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NASA NTRS1982

Onboard processing for a 30/20 GHz communications satellite

A systems configuration for the baseband processor for a TDMA communications satellite utilizing the 30 GHz uplink and 20 GHz downlink bands will be discussed. The baseband processor functions include QPSK burst demodulation, convolutional decoding, data routing, encoding, QPSK modulation, and antenna steering. The performance of the burst demodulator will be examined. Power and weight estimates for the baseband processor will be presented.

Reisenfeld, S.↗

NASA NTRS1983

The sun at 1.4 GHz - Intensity and polarization

1.4 GHz radio pictures of the sun are presented which were made on 1981 September 26 using the VLA with a resolution of 40 arcsec. Features observed include active regions, limb brightening, coronal holes and filament channels; all correspond well with features seen in H-alpha or He 10830 A, and can be explained as relative enhancements or depressions of free-free brmsstrahlung from the corona and upper transition region. The degree of circular polarization of the radiation from active regions ranges up to 0.2 and the sense corresponds, with a few exceptions, with the polarity of the photospheric magnetograms, even though the 1.4 GHz radiation arises from the corona at a height of 10 to 50 Mm. The polarization is in the sense of the x-mode and is highest near the edges of active regions, whereas the brightness is highest (maximum of 2.2 x 10 to the 6th K) near the line of zero polarization.

Dulk, G. A.↗

NASA NTRS1983

A 20-GHz IMPATT transmitter, summary

A three stage IMPATT diode amplifier capable of a 16 W CW output and a 2 dB bandwidth of 117 MHz was developed. On the component side, high performance circulators with a 0.2 dB insertion loss and bandwidth of 5 GHz were fabricated. State of the art GaAs IMPATT diodes incorporating diamond heat sink and double Read doping profile were also developed. The diodes are capable of a 2.5 W CW output. A few diodes achieved power outputs as high as 3 W. On the circuit side, high gain (up to 12 dB per stage) single diode, multituned circuits capable of 2 GHz and 930 MHx bandwidth were developed as the first and second stages, respectively, of the amplifier. A 12 diode waveguide cavity combiner was developed as the output stage. The output stage utilized commercially available single drift GaAs IMPATT diodes.

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NASA NTRS1984

183 GHz water line variation: An energetic outburst in orion KL

Observations of the 3(13)-2(20) transition of water vapor in the direction of Ori MC1 in 1980 February show a 50% flux increase and an apparent additional red shift of approximately 2 km/s relative to the line observed in 1977 December. From a detailed examination of the amplitude and frequency calibration, it appears unlikely that the effect is due to systematic error. The increase is attributed to the appearance of a new component at a velocity of 12 km/s with respect to the local standard of rest. The new component also has broad wings. Increased emission from a region in the high-velocity core of Ori MC1 can be due either to additional far-IR radiation to pump the 1983 GHz transition or to a change in the physical conditions in the gas. Statistical equilibrium calculations using the large-velocity-gradient formalism were carried out to develop a model for the emission. The calculations support a model in which the gas in the region of enhanced emission is hotter than the dust. The temporal coincidence between the 183 GHZ increase and the 22 GH1 water maser outburst suggests a common, impulsive cause, which has heated the gas in a part of the HV source, enhancing the emission in both transitions.

Kuiper, T. B. H.↗

NASA NTRS1984

A search for 183-GHz emission from water in late-type stars

A search was made for 183 GHz line emission from water vapor in the direction of twelve Mira and two semiregular variables. Upper limits to the emission are in the range of 2000 to 5000 Jy. It is estimated that thermal emission from the inner regions of late type stellar envelopes will be on the order of ten Jy. Maser emission, according to one model, would be an order of magnitude stronger. From the limited set sampled, the possibility of very strong maser emission at 183 GHz cannot yet be ruled out.

Kuiper, T. B. H.↗

NASA NTRS1983

Low-noise 115-GHz receiver using superconducting tunnel junctions

A 110-118-GHz receiver based on a superconducting quasiparticle tunnel junction mixer is described. The single-sideband noise temperature is as low as 68 + or - 3 K. This is nearly twice the sensitivity of any other receiver at this frequency. The receiver was designed using a low-frequency scale model in conjunction with the quantum mixer theory. A scaled version of the receiver for operation at 46 GHz has a single-sideband noise temperature of 55 K. The factors leading to the success of this design are discussed.

Pan, S.-K.↗

NASA NTRS1983

A three-stage power amplifier for a 20 GHz monolithic transmit module

Design, fabrication, and test results of a three-stage GaAs monolithic power amplifier covering the 17.7 to 20.2 GHz band are described. Intermediate results for single and two-stage amplifiers are also presented. The 1.5 x 3.1 millimeter three-stage amplifier chip has 15 dB gain from 16.5 to 20.2 GHz. Measured saturated output power is between +20 and +21 dBm with improvement expected from minor circuit and device changes.

Petersen, W. C.↗

NASA NTRS1984

A new multiple beam satellite antenna for 30/20 GHz communications coverage of CONUS-experimental evaluation

Additional frequency bands are needed to satisfy requirements related to the rapid growth of satellite communications, and the utilization of the 30/20 GHz frequencies is being considered. The present investigation is concerned with the experimental verification phase of an antenna technology study sponsored by NASA. The feasibility of narrow (0.3 degree) directive beam scanning over the entire continental U.S. (CONUS) from a single antenna at 30/20 GHz is demonstrated. The POC (Proof-of-Concept) model is based on an employment of an offset shaped dual reflector optics. The main reflector and the subreflector are both fabricated from aluminum. Attention is given to feed array and beam-forming network, multiple beam antenna range tests, an analysis, and test results.

Smoll, A. E.↗

NASA NTRS1984

183 GHz water line variation - An energetic outburst in Orion KL

Observations of the 3(13)-2(20) transition of water vapor in the direction of Ori MC1 in 1980 February show a 50 percent flux increase and an apparent additional red shift of approximately 2 km/s relative to the line observed in 1977 December. From a detailed examination of the amplitude and frequency calibration, it appears unlikely that the effect is due to systematic error. The increase is attributed to the appearance of a new component at a velocity of 12 km/s with respect to the local standard of rest. The new component also has broad wings. Increased emission from a region in the high-velocity core of Ori MC1 can be due either to additional far-IR radiation to pump the 1983 GHz transition or to a change in the physical conditions in the gas. Statistical equilibrium calculations using the large-velocity-gradient formalism were carried out to develop a model for the emission. The calculations support a model in which the gas in the region of enhanced emission is hotter than the dust. The temporal coincidence between the 183 GHz increase and the 22 GH1 water maser outburst suggests a common, impulsive cause, which has heated the gas in a part of the HV source, enhancing the emission in both transitions.

Kuiper, T. B. H.↗

NASA NTRS1983

Advanced 30/20 GHz multiple-beam antennas for communications satellites

Design concepts under development utilize two separate spacecraft antenna systems, one uplink at 30 GHz and the other a downlink at 20 GHz, where each antenna provides multiple fixed and scanning beams. Two contractors completed configuration trade-off studies and breadboarding of critical technology components, and are fabricating and testing proof-of-concept (POC) models to demonstrate the technology feasibility. Technology developments required for the proposed systems are presented, along with each contractor's progress to date. The technology development areas discussed include: (1) offset Cassegrain and shaped reflector systems for narrow beams with low sidelobes and wideangle off-axis scan; (2) diplexed beam-forming networks for dual polarization, low sidelobes, and fixed and scan-beam operation; (3) fast switching networks for scanning beams; and (4) fabrication of precision feed components and large offset reflectors.

Myhre, R. W.↗

NASA NTRS1984

60-GHz integrated-circuit high data rate quadriphase shift keying exciter and modulator

An integrated-circuit quadriphase shift keying (QPSK) exciter and modulator have demonstrated excellent performance directly modulating a carrier frequency of 60 GHz with an output phase error of less than 3 degrees and maximum amplitude error of 0.5 dB. The circuit consists of a 60-GHz Gunn VCO phase-locked to a low-frequency reference source, a 4th subharmonic mixer, and a QPSK modlator packaged into a small volume of 1.8 x 2.5 x 0.35 in. The use of microstrip has the advantages of small size, light-weight, and low-cost fabrication. The unit has the potential for multigigabit data rate applications.

Grote, A.↗

NASA NTRS1984

A search for 183 GHz emission from water in late-type stars

Kuiper, T. B. H.↗

NASA NTRS1985

Development and use of the computer software package for planning the 12 GHz broadcasting-satellite service at RARC '83

The 1983 Regional Administrative Radio Conference (RARC '83) had mainly the objective to draw up a plan of detailed frequency assignments and orbital positions for the 12 GHz broadcasting-satellite service (BSS) in ITU Region 2 (the Western Hemisphere) and associated feeder links (earth-to-space) in the 17 GHz band. It was found that for RARC '83 new planning methods and procedures would be needed. The new requirements made it necessary to develop a new generation of planning software. Attention is given to the development of the computer programs to be used at the conference, the package of computer programs, and the use of the computer programs.

Bowen, R. R.↗

NASA NTRS1984

Modeling of NASA's 30/20 GHz satellite communications system

NASA is in the process of developing technology for a 30/20 GHz satellite communications link. Currently hardware is being assembled for a test transponder. A simulation package is being developed to study the link performance in the presence of interference and noise. This requires developing models for the components of the system. This paper describes techniques used to model the components for which data is available. Results of experiments performed using these models are described. A brief overview of NASA's 30/20 GHz communications satellite program is also included.

Kwatra, S. C.↗

NASA NTRS1984

Passive microwave rain estimation over land and ocean at 37 GHz

The use of Nimbus-7 Scanning Multichannel Microwave Radiometer brightness-temperature data to estimate rain rates is discussed in a review of the author's recent experimental investigations. The performance of multiple-frequency spring, summer, and fall rain-rate algorithms for use over land; a single-frequency (37-GHz) algorithm for use over warm oceans; and 37-GHz brightness-temperature criteria for detecting severe thunderstorms is presented in graphs and tables and briefly characterized. The potential value of a microwave radiometer in GEO is indicated.

Spencer, R. W.↗

NASA NTRS1985

Test results for 20-GHz GaAs FET spacecraft power amplifier

Test were conducted to measure the performance of the 20-GHz solid state, proof-of-concept amplifier. The amplifier operates over the 17.7 to 20.2-GHz frequency range and uses high power gallium arsenide field effect transistors. The amplifier design and test methods are briefly described. NASA and contractor performance data are compared.

Shalkhauser, K. A.↗

NASA NTRS1986

Near-field testing of the 30 GHz TRW proof-of-concept multibeam antenna

Near-field testing was conducted on the 30 GHz TRW proof-of-concept (POC) Multibeam Antenna (MBA). The TRW POC MBA is a dual offset Cassegrain reflector system using a 2.7 m main reflector. This configuration was selected to assess the ability to create both multiple fixed and scanned spot beams. The POC configuration investigated frequency reuse via spatial separation of beams, polarization selectivity and time division multiple access scanning at 30 GHz. Measurements of directivity, sidelobe level, and pattern were made at NASA Lewis Research Center's Near-Field Antenna Test Facility. Presented in this paper are complete results of these measurements. Included is a detailed discussion of all testing procedures and parameters. Results of additional testing used to evaluate diffraction effects of the subreflector and distortions of the main reflector are also presented.

Kunath, R. R., Jr.↗

NASA NTRS1984

The 60 GHz antenna system analyses for intersatellite links, phase B

The purpose of this study is first to investigate, classify, and compare applicable antenna systems capable of establishing and maintaining intersatellite links at 60 GHz and secondly to select the most applicable system for a detailed conceptual design. The results are to be applicable to the development of intersatellite links at 60 GHz for future programs. Design goals are listed.

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