DSS 43 antenna gain analysis for Voyager Uranus encounter: 8.45-GHz radio science data correction

A malfunction of the Deep Space Network (DSN) 64-meter antenna in Australia forced the antenna to operate with a mispositioned subreflector during the Voyager Uranus encounter period (January 24, 1986). Because of changing main reflector shape and quadripod position as a function of elevation angle, the antenna gain and pointing were not as expected, and the 8.45 GHz received signal level changed during the pass. The study described here used the Geometrical Theory of Diffraction (GTD) analysis to determine actual antenna gain and pointing during that period in an attempt to reconstruct the radio science data. It is found that the 1.4 dB of signal variation can be accounted for by antenna geometry changes and pointing error. Suggested modifications to the values measured during the pass are presented. Additionally, an extremely useful tool for the analysis of gravity deformed reflectors was developed for use in future antenna design and analysis projects

Linear-phase approximation in the triangular facet near-field physical optics computer program

Analyses of reflector antenna surfaces use a computer program based on a discrete approximation of the radiation integral. The calculation replaces the actual surface with a triangular facet representation; the physical optics current is assumed to be constant over each facet. Described here is a method of calculation using linear-phase approximation of the surface currents of parabolas, ellipses, and shaped subreflectors and compares results with a previous program that used a constant-phase approximation of the triangular facets. The results show that the linear-phase approximation is a significant improvement over the constant-phase approximation, and enables computation of 100 to 1,000 lambda reflectors within a reasonable time on a Cray computer

Posters As Journals

Digital art enables me to subjectively express myself, which I sometimes yearn for when doing graphic design work. These posters serve as an index of my state of mind at the moments they were created. Although abstract, my work uses typography, shape, and light to communicate specific yet tenuous moods and atmospheres that can stand in for my journal entries

Design and performance analysis of the DSS-13 beam waveguide antenna

A new 34 m research and development antenna is currently being constructed prior to introducing beam waveguide (BWG) antennas and Ka-band (32 GHz) frequencies into the NASA/JPL Deep Space Network. The new 34 m antenna, fed with either a center or bypass BWG, will lose less than 0.2 dB (excluding surface root mean square and mirror misalignment losses), as compared with a standard-fed Cassegrain antenna a X- (8.4 GHz) and Ka-bands. The antenna is currently under construction and is scheduled to be completed July 1990. Phase 1 of the project is for independent X- and Ka-band receive-only tests. Phase 2 of the project is for simultaneous S- (2.3 GHz) and X-band or X- and Ka-band operation, and the design is currently under way

Dual-shaped offset reflector antenna designs from solutions of the geometrical optics first-order partial differential equations

In obtaining solutions to the first-order nonlinear partial differential equations (PDEs) for synthesizing offset dual-shaped reflectors, it is found that previously observed computational problems can be avoided if the integration of the PDEs is started from an inner projected perimeter and integrated outward rather than starting from an outer projected perimeter and integrating inward. This procedure, however, introduces a new parameter, the main reflector inner perimeter radius p(o), when given a subreflector inner angle 0(o). Furthermore, a desired outer projected perimeter (e.g., a circle) is no longer guaranteed. Stability of the integration is maintained if some of the initial parameters are determined first from an approximate solution to the PDEs. A one-, two-, or three-parameter optimization algorithm can then be used to obtain a best set of parameters yielding a close fit to the desired projected outer rim. Good low cross-polarization mapping functions are also obtained. These methods are illustrated by synthesis of a high-gain offset-shaped Cassegrainian antenna and a low-noise offset-shaped Gregorian antenna

ASSESSMENT OF CRITICAL THINKING SKILLS IN PRINCIPLES OF MACROECONOMICS USING THE 21ST CENTURY BLOOM’S TAXONOMY MODEL

Studies on critical thinking skills development with specific curriculum materials and instructional methods in economics are few and have been highly theoretical. This paper outlines the framework for developing the 21st Century Bloom’s Taxonomy model across a four-year undergraduate curriculum, enabling students to master critical thinking skills through a clearly defined six-stage process. An example Country Report project from an undergraduate Principles of Macroeconomics course is presented to demonstrate a specific strategy for advancing and assessing critical thinking skills. A critical thinking assessment instrument is also presented to compare student and instructor evaluations from the Country Report assignment.  Article visualizations