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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Achievable flatness in a large microwave power transmitting antenna

A dual reference SPS system with pseudoisotropic graphite composite as a representative dimensionally stable composite was studied. The loads, accelerations, thermal environments, temperatures and distortions were calculated for a variety of operational SPS conditions along with statistical considerations of material properties, manufacturing tolerances, measurement accuracy and the resulting loss of sight (LOS) and local slope distributions. A LOS error and a subarray rms slope error of two arc minutes can be achieved with a passive system. Results show that existing materials measurement, manufacturing, assembly and alignment techniques can be used to build the microwave power transmission system antenna structure. Manufacturing tolerance can be critical to rms slope error. The slope error budget can be met with a passive system. Structural joints without free play are essential in the assembly of the large truss structure. Variations in material properties, particularly for coefficient of thermal expansion from part to part, is more significant than actual value.

Ried, R. C.↗
NASA NTRS1975

Reception-Conversion Subsystem (RXCV) for microwave power transmission system

As part of a program to demonstrate the feasibility of power transmission from space, an approximately 25 sq m Reception-Conversion Subsystem was designed and tested. The device collects high power microwave energy, converts it into dc, and dissipates it in an instrumented demonstration load.

Raytheon Company↗
NASA NTRS1994

High-resolution imaging of rain systems with the advanced microwave precipitation radiometer

An advanced Microwave Precipitation Radiometer (AMPR) has been developed and flown in the NASA ER-2-high-altitude aircraft for imaging various atmospheric and surface processes, primarily the internal structure of rain clouds. The AMPR is a scanning four-frequency total power microwave radiometer that is externally calibrated with high-emissivity warm and cold loads. Separate antenna systems allow the sampling of the 10.7- and 19.35-GHz channels at the same spatial resolution, while the 37.1- and 85.5-GHz channels utilize the same multifrequency feedhorn as the 19.35-GHz channel. Spatial resolutions from an aircraft altitude of 20-km range from 0.6 km at 85.5 GHz to 2.8 km at 19.35 and 10.7 GHz. All channels are sampled every 0.6 km in both along-track and cross-track directions, leading to a contiguous sampling pattern of the 85.5-GHz 3-dB beamwidth footprints, 2.3X oversampling of the 37.1-GHz data, and 4.4X oversampling of the 19.35- and 10.7-GHz data. Radiometer temperature sensitivities range from 0.2 to 0.5 C. Details of the system are described, including two different calibration systems and their effect on the data collected. Examples of oceanic rain systems are presented from Florida and the tropical west Pacific that illustrate the wide variety of cloud water, rainwater, and precipitation-size ice combinations that are observable from aircraft altitudes.

Spencer, Roy W.↗
NASA NTRS1982

A ground-simulator investigation of helicopter longitudinal flying qualities for instrument approach

A ground-simulation experiment was conducted to investigate the direct and interactive influences of several longitudinal static and dynamic stability parameters on helicopter flying qualities during terminal-area operations in instrument conditions. Variations that were examined included five levels of static control-position gradients ranging from stable to unstable; two levels of dynamic stability for the long-period oscillation; two levels of the steady-state pitch speed gradient; two levels of angle-of-attack stability and pitch-rate damping; and two levels of stability and control augmentation. These variations were examined initially in calm air and thin in simulated light-to-moderate turbulence and wind shear. Five pilots performed a total of 223 evaluations of these parameters for a representative microwave landing system precision approach task conducted in a dual-pilot crew-loading situation.

Lebacqz, J. V.↗
NASA NTRS1988

Dual passband dichroic plate for X-band

A need arose in the Deep Space Network for a dichroic plate that would simultaneously pass two desired frequency bands in the X-band region. In addition, the plate must be totally reflective for S-band frequencies. A dielectrically loaded dichroic plate is described that was developed to meet this need. The unique microwave properties that the new dichroic plate had to possess were: (1) insertion losses of less than 0.04 dB for X-band uplink frequencies centered at 7167 MHz and for X-band downlink frequencies centered at about 8425 MHz; (2) insertion losses that met the low loss requirements at 30 deg incidence angle simultaneously for both parallel and perpendicular polarizations; (3) total reflectivity at S-band frequencies; and (4) ability to maintain these electrical characteristics while passing 100 kW of CW power at X-band or while reflecting 100 kW of CW power at S-band. The dual passband dichroic plate is a thick metallic plate having an array of periodic round holes filled with Teflon plugs. Test results on an experimental prototype plate indicate that it is technically possible to design a dielectrically filled dichroic plate that meets all of the technical requirements.

Otoshi, T. Y.↗
NASA NTRS1990

The analysis of reactively loaded microstrip antennas by finite difference time domain modelling

In recent years, much interest has been shown in the use of printed circuit antennas in mobile satellite and communications terminals at microwave frequencies. Although such antennas have many advantages in weight and profile size over more conventional reflector/horn configurations, they do, however, suffer from an inherently narrow bandwidth. A way of optimizing the bandwidth of such antennas by an electronic tuning technique using a loaded probe mounted within the antenna structure is examined, and the resulting far-field radiation patterns are shown. Simulation results from a 2D finite difference time domain (FDTD) model for a rectangular microstrip antenna loaded with shorting pins are given and compared to results obtained with an actual antenna. It is hoped that this work will result in a design package for the analysis of microstrip patch antenna elements.

Hilton, G. S.↗
NASA NTRS1987

An analysis of electromagnetic coupling and eigenfrequencies for microwave electrothermal thruster discharges

This paper discusses the basic approach to developing a comprehensive electromagnetic model for a microwave electrothermal discharge. The discharge and surrounding region are modeled as a section of waveguide loaded with a uniform, cold, lossy plasma. A characteristic equation has been derived describing all possible system modes. In particular the TM(01) mode is numerically solved. Propagation and attenuation constants for the TM(01) mode are found numerically for a given range of electron-neutral collision frequencies and plasma densities. Results are used to interpret a number of experimental observations in helium. Specifically, they are used to explain high coupling efficiencies and ease of cavity tuning at high pressures.

Frasch, L. L.↗
NASA NTRS1996

Automation of Data Analysis Programs Used in the Cryogenic Characterization of Superconducting Microwave Resonators

Knowledge of the microwave properties at cryogenic temperatures of components fabricated using High-Temperature-Superconductors (HTS) is useful in the design of HTS-based microwave circuits. Therefore, fast and reliable characterization techniques have been developed to study the aforementioned properties. In this paper, we discuss computer analysis techniques employed in the cryogenic characterization of HTS-based resonators. The revised data analysis process requires minimal user input. and organizes the data in a form that is easily accessible by the user for further examination. These programs retrieve data generated during the cryogenic characterization at microwave frequencies of HTS based resonators and use it to calculate parameters such as the loaded and unloaded quality factors (Q and Q(sub o), respectively), the resonant frequency (f(sub o)), and the coupling coefficient (k), which are important quantities in the evaluation of HTS resonators. While the data are also stored for further use, the programs allow the user to obtain a graphical representation of any of the measured parameters as a function of temperature soon after the completion of the cryogenic measurement cycle. Although these programs were developed to study planar HTS-based resonators operating in the reflection mode, they could also be used in the cryogenic characterization of two ports (i.e., reflection/transmission) resonators.

Creason, A. S.↗
NASA NTRS2002

Experimental Analysis of Reduced-Sized Coplanar Waveguide Transmission Lines

An experimental investigation of the use of capacitive loading of coplanar waveguides to reduce their line length and, thus the size, of monolithic microwave integrated circuits is presented. The reduced sized coplanar waveguides are compared to unloaded transmission lines and to lumped element transmission line segments. The phase bandwidth, defined by 2 percent error in S(sub 21), and the return loss bandwidth, defined by a return loss greater than 15 dB, of coplanar waveguides reduced from 0 to 90 percent are compared, and the insertion loss as a function of the size reduction is presented.

Ponchak, George E.↗
NASA NTRS1988

Grid oscillators

Loading a two-dimensional grid with active devices offers a means of combining the power of solid-state oscillators in the microwave and millimeter-wave range. The grid structure allows a large number of negative resistance devices to be combined. This approach is attractive because the active devices do not require an external locking signal, and the combining is done in free space. In addition, the loaded grid is a planar structure amenable to monolithic integration. Measurements on a 25-MESFET grid at 9.7 GHz show power-combining and frequency-locking without an external locking signal, with an ERP of 37 W. Experimental far-field patterns agree with theoretical results obtained using reciprocity.

Popovic, Zorana B.↗
NASA NTRS1992

Electromagnetic scattering from microwave absorbers - Laboratory verification of the coupled wave theory

W-band measurements of the bistatic scattering function of some common microwave absorbing structures, including periodic wedge-type and pyramid-type iron-epoxy calibration loads and flat carbon-foam 'Echosorb' samples, were made using a network analyzer interface to a focused-lens scattering range. Swept frequency measurements over the 75-100 GHz band revealed specular and Bragg reflection characteristics in the measured data.

Gasiewski, A. J.↗
NASA NTRS1984

Electromagnetic plasma models for microwave plasma cavity reactors

A procedure used to design cavity applicators that efficiently produce cylindrical and disk microwave discharges is reviewed. In contrast to most microwave applicators these cavities utilize single mode excitation of the plasma. This method of excitation has the advantage of providing efficient coupling (zero reflected power) to the plasma over a wide range of discharge loading conditions while also allowing, if desired, electric feedback control of the heating process. The design procedure is generalized to any lossy dielectric. Experimental and theoretical research required to further understand microwave discharges is also discussed.

Frasch, L.↗
NASA NTRS2013

Microwave Frequency Polarizers

This article describes the fabrication and analysis of microwave frequency polarizing grids. The grids are designed to measure polarization from the cosmic microwave background. It is effective in the range of 500 to 1500 micron wavelength. It is cryogenic compatible and highly robust to high load impacts. Each grid is fabricated using an array of different assembly processes which vary in the types of tension mechanisms to the shape and size of the grids. We provide a comprehensive study on the analysis of the grids' wire heights, diameters, and spacing.

polarization↗
NASA NTRS1979

Perception and performance in flight simulators: The contribution of vestibular, visual, and auditory information

The pilot's perception and performance in flight simulators is examined. The areas investigated include: vestibular stimulation, flight management and man cockpit information interfacing, and visual perception in flight simulation. The effects of higher levels of rotary acceleration on response time to constant acceleration, tracking performance, and thresholds for angular acceleration are examined. Areas of flight management examined are cockpit display of traffic information, work load, synthetic speech call outs during the landing phase of flight, perceptual factors in the use of a microwave landing system, automatic speech recognition, automation of aircraft operation, and total simulation of flight training.

Source record↗
NASA NTRS1990

Rotary Ball Locking Mechanism

Ball locking mechanism links input drive shaft to output shaft and disengages two shafts from each other when it locks output shaft at either of two fixed angular positions. Part of drive system turning microwave antenna 143.5 degrees between stowage and employment orientations and holds it at either orientation without back-loading drive motor and gears. Angular interval and dimensions modified for use in robotic or other actuators in which desirable to "rest" drive trains while locking actuators at fixed positions.

Holman, Earl V.↗
NASA NTRS1995

Application of FEM to estimate complex permittivity of dielectric material at microwave frequency using waveguide measurements

A simple waveguide measurement technique is presented to determine the complex dielectric constant of a dielectric material. The dielectric sample is loaded in a shorted x-band rectangular waveguide. Using a network analyzer; the reflection coefficient of the shorted waveguide (loaded with sample) is measured. Using the Finite Element Method (FEM), the exact reflection coefficient of the shorted waveguide (loaded with sample) is determined as a function of the dielectric constant. Matching the measured value of the reflection coefficient with the reflection coefficient calculated using the FEM utilizing the Newton-Raphson Method, an estimate of the dielectric constant of a dielectric material is obtained. A comparison of estimated values of dielectric constant obtained from simple waveguide modal theory and the present approach is presented.

Deshpande, M. D.↗
NASA NTRS2008

A Novel 24 Ghz One-Shot Rapid and Portable Microwave Imaging System (Camera)

A novel 2D microwave imaging system at 24 GHz based on MST techniques. Enhanced sensitivity and SNR by utilizing PIN diode-loaded resonant slots. Specific slot and array design to increase transmission and reduce cross -coupling. Real-time imaging at a rate in excess of 30 images per second. Reflection as well transmission mode capabilities. Utility and application for electric field distribution mapping related to: Nondestructive Testing (NDT), imaging applications (SAR, Holography), and antenna pattern measurements.

Ghasr, M.T.↗