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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

A 4-W 56-dB gain microstrip amplifier at 15 GHz utilizing GaAs FET's and IMPATT diodes

Performance results and design considerations are presented for an all solid-state Ku-band power amplifier which is feasible for use in PM communication systems for airborne or spacecraft transmitter applications. A six-stage GaAs FET preamplifier and a driver and balanced power amplifier utilizing GaAs IMPATT diodes operating in the injection locked oscillator mode are discussed. For high power and efficiency Schottky-Read IMPATT's with low-high-low doping profiles are employed. For improved reliability the IMPATT's incorporate a TiW barrier metallization to retard degradation of the IMPATT's. Results of accelerated life testing of the IMPATT devices are also presented.

Sokolov, V.↗
NASA NTRS1990

Microwave conductivity of laser ablated YBaCuO superconducting films and its relation to microstrip transmission line

The discovery of high temperature superconductor oxides has raised the possibility of a new class of millimeter and microwave devices operating at temperatures considerably higher than liquid helium temperatures. Therefore, materials properties such as conductivity, current density, and sheet resistance as a function of temperature and frequency, possible anisotropies, moisture absorption, thermal expansion, and others, have to be well characterized and understood. The millimeter wave response was studied of laser ablated YBa2Cu3O(7-x)/LaAlO3 thin films as a function of temperature and frequency. In particular, the evaluation of their microwave conductivity was emphasized, since knowledge of this parameter provides a basis for the derivation of other relevant properties of these superconducting oxides, and for using them in the fabrication of actual passive circuits. The microwave conductivity for these films was measured at frequencies from 26.5 to 40.0 GHz, in the temperature range from 20 to 300 K. The values of the conductivity are obtained from the millimeter wave power transmitted through the films, using a two fluid model.

Bhasin, K. B.↗
NASA NTRS1989

Analysis of reactively loaded microstrip disk antenna

The moment method solution to the problem of a reactively loaded circular patch is presented. Using the reaction integral equation in conjuction with the method of moments, parameters of the Thevenin's equivalent network for the loaded patch are obtained. From the equivalent network parameters an expression for the imput impedance of the loaded patch is derived. A design procedure for a circularly polarized disk antenna is presented. Computed results are compared with the experimental data.

Deshpande, M. D.↗
NASA NTRS1990

Microstrip subarray with coplanar and stacked parasitic elements

A parasitic subarray configuration combining the coplanar and stacked geometries is proposed and studied. It is numerically shown that a two-layer cross offers a gain enhancement of several decibels compared with either the coplanar cross or the two-layer electromagnetically coupled antenna. Preliminary experimental results appear to be in agreement with this estimate.

Lee, K. F.↗
NASA NTRS1990

Circular polarisation characteristics of stacked microstrip antennas

Experimental results on the circular polarization (CP) characteristics of a two-layer electromagnetically coupled (EMCP) antenna are presented. Compared to the single CP patch antenna, the two-layer EMCP antenna with proper spacings can provide better axial ratio and directivity.

Lee, R. Q.↗
NASA NTRS1991

Microwave conductivity of laser ablated YBa2Cu3O(7-delta) superconducting films and its relation to microstrip transmission line performance

The discovery of high temperature superconductor oxides has raised the possibility of a new class of millimeter and microwave devices operating at temperatures considerably higher than liquid helium temperatures. Therefore, materials properties such as conductivity, current density, and sheet resistance as a function of temperature and frequency, possible anisotropies, moisture absorption, thermal expansion, and others, have to be well characterized and understood. The millimeter wave response of laser ablated YBa2Cu3O(7-delta)/LaAlO3 thin films was studied as a function of temperature and frequency. In particular, the evaluation of their microwave conductivity was emphasized, since knowledge of this parameter provides a basis for the derivation of other relevant properties of these superconducting oxides, and for using them in the fabrication of actual passive circuits. The microwave conductivity for these films was measured at frequencies from 26.5 to 40.0 GHz, in the temperature range from 20 to 300 K. The values of the conductivity are obtained from the millimeter wave power transmitted through the films, using a two fluid model.

Bhasin, K. B.↗
NASA NTRS1992

RCS reduction of a microstrip patch using lumped loads

In this report we consider the radar cross section (RCS) of a single rectangular patch antenna in a recessed cavity. Using a previously developed finite element-boundary integral method code, a study is performed on the patch's RCS as a function of frequency. To reduce the RCS of the patch at the resonant frequency, lumped (resistive) loads are placed at the edges of the patch. The effects of the lumped loads on the patch's RCS and gain are examined and it is observed that the RCS and gain are reduced as the as the load value decreases, whereas the antenna's bandwidth is increased. At resonance, the usual relations between the RCS and gain is observed, but it is shown that this relation no longer holds at frequencies away from resonance.

Volakis, John L.↗
NASA NTRS1992

A scheme to alter the resonant frequency of the microstrip patch antenna

Simple schemes are presented for altering the resonant frequency of a rectangular patch antenna without the need to change its size. In particular, by placing a perturbance below the patch it is shown that as much as 20 percent increase and 30 percent decrease from the resonant frequency of the unperturbed patch can be achieved. The specific configurations considered in this letter include a cavity-backed, aperture-backed, and protrusion-backed patch, and for each case design curves are presented.

Volakis, John L.↗
NASA NTRS1993

Resistively Loaded Microstrip-Patch Antenna

Strips of thin resistive material added near two edges of conventional micro-strip-patch antenna. Bandwidth doubled by simple modification. Optimum bandwidth performance obtained by adjustment of shapes, resistances, and locations of resistive strips.

Bailey, Marion C.↗
NASA NTRS1992

Electromagnetic scattering and radiation from microstrip patch antennas and spirals residing in a cavity

A new hybrid method is presented for the analysis of the scattering and radiation by conformal antennas and arrays comprised of circular or rectangular elements. In addition, calculations for cavity-backed spiral antennas are given. The method employs a finite element formulation within the cavity and the boundary integral (exact boundary condition) for terminating the mesh. By virtue of the finite element discretization, the method has no restrictions on the geometry and composition of the cavity or its termination. Furthermore, because of the convolutional nature of the boundary integral and the inherent sparseness of the finite element matrix, the storage requirement is kept very low at O(n). These unique features of the method have already been exploited in other scattering applications and have permitted the analysis of large-size structures with remarkable efficiency. In this report, we describe the method's formulation and implementation for circular and rectangular patch antennas in different superstrate and substrate configurations which may also include the presence of lumped loads and resistive sheets/cards. Also, various modelling approaches are investigated and implemented for characterizing a variety of feed structures to permit the computation of the input impedance and radiation pattern. Many computational examples for rectangular and circular patch configurations are presented which demonstrate the method's versatility, modeling capability and accuracy.

Volakis, J. L.↗
NASA NTRS1993

Input impedance of coaxially fed rectangular microstrip antenna on electrically thick substrate

A full-wave spectral domain analysis has been used to obtain input-impedance results for a probe-fed rectangular-patch antenna, modeling the source as a magnetic-current frill. Multiple modes are used in the probe surface current to account for axial and azimuthal variations. It is established that maximum resistance is dependent on the substrate loss tangent. The axial variation of the probe current must be taken into account for substrate thicknesses greater than about 0.02 wavelengths.

Chen, Wei↗
NASA NTRS1998

A Novel K-Band Tunable Microstrip Bandpass Filter Using a Thin Film HTS/Ferroelectric/ Dielectric Configuration

We report on YBCO/strontium titanate (STO) thin film K-band tunable bandpass filters on lanthanum aluminate substrates. The 2 pole filters were designed for a center frequency of 19 GHz and 4% bandwidth. Tunability is achieved through the non-linear dc electric field dependence of the relative dielectric constant of STO (epsilon-rSTO). Center frequency shifts greater than 2 GHz were obtained at a 400V bipolar dc bias at temperatures below 77K, with minimum degradation in the insertion loss of the filters.

Subramanyam, G.↗
NASA NTRS1999

Thin Film Ba(x) Sr(1-x)TiO3 Coupled Microstrip Ku- and K-band Phase Shifters

In this report authors found that the: (1) Best room temperature CMPS performance seen on 1% Mn-doped Ba(0.6)Sr(0.4)TiO3 annealed films on MgO: K = 74 C/dB. Phase Shift/coupled length: 1427 C/cm (2) Attempt to improve phase shifters through thicker as-deposited films stymied by declining film quality with film thickness. Annealing may alleviate this problem. (3) CMPS phase shift at Ku-band didn't experience the great rise in tunability seen in 1 MHz epsilon(sub r)(0) data. (4) While CMPS circuits may be well suited for arrays, simpler circuits like CPW would be more useful for characterizing epsilon(sub r) and tan(delta) at Ku-and K-band. (5) New substrates and designs are being tested.

VanKeuls, F. W.↗
NASA NTRS1999

A Dual-polarized Microstrip Subarray Antenna for an Inflatable L-band Synthetic Aperture Radar

Inflatable technology has been identified as a potential solution to the problem of achieving small mass, high packaging efficiency, and reliable deployment for future NASA spaceborne synthetic aperture radar (SAR) antennas. Presently, there exists a requirement for a dual-polarized L-band SAR antenna with an aperture size of 10m x 3m, a center frequency of 1.25GHz, a bandwidth of 80MHz, electronic beam scanning, and a mass of less than 100kg. The work presented below is part of the ongoing effort to develop such an inflatable antenna array.

Zawadzki, Mark↗
NASA NTRS2001

Ferroelectric/Semiconductor Tunable Microstrip Patch Antenna Developed

A lithographically printed microwave antenna that can be switched and tuned has been developed. The structure consists of a rectangular metallic "patch" radiator patterned on a thin ferroelectric film that was grown on high-resistivity silicon. Such an antenna may one day enable a single-phased array aperture to transmit and receive signals at different frequencies, or it may provide a simple way to reconfigure fractal arrays for communications and radar applications.

Romanofsky, Robert R.↗
NASA NTRS1998

Ultra-Wideband UHF Microstrip Array for GeoSAR Application

GeoSAR is a program sponsored by DARPA (Defense Advanced Research Projects Agency) and NASA (National Aeronautics and Space Administration) to develop an airborne, radar- based, commercial terrain mapping system for identification of geologic, seismic, and environmental information, it has two (dual-band at X and UHF) state-of-the-art interferometric synthetic aperture radar (SAR) ground mapping systems. The UHF interferometric system is utilized to penetrate the vegetation canopy and obtain true ground surface height information, while the Xband system will provide capability of mapping the top foliage surface. This paper presents the UHF antenna system where the required center frequency is 350 MHz with a 160 MHz of bandwidth (46% from 270 MHz to 430 MHz). The antenna is required to have dual-linear polarization with a peak gain of 10 dB at the center frequency and a minimum gain of 8 dB toward two ends of the frequency band. One of the most challenging tasks, in addition to achieving the 46% bandwidth, is to develop an antenna with small enough size to fit in the wing-tip pod of a Gulfstream II aircraft.

Thomas, Robert F.↗