Browsing by Author "LaPean, James William"

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    Analysis of infinite arrays of arbitrarily shaped planar radiating elements using a Floquet mode based Method of Moments approach
    LaPean, James William (Virginia Tech, 1996-04-29)
    Large phased array antennas are theoretically capable of delivering the directive gain of similarly sized aperture antennas while offering electronic beam scanning capabilities and greater operational flexibility. Unfortunately, the high cost associated with large phased antenna arrays has limited their use to highly specialized applications where no other antenna system configuration is possible. The recent development of less expensive microwave active devices has led to a renewed interest in large phased antenna arrays. These devices allow the amplification and signal processing required in phased antenna arrays to be distributed among many identical modules which combine the amplification, feed network, and radiating element sections of traditional antenna arrays. These modules can then be produced at a lower unit cost and result in an antenna system which is more easily integrated and repaired. The practicality of large phased antenna arrays is still limited by the great difficulty experienced in predicting their performance. Mutual coupling effects between the radiating elements produce significant variations from ideal array theory. The prediction and reduction of these effects requires a characterization approach which is computational rather than experimenta1. This document presents a new approach which allows the characterization of arbitrarily shaped planar radiating elements printed on a dielectric support slab backed by a perfect electric conductor ground plane. This analysis approach uses a Method of Moments technique to determine the electric current distribution over a set of bi-triangular sub-domain elements describing a single radiating element. The effects of mutual coupling in the fully active infinite antenna array are included in the analysis by a Floquet mode based Green's function used in the Method of Moments analysis. This characterization technique has been implemented in the computational electromagnetics code ASIA (Analysis Software for Infinite Arrays), The analysis approach presented here is validated by comparison with published input impedance data for two different radiating elements. Finally, preliminary analysis results are shown for a more complex radiating element.
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    Beam scanning offset Casegrain reflector antennas by subreflector movement
    LaPean, James William (Virginia Tech, 1993-11-05)
    In 1987 a NASA panel recommended the creation of the Mission to Planet Earth. This mission was intended to apply to remote sensing experience of the space community to earth remote sensing to enhance the understanding of the climatalogical processes of our planet and to determine if, and to what extent, the hydrological cycle of Earth is being affected by human activity. One of the systems required for the mission was a wide scanning, high gain reflector antenna system for use in radiometric remote sensing from geostationary orbit. This work describes research conducted at Virginia Tech into techniques for beam scanning offset Cassegrain reflector antennas by subreflector translation and rotation. Background material relevant to beam scanning antenna systems and offset Cassegrain reflector antenna system is presented. A test case is developed based on the background material. The test case is beam scanned using two geometrical optics methods of determining the optimum subreflector position for the desired scanned beam direction. Physical optics far-field results are given for the beam scanned systems. The test case system is found to be capable of beam scanning over a range of 35 half-power beamwidths while maintaining a 90% beam efficiency or 50 half-power beamwidths while maintaining less than 1 dB of gain loss during scanning.