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At least 1,693 records · Page 94

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NASA NTRS1986

Performance characteristics for an array of two receiving systems with equal apertures and enhanced radio frequency carrier margin improvement

Enhanced radio frequency carrier margin improvement for arrayed receiving systems for coherent reception of phase modulated signals with residual carrier provides a significant reduction in carrier loop phase noise and an increase in the signal to noise ratio in the RF carrier tracking loop with an attendant in telemetry radio loss. A significant increase in doppler frequency rate capability is also realized relative to operating at a narrower tracking loop bandwidth to obtain the same carrier sensitivity improvement. These performance characteristics are examined for an array of two receiving sysems with equal apertures and statistically independent prediction noise.

Brockman, M. H.↗

NASA NTRS1985

Pvarray: A software tool for photovoltaic array design

The application of PVARRAY, a software program for design of photovoltaic arrays are described. Results of sample parametric studies on array configurations are presented. It is concluded that PVARRAY could simulate a variety of configurations.

Burger, D. R.↗

NASA NTRS1986

Measuring the energy spectrum of primary cosmic rays with the Yakutsk EAS array

The Yakutsk Extensive Air Showers (EAS) array was designed for detecting the showers generated by the 10 to the 47th power to 10 to the 20th power eV primary cosmic rays and consists of numerous electron, muon, and Cerenkov light detectors arranged on a 20 sq km area terrain. The array is featured by the feasibility to detect the EAS-produced Cerenkov light, hence, as will be shown, to find the mean energy of the primary particles generating an ensemble of EAS of given size. Date collected is discussed.

Khristiansen, G. B.↗

NASA NTRS1986

Studies of air showers produced by primaries 10(16) eV using a combined scintillation and water-Cerenkov array

An array of 8 x 1.0 sq m plastic scintillation counters and 13 water-Cerenkov detectors (1 to 13.5 sq m) were operated at the center of the Haverah Park array to study some features of air showers produced by 10(16) eV primaries. Measurements of the scintillator lateral distribution function, the water-Cerenkov lateral distribution function, and of the distance dependence of the Cerenkov/scintillator ratio are described.

Brooke, G.↗

NASA NTRS1986

Centroid tracking with area array detectors

A computer program (ALGEVAL) has been developed to simulate the position estimating behavior of a centroid estimator algorithm using data typical of optical point spread function data recorded by an area array detector. Typical results are shown of varying detector properties and optical point spread function types. The detector parameters currently available for study include read noise mean value, dark current mean value and spatial variation, charge transfer efficiency and point spread function location, saturation level, signal level and pixel size. The program is capable of calculating any order centroid using an array size from 2 x 2 to 15 x 15 pixels. The output of the program is either a performance map, histogram data or tabluar data. A number of further developments are recommended.

Glavich, T. A.↗

NASA NTRS1984

Integrated detector array technology for infrared astronomy

The status of laboratory and telescope tests of integrated infrared detector array technology for astronomical applications is described. The devices tested represent a number of extrinsic and intrinsic detector materials and various multiplexer designs. Infrared arrays have now been used in successful astronomical applications. These have shown that device sensitivities can be comparable to those of discrete detector systems and excellent astronomical imagery can be produced.

Mccreight, c. R.↗

NASA NTRS1984

Astronomical camera using a high-performance indium antimonide linear array

The development and current status of InSb line arrays for astronomy are reviewed. Instrument concepts are currently being developed for an infrared instrument for NASA's Space Telescope which would use such detectors for both spectroscopy and imaging. Preliminary performance measurements are given for a simple pushbroom camera, using a 128-element line array, designed for operation on the 24-inch Cassegrain telescope at the JPL Table Mountain Observatory. The design and construction of the camera are described.

Herring, M.↗

NASA NTRS1985

Power conversion efficiency of semiconductor injection lasers and laser arrays in CW operation

The problem of optimizing power conversion efficiency of semiconductor lasers and laser arrays and minimizing efficiency degradation due to temperature effects is treated. A method for calculating this efficiency is described and some calculated results are presented and discussed. Under some conditions, a small increase in the thermal resistance of the device can result in a large reduction of its efficiency. Temperature effects are important in high-power semiconductor laser, and in particular in laser arrays, where low thermal resistance heat sinking may be crucial to the device operation.

Katz, J.↗

NASA NTRS1985

8.3 and 12.4 micron imaging of the Galactic Center source complex with the Goddard infrared array camera

A 30 x 30 arcsec field at the Galactic Center (1.5 x 1.5 parsec) was mapped at 8.3 microns and 12.41 microns with high spatial resolution and accurate relative astrometry, using the 16 x 16 Si:Bi accumulation mode charge injection device Goddard infrared array camera. The design and performance of the array camera detector electronics system and image data processing techniques are discussed. Color temperature and dust opacity distributions derived from the spatially accurate images indicate that the compact infrared sources and the large scale ridge structure are bounded by warmer, more diffuse material. None of the objects appear to be heated appreciably by internal luminosity sources. These results are consistent with the model proposing that the complex is heated externally by a strong luminosity source at the Galactic Center, which dominates the energetics of the inner few parsecs of the galaxy.

Gezari, D. Y.↗

NASA NTRS1986

Adaptive antenna arrays for weak interfering signals

It is shown that conventional adaptive arrays are unable to suppress weak interfering signals. To overcome this problem, the feedback loops controlling the array weights were modified, reducing the noise level by reducing the correlation between the noise components of the two inputs to the loop correlator. Various techniques to decorrelate these noise components are discussed. An expression is derived for the amount of noise decorrelation required to achieve a specified interference suppression. The results are of interest in connection with satellite communications.

Gupta, I. J.↗

NASA NTRS1985

Gain saturation effects in supermodes of phase-locked semiconductor laser arrays

A basic modal analysis that includes gain saturation effects in phase-locked semiconductor laser arrays is presented. For a particular supermode operation, different lasers in the array emit different amounts of light, and hence their (waveguide) propagation constants are modified differently. Solving the lasers' rate equations self-consistently with the coupled-mode wave equations seems to provide an answer that is in much better agreement with experimental results than the result using only the coupled-mode analysis.

Katz, J.↗

NASA NTRS1987

Injection Phase-Locked Laser-Diode Array

Phase-coherent emission with negligible far-field supermodes produced by proposed surface-emitting laser-diode array stimulated by holographically directed emission from single master diode. To achieve same coherence and output power, single laser diode requires high power density, which substantially reduces working lifetime. Proposed integrated optical array useful in communications

Lesh, James R.↗

NASA NTRS1986

The development and test of multi-anode microchannel array detector systems. Part 2: Soft X-ray detectors

Multi-Anode Microchannel Array (MAMA) detector systems with formats of 256 x 1024 pixels and active areas of 6 x 26 square mm are now under evaluation at visible, ultraviolet and soft x-ray wavelengths. Very-large-format versions of the MAMA detectors with formats of 2048 x 2048 pixels and active areas of 52 x 52 square mm are under development for use in the NASA Goddard Space Flight Center's Space Telescope Imaging Spectrograph (STIS). Open-structure versions of these detectors with CsI photocathodes can provide a high-resolution imaging capability at extreme ultraviolet (EUV) and soft x-ray wavelengths and can deliver a maximum count rate from each array in excess of 1 million counts s-1. In addition, these detector systems have the unique capability to determine the arrival time of a detected photon to an accuracy of 100 ns or better. The construction, mode-of-operation and performance characteristics of the MAMA detectors are described and the program for the development of the very-large-format detectors is outlined.

Timothy, J. G.↗

NASA NTRS1986

The NOAA TOGA antenna array

The Aeronomy Laboratory recently installed a 100 x 100 meter array antenna with limited beam steering on Christmas Island as a part of the TOGA (Tropical Ocean and Global Atmosphere) program. The array and the associated beam steering and indicating hardware are described.

Ecklund, W. L.↗

NASA NTRS1986

A 405-MHz, 5-beam phased array antenna

The Wave Propagation Lab. has completed the design and construction of a phased array antenna for use at 405.25 MHz for atmospheric wind profiling. The steering geometry of the sequentially switched beam is shown. The Yagi-Uda antenna elements are arranged on a square grid whose axes are 45 deg with respect to the cardinal directions. By constraining the phase difference between rows of identically phased elements to an even, integral submultiple of 360 deg, symmetries appear in the phasing maps which reduce the switching hardware. The vertical beam is generated by switching around the four beam circuitry which results in identical phasing on all of the elements. After the 18 signals are synthesized they are split and distributed about the array while maintaining proper phasing because of the symmetries. Computer simulations were employed in the design process.

Law, D. C.↗

NASA NTRS1986

Development of low-temperature transistor modules to improve the MSFC mid-infrared array

This report describes the low-temperature transistor modules designed for use with the MSFC mid-infrared array. The modules were developed in the Space Science Laboratory at Marshall Space Flight Center with Center Director's Discretionary Funds. The transistors (JFETs), which operate at a temperature of 77 K, are epoxied to a copper surface attached to a Teflon substrate. The module substrate insulates the JFETs from the 1.5K detector work surfaces and provides a convenient mounting structure for additional components such as solder pins. These modules have maintained their structural integrity during repeated temperature cycling, and they have to be convenient during maintenance and servicing of the infrared array.

Telesco, C. M.↗

NASA NTRS1986

Evaluation of Rockwell HgCdTe arrays for astronomical use

The 32 x 32 HgCdTe array manufactured by Rockwell International was proven to be a highly competitive detector type for use at wavelengths shorter than 2.5 microns. The goal of a K=+16 sky survey using this array attached to the Steward Observatory Transit Telescope is clearly within reach. The detector material exhibits high quantum efficiency and low dark currents indicating that its usefulness may extend beyond its use with a CCD readout on groundbased telescopes.

Lebofsky, M. J.↗

NASA NTRS1986

Si:As BIB detector arrays

Highlights of the results obtained on arsenic-doped silicon blocked impurity band (BIB) detectors and arrays since the invention of the BIB concept a few years ago are presented. After a brief introduction and a description of the BIB concept, data will be given on single detector performance. Then different arrays that were fabricated will be described and test data presented.

Bharat, R.↗