Engineering topics

Hwu, Shian U.

Publications and source records attributed to Hwu, Shian U..

21 records · Page 2

NASA NTRS1993

Space Station UCS antenna pattern computation and measurement

The purpose of this paper is to analyze the interference to the Space Station Ultrahigh Frequency (UHF) Communication Subsystem (UCS) antenna radiation pattern due to its environment - Space Station. A hybrid Computational Electromagnetics (CEM) technique was applied in this study. The antenna was modeled using the Method of Moments (MOM) and the radiation patterns were computed using the Uniform Geometrical Theory of Diffraction (GTD) in which the effects of the reflected and diffracted fields from surfaces, edges, and vertices of the Space Station structures were included. In order to validate the CEM techniques, and to provide confidence in the computer-generated results, a comparison with experimental measurements was made for a 1/15 scale Space Station mockup. Based on the results accomplished, good agreement on experimental and computed results was obtained. The computed results using the CEM techniques for the Space Station UCS antenna pattern predictions have been validated.

Hwu, Shian U.↗

NASA NTRS1992

Scattering effects of Space Station structure on Assembly/Contingency Subsystem (ACS) antenna performance

ACS antenna patterns were computed using the Geometrical Theory of Diffraction (GTD) modeling technique in which the multipath interference from the Space Station structures was included. The accuracy of the numerical results obtained is verified by comparing them against a series of RF anechoic chamber measurements. Less than 1 dB degradation is expected if a +/- 15 deg cone is used to protect the ACS high gain antenna boresight pattern; a +/- 20 deg cone is required if no more than 0.5 dB gain degradation is desired.

Hwu, Shian U.↗

NASA NTRS1992

Scattering effects of solar panel on Space Station Space-To-Ground (SGS) antenna performance

The purpose of this study is to characterize the scattering effects of a solar panel on the Space Station Space-to-Ground Subsystem reflector antenna when the antenna is operated in the RF tracking (difference) mode. This analysis is based on a combination of geometrical theory of diffraction and aperture integration techniques. The advantage of this combination method is its capability in predicting reflector antenna patterns not only in the forward region but also in the far-out sidelobes and backlobes. To verify the analytical model, measurements were performed on the Johnson Space Center far-field antenna test facility. Good agreement between computed and measured results was obtained. It was shown from computation and experiment that the solar panel scattering interference causes a shift in null position, a decrease in the depth of the null, as well as a decrease in the gain on the antenna difference mode patterns.

Hwu, Shian U.↗