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  • 1
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    Analysis of finite phased arrays of circular microstrip patches (1989)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: A method is presented for analyzing a finite planar array of circular microstrip patches fed by coaxial probes. The self- and mutual impedances between array elements are calculated using the method of moments with the dyadic Green's function for a dielectric layer on a ground plane. The patch circuits are determined by using the reaction integral equation. The active input impedance as well as the active element pattern of the array are computed from a knowledge of the resultant patch currents. The calculated results for two-element and eight-element linear arrays are in good agreement with experimental data. The active reflection coefficient and element pattern for the center and edge elements of a two-dimensional array as a function of scan angle are also presented.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Antennas and Propagation (ISSN 0018-926X); 37; 1355-136
    Format: text
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  • 2
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    Analysis of elliptical and circular microstrip antennas using moment method (1985)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: A method of calculating the input impedance of either a circular or a slightly elliptical microstrip antenna excited by a coaxial probe is presented. Using the reaction integral equation and the exact dyadic Green's function, the finite substrate thickness is taken into account in the formulation. Good agreement with experimental results for an elliptical patch is obtained and a design procedure for a circularly polarized antenna is presented.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Antennas and Propagation (ISSN 0018-926X); AP-33; 954-959
    Format: text
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  • 3
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    NASA Charge Coupled Device (CCD) Spectrometer System (NCSS) (1988)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: A small lightweight NCSS was designed, constructed, and is now being bench tested at Wallops. The unit provides 256, 2.7 nm wide channels in the visible spectrum from approximately 400 to 1100 nm. The present input slit provides a spectral impulse response of about 10 nm. Up to five NCSS sensors may be bused to one data system interface. The NCSS contains a high speed, 16 bit analog to digital converter (ADC) with an integral wide-band sample-and-hold amplifier. The NCSS was developed primarily for use with the Airbone Oceanographic Lidar (AOL). A prototype NCSS is presently interfaced to the AOL. The AOL will use two new NCSS units onboard the Goddard P-3A aircraft. They will provide the AOL with high resolution sky and ocean spectra. The up-looking NCSS will provide the AOL data system (AOLDS) with down-welling solar radiance, and the down-looking NCSS will provide ocean color spectra. The solar radiance will be used to correct various ocean color algorithms now being researched.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Laboratory for Oceans; p 91-94
    Format: application/pdf
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  • 4
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    Advanced altimetry (1988)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The radar altimeter being developed for the Ocean Topography Experiment (TOPEX) will have an inherent instrument precision of 2 to 3 cm. While some minor refinements may be possible in the future, major geophysical advances could be made if altimetric measurements over a wide swath of the Earth's surface were possible. The NASA Headquarters Oceanic Processes Branch is supporting a 3-year investigation of the technological issues inherent in the precision measurement of topography from spaceborne platforms at angles off-nadir. To explore the off-nadir measurement of topography, a flexible, airborne radar instrument system is being developed. Its hardware design is now complete, and it is made up of several subsystems. The antenna selected is a dielectric lens of .894 m diameter. The RF subsystem uses phase-locked oscillators, FET solid-state amplifiers, and times four frequency multipliers to develop a transmit signal at a frequency of 36.0 GHz and a local oscillator signal at a frequency of 35.4 GHz. Lecroy 6880 digitizers under computer control digitize the five receiver outputs. The digital subsystem consists of six single-board Heurikon processors. At this time, the instrument construction continues with final system integration planned for November 1988.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Laboratory for Oceans; p 45-47
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  • 5
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    The 15-meter antenna performance optimization using an interdisciplinary approach (1988)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: A 15-meter diameter deployable antenna has been built and is being used as an experimental test system with which to develop interdisciplinary controls, structures, and electromagnetics technology for large space antennas. The program objective is to study interdisciplinary issues important in optimizing large space antenna performance for a variety of potential users. The 15-meter antenna utilizes a hoop column structural concept with a gold-plated molybdenum mesh reflector. One feature of the design is the use of adjustable control cables to improve the paraboloid reflector shape. Manual adjustment of the cords after initial deployment improved surface smoothness relative to the build accuracy from 0.140 in. RMS to 0.070 in. Preliminary structural dynamics tests and near-field electromagnetic tests were made. The antenna is now being modified for further testing. Modifications include addition of a precise motorized control cord adjustment system to make the reflector surface smoother and an adaptive feed for electronic compensation of reflector surface distortions. Although the previous test results show good agreement between calculated and measured values, additional work is needed to study modelling limits for each discipline, evaluate the potential of adaptive feed compensation, and study closed-loop control performance in a dynamic environment.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Jet Propulsion Lab., Proceedings of the Mobile Satellite Conference; p 465-470
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  • 6
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    An astronomy camera for low background applications in the 1.0 to 2.5 micron spectral region (1989)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: A description is given of a low-background astronomy camera system based on a short wavelength (1.0-2.5 micron) 128 x 128 focal plane array. The camera is designed to accept either a HgCdTe array for the 1-2.5 micron spectral region or an InSb array for the 3-5 micron spectral region. A cryogenic folded optical system is utilized to control excess stray light along with a cold eight-position filter wheel for spectral filtering. The camera head and electronics will also accept a 256 x 256 focal plane. Engineering evaluation of the system and two engineering runs at the JPL Table Mountain Observatory have been completed. System design, engineering performance, and sample imagery are presented.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: IEEE Transactions on Nuclear Science (ISSN 0018-9499); 36; 941-945
    Format: text
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  • 7
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    Visible and infrared linear detector arrays for the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) instrument uses four separate focal plane assemblies consisting of line array detectors that are multiplexed to a common J-FET preamp using a FET switch multiplexing (MUX) technique. A 32-element silicon line array covers the spectral range from 0.41 to 0.70 microns. Three additional 64-element indium antimonide (InSb) line arrays cover the spectral range from 0.68 to 2.45 microns. The spectral sampling interval per detector element is nominally 9.8 nm, giving a total of 224 spectral channels. All focal planes operate at liquid nitrogen temperature and are housed in separate dewars. Electrical performance characteristics include a read noise of less than 1000 e(-) in all channels, response and dark nonuniformity of 5 percent peak to peak, and quantum efficiency of greater than 60 percent.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Airborne Visible/Infrared Imaging Spectrometer (AVIRIS). A Description of the Sensor, Ground Data Processing Facility, Laboratory Calibration, and First Results; Airborne Visible(Inf
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  • 8
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    Advanced high temperature static strain sensor development (1986)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: An examination was made into various techniques to be used to measure static strain in gas turbine liners at temperatures up to 1150 K (1600 F). The methods evaluated included thin film and wire resistive devices, optical fibers, surface acoustic waves, the laser speckle technique with a heterodyne readout, optical surface image and reflective approaches and capacitive devices. A preliminary experimental program to develop a thin film capacitive device was dropped because calculations showed that it would be too sensitive to thermal gradients. In a final evaluation program, the laser speckle technique appeared to work well up to 1150 K when it was used through a relatively stagnant air path. The surface guided acoustic wave approach appeared to be interesting but to require too much development effort for the funds available. Efforts to develop a FeCrAl resistive strain gage system were only partially successful and this part of the effort was finally reduced to a characterization study of the properties of the 25 micron diameter FeCrAl (Kanthal A-1) wire. It was concluded that this particular alloy was not suitable for use as the resistive element in a strain gage above about 1000 K.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: NASA-CR-179520 , NAS 1.26:179520 , R86-995875-28
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  • 9
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    High temperature static strain gage alloy development program (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The literature, applicable theory and finally an experimental program were used to identify new candidate alloy systems for use as the electrical resistance elements in static strain gages up to 1250K. The program goals were 50 hours of use in the environment of a test stand gas turbine engine with measurement accuracies equal to or better than 10 percent of full scale for strains up to + or - 2000 microstrain. As part of this effort, a computerized electrical resistance measurement system was constructed for use at temperatures between 300K and 1250K and heating and cooling rates of 250K/min and 10K/min. The two best alloys were an iron-chromium-aluminum alloy and a palladium base alloy. Although significant progress was made, it was concluded that a considerable additional effort would be needed to fully optimize and evaluate these candidate systems.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: NASA-CR-174833 , NAS 1.26:174833 , R85-915952-13
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  • 10
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    A novel method of calculating far-field patterns of large aperture antennas (1986)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A method is described for calculation of the radiation pattern of large aperture antennas. A piece-wise linear approximation of the aperture field using overlapping pyramidal basis functions allows the radiation pattern of an aperture antenna to be calculated as though it were a two-dimensional array. The calculation of radiation pattern data versus theta and phi, suitable for 3-D or contour plot algorithms, is achieved by locating the array in the yz-plane and performing a summation over the aperture field data sampled on a square grid. A FORTRAN subroutine is provided for performing radiation pattern calculations. Numerical results are included to demonstrate the accuracy and convergence of the method. These numerical results indicate that typical accuracies of + or - 0.1 dB for Directivity, + or - dB for the 1st Sidelobe Level, and + - 2dB for the 2nd Sidelobe Level can be obtained with an aperture grid of 45x45 points and requires approximately 0.02 seconds CPU time per far-field data point on a VAX 11/750 with a floating point accelerator.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-TM-87644 , NAS 1.15:87644
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