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Stutzman, Warren L.

Publications and source records attributed to Stutzman, Warren L..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Wide scanning spherical antenna

A novel method for calculating the surface shapes for subreflectors in a suboptic assembly of a tri-reflector spherical antenna system is introduced, modeled from a generalization of Galindo-Israel's method of solving partial differential equations to correct for spherical aberration and provide uniform feed to aperture mapping. In a first embodiment, the suboptic assembly moves as a single unit to achieve scan while the main reflector remains stationary. A feed horn is tilted during scan to maintain the illuminated area on the main spherical reflector fixed throughout the scan thereby eliminating the need to oversize the main spherical reflector. In an alternate embodiment, both the main spherical reflector and the suboptic assembly are fixed. A flat mirror is used to create a virtual image of the suboptic assembly. Scan is achieved by rotating the mirror about the spherical center of the main reflector. The feed horn is tilted during scan to maintain the illuminated area on the main spherical reflector fixed throughout the scan.

Shen, Bing↗
NASA NTRS1994

Beam scanning offset Cassegrain reflector antennas by subreflector movement

In 1987 a NASA panel recommended the creation of the Mission to Planet Earth. This mission was intended to apply to remote sensing experience of the space community to earth remote sensing to enhance the understanding of the climatological processes of our planet and to determine if, and to what extent, the hydrological cycle of Earth is being affected by human activity. One of the systems required for the mission was a wide scanning, high gain reflector antenna system for use in radiometric remote sensing from geostationary orbit. This work describes research conducted at Virginia Tech into techniques for beam scanning offset Cassegrain reflector antennas by subreflector translation and rotation. Background material relevant to beam scanning antenna systems and offset Cassegrain reflector antenna system is presented. A test case is developed based on the background material. The test case is beam scanned using two geometrical optics methods of determining the optimum subreflector position for the desired scanned beam direction. Physical optics far-field results are given for the beam scanned systems. The test case system is found to be capable of beam scanning over a range of 35 half-power beamwidths while maintaining a 90 percent beam efficiency or 50 half-power beamwidths while maintaining less than l dB of gain loss during scanning.

Lapean, James W., Jr.↗
NASA NTRS1993

Statistical results from the Virginia Tech propagation experiment using the Olympus 12, 20, and 30 GHz satellite beacons

Virginia Tech has performed a comprehensive propagation experiment using the Olympus satellite beacons at 12.5, 19.77, and 29.66 GHz (which we refer to as 12, 20, and 30 GHz). Four receive terminals were designed and constructed, one terminal at each frequency plus a portable one with 20 and 30 GHz receivers for microscale and scintillation studies. Total power radiometers were included in each terminal in order to set the clear air reference level for each beacon and also to predict path attenuation. More details on the equipment and the experiment design are found elsewhere. Statistical results for one year of data collection were analyzed. In addition, the following studies were performed: a microdiversity experiment in which two closely spaced 20 GHz receivers were used; a comparison of total power and Dicke switched radiometer measurements, frequency scaling of scintillations, and adaptive power control algorithm development. Statistical results are reported.

Stutzman, Warren L.↗
NASA NTRS1993

The ACTS propagation terminal delivery and support

Viewgraphs on the Advanced Communications Technology Satellite (ACTS) propagation terminal delivery and support are included. Topics covered include: the ACTS propagation terminal (APT) development program; terminal overview; physical units; test results; status of terminals and schedule; shipping cartons; and site support.

Stutzman, Warren L.↗
NASA NTRS1993

Design of scanning spherical trireflector antennas with high aperture efficiency

It is frequently desirable to scan the main beam of a large antenna system without moving the main aperture structure. Spherical reflectors have excellent potential in this application. However, they are not commonly used because of poor aperture efficiency and high side lobes in traditional implementations. This paper introduces a new dual-subreflector feed system design which does not require oversizing the spherical main reflector to accommodate scan and yet permits a controlled aperture illumination. The design yields high aperture efficiency, low cross-polarization, and low side lobes.

Shen, Bing↗
NASA NTRS1993

Microscale diversity in satellite communications

Results from an investigation into a microscale diversity scheme for the purpose of mitigating attenuation due to tropospheric scintillations are presented. Data from an experiment using the 20 GHz Olympus satellite beacon were analyzed to evaluate the performance of short-baseline site-diversity systems. Results indicate that with a baseline separation of about 50 m the signals received by the main and diversity terminals become decorrelated. Examination of several high-scintillation events shows that such a diversity technique could substantially increase the uptime of low-power-margin VSAT systems. The performance of microscale diversity for several baseline separations is evaluated in terms of a parameter called diversity recovery. Applications and conditions under which microscale diversity performs best are addressed.

Cardoso, J. C.↗
NASA NTRS1993

The Ka-Band Propagation Measurements campaign at JPL

The objectives of the JPL-managed Propagation Program are discussed, and the types of activities performed to meet these objectives are described. Particular consideration is given to activities of the NASA-sponsored Ka-Band Propagation Measurement campaign, which was established to investigate the applicability of using the Ka-band (20/30 GHz) for satellite telecommunications via ESA's OLYMPUS satellite, which is a precursor to NASA's ACTS. The basic physics involved in this problem are discussed, and the OLYMPUS-program data collected to date are reviewed.

Chakraborty, D.↗
NASA NTRS1992

ACTS propagation terminal update

The activities at Virginia Polytechnic Institute and State University in preparation for the February 1993 launch of ACTS are summarized. ACTS propagation terminals (APT) are being constructed to receive the 20 and 27.5 GHz ACTS beacon signals. Total power radiometers operating at the same frequencies are integrated into the terminal for use in level setting. Recent progress and plans for APT's are reported.

Stutzman, Warren L.↗
NASA NTRS1992

Model predicts rain attenuation in satellite links

A model is developed which is capable of predicting the performance of satellite communication systems without complicated mathematics and case-specific physical assumptions while still embodying a general understanding of the structure and properties of rain. The Simple Attenuation Model (SAM) allows the prediction of earth-space rain attenuation at any location in the world for any elevation angle above a few degrees from 10 to 35 GHz. Comparisons of SAM predictions and measured data are presented for selected sites.

Stutzman, Warren L.↗
NASA NTRS1992

Modeling and simulation of mobile satellite propagation

Mobile satellite systems are subject to severe fading due to blockage of the line-of-sight (LOS) path by roadside vegetation. A thorough understanding of the fading effects is necessary for the design of a reliable land mobile satellite system (LMSS). Analytical and empirical models are presented for predicting fade statistics for vegetative shadowing of mobile satellite terminals. A software simulator for generating simulated fade data is also presented. A physical model relating physical path parameters to propagation model parameters is presented, and results using the model are shown.

Barts, R. M.↗
NASA NTRS1992

The Olympus and ACTS propagation measurement campaigns in the U.S

The Jet Propulsion Laboratory under the auspices of NASA carries out radiowave propagation studies for satellite communications. As a prelude to the ACTS experiments, it was considered prudent to gather experience in 20/30 GHz propagation using the Olympus satellite beacons at 12, 20, and 30 GHz. Therefore, NASA funded an experiment program with Virginia Tech under JPL management to develop hardware and to collect data for the Olympus campaign. The paper reviews the results of the Olympus campaign. The experience gathered from this campaign is beneficial to the forthcoming ACTS propagation program which is also discussed in this paper.

Stutzman, Warren L.↗
NASA NTRS1992

A pattern synthesis technique for array feeds to improve radiation performance of large distorted reflector antennas

Technologies exist for construction of antennas with adaptive surfaces that can compensate for many of the larger distortions caused by thermal and gravitational forces. However, as the frequency and size of the reflectors increase, the subtle surface errors become significant and degrade the overall electromagnetic performance. Electronic compensation through an adaptive feed array offers a means for mitigation of surface distortion effects. A pattern synthesis approach for electromagnetic compensation of surface error is presented. The pattern synthesis approach uses a localized algorithm in which pattern corrections are directed toward specific portions of the pattern requiring improvement. The pattern synthesis technique uses radiation pattern data to perform the compensation.

Smith, William T.↗
NASA NTRS1991

Large deployable antenna program. Phase 1: Technology assessment and mission architecture

The program was initiated to investigate the availability of critical large deployable antenna technologies which would enable microwave remote sensing missions from geostationary orbits as required for Mission to Planet Earth. Program goals for the large antenna were: 40-meter diameter, offset-fed paraboloid, and surface precision of 0.1 mm rms. Phase 1 goals were: to review the state-of-the-art for large, precise, wide-scanning radiometers up to 60 GHz; to assess critical technologies necessary for selected concepts; to develop mission architecture for these concepts; and to evaluate generic technologies to support the large deployable reflectors necessary for these missions. Selected results of the study show that deployable reflectors using furlable segments are limited by surface precision goals to 12 meters in diameter, current launch vehicles can place in geostationary only a 20-meter class antenna, and conceptual designs using stiff reflectors are possible with areal densities of 2.4 deg/sq m.

Rogers, Craig A.↗
NASA NTRS1991

The science benefits of and the antenna requirements for microwave remote sensing from geostationary orbit

The primary objective of the Large Space Antenna (LSA) Science Panel was to evaluate the science benefits that can be realized with a 25-meter class antenna in a microwave/millimeter wave remote sensing system in geostationary orbit. The panel concluded that a 25-meter or larger antenna in geostationary orbit can serve significant passive remote sensing needs in the 10 to 60 GHz frequency range, including measurements of precipitation, water vapor, atmospheric temperature profile, ocean surface wind speed, oceanic cloud liquid water content, and snow cover. In addition, cloud base height, atmospheric wind profile, and ocean currents can potentially be measured using active sensors with the 25-meter antenna. Other environmental parameters, particularly those that do not require high temporal resolution, are better served by low Earth orbit based sensors.

Stutzman, Warren L.↗
NASA NTRS1990

ACTS propagation terminal prototype planning and design

The planning and design of a prototype propagation receiving terminal for beacon signals at 27 and 20 GHz bands are examined. The developmental plan is discussed, followed by technical design considerations including, the Advanced Communications Technology Satellite (ACTS) system salient features and frequency plan, beacon signal parameters and specifications, system calculations, and terminal hardware design issues.

Davarian, Faramaz↗
NASA NTRS1989

LMSS modeling status report

The need to develop accurate models for secondary statistics of fading land mobile satellite signals has motivated a study of fading signal autocorrelations and multipath spectrum. Results of autocorrelations and power spectral densities from measured data are presented and comparisons to multipath spectrum models are made.

Stutzman, Warren L.↗
NASA NTRS1989

US Activity with the OLYMPUS satellite

Future communication systems will move toward the 20 to 30 GHz frequency range for wider bandwidth and reduced interference, and will use small earth terminals. The ESA satellite OLYMPUS is scheduled for launch this June and will be ready for use in October. OLYMPUS has 12, 20, and 30 GHz beacons. Virginia Tech and Michigan Tech are working with NASA/JPL on an OLYMPUS experiment and hardware development program. OLYMPUS beacons provide coverage of the east coast of the US sufficient for attenuation measurements. The planned hardware for the OLYMPUS experiments is illustrated. The components of the experiment are summarized. A block diagram level overview of a typical channel is given and one of the four RF front ends is shown.

Stutzman, Warren L.↗