difficult to meet. Extreme care was necessary in designing the feed, especially from a performance stability perspective. Thermal variations due to the spacecraft going in and out of eclipse during orbit and direct solar radiation into the horn are just two of the challenges faced during the design phase. In this paper, the basic concepts behind the design of SMAP's feed will be discussed. Each component of the feed will be analyzed in detail with particular emphasis on its impact on major RF requirements. Overall performance of the feed will also be discussed.

deployable reflector↗
NASA NTRS1989

Millimeter and submillimeter wave antenna structure

An integrated circuit antenna structure for transmitting or receiving millimeter and/or submillimeter wave radiation having an antenna relatively unimpaired by the antenna mounting arrangment is disclosed herein. The antenna structure of the present invention includes a horn disposed on a substrate for focusing electromagnetic energy with respect to an antenna. The antenna is suspended relative to the horn to receive or transmit the electromagnetic energy focused thereby.

Rebiez, Gabriel M.↗
NASA NTRS1982

Dipole-Excited Ring Antenna

Dipole radiator drives ring radiator in compact C-band antenna. Antenna can be mounted flush with surface. Compared with horn or parabolic dish with same aperature, new ring antenna has greater gain, lower side lobes, and narrower beam width. Used on vehicles requiring flush-mounted antennas with very directive signals. Used as radar altimeter antenna for aircraft.

Ellis, H., Jr↗
NASA NTRS2001

Satellite-Tracking Millimeter-Wave Reflector Antenna System For Mobile Satellite-Tracking

A miniature dual-band two-way mobile satellite-tracking antenna system mounted on a movable vehicle includes a miniature parabolic reflector dish having an elliptical aperture with major and minor elliptical axes aligned horizontally and vertically, respectively, to maximize azimuthal directionality and minimize elevational directionality to an extent corresponding to expected pitch excursions of the movable ground vehicle. A feed-horn has a back end and an open front end facing the reflector dish and has vertical side walls opening out from the back end to the front end at a lesser horn angle and horizontal top and bottom walls opening out from the back end to the front end at a greater horn angle. An RF circuit couples two different signal bands between the feed-horn and the user. An antenna attitude controller maintains an antenna azimuth direction relative to the satellite by rotating it in azimuth in response to sensed yaw motions of the movable ground vehicle so as to compensate for the yaw motions to within a pointing error angle. The controller sinusoidally dithers the antenna through a small azimuth dither angle greater than the pointing error angle while sensing a signal from the satellite received at the reflector dish, and deduces the pointing angle error from dither-induced fluctuations in the received signal.

Densmore, Arthur C.↗
NASA NTRS1995

A satellite-tracking millimeter-wave reflector antenna system for mobile satellite-tracking

A miniature dual-band two-way mobile satellite tracking antenna system mounted on a movable ground vehicle includes a miniature parabolic reflector dish having an elliptical aperture with major and minor elliptical axes aligned horizontally and vertically, respectively, to maximize azimuthal directionality and minimize elevational directionality to an extent corresponding to expected pitch excursions of the movable ground vehicle. A feed-horn has a back end and an open front end facing the reflector dish and has vertical side walls opening out from the back end to the front end at a lesser horn angle and horizontal top and bottom walls opening out from the back end to the front end at a greater horn angle. An RF circuit couples two different signal bands between the feed-horn and the user. An antenna attitude controller maintains an antenna azimuth direction relative to the satellite by rotating it in azimuth in response to sensed yaw motions of the movable ground vehicle so as to compensate for the yaw motions to within a pointing error angle. The controller sinusoidally dithers the antenna through a small azimuth dither angle greater than the pointing error angle while sensing a signal from the satellite received at the reflector dish, and deduces the pointing angle error from dither-induced fluctuations in the received signal.

Densmore, Arthur C.↗
NASA NTRS1987

Phase-Center Extension for a Microwave Feed Horn

Corrugated cylindrical tube relocates phase center of Cassegrain antenna feed. Proposed modification increases aperture of Cassegrain antenna from 64 to 70 m. Relatively inexpensive extension moves phase center of feed without incurring cost of redesigning horn and relocating low-noise equipment. Extension does not affect polarization characteristics of feed.

Hartop, R. W.↗
NASA NTRS2000

Low-Cost Tracking Ground Terminal Designed to Use Cryogenically Cooled Electronics

A computer-controlled, tracking ground terminal will be assembled at the NASA Glenn Research Center at Lewis Field to receive signals transmitted by the Glenn's Direct Data Distribution (D3) payload planned for a shuttle flight in low Earth orbit. The terminal will enable direct data reception of up to two 622-megabits-per-second (Mbps) beams from the space-based, K-band (19.05-GHz) transmitting array at an end-user bit error rate of up to 10(exp -12). The ground terminal will include a 0.9-m-diameter receive-only Cassegrain reflector antenna with a corrugated feed horn incorporating a dual circularly polarized, K-band feed assembly mounted on a multiaxis, gimbaled tracking pedestal as well as electronics to receive the downlink signals. The tracking system will acquire and automatically track the shuttle through the sky for all elevations greater than 20 above the horizon. The receiving electronics for the ground terminal consist of a six-pole microstrip bandpass filter, a three-stage monolithic microwave integrated circuit (MMIC) amplifier, and a Stirling cycle cryocooler (1 W at 80 K). The Sterling cycle cryocooler cools the front end of the receiver, also known as the low-noise amplifier (LNA), to about 77 K. Cryocooling the LNA significantly increases receiver performance, which is necessary so that it can use the antenna, which has an aperture of only 0.9 m. The following drawing illustrates the cryoterminal.

Wald, Lawrence W.↗
NASA NTRS1980

Dual-frequency bidirectional antenna

Simultaneous two-way communication at 20 and 30 GHz is possible with versatile paraboloid-dish antenna. Developed for two-way communications between Space Shuttle and ground station, antenna includes parabolic reflector, feed horn, waveguide network, and single-axis gimbal mounting. System resolution and accuracy are better than 1 percent.

Kummer, W. H.↗
NASA NTRS1985

Remote sensing of directional wave spectra using the surface contour radar

A unique radio-oceanographic remote sensing instrument was developed. The 36 GHz airborne Surface Contour Radar (SCR) remotely produces a real-time topographical map of the sea surface beneath the aircraft. It can routinely produce ocean directional wave spectra with off-line data processing. The transmitter is a coherent dual-frequency device that uses pulse compression to compensate for the limited available power at Ka band. The radar has selectable pulse widths of 1, 2, 4, and 10 nanoseconds. The transmitting antenna is a 58 lambda horn fed dielectric lens whose axis is parallel to the longitudinal axis of the aircraft. It illuminates an elliptical mirror which is oriented 45 deg to the lens' longitudinal axis to deflect the beam towards the region beneath the aircraft. The mirror is oscillated in a sinusoidal fashion through mechanical linkages driven to a variable speed motor to scan the transmitter beam (1.2 deg X 1.2 deg) with + or - 16 deg of the perpendicular to the aircraft wings in the plane perpendicular to the aircraft flight direction.

Walsh, E. J.↗
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 NTRS1989

Large space systems antenna technology

Program objectives; approach; surface characterization of large scale antennas; adaptive feed-multimode horn and array configuration; and technology benefits of CSEI program are outlined. This presentation is represented by viewgraphs only.

Campbell, Thomas G.↗
NASA NTRS1979

Shuttle orbiter Ku-band radar/communications system design evaluation: High gain antenna/widebeam horn

The physical characteristics of the high gain antenna reflector and feed elements are described. Deficiencies in the sum feed are discussed, and lack of atmospheric venting is posed as a potential problem area. The measured RF performance of the high gain antenna is examined and the high sidelobe levels measured are related to the physical characteristics of the antenna. An examination of the attributes of the feed which might be influenced by temperature extremes shows that the antenna should be insensitive to temperature variations. Because the feed support bipod structure is considered a significant contributor to the high sidelobe levels measured in the azimuth plane, pod relocation, material changes, and shaping are suggested as improvements. Alternate feed designs are presented to further improve system performance. The widebeam horn and potential temperature effects due to the polarizer are discussed as well as in the effects of linear polarization on TDRS acquisition, and the effects of circular polarization on radar sidelobe avoidance. The radar detection probability is analyzed as a function of scan overlap and target range.

Iwasaki, R.↗