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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

The influence of polarization on millimeter wave propagation through rain

A program for the measurement and analysis of the depolarization and differential attenuation that occur when millimeter wave signals propagate through rain is described. Initial data are taken along a 1.43 km path at 17.65 GHz and a supporting theoretical model is developed to relate the propagation effects to rainfall rate and wind velocity. A block diagram of the overall experiment is included. It consists of: (1) an RF system (millimeter wave transmitter and receiver), (2) transmitting and receiving antennas, (3) a weather system with rain gauges, wind sensors, and drop counters, and (4) a digital control, processing, and data storage system.

Bostian, C. W.↗
NASA NTRS1986

RF characterization of monolithic microwave and mm-wave ICs

A number of fixturing techniques compatible with automatic network analysis are presented. The fixtures are capable of characterizing GaAs Monolithic Microwave Integrated Circuits (MMICs) at K and Ka band. Several different transitions are used to couple the RF test port to microstrip. Fixtures which provide chip level de-embedding are included. In addition, two advanced characterization techniques are assessed.

Romanofsky, R. R.↗
NASA NTRS1969

A positive taper traveling-wave tube

Synchronism can be maintained between the RF beam current and the circuit electromagnetic waves over substantially the entire length of a traveling-wave tube by increasing the pitch of the last portion of the helical wave structure. There is no loss of linearity or beam conversion efficiency.

Grechberg, R. W.↗
NASA NTRS1996

Simulation of TunneLadder Traveling-Wave Tube Input/Output Coupler Characteristics Using MAFIA

RF input/output coupler characteristics for the TunneLadder traveling-wave tube have been calculated using the three-dimensional computer code, MAFIA and compared to experimental data with good agreement. Theory behind coupling of the TunneLadder interaction circuit to input and output waveguides is presented and VSWR data is calculated for variations on principal coupler dimensions to provide insight into manufacturing tolerances necessary for acceptable performance. Accuracy of results using MAFIA demonstrates how experimental hardware testing of three-dimensional coupler designs can be reduced.

Kory, Carol L.↗
NASA NTRS2006

Status of the PAPPA experiment

The Primordial Anisotropy Polarization Pathfinder Array (PAPPA) is a balloonborne instrument to measure the polarization of the cosmic microwave background and search for the signature of primordial gravity waves. PAPPA uses a novel marriage of RF phase modulation and millimeter-wave bolometric detectors to produce a "polarimeter-on-a-chip" capable of simultaneously measuring the Stokes I, Q, and U parameters on the sky. I will discuss the current status and future plans for PAPPA.

Kogut, Alan↗
NASA NTRS1969

Optimum FM pre-emphasis

Calibrated RF signal generator, precision RF attenuator, and a wave analyzer are used to determine the spectral noise characteristics in the baseband of receiver as a function of RF input power.

Merz, K. W.↗
NASA NTRS1974

A Shuttle/SpaceLab RF environment survey facility

This paper describes some of the basic system considerations of a proposed experiment for monitoring and measuring the global electromagnetic radiation environment. RF spectrum coverage for this spaceborne survey facility is anticipated to be quite broad and will include selected frequency bands ranging from UHF to millimeter waves. By establishing this RF environment survey facility, a broad data base of useful electromagnetic field intensity information will be developed. This, in turn, should help both the regulatory agencies and user community in terms of future frequency planning and system design by avoiding unwarranted interference. It is proposed that this experiment be flown as a future test bed during the Shuttle/Spacelab era for continuously gathering and updating information on earth-emitted electromagnetic emissions on a global scale.

Taylor, R. E.↗
NASA NTRS2001

Discrete-State Simulated Annealing For Traveling-Wave Tube Slow-Wave Circuit Optimization

Algorithms based on the global optimization technique of simulated annealing (SA) have proven useful in designing traveling-wave tube (TWT) slow-wave circuits for high RF power efficiency. The characteristic of SA that enables it to determine a globally optimized solution is its ability to accept non-improving moves in a controlled manner. In the initial stages of the optimization, the algorithm moves freely through configuration space, accepting most of the proposed designs. This freedom of movement allows non-intuitive designs to be explored rather than restricting the optimization to local improvement upon the initial configuration. As the optimization proceeds, the rate of acceptance of non-improving moves is gradually reduced until the algorithm converges to the optimized solution. The rate at which the freedom of movement is decreased is known as the annealing or cooling schedule of the SA algorithm. The main disadvantage of SA is that there is not a rigorous theoretical foundation for determining the parameters of the cooling schedule. The choice of these parameters is highly problem dependent and the designer needs to experiment in order to determine values that will provide a good optimization in a reasonable amount of computational time. This experimentation can absorb a large amount of time especially when the algorithm is being applied to a new type of design. In order to eliminate this disadvantage, a variation of SA known as discrete-state simulated annealing (DSSA), was recently developed. DSSA provides the theoretical foundation for a generic cooling schedule which is problem independent, Results of similar quality to SA can be obtained, but without the extra computational time required to tune the cooling parameters. Two algorithm variations based on DSSA were developed and programmed into a Microsoft Excel spreadsheet graphical user interface (GUI) to the two-dimensional nonlinear multisignal helix traveling-wave amplifier analysis program TWA3. The algorithms were used to optimize the computed RF efficiency of a TWT by determining the phase velocity profile of the slow-wave circuit. The mathematical theory and computational details of the DSSA algorithms will be presented and results will be compared to those obtained with a SA algorithm.

Wilson, Jeffrey D.↗
NASA NTRS1983

Using SAW Resonators in RF Oscillators

Surface-acoustic-wave (SAW) resonators used as frequency-determining elements in radio-frequency oscillators circuits. Oscillators are frequencymodulated, phase-modulated, or pulse-modulated. SAW resonators are especially applicable to low-power subminiature applications, such as biotelemetry and wind-tunnel instrumentation, where they advantageously replace crystals. Resonators are smaller than crystals and very thin--advantage where small package size is important.

Westbrook, R. M.↗
NASA NTRS1981

Traveling-wave tube efficiency improvement with textured pyrolytic graphite multistage depressed collector electrodes

The improved efficiency of a multistage depressed collector (MDC) with ion-beam textured pyrolytic graphite electrode surfaces is demonstrated by comparison with the performance of other MDC's tested with the same microwave RF amplifier traveling-wave tube (TWT). Because of the sensitivity of overall TWT efficiency to collector efficiency, significant improvements in TWT performance are possible with the use of textured pyrolytic graphite MDC's.

Curren, A. N.↗
NASA NTRS2000

Investigation of Fully Three-Dimensional Helical RF Field Effects on TWT Beam/Circuit Interaction

A fully three-dimensional (3D), time-dependent, helical traveling wave-tube (TWT) interaction model has been developed using the electromagnetic particle-in-cell (PIC) code MAFIA. The model includes a short section of helical slow-wave circuit with excitation fed by RF input/output couplers, and electron beam contained by periodic permanent magnet (PPM) focusing. All components of the model are simulated in three dimensions allowing the effects of the fully 3D helical fields on RF circuit/beam interaction to be investigated for the first time. The development of the interaction model is presented, and predicted TWT performance using 2.5D and 3D models is compared to investigate the effect of conventional approximations used in TWT analyses.

Kory, Carol L.↗
NASA NTRS1980

Acousto-optic spectrometer for radio astronomy

Recent developments in acousto-optic techniques and in photodetector arrays have made feasible a new type of RF spectrometer, offering the advantages of wide bandwidth, high resolution, large number of channels in compact, lightweight, energy efficient, and relatively low cost systems. Such a system employs an acousto-optic diffraction cell which serves the key role of converting RF signals to ultrasonic traveling-waves modulating the optical index of the cell. The cell is illuminated across its aperture by a monochromatic laser beam. A fraction of the light is diffracted by the acoustic waves. A focusing lens follows the cell and essentially performs a Fourier transform of the RF signal into a far-field intensity pattern. CSIRO in Australia and the Tokyo Astronomical Observatory in Japan have taken the lead in using acousto-optic techniques in astronomical applications. The first practical device was successfully made at CSIRO for obtaining dynamical spectrographs of solar radio emission.

Chin, G.↗
NASA NTRS1998

Fast, high sensitivity dewpoint hygrometer

A dewpoint/frostpoint hygrometer that uses a surface moisture-sensitive sensor as part of an RF oscillator circuit with feedback control of the sensor temperature to maintain equilibrium at the sensor surface between ambient water vapor and condensed water/ice. The invention is preferably implemented using a surface acoustic wave (SAW) device in an RF oscillator circuit configured to generate a condensation-dependent output signal, a temperature sensor to measure the temperature of the SAW device and to distinguish between condensation-dependent and temperature-dependent signals, a temperature regulating device to control the temperature of the SAW device, and a feedback control system configured to keep the condensation-dependent signal nearly constant over time in the presence of time-varying humidity, corrected for temperature. The effect of this response is to heat or cool the surface moisture-sensitive device, which shifts the equilibrium with respect to evaporation and condensation at the surface of the device. The equilibrium temperature under feedback control is a measure of dewpoint or frostpoint.

Hoenk, Michael E.↗
NASA NTRS1977

A contribution to computer analysis of coupled-cavity traveling wave tubes

A flexible accurate large-signal computer program has been developed for the design of coupled-cavity traveling wave tubes. The program is written for a TSS-360 time sharing system. The beam is described by a disk model and the slow wave structure by a sequence of cavities or cells. The computational approach is arranged so that each cavity may have different geometrical or electrical parameters than its neighbors. This allows the program user to simulate a tube of almost arbitrary complexity. Input and output couplers, severs, complicated velocity tapers, and other features peculiar to one or a few cavities may be modeled by a correct choice of input data. The beam-wave interaction is handled by a new approach in which the RF fields are expanded in solutions to the TM wave equation retaining all significant space harmonics. The program was used to perform a design study of the TWT developed for the CTS satellite. Good agreement was obtained between the predictions of the program and the measured performance of the flight tube. The internal check on power balance was satisfied within plus or minus 0.2 per cent of input beam power.

Connolly, D. J.↗
NASA NTRS1995

Facility for the evaluation of space communications and related systems

NASA Lewis Research Center's Communications Projects Branch has developed a facility for the evaluation of space communications systems and related types of systems, called the Advanced Space Communications (ASC) Laboratory. The ASC Lab includes instrumentation, testbed hardware, and experiment control and monitor software for the evaluation of components, subsystems, systems, and networks. The ASC lab has capabilities to perform radiofrequency (RF), microwave, and millimeter-wave characterizations as well as measurements using low, medium, or high data rate digital signals. In addition to laboratory measurements, the ASC Lab also includes integrated satellite ground terminals allowing experimentation and measurements accessing operational satellites through real space links.

Kerczewski, Robert J.↗
NASA NTRS2001

Power Divider for Harmonically Rich Waveforms

A power divider divides an RF signal into two output signals having a phase difference of 180° or a multiple thereof. When the RF signal is a square wave or another harmonically rich signal. the phases of the fundamental and the harmonics have the proper relationship. The divider can be implemented in the form of rnicrostrips on a board, with one of the output microstrips having several bends to provide a different electrical length from the other.

William Herbert Sims, III↗