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![Research paper thumbnail of Analysis of reflector antennas through the World Wide Web [EM Programmer's Notebook]](https://attachments.academia-assets.com/52091522/thumbnails/1.jpg)
](IEEE Antennas and Propagation Magazine, 2000
This column frequently features papers describing various computer codes, and this was indeed one... more This column frequently features papers describing various computer codes, and this was indeed one of the original aims of the column. The Internet has made it exceptionally easy to distribute such software, and the majority of our columns include sites from which to download the software described in the paper. This issue's contribution addresses reflector-antenna analysis; in the June 2005 column, a paper was published on using the same Jacobi-Bessel series method for analyzing reflector antennas, using MATHCADO-What distinguishes this issue's paper is the use of the internet to actually run the code, via Java applets within the browser.
Forest Science, Nov 30, 1983
Modern Antenna Handbook, 2008
Autotestcon 85 Proceedings of the International Automatic Testing Conference, May 1, 1985
In this paper a new concept is introduced for wide bandwidth operation of array antennas. The sha... more In this paper a new concept is introduced for wide bandwidth operation of array antennas. The shared aperture array consists of partially filled layers of elements, one layer for each octave of bandwidth. An experimental program verified the concept. Cavity-backed spiral antennas were found to be ideal elements for use in the shared aperture array.
IEEE Transactions on Antennas and Propagation, 1975
Observed electromagnetic wave depolarization in forward propagation due to precipitation tends to... more Observed electromagnetic wave depolarization in forward propagation due to precipitation tends to distribute statistically about some mean level of depolarization. This is due to random rain parameters that cause this depolarization. Using a drop-size modified depolarization model, we have analyzed the statistical scatter of the cross polarization ratio due to random distributions of drop population and size and found a standard deviation of approximately 2.5 dB about the mean, independent of frequency.
The theoretical fundamentals and mathematical definitions for calculations involved with dual pol... more The theoretical fundamentals and mathematical definitions for calculations involved with dual polarized radio links are given. Detailed derivations and results are discussed for several formulations applied to a general dual polarized radio link.
Future communication systems will move toward the 20 to 30 GHz frequency range for wider bandwidt... more Future communication systems will move toward the 20 to 30 GHz frequency range for wider bandwidth and reduced interference, and will use small earth terminals. The ESA satellite OLYMPUS is scheduled for launch this June and will be ready for use in October. OLYMPUS has 12, 20, and 30 GHz beacons. Virginia Tech and Michigan Tech are working with NASA/JPL on an OLYMPUS experiment and hardware development program. OLYMPUS beacons provide coverage of the east coast of the US sufficient for attenuation measurements. The planned hardware for the OLYMPUS experiments is illustrated. The components of the experiment are summarized. A block diagram level overview of a typical channel is given and one of the four RF front ends is shown.
... 47 3 The Method of Ordered Multiple Interactions 50 3.1 The MOMI integral equation and the MO... more ... 47 3 The Method of Ordered Multiple Interactions 50 3.1 The MOMI integral equation and the MOMI series . . . . . 51 3.1.1 Normalized Residual Error . ... 55 3.2 On the convergence of the MOMI series . . . . . ...
Final Report Virginia Polytechnic Inst and State Univ Blacksburg Dept of Electrical Engineering, Mar 1, 1994
In 1987 a NASA panel recommended the creation of the Mission to Planet Earth. This mission was in... more 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 climatological 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 percent beam efficiency or 50 half-power beamwidths while maintaining less than l dB of gain loss during scanning.
Scientific American, 1998
This dissertation reports results of an investigation into the performance of adaptive beamformin... more This dissertation reports results of an investigation into the performance of adaptive beamforming and diversity combining using antenna arrays that can be mounted on handheld radios. Handheld arrays show great promise for improving the coverage, capacity, and power efficiency of wireless communication systems.
Final Report 25 Feb 1988 24 Feb 1989 Virginia Polytechnic Inst and State Univ Blacksburg Dept of Electrical Engineering, 1989
Surface errors on parabolic reflector antennas degrade the overall performance of the antenna. Th... more Surface errors on parabolic reflector antennas degrade the overall performance of the antenna. The errors are in the form of roughness on the surface, distortions in the shape, or structural design details. They cause amplitude and phase errors in the aperture field which lower the gain, raise the sidelobes, and fill in the nulls. These are major problems in large space reflector antennas. Planned mobile satellite communications systems having limited signal margin need high gain from the space reflectors. Future multiple beam antenna systems requiring spatial isolation to allow frequency reuse could be rendered useless if high sidelobes are present. High sidelobes are also responsible for noise. Ways of compensating for surface errors by pattern synthesis using an array of feed antennas are examined. Pattern corrections are directed specifically toward portions of the pattern requiring improvements. The pattern synthesis does not require knowledge of the surface errors. Both the amplitude and phase of the high side lobes caused by the distortion are required.
14th International Communication Satellite Systems Conference and Exhibit, 1992
Radio Science, 2009
1] The fundamental-limit theory of antennas provides a theoretical limit to assist in the evaluat... more 1] The fundamental-limit theory of antennas provides a theoretical limit to assist in the evaluation of antenna performance in terms of antenna size, fractional impedance bandwidth, and gain. The limit is very useful in practice, giving a basis for restricting the design search to a class of realizable antennas based on size and performance. Previous research on the limit theory focused on electrically small, resonant antennas. In this paper, we discuss how the classical fundamental-limit theory can be interpreted for ultrawideband antennas. The frequency response of Chu's equivalent circuit model for spherical modes suggests the concept of an ideal antenna. The transfer function of the ideal antenna, showing ultrawideband antenna characteristics, simply has an entire function and two complex poles. In this paper, an antenna design strategy is developed based on observations of ideal antenna characteristics. A process is presented for evaluating how well an ultrawideband antenna can approach the theoretical size limit based on the 3-dB cutoff frequencies of spherical modes.
IEEE Antennas and Propagation Magazine, 2000
This column frequently features papers describing various computer codes, and this was indeed one... more This column frequently features papers describing various computer codes, and this was indeed one of the original aims of the column. The Internet has made it exceptionally easy to distribute such software, and the majority of our columns include sites from which to download the software described in the paper. This issue's contribution addresses reflector-antenna analysis; in the June 2005 column, a paper was published on using the same Jacobi-Bessel series method for analyzing reflector antennas, using MATHCADO-What distinguishes this issue's paper is the use of the internet to actually run the code, via Java applets within the browser.
Forest Science, Nov 30, 1983
Modern Antenna Handbook, 2008
Autotestcon 85 Proceedings of the International Automatic Testing Conference, May 1, 1985
In this paper a new concept is introduced for wide bandwidth operation of array antennas. The sha... more In this paper a new concept is introduced for wide bandwidth operation of array antennas. The shared aperture array consists of partially filled layers of elements, one layer for each octave of bandwidth. An experimental program verified the concept. Cavity-backed spiral antennas were found to be ideal elements for use in the shared aperture array.
IEEE Transactions on Antennas and Propagation, 1975
Observed electromagnetic wave depolarization in forward propagation due to precipitation tends to... more Observed electromagnetic wave depolarization in forward propagation due to precipitation tends to distribute statistically about some mean level of depolarization. This is due to random rain parameters that cause this depolarization. Using a drop-size modified depolarization model, we have analyzed the statistical scatter of the cross polarization ratio due to random distributions of drop population and size and found a standard deviation of approximately 2.5 dB about the mean, independent of frequency.
The theoretical fundamentals and mathematical definitions for calculations involved with dual pol... more The theoretical fundamentals and mathematical definitions for calculations involved with dual polarized radio links are given. Detailed derivations and results are discussed for several formulations applied to a general dual polarized radio link.
Future communication systems will move toward the 20 to 30 GHz frequency range for wider bandwidt... more Future communication systems will move toward the 20 to 30 GHz frequency range for wider bandwidth and reduced interference, and will use small earth terminals. The ESA satellite OLYMPUS is scheduled for launch this June and will be ready for use in October. OLYMPUS has 12, 20, and 30 GHz beacons. Virginia Tech and Michigan Tech are working with NASA/JPL on an OLYMPUS experiment and hardware development program. OLYMPUS beacons provide coverage of the east coast of the US sufficient for attenuation measurements. The planned hardware for the OLYMPUS experiments is illustrated. The components of the experiment are summarized. A block diagram level overview of a typical channel is given and one of the four RF front ends is shown.
... 47 3 The Method of Ordered Multiple Interactions 50 3.1 The MOMI integral equation and the MO... more ... 47 3 The Method of Ordered Multiple Interactions 50 3.1 The MOMI integral equation and the MOMI series . . . . . 51 3.1.1 Normalized Residual Error . ... 55 3.2 On the convergence of the MOMI series . . . . . ...
Final Report Virginia Polytechnic Inst and State Univ Blacksburg Dept of Electrical Engineering, Mar 1, 1994
In 1987 a NASA panel recommended the creation of the Mission to Planet Earth. This mission was in... more 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 climatological 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 percent beam efficiency or 50 half-power beamwidths while maintaining less than l dB of gain loss during scanning.
Scientific American, 1998
This dissertation reports results of an investigation into the performance of adaptive beamformin... more This dissertation reports results of an investigation into the performance of adaptive beamforming and diversity combining using antenna arrays that can be mounted on handheld radios. Handheld arrays show great promise for improving the coverage, capacity, and power efficiency of wireless communication systems.
Final Report 25 Feb 1988 24 Feb 1989 Virginia Polytechnic Inst and State Univ Blacksburg Dept of Electrical Engineering, 1989
Surface errors on parabolic reflector antennas degrade the overall performance of the antenna. Th... more Surface errors on parabolic reflector antennas degrade the overall performance of the antenna. The errors are in the form of roughness on the surface, distortions in the shape, or structural design details. They cause amplitude and phase errors in the aperture field which lower the gain, raise the sidelobes, and fill in the nulls. These are major problems in large space reflector antennas. Planned mobile satellite communications systems having limited signal margin need high gain from the space reflectors. Future multiple beam antenna systems requiring spatial isolation to allow frequency reuse could be rendered useless if high sidelobes are present. High sidelobes are also responsible for noise. Ways of compensating for surface errors by pattern synthesis using an array of feed antennas are examined. Pattern corrections are directed specifically toward portions of the pattern requiring improvements. The pattern synthesis does not require knowledge of the surface errors. Both the amplitude and phase of the high side lobes caused by the distortion are required.
14th International Communication Satellite Systems Conference and Exhibit, 1992
Radio Science, 2009
1] The fundamental-limit theory of antennas provides a theoretical limit to assist in the evaluat... more 1] The fundamental-limit theory of antennas provides a theoretical limit to assist in the evaluation of antenna performance in terms of antenna size, fractional impedance bandwidth, and gain. The limit is very useful in practice, giving a basis for restricting the design search to a class of realizable antennas based on size and performance. Previous research on the limit theory focused on electrically small, resonant antennas. In this paper, we discuss how the classical fundamental-limit theory can be interpreted for ultrawideband antennas. The frequency response of Chu's equivalent circuit model for spherical modes suggests the concept of an ideal antenna. The transfer function of the ideal antenna, showing ultrawideband antenna characteristics, simply has an entire function and two complex poles. In this paper, an antenna design strategy is developed based on observations of ideal antenna characteristics. A process is presented for evaluating how well an ultrawideband antenna can approach the theoretical size limit based on the 3-dB cutoff frequencies of spherical modes.