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NASA NTRS1988

Millimeter-wave diode-grid phase shifters

Monolithic diode grids have been fabricated on 2-cm square gallium-arsenide wafers with 1600 Schottky-barrier varactor diodes. Shorted diodes are detected with a liquid-crystal technique, and the bad diodes are removed with an ultrasonic probe. A small-aperture reflectometer that uses wavefront division interference was developed to measure the reflection coefficient of the grids. A phase shift of 70 deg with a 7-dB loss was obtained at 93 GHz when the bias on the diode grid was changed from -3 V to 1 V. A simple transmission-line grid model, together with the measured low-frequency parameters for the diodes, was shown to predict the measured performance over the entire capacitive bias range of the diodes, as well as over the complete reactive tuning range provided by a reflector behind the grid, and over a wide range of frequencies from 33 GHz to 141 GHz. This shows that the transmission-line model and the measured low-frequency diode parameters can be used to design an electronic beam-steering array and to predict its performance. An electronic beam-steering array made of a pair of grids using state-of-the-art diodes with 5-ohm series resistances would have a loss of 1.4 dB at 90 GHz.

Lam, Wayne W.↗

NASA NTRS1988

Ultraviolet spectroscopy of R Coronae Borealis

Observations of the hydrogen-deficient supergiant R CrB were obtained with the IUE over an interval of 54 days in order to study the nature of this star's irregular, small-amplitude variations in light. By chance, the series of observations coincided with a dip in the light intermediate between the normal fluctuations and the deep declines associated with the formation of an obscuring dust cloud. High-resolution spectra have been used to search for radial velocity variations, while low-resolution spectra yield ultraviolet light curves down to 1810 A. Both types of spectra have been analyzed for indications of temperature changes. It is found that a combination of photospheric temperature variation and variable extinction is necessary to account for the details of the observations. A simple, ad hoc, periodic model is presented in which the amount of obscuring dust varies in proportion to the drop in temperature, but at a later time, reproduces the wavelength dependence of both the amplitudes and phase shifts of the light curves. The radial velocities are consistent with pulsation being responsible for the temperature variation.

Holm, A. V.↗

NASA NTRS1987

False lock performance in polarity-type Costas receivers in the presence of periodic data patterns

The authors address the false-lock performance of receivers which use polarity-type Costas loops for the carrier recovery of unbalanced quadrature phase-shift keyed (QPSK), asynchronous QPSK or binary PSK (BPSK) signals in the presence of periodic data patterns. The potential false-lock frequencies are first identified. Expressions for both true-lock and false-lock components are also derived, thereby allowing numerical evaluation of various key parameters for cases of practical interest.

Wang, James June-Ming↗

NASA NTRS1988

The morphology and meteorology of Southern Hemisphere spring total ozone mini-holes

Two case studies of miniholes, rapid ozone decreases, noted in 1987 near the base of the Antarctic peninsula are studied using a digital filter. The results show a strong correlation of the total ozone minihole with a temperature minihole (a negative temperature perturbation), and a westward tilt with altitude of the temperature minihole. The ozone minihole is phase shifted both slightly to the east of a high in the geopotential height field and slightly to the west of a local low in the Ertel potential vorticity field.

Newman, Paul A.↗

NASA NTRS1988

Evaluation of the communications impact of a low power arcjet thruster

The interaction of a 1 kW arcjet thruster plume with a communications signal is evaluated. A two-parameter, source flow equation has been used to represent the far flow field distribution of the arcjet plume in a realistic spacecraft configuration. Modelling the plume as a plasma slab, the interaction of the plume with a 4 GHz communications signal is then evaluated in terms of signal attenuation and phase shift between transmitting and receiving antennas. Except for propagation paths which pass very near the arcjet source, the impacts to transmission appear to be negligible. The dominant signal loss mechanism is refraction of the beam rather than absorption losses due to collisions. However, significant reflection of the signal at the sharp vacuum-plasma boundary may also occur for propagation paths which pass near the source.

Carney, Lynnette M.↗

NASA NTRS1989

Review Of Fiber-Optic Electric-Field Sensors

Tutorial paper reviews state of art in fiber-optic sensors of alternating electric fields. Because such sensors are made entirely of dielectric materials, they are relatively transparent to incident electric fields; they do not distort fields significantly. Paper presents equations that express relationships among stress, strain, and electric field in piezoactive plastic and equations for phase shift in terms of photoelastic coefficients and strains in optical fiber.

De Paula, Ramon P.↗

NASA NTRS1989

Fast Correction For Doppler In MDPSK Signals

Detector of multiple differential phase-shift-keyed (MDPSK) signals designed to effect combination of open-loop estimation of frequency and differential detection of digital modulation. Improved design expected to decrease probability of bit errors in situations in which carrier frequency uncertain and signals transmitted in bursts too short to allow closed-loop tracking of carrier frequency - for example, in transmission of digitally-coded voice signals in land-mobile/satellite communications at ultra-high frequencies.

Simon, M. K.↗

NASA NTRS1989

Digital 8-DPSK Modem For Trellis-Coded Communication

Digital real-time modem processes octuple differential-phase-shift-keyed trellis-coded modulation. Intended for use in communicating data at rate up to 4.8 kb/s in land-mobile satellite channel (Rician fading) of 5-kHz bandwidth at carrier frequency of 1 to 2 GHz. Modulator and demodulator contain digital signal processors performing modem functions. Design flexible in that functions altered via software. Modem successfully tested and evaluated in both laboratory and field experiments, including recent full-scale satellite experiment. In all cases, modem performed within 1 dB of theory. Other communication systems benefitting from this type of modem include land mobile (without satellites), paging, digitized voice, and frequency-modulation subcarrier data broadcasting.

Jedrey, T. C.↗

NASA NTRS1989

Making A Circular-Harmonic Filter

Optical image-correlating system made rotationally invariant. Experiment shows circular-harmonic filter generated optically. Hologram made by phase-shifted-double-exposure procedure. Filter used in optical image-recognition system based on correlation between target (image to be recognized) and matched spatial filter. In addition to usual invariance under translation of target, circular harmonic filter invariant under rotation of target; peak intensity of illumination at origin of correlation plane does not vary when target rotated about optical axis.

Cheng, Yeou Yen↗

NASA NTRS1988

Facility for interferometric testing of 1.25-m mirrors at liquid helium temperatures

A concept is presented for a national cryogenic optics test facility capable of optical characterization of 1.25 m diameter optics having focal lengths up to 6.2 m at temperatures from 300 K to near 4 K. The facility will be comprised of a large Dewar with a phase shift interferometer, a two stage vacuum system employing a turbomolecular pump, and an integral vibration isolation system. The entire facility will be housed in a concrete site with a massive floor to assist in reducing vibration during optical tests. By providing interchangeable sections, the overall height of the Dewar can be adjusted to provide for testing of shorter focal length optics. The background for the facility is discussed along with the facility location, and the requirements and the performance considerations which drive the Dewar design with respect to the vibration isolation system, vacuum system, and optical interferometry.

Salerno, Louis J.↗

NASA NTRS1989

Launch commit criteria performance trending analysis, phase 1, revision A. SRM and QA mission services

An assessment of quantitative methods and measures for measuring launch commit criteria (LCC) performance measurement trends is made. A statistical performance trending analysis pilot study was processed and compared to STS-26 mission data. This study used four selected shuttle measurement types (solid rocket booster, external tank, space shuttle main engine, and range safety switch safe and arm device) from the five missions prior to mission 51-L. After obtaining raw data coordinates, each set of measurements was processed to obtain statistical confidence bounds and mean data profiles for each of the selected measurement types. STS-26 measurements were compared to the statistical data base profiles to verify the statistical capability of assessing occurrences of data trend anomalies and abnormal time-varying operational conditions associated with data amplitude and phase shifts.

Source record↗

NASA NTRS1989

The 5-kW arcjet power electronics

The initial design and evaluation of a 5 kW arcjet power electronics breadboard which as been integrated with a modified 1 kW design laboratory arcjet is presented. A single stage, 5 kW full bridge, pulse width modulated (PWM), power converter was developed which was phase shift regulated. The converter used metal oxide semiconductor field effect transistor (MOSFET) power switches and incorporated current mode control and an integral arcjet pulse ignition circuit. The unoptimized power efficiency was 93.5 and 93.9 percent at 5 kW and 50A output at input voltages of 130 and 150V, respectively. Line and load current regulation at 50A output was within one percent. The converter provided up to 6.6 kW to the arcjet with simulated ammonia used as a propellant.

Gruber, R. P.↗

NASA NTRS1989

Aeronautical mobile TDMA/MCTDMA system

A multiple carrier Time Division Multiple Access (TDMA) system capable of supporting voice, stream data, and packet data traffic between aircraft and ground terminals is presented. Demand assignment permits efficient resource sharing for voice and stream data. The bandwidth efficiency of uncoded A Quadrature Phase Shift Keying (AQPSK) is 1 bps/Hz. High time efficiency (approximately equals 83 percent) is achieved through the use of symbol synchronous TDMA. Demodulation is achieved without loop hang-up while requiring only a 16 symbol preamble each burst. A concatenated coding system provides reliable transmission under multipath conditions.

Magill, Thomas↗

NASA NTRS1989

The upper-branch stability of compressible boundary layer flows

The upper-branch linear and nonlinear stability of compressible boundary layer flows is studied using the approach of Smith and Bodonyi (1982) for a similar incompressible problem. Both pressure gradient boundary layers and Blasius flow are considered with and without heat transfer, and the neutral eigenrelations incorporating compressibility effects are obtained explicitly. The compressible nonlinear viscous critical layer equations are derived and solved numerically and the results indicate some solutions with positive phase shift across the critical layer. Various limiting cases are investigated including the case of much larger disturbance amplitudes and this indicates the structure for the strongly nonlinear critical layer of the Benney-Bergeon (1969) type. It is also shown how a match with the inviscid neutral inflexional modes arising from the generalized inflexion point criterion, is achieved.

Gajjar, J. S. B.↗

NASA NTRS1988

The performance of trellis coded multilevel DPSK on a fading mobile satellite channel

The performance of trellis-coded multilevel differential phase-shift-keying (MDPSK) modulation over Rician and Rayleigh fading channels is discussed. For operation at L-band, this signalling technique leads to a more robust system than the coherent system with dual pilot tone calibration previously proposed for UHF. The results are obtained using a combination of analysis and simulation. The analysis shows that the design criterion for trellis codes to be operated on fading channels with interleaving/deinterleaving is no longer free Euclidean distance. The correct design criterion for optimizing bit error probability of trellis coded MDPSD over fading channels is presented along with examples illustrating its application.

Simon, Marvin K.↗

NASA NTRS1988

A lower bound on the minimum Euclidean distance of trellis-coded modulation schemes

A lower bound on the minimum free Euclidean distance of trellis-coded modulation (TCM) is derived that guarantees the existence of good TCM codes of any complexity. The bound is used to compare trellis codes combined with phase-shift keying, pulse amplitude modulation, and quadrature amplitude-shift keying modulation. This random coding bound is the first lower bound on the free distance of trellis codes, is tighter than any upper bound for large constraint lengths, and predicts the asymptotic performance of TCM when the complexity of the code becomes large. The bound can be used with any code rate and any modulation scheme and shows that the free distance increases linearly with the constraint length for large values of the constraint length.

Rouanne, Marc↗

NASA NTRS1989

5-kW arcjet power electronics

Gruber, R. P.↗

NASA NTRS1990

Crystal Oscillators Operate Beyond Rated Frequencies

Amplifiers with single-pole frequency responses used in their "roll-off" regions. Class of crystal oscillators based on use of negative-voltage-gain amplifiers at frequencies well into "roll-off" frequency regions of their gain-versus-frequency curves. Defining characteristic helps keep costs of oscillators low; not necessary to use more expensive amplifiers that have flat frequency responses out to desired operating frequencies. Enables amplifier to produce phase shift necessary for oscillation, reducing cost further by eliminating need for some of passive components in oscillators of more conventional design.

Kleinberg, Leonard L.↗