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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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Tubes in space - Very much alive

Some advantages of TWTs over SSDs are discussed. Wideband TWTs have been developed which can produce 20 W of RF power at 20 GHz with 40 percent efficiency, a figure three or four times that available from SSDs such as FETs. The basic performance of TWTs exceeds that of SSDs for any given bandwidth and frequency. SSDs are transit time limited, and their performance deteriorates fundamentally as the reciprocal of the square of the operating frequency. Power limits for SSDs have been reached or are quickly being approached. Free electron devices such as tubes have an efficiency advantage because electrons in the vacuum travel faster than bulk charges in SSDs. Combined SSD devices are prone to burnout and incur penalties due to the need to dissipate heat. TWTs have a 6.7:1 advantage in radiator area ratio. Recent progress in TWT technology has produced a tenfold increase in CW output power, doubled to quadrupled the efficiency, and pushed frequency ranges into the terahertz region, orders of magnitude beyond the SSD cutoff.

Kosmahl, H. G.↗
NASA NTRS1982

Near-infrared linear array spectrometer for space applications

A 128-element InSb linear detector array read out with a field effect transistor (FET) multiplexing scheme has been developed at the Jet Propulsion Laboratory. State-of-the-art NEP, uniform response, on-detector charge integration, and very low focal plane heat load compared to that of discrete detector arrays allows this type of array to open new possibilities for spaceborne near-infrared imaging spectrometers. Large number of cooled detector elements are feasible with the new technology, making it practical to design sensitive spectrometers even for spinning spacecraft where simultaneous wavelength coverage is necessary to avoid confusion of spatial with spectral variations.

Apt, J.↗
NASA NTRS1983

GaAs microwave devices and circuits with submicron electron-beam defined features

This paper describes the fabrication and application of GaAs FET's, both as discrete microwave devices and as the key active components in monolithic microwave integrated circuits. The performance of these devices and circuits is discussed for frequencies ranging from 3 to 25 GHz. The crucial fabrication step is the formation of the submicron gate by electron-beam lithography.

Wisseman, W. R.↗
NASA NTRS1982

A comparative study of real-time spaceborne synthetic aperture radar processing techniques

A review of various spaceborne synthetic aperture radar (SAR) processing algorithms and their associated real-time SAR processor architectures is given in this paper. The processing complexity for each real-time SAR processor is presented next. A complexity comparison is then given based on the Seasat SAR parameters. It is shown that the frequency/time domain hybrid fast correlation and the two-stage fast Fourier transform (FET) approaches are the two most cost-effective choices for real-time spaceborne SAR processing. Finally, a discussion on future development trends in real-time spaceborne SAR processing is given.

Liu, K. Y.↗
NASA NTRS1983

The 30 GHz communications satellite low noise receiver

A Ka-band low noise front end in proof of concept (POC) model form for ultimate spaceborne communications receiver deployment was developed. The low noise receiver consists of a 27.5 to 30.0 GHz image enhanced mixer integrated with a 3.7 to 6.2 GHz FET low noise IF amplifier and driven by a self contained 23.8 GHz phase locked local oscillator source. The measured level of receiver performance over the 27.3 to 30.0 GHz RF/3.7 to 6.2 GHz IF band includes 5.5 to 6.5 dB (typ) SSB noise figure, 20.5 + or - 1.5 dB conversion gain and +23 dBm minimum third order two tone intermodulation output intercept point.

Steffek, L. J.↗
NASA NTRS1984

SETI Investigations at Jodrell Bank, England: September Through November 1983

The radiofrequency interference RFI environment was examined in the frequency band 1404 to 1444 MHz using the DSN Advanced Systems' Radio Frequency Interference Surveillance System. An uncooled FET amplifier was placed on the 12.8-m antenna, and unlimited observing time was made available to the SETI project. One night of observing at 1667 MHz was made available on the 76 m antenna. Preliminary results of four investigations are reported: (1) full scans of the horizon, cataloging RFI events between 1404 and 1444 MHz; (2) lunar reflections of terrestrial RFI signals between 1424 and 1444 MHz; (3) noise background distortions caused by galactic neutral hydrogen emission at 1420.4 MHz; and (4) low sensitivity search for spectral features of F, G, and K stars.

Downs, G. S.↗
NASA NTRS1984

Effect of RF Filtering on the Performance of Uncoded PCM/PM Telemetry Channels

A method for calculating the increase in received telemetry signal power required to compensate for the use of a radio frequency interference (RFI) filter in front of the DSN receiving system low-noise amplifier is described. The telemetry system for which the degradation is calculated is an uncoded PCM/PM system in which the NRZ data directly modulates the carrier at a modulation level which leaves a discrete carrier. A phase-locked loop in the RF receiver tracks the discrete carrier and coherently demodulates the PCM data. The RFI filter may be a series of Butterworth, Tchebychev, or Bessel low-pass, high-pass, band-pass, or band-reject filters, each with arbitrary bandwidth, number of poles, and, for band-pass or band-reject filters, resonant frequency. The only restriction is that the RFI filter must have only simple poles. Numerical results are presented for the RFI filters the DSN plans to place in front of the S-band FET, S-band maser, and X-band maser low noise amplifiers. The main conclusion is that the filters will produce negligible degradation at data rates below 4 Mbps.

Koerner, M. A.↗
NASA NTRS1984

Integrating IR detector imaging systems

An integrating IR detector array for imaging is provided in a hybrid circuit with InSb mesa diodes in a linear array, a single J-FET preamplifier for readout, and a silicon integrated circuit multiplexer. Thin film conductors in a fan out pattern deposited on an Al2O3 substrate connect the diodes to the multiplexer, and thick film conductors also connect the reset switch and preamplifier to the multiplexer. Two phase clock pulses are applied with a logic return signal to the multiplexer through triax comprised of three thin film conductors deposited between layers. A lens focuses a scanned image onto the diode array for horizontal read out while a scanning mirror provides vertical scan.

Bailey, G. C.↗
NASA NTRS1982

A study of the high frequency limitations of series resonant converters

A transformer induced oscillation in series resonant (SR) converters is studied. It may occur in the discontinuous current mode. The source of the oscillation is an unexpected resonant circuit formed by normal resonance components in series with the magnetizing inductance of the output transformers. The methods for achieving cyclic stability are: to use a half bridge SR converter where q0.5. Q should be as close to 1.0 as possible. If 0.5q1.0, the instability will be avoided if psi2/3q-1/3. The second objective was to investigate a power field effect transistor (FET) version of the SR converter capable of operating at frequencies above 100 KHz, to study component stress and losses at various frequencies.

Stuart, T. A.↗
NASA NTRS1984

A Battery Charger and State of Charge Indicator

A battery charger which has a full wave rectifier in series with a transformer isolated 20 kHz dc-dc converter with high frequency switches, which are programmed to actively shape the input dc line current to be a mirror image of the ac line voltage is discussed. The power circuit operates at 2 kW peak and 1 kW average power. The BC/SCI has two major subsystems: (1) the battery charger power electronics with its controls; and (2) a microcomputer subsystem which is used to acquire battery terminal data and exercise the state of charge software programs. The state of charge definition employed is the energy remaining in the battery when extracted at a 10 kW rate divided by the energy capacity of a fully charged new battery. The battery charger circuit is an isolated boost converter operating at an internal frequency of 20 kHz. The switches selected for the battery charger are the single most important item in determining its efficiency. The combination of voltage and current requirements dictate the use of high power NPN Darlington switching transistors. The power circuit topology is a three switch design which utilizes a power FET on the center tap of the isolation transformer and the power Darlingtons on each of the two ends. An analog control system is employed to accomplish active input current waveshaping as well as the necessary regulation.

Latos, T. S.↗
NASA NTRS1983

A Ka-band GaAs monolithic phase shifter

The design and performance of a GaAs monolithic 180-degree one-bit switched line phase shifter test circuit for Ka-band operation is presented. A self-aligned gate (SAG) fabrication technique is also described that reduces resistive parasitics in the switching FET's. Over the 27.5-30 GHz band, typical measured differential insertion phase is within 10-20 deg of the ideal time delay characteristic. Over the same band, the insertion loss for the SAG phase shifter is about 2.5-3 dB per bit. The SAG fabrication technique holds promise in reducing phase shifter insertion loss to about 1.5 dB/bit for 30-GHz operation.

Sokolov, V.↗
NASA NTRS1984

The ACTS Flight System - Cost-Effective Advanced Communications Technology

The multibeam communications package (MCP) for the Advanced Communications Technology Satellite (ACTS) to be STS-launched by NASA in 1988 for experimental demonstration of satellite-switched TDMA (at 220 Mbit/sec) and baseband-processor signal routing (at 110 or 27.5 Mbit/sec) is characterized. The developmental history of the ACTS, the program definition, and the spacecraft-bus and MCP parameters are reviewed and illustrated with drawings, block diagrams, and maps of the coverage plan. Advanced features of the MPC include 4.5-dB-noise-figure 30-GHz FET amplifiers and 20-GHz TWTA transmitters which provide either 40-W or 8-W RF output, depending on rain conditions. The technologies being tested in ACTS can give frequency-reuse factors as high as 20, thus greatly expanding the orbit/spectrum resources available for U.S. communications use.

Holmes, W. M., Jr.↗
NASA NTRS1982

Integrating 128 element InSb array - Recent results

There has been a continuing evolution toward larger arrays of infrared detectors, and the technology base derived from the Galileo Near Infrared Mapping Spectrometer (NIMS) has been expanded to linear arrays including from 128 to 512 elements. This advance is based on the commercial availability of high-quality InSb photodiodes and 128/256 element FET switch MUX's (multiplexing elements). The present investigation is concerned with an experimental 128-element linear imager using InSb detectors and silicon MUX for readout. Attention is given to detector array electrical characteristics, the detector readout architecture, noise, and special effects.

Bailey, G.↗
NASA NTRS1984

0.5 W 2-21 GHz monolithic GaAs distributed amplifier

A novel circuit concept to reduce the gate loss using series capacitors on the gate feeding lines has been implemented for a distributed amplifier design. It has significantly increased the gate width of the amplifier with a resultant increase of the broadband output power and efficiency. A monolithic GaAs distributed amplifier using 6 x 300-micron FETs has achieved a record output power of 0.5 W over the 2 to 21 GHz frequency band with at least 4 dB gain. The power-added efficiency was 14 percent. The linear gain was 5 plus or minus 1 dB over the same frequency band.

Kim, B.↗
NASA NTRS1983

Communications and logic systems at millimeter wave frequencies

Activities in materials development, lithography, FET experiments, and mixer diode fabrication are reported. In addition, articles are presented which address leakage effects in n-GaAs MESFET's and lateral nonuniform doping in GaAs MESFET's.

Source record↗
NASA NTRS1983

Communications and logic systems at millimeter wave frequencies, summary

During the contract period an AsCl3 epitaxial system used to provide buffer layers for FET structures was constructed. A submicron lithographic processes using deep U.V. techniques was developed and, employing these techniques, a working .5 micron gate device was produced. In addition, the development of submicron mixer diodes continued. The gettering of substrates of a technique to improve the mobility of ionimplantated layers was investigated. The result of this experiment showed a correlation between improved hall mobilities and gettered substrates. Finally, several theoretical studies are reported.

Source record↗
NASA NTRS1983

Status of NASA's multibeam communications technology program

Progress with prototype components for demonstrating an acceptable performance level for multibeam 30/20 GHz satellite communications scheduled for service in 1988 is summarized. Numerous companies were contracted by NASA for the various components and subsystems, which include 20 GHz transmitters, a traveling wave tube transmitter, an IMPATT amplifier, a GaAs FET amplifier, a 30 GHz low noise receiver, a trunking matrix switch, and a baseband processor. The key system is a 20 GHz offset dual reflector antenna with shaped surfaces for multibeam transmission. Tests to date have indicated success at meeting the performance objectives.

Santarpia, D. E.↗