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At least 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Analysis of cylindrical wrap-around and doubly conformal patch antennas by way of the finite element-artificial absorber method

The goal of this project was to develop analysis codes for computing the scattering and radiation of antennas on cylindrically and doubly conformal platforms. The finite element-boundary integral (FE-BI) method has been shown to accurately model the scattering and radiation of cavity-backed patch antennas. Unfortunately extension of this rigorous technique to coated or doubly curved platforms is cumbersome and inefficient. An alternative approximate approach is to employ an absorbing boundary condition (ABC) for terminating the finite element mesh thus avoiding use of a Green's function. A FE-ABC method is used to calculate the radar cross section (RCS) and radiation pattern of a cavity-backed patch antenna which is recessed within a metallic surface. It is shown that this approach is accurate for RCS and antenna pattern calculations with an ABC surface displaced as little as 0.3 lambda from the cavity aperture. These patch antennas may have a dielectric overlay which may also be modeled with this technique.

Volakis, J. L.↗
NASA NTRS1994

Linear quadratic Gaussian and feedforward controllers for the DSS-13 antenna

The controller development and the tracking performance evaluation for the DSS-13 antenna are presented. A trajectory preprocessor, linear quadratic Gaussian (LQG) controller, feedforward controller, and their combination were designed, built, analyzed, and tested. The antenna exhibits nonlinear behavior when the input to the antenna and/or the derivative of this input exceeds the imposed limits; for slewing and acquisition commands, these limits are typically violated. A trajectory preprocessor was designed to ensure that the antenna behaves linearly, just to prevent nonlinear limit cycling. The estimator model for the LQG controller was identified from the data obtained from the field test. Based on an LQG balanced representation, a reduced-order LQG controller was obtained. The feedforward controller and the combination of the LQG and feedforward controller were also investigated. The performance of the controllers was evaluated with the tracking errors (due to following a trajectory) and the disturbance errors (due to the disturbances acting on the antenna). The LQG controller has good disturbance rejection properties and satisfactory tracking errors. The feedforward controller has small tracking errors but poor disturbance rejection properties. The combined LQG and feedforward controller exhibits small tracking errors as well as good disturbance rejection properties. However, the cost for this performance is the complexity of the controller.

Gawronski, W. K.↗
NASA NTRS1995

Design considerations for an archimedean slot spiral antenna

The design goal is to develop a 118-157 MHz, vertically polarized, low-profile (or conformal) antenna as a replacement for VHF AM blade antennas on aircraft. This design is to be arrived at by scaling the dimensions of an antenna designed for a center frequency of 1.1 GHz. The design prior to scaling may have the following maximum dimensions: diameter less than 3.70 in. and thickness less than 0.50 in. Although a four-arm spiral design was originally suggested, a two-arm spiral may also be used, as both mode-1 and mode-2 (sum and difference) radiation patterns aren't required. While a four-arm spiral can easily be designed should both sum and difference patterns be required, the two-arm design will provide the required sum pattern and simplify the design problem somewhat: only one feed is required, and the feed area geometry is more straightforward. Polarization requirements dictate that a slot spiral be used, as opposed to a wire spiral. Two similar radiating structures were considered. The first is the standard archimedean spiral antenna. The second is a hollow archimedean spiral antenna, essentially a standard archimedean spiral with the inner portion removed.

Nurnberger, Michael W.↗
NASA NTRS1994

Synthesis of a large communications aperture using small antennas

In this report we compare the cost of an array of small antennas to that of a single large antenna assuming both the array and single large antenna have equal performance and availability. The single large antenna is taken to be one of the 70-m antennas of the Deep Space Network. The cost of the array is estimated as a function of the array element diameter for three different values of system noise temperature corresponding to three different packaging schemes for the first amplifier. Array elements are taken to be fully steerable paraboloids and their cost estimates were obtained from commercial vendors. Array loss mechanisms and calibration problems are discussed. For array elements in the range 3 - 35 m there is no minimum in the cost versus diameter curve for the three system temperatures that were studied.

Resch, George M.↗
NASA NTRS1995

Layout Of Antennas And Cables In A Large Array

Layout devised to minimize total land area occupied by large phased array of antennas and to minimize total length of cables in array. In original intended application, array expanded version of array of paraboloidal-dish microwave communication antennas of Deep Space Network. Layout also advantageous for other phased arrays of antennas and antenna elements, including notably printed-circuit microwave antenna arrays.

Logan, Ronald T., Jr.↗
NASA NTRS1995

Two Optical-Beam-Forming Concepts For Array Antennas

Two optical-beam-forming concepts selected for development of phased-array antennas. Involve use of novel combinations of optical and electronic techniques to distribute radio-frequency signal to or from antenna elements in array: phase and amplitude of radio-frequency signal traveling to or from each element controlled in such way to cause array as whole to transmit or receive signal in desired spatial pattern, steered, narrowed, broadened, or otherwise varied. Techniques result in compact, lightweight beam-steering antennas. Potential applications include steered-beam or quasi-optical microwave antennas in communication and radar systems, remote control of antennas in general, and photonic communication. With some modifications, transmitting and receiving configurations incorporated into single system.

Wu, Te-Kao↗
NASA NTRS1996

GPS Attitude Determination Using Deployable-Mounted Antennas

The primary objective of this investigation is to develop a method to solve for spacecraft attitude in the presence of potential incomplete antenna deployment. Most research on the use of the Global Positioning System (GPS) in attitude determination has assumed that the antenna baselines are known to less than 5 centimeters, or one quarter of the GPS signal wavelength. However, if the GPS antennas are mounted on a deployable fixture such as a solar panel, the actual antenna positions will not necessarily be within 5 cm of nominal. Incomplete antenna deployment could cause the baselines to be grossly in error, perhaps by as much as a meter. Overcoming this large uncertainty in order to accurately determine attitude is the focus of this study. To this end, a two-step solution method is proposed. The first step uses a least-squares estimate of the baselines to geometrically calculate the deployment angle errors of the solar panels. For the spacecraft under investigation, the first step determines the baselines to 3-4 cm with 4-8 minutes of data. A Kalman filter is then used to complete the attitude determination process, resulting in typical attitude errors of 0.50.

Osborne, Michael L.↗
NASA NTRS1996

Ka-band monopulse antenna-pointing systems analysis and simulation

NASA 's Deep Space Network (DSN) has been using both 70-m and 34-m reflector antennas to communicate with spacecraft at S-band (2.3 GHz) and X-band (8.45 GHz). To improve the quality of telecommunication and to meet future mission requirements, JPL has been developing 34-m Ka-band (32-GHz) beam waveguide antennas. Presently, antenna pointing operates in either the open-loop mode with blind pointing using navigation predicts or the closed-loop mode with conical scan (conscan). Pointing accuracy under normal conscan operating conditions is in the neighborhood of 5 mdeg. This is acceptable at S- and X-bands, but not enough at Ka-band. Due to the narrow beamwidth at Ka-band, it is important to improve pointing accuracy significantly (approximately 2 mdeg). Monopulse antenna tracking is one scheme being developed to meet the stringent pointing-accuracy requirement at Ka-band. Other advantages of monopulse tracking include low sensitivity to signal amplitude fluctuations as well as single-pulse processing for acquisition and tracking. This article presents system modeling, signal processing, simulation, and implementation of Ka-band monopulse tracking feed for antennas in NASA/DSN ground stations.

Lo, V. Y.↗
NASA NTRS1995

System and antenna design considerations for highly elliptical orbits as applied to the proposed Archimedes Constellation

The paper discusses various aspects of the system design for a satellite in a highly elliptical inclined orbit, and presents a number of antenna design options for the proposed Archimedes mission. A satellite constellation was studied for the provision of multi media communication services in the L and S Band for northern latitudes. The inclined elliptical orbit would allow coverage of Europe, America, and East Asia. Using Canada and North America as the baseline coverage area, this paper addresses system considerations such as the satellite configuration and pointing, beam configuration, and requirements for antennas. A trade-off is performed among several antenna candidates including a direct radiating array, a focal-fed reflector, and a single reflector imaging system. Antenna geometry, performance, and beam forming methods are described. The impact of the designs on the antenna deployment is discussed.

Paynter, C.↗
NASA NTRS1995

A Ka-band helical antenna

A number of Ka-band satellite systems have been proposed to provide wide band personal communications services to terminals employing small antennas. Work has been performed looking at the use of helical antenna elements to provide an efficient low-cost antenna at these frequencies. Although helices are not planar, at Ka-band they are less than 2.5 cm in height and thus are suitable for these applications. This paper describes the design and development of a broadband helical antenna element. The work performed on: feed configurations, matching techniques, ground plane structures, broadbanding, and the effects of dielectric loading are discussed. Experimental measurements performed during the development of the helical antenna element are presented.

deLeseleuc, Michel↗
NASA NTRS1993

Inflatable Antenna Microwave Radiometer for Soil Moisture Measurement

Microwave measurements of soil moisture are not being obtained at the required spatial Earth resolution with current technology. Recently, new novel designs for lightweight reflector systems have been developed using deployable inflatable antenna structures which could enable lightweight real-aperture radiometers. In consideration of this, a study was conducted at the NASA Langley Research Center (LaRC) to determine the feasibility of developing a microwave radiometer system using inflatable reflector antenna technology to obtain high spatial resolution radiometric measurements of soil moisture from low Earth orbit and which could be used with a small and cost effective launch vehicle. The required high resolution with reasonable swath width coupled with the L-band measurement frequency for soil moisture dictated the use of a large (30 meter class) real aperture antenna in conjunction with a pushbroom antenna beam configuration and noise-injection type radiometer designs at 1.4 and 4.3 GHz to produce a 370 kilometer cross-track swath with a 10 kilometer resolution that could be packaged for launch with a Titan 2 class vehicle. This study includes design of the inflatable structure, control analysis, structural and thermal analysis, antenna and feed design, radiometer design, payload packaging, orbital analysis, and electromagnetic losses in the thin membrane inflatable materials.

Bailey, M. C.↗
NASA NTRS1996

Microstrip patch antenna receiving array operating in the Ku band

Microstrip patch antennas were first investigated from the idea that it would be highly advantageous to fabricate radiating elements (antennas) on the same dielectric substrate as RF circuitry and transmission lines. Other advantages were soon discovered to be its lightweight, low profile, conformability to shaped surfaces, and low manufacturing costs. Unfortunately, these same patches continually exhibit narrow bandwidths, wide beamwidths, and low antenna gain. This thesis will present the design and experimental results of a microstrip patch antenna receiving array operating in the Ku band. An antenna array will be designed in an attempt to improve its performance over a single patch. Most Ku band information signals are either wide band television images or narrow band data and voice channels. An attempt to improve the gain of the array by introducing parasitic patches on top of the array will also be presented in this thesis.

Walcher, Douglas A.↗
NASA NTRS1998

Simulation of Conformal Spiral Slot Antennas on Composite Platforms

During the course of the grant, we wrote and distributed about 12 reports and an equal number of journal papers supported fully or in part by this grant. The list of reports (title & abstract) and papers are given in Appendices A and B. This grant has indeed been instrumental in developing a robust hybrid finite element method for the analysis of complex broadband antennas on doubly curved platforms. Previous to the grant, our capability was limited to simple printed patch antennas on mostly planar platforms. More specifically: (1) mixed element formulations were developed and new edge-based prisms were introduced; (2) these elements were important in permitting flexibility in geometry gridding for most antennas of interest; (3) new perfectly matched absorbers were introduced for mesh truncations associated with highly curved surfaces; (4) fast integral algorithms were introduced for boundary integral truncations reducing CPU time from O(N-2) down to O(N-1.5) or less; (5) frequency extrapolation schemes were developed for efficient broadband performance evaluations. This activity has been successfully continued by NASA researchers; (6) computer codes were developed and extensively tested for several broadband configurations. These include FEMA-CYL, FEMA-PRISM and FEMA-TETRA written by L. Kempel, T. Ozdemir and J. Gong, respectively; (7) a new infinite balun feed was designed nearly constant impedance over the 800-3000 MHz operational band; (8) a complete slot spiral antenna was developed, fabricated and tested at NASA Langley. This new design is a culmination of the projects goals and integrates the computational and experimental efforts. this antenna design resulted in a U.S. patent and was revised three times to achieve the desired bandwidth and gain requirements from 800-3000 MHz.

Volakis, J. L.↗
NASA NTRS1996

Ka-Band Monopulse Antenna-Pointing Systems Analysis and Simulation

NASA's Deep Space Network (DSN) has been using both 70-m and 34-m reflector antennas to communicate with spacecraft at S-band (2.3 GHz) and X-band (8.45 GHz). To improve the quality of telecommunication and to meet future mission requirements, JPL has been developing 34-m Ka-band (32-GHz) beamwave guide antennas. Presently, antenna pointing operates in either the open-loop mode with blind pointing using navigation predicts or the closed-loop mode with conical scan (conscan). Pointing accuracy under normal conscan operating conditions is in the neighborhood of 5 mdeg. This is acceptable at S- and X-bands, but not enough at Ka-band. Due to the narrow beamwidth at Ka-band, it is important to improve pointing accuracy significantly (approx. 2 mdeg). Monopulse antenna tracking is one scheme being developed to meet the stringent pointing-accuracy requirement at Ka-band. Other advantages of monopulse tracking include low sensitivity to signal amplitude fluctuations as well as single-pulse processing for acquisition and tracking. This article presents system modeling, signal processing, simulation, and implementation of Ka-band monopulse tracking feed for antennas in NASA/DSN ground stations.

Lo, V. Y.↗
NASA NTRS1997

Low Cost Large Space Antennas

The mobile communication community could significantly benefit from the availability of low-cost, large space-deployable antennas. A new class of space structures, called inflatable deployable structures, will become an option for this industry in the near future. This new technology recently made significant progress with respect to reducing the risk of flying large inflatable structures in space. This progress can be attributed to the successful space flight of the Inflatable Antenna Experiment in May of 1996, which prompted the initiation of the NASA portion of the joint NASA/DOD coordinated Space Inflatables Program, which will develop the technology to be used in future mobile communications antennas along with other users. The NASA/DOD coordinated Space Inflatables Program was initiated in 1997 as a direct result of the Inflatable Antenna Experiment. The program adds a new NASA initiative to a substantial DOD program that involves developing a series of ground test hardware, starting with 3 meter diameter units and advancing the manufacturing techniques to fabricate a 25 meter ground demonstrator unit with surface accuracy exceeding the requirements for mobile communication applications. Simultaneously, the program will be advancing the state of the art in several important inflatable technology areas, such as developing rigidizable materials for struts and tori and investigating thin film technology issues, such as application of coatings, property measurement and materials processing and assembly techniques. A very important technology area being addressed by the program is deployment control techniques. The program will sponsor activities that will lead to understanding the effects of material strain energy release, residual air in the stowed structure, and the design of the launch restraint and release system needed to control deployment dynamics. Other technology areas directly applicable to developing inflatable mobile communication antennas in the near future are analytical performance prediction tools, configuration studies and miniaturizing the inflation systems.

Chmielewski, Artur B.↗
NASA NTRS1997

Non-Gimbaled Antenna Pointing

The small satellite community has been interested in accessing fixed ground stations for means of space-to-ground transmissions, although a problem arises from the limited global coverage. There is a growing interest for using the Space Network (SN) or Tracking and Data Relay Satellites (TDRS) as the primary support for communications because of the coverage it provides. This thesis will address the potential for satellite access of the Space Network with a non-gimbaled antenna configuration and low-power, coded transmission. The non-gimbaled antenna and the TDRS satellites, TDRS-East, TDRS-West, and TDRS-Zone of Exclusion, were configured in an orbital analysis software package called Satellite Tool Kit to emulate the three-dimensional position of the satellites. The access potential, which is the average number of contacts per day and the average time per contact, were obtained through simulations run over a 30-day period to gain all the possible orientations. The orbital altitude was varied from 600 km through 1200 km with the results being a function of orbital inclination angles varying from 20 deg through 100 deg and pointing half-angles of I0 deg through 40 deg. To compare the validity of the simulations, Jet Propulsion Laboratory granted the use of the TOPEX satellite. The TOPEX satellite was configured to emulate a spin-stabilized antenna with its communications antenna stowed in the zenith-pointing direction. This mimicked the antenna pointing spin-stabilized satellite in the simulations. To make valid comparisons, the TOPEX orbital parameters were entered into Satellite Tool Kit and simulated over five test times provided by Jet Propulsion Laboratory.

Vigil, Jeannine S.↗
NASA NTRS1998

AAH Cage Out-Link and In-Link Antenna Characterization

This final report encapsulates the accomplishments of the third year of work on an Advanced Biotelemetry System (ABTS). Overall MU/ABTS project objectives are to provide a biotelemetry system that can collect data from and send commands to an implanted biotransceiver. This system will provide for studies of rodent development in space. The system must be capable of operating in a metal animal cage environment. An important goal is the development of a small, "smart", micropower, implantable biotransceiver with eight-channel data output and single channel command input capabilities with the flexibility for easy customization for a variety of physiologic investigations. The NASA Ames/Marquette University Joint Research work has been devoted to the system design of such a new state of the art biotelemetry system, having multiple physiologic inputs, and bi-directional data transfer capabilities. This work has provided a successful prototype system that connects, by two-way radio links, an addressable biotelemetry system that provides communication between an animal biotelemeter prototype and a personal computer. The operational features of the prototype system are: (1) two-way PCM communication with implanted biotelemeter; (2) microcontroller based biotelemeter; (3) out-link: wideband FSK (60 kBaud); (4) in-link: OOK (2.4 kbaud); (5) septum antenna arrays (In/Out-Links); and (6) personal computer data interface. The important requirement of this third year's work, to demonstrate two-way communication with transmit and receive antennas inside the metal animal cage, has been successfully accomplished. The advances discussed in this report demonstrate that the AAH cage antenna system can provide Out-link and In-link capability for the ABTS bi-directional telemetry system, and can serve as a benchmark for project status. Additions and enhancements to the most recent (April 1997) prototype cage and antenna have been implemented. The implementation, testing, and documentation was accomplished at the Biotelemetry Laboratory at Marquette University with Out-Link (slot) antenna design assistance was provided.

Jeutter, Dean C.↗
NASA NTRS1999

Command Preprocessor for Radiotelescopes and Microwave Antennas

The LQG controllers, designed for the NASA Deep Space Network antennas have small tracking errors and are resistant to wind disturbances. However, during antenna slewing, they induce limit cycling caused by the violation of the antenna rate and acceleration limits. This problem can be avoided by introduction of a command that does not exceed the limits. The command preprocessor presented in this paper generates a command that is equal to the original command if the latter does not exceed the limits, and varies with the maximal (or minimal) allowable rate and acceleration if the limits are met or exceeded. It is comparatively simple since it requires only knowledge of the command at the current and the previous time instants, while other known preprocessors require knowledge of the terminal state and the acquisition time. Thus, the presented preprocessor is more suitable for implementation. In this article analysis of the preprocessor is presented. Also the performances of the preprocessor itself, and of the antenna with the preprocessor is illustrated with typical antenna commands.

Gawronski, Wodek↗