The Experts below are selected from a list of 255 Experts worldwide ranked by ideXlab platform
C J Stevens - One of the best experts on this subject based on the ideXlab platform.
-
broadband multiband conformal Circular Beam steering array
IEEE Transactions on Antennas and Propagation, 2006Co-Authors: J J H Wang, D J Triplett, C J StevensAbstract:A new approach for a broadband/multiband conformal Circular Beam-steering array is presented with both theory and experimental data. The array is low-profile, suitable for conformal mounting on a platform. It has an omnidirectional coverage with a unidirectional Beam that aims at a moderate directivity of 5 to 15 dBi. It consists of a center driven element and parasitic surface waveguide elements symmetrically positioned in the periphery, for electronic Beam steering and Beam forming to enhance RF connectivity and/or spectral efficiency. This array can achieve ultrawideband multiband performance and low-profile conformability unattainable by conventional array approaches. In addition, its cost is estimated to be an order of magnitude lower than that of conventional Beam-steering arrays. Breadboard and brassboard development efforts for the array have essentially achieved a bandwidth of 1.0-2.5 GHz. A larger bandwidth is feasible since its driven element has achieved a continuous 10:1 bandwidth, and since the surface waveguide elements could achieve a multioctave bandwidth similar to the broadbanding path from the Yagi-Uda array to the LP array
-
broadband multiband conformal Circular Beam steering array
International Microwave Symposium, 2005Co-Authors: J J H Wang, D J Triplett, C J StevensAbstract:A new approach for a broadband/multiband conformal Circular Beam-steering array is presented with essential experimental data. The array is low-profile, suitable for conformal mounting on a platform. It has an omnidirectional coverage with a unidirectional Beam that generally aims at a moderate directivity of 6 to 15 dBi. It consists of a center driven element and parasitic surface waveguide elements in the periphery for Beam steering. This array can achieve ultra-wideband multiband performance and low-profile conformability unattainable by conventional array approaches. In addition, its cost is an order of magnitude lower than that of conventional Beam-steering array. At present, its broadband/multiband performance is only limited by its surface waveguide elements since its driven element has achieved continuous 10:1 bandwidth.
M C H Wright - One of the best experts on this subject based on the ideXlab platform.
-
the allen telescope array twenty centimeter survey a 700 square degree multi epoch radio data set ii individual epoch transient statistics
The Astrophysical Journal, 2011Co-Authors: Steve Croft, Geoffrey C Bower, Garrett K Keating, C J Law, David Whysong, Peter K G Williams, M C H WrightAbstract:We present our second paper on the Allen Telescope Array Twenty-centimeter Survey (ATATS), a multi-epoch, {approx}700 deg{sup 2} radio image and catalog at 1.4 GHz. The survey is designed to detect rare, bright transients as well as to commission the ATA's wide-field survey capabilities. ATATS explores the challenges of multi-epoch transient and variable source surveys in the domain of dynamic range limits and changing (u, v) coverage. Here, we present images made using data from the individual epochs, as well as a revised image combining data from all ATATS epochs. The combined image has rms noise {sigma} = 3.96 mJy Beam{sup -1}, with a Circular Beam of 150'' FWHM. The catalog, generated using a false detection rate algorithm, contains 4984 sources and is >90% complete to 37.9 mJy. The catalogs generated from snapshot images of the individual epochs contain between 1170 and 2019 sources over the 564 deg{sup 2} area in common to all epochs. The 90% completeness limits of the single-epoch catalogs range from 98.6 to 232 mJy. We compare the catalog generated from the combined image to those from individual epochs, and from the NRAO VLA Sky Survey, a legacy survey at the same frequency. We are ablemore » to place new constraints on the transient population: fewer than 6 x 10{sup -4} transients deg{sup -2}, for transients brighter than 350 mJy with characteristic timescales of minutes to days. This strongly rules out an astronomical origin for the {approx}1 Jy sources reported by Matsumura et al. based on their stated rate of 3.1 x 10{sup -3} deg{sup -2}.« less
-
the allen telescope array twenty centimeter survey a 700 square degree multi epoch radio dataset ii individual epoch transient statistics
arXiv: Cosmology and Nongalactic Astrophysics, 2011Co-Authors: Steve Croft, Geoffrey C Bower, Garrett K Keating, C J Law, David Whysong, Peter K G Williams, M C H WrightAbstract:We present our second paper on the Allen Telescope Array Twenty-centimeter Survey (ATATS), a multi-epoch, ~700 sq. deg. radio image and catalog at 1.4 GHz. The survey is designed to detect rare, bright transients as well as to commission the ATA's wide-field survey capabilities. ATATS explores the challenges of multi-epoch transient and variable source surveys in the domain of dynamic range limits and changing (u,v) coverage. Here we present images made using data from the individual epochs, as well as a revised image combining data from all ATATS epochs. The combined image has RMS noise 3.96 mJy / Beam, with a Circular Beam of 150 arcsec FWHM. The catalog, generated using a false detection rate algorithm, contains 4984 sources, and is >90% complete to 37.9 mJy. The catalogs generated from snapshot images of the individual epochs contain between 1170 and 2019 sources over the 564 sq. deg. area in common to all epochs. The 90% completeness limits of the single epoch catalogs range from 98.6 to 232 mJy. We compare the catalog generated from the combined image to those from individual epochs, and from the NRAO VLA Sky Survey (NVSS), a legacy survey at the same frequency. We are able to place new constraints on the transient population: fewer than 6e-4 transients / sq. deg., for transients brighter than 350 mJy with characteristic timescales of minutes to days. This strongly rules out an astronomical origin for the ~1 Jy sources reported by Matsumura et al. (2009), based on their stated rate of 3.1e-3 / sq. deg.
Steve Croft - One of the best experts on this subject based on the ideXlab platform.
-
the allen telescope array twenty centimeter survey a 700 square degree multi epoch radio data set ii individual epoch transient statistics
The Astrophysical Journal, 2011Co-Authors: Steve Croft, Geoffrey C Bower, Garrett K Keating, C J Law, David Whysong, Peter K G Williams, M C H WrightAbstract:We present our second paper on the Allen Telescope Array Twenty-centimeter Survey (ATATS), a multi-epoch, {approx}700 deg{sup 2} radio image and catalog at 1.4 GHz. The survey is designed to detect rare, bright transients as well as to commission the ATA's wide-field survey capabilities. ATATS explores the challenges of multi-epoch transient and variable source surveys in the domain of dynamic range limits and changing (u, v) coverage. Here, we present images made using data from the individual epochs, as well as a revised image combining data from all ATATS epochs. The combined image has rms noise {sigma} = 3.96 mJy Beam{sup -1}, with a Circular Beam of 150'' FWHM. The catalog, generated using a false detection rate algorithm, contains 4984 sources and is >90% complete to 37.9 mJy. The catalogs generated from snapshot images of the individual epochs contain between 1170 and 2019 sources over the 564 deg{sup 2} area in common to all epochs. The 90% completeness limits of the single-epoch catalogs range from 98.6 to 232 mJy. We compare the catalog generated from the combined image to those from individual epochs, and from the NRAO VLA Sky Survey, a legacy survey at the same frequency. We are ablemore » to place new constraints on the transient population: fewer than 6 x 10{sup -4} transients deg{sup -2}, for transients brighter than 350 mJy with characteristic timescales of minutes to days. This strongly rules out an astronomical origin for the {approx}1 Jy sources reported by Matsumura et al. based on their stated rate of 3.1 x 10{sup -3} deg{sup -2}.« less
-
the allen telescope array twenty centimeter survey a 700 square degree multi epoch radio dataset ii individual epoch transient statistics
arXiv: Cosmology and Nongalactic Astrophysics, 2011Co-Authors: Steve Croft, Geoffrey C Bower, Garrett K Keating, C J Law, David Whysong, Peter K G Williams, M C H WrightAbstract:We present our second paper on the Allen Telescope Array Twenty-centimeter Survey (ATATS), a multi-epoch, ~700 sq. deg. radio image and catalog at 1.4 GHz. The survey is designed to detect rare, bright transients as well as to commission the ATA's wide-field survey capabilities. ATATS explores the challenges of multi-epoch transient and variable source surveys in the domain of dynamic range limits and changing (u,v) coverage. Here we present images made using data from the individual epochs, as well as a revised image combining data from all ATATS epochs. The combined image has RMS noise 3.96 mJy / Beam, with a Circular Beam of 150 arcsec FWHM. The catalog, generated using a false detection rate algorithm, contains 4984 sources, and is >90% complete to 37.9 mJy. The catalogs generated from snapshot images of the individual epochs contain between 1170 and 2019 sources over the 564 sq. deg. area in common to all epochs. The 90% completeness limits of the single epoch catalogs range from 98.6 to 232 mJy. We compare the catalog generated from the combined image to those from individual epochs, and from the NRAO VLA Sky Survey (NVSS), a legacy survey at the same frequency. We are able to place new constraints on the transient population: fewer than 6e-4 transients / sq. deg., for transients brighter than 350 mJy with characteristic timescales of minutes to days. This strongly rules out an astronomical origin for the ~1 Jy sources reported by Matsumura et al. (2009), based on their stated rate of 3.1e-3 / sq. deg.
-
the allen telescope array twenty centimeter survey a 690 square degree 12 epoch radio dataset i catalog and long duration transient statistics
arXiv: Cosmology and Nongalactic Astrophysics, 2010Co-Authors: Steve Croft, Geoffrey C Bower, R F Ackermann, Shannon Atkinson, D C Backer, Peter Backus, William C Barott, Amber Bauermeister, Leo Blitz, D C J BockAbstract:We present the Allen Telescope Array Twenty-centimeter Survey (ATATS), a multi-epoch (12 visits), 690 square degree radio image and catalog at 1.4GHz. The survey is designed to detect rare, very bright transients as well as to verify the capabilities of the ATA to form large mosaics. The combined image using data from all 12 ATATS epochs has RMS noise sigma = 3.94mJy / Beam and dynamic range 180, with a Circular Beam of 150 arcsec FWHM. It contains 4408 sources to a limiting sensitivity of S = 20 mJy / Beam. We compare the catalog generated from this 12-epoch combined image to the NRAO VLA Sky Survey (NVSS), a legacy survey at the same frequency, and find that we can measure source positions to better than ~20 arcsec. For sources above the ATATS completeness limit, the median flux density is 97% of the median value for matched NVSS sources, indicative of an accurate overall flux calibration. We examine the effects of source confusion due to the effects of differing resolution between ATATS and NVSS on our ability to compare flux densities. We detect no transients at flux densities greater than 40 mJy in comparison with NVSS, and place a 2-sigma upper limit on the transient rate for such sources of 0.004 per square degree. These results suggest that the > 1 Jy transients reported by Matsumura et al. (2009) may not be true transients, but rather variable sources at their flux density threshold.
J J H Wang - One of the best experts on this subject based on the ideXlab platform.
-
broadband multiband conformal Circular Beam steering array
IEEE Transactions on Antennas and Propagation, 2006Co-Authors: J J H Wang, D J Triplett, C J StevensAbstract:A new approach for a broadband/multiband conformal Circular Beam-steering array is presented with both theory and experimental data. The array is low-profile, suitable for conformal mounting on a platform. It has an omnidirectional coverage with a unidirectional Beam that aims at a moderate directivity of 5 to 15 dBi. It consists of a center driven element and parasitic surface waveguide elements symmetrically positioned in the periphery, for electronic Beam steering and Beam forming to enhance RF connectivity and/or spectral efficiency. This array can achieve ultrawideband multiband performance and low-profile conformability unattainable by conventional array approaches. In addition, its cost is estimated to be an order of magnitude lower than that of conventional Beam-steering arrays. Breadboard and brassboard development efforts for the array have essentially achieved a bandwidth of 1.0-2.5 GHz. A larger bandwidth is feasible since its driven element has achieved a continuous 10:1 bandwidth, and since the surface waveguide elements could achieve a multioctave bandwidth similar to the broadbanding path from the Yagi-Uda array to the LP array
-
broadband multiband conformal Circular Beam steering array
International Microwave Symposium, 2005Co-Authors: J J H Wang, D J Triplett, C J StevensAbstract:A new approach for a broadband/multiband conformal Circular Beam-steering array is presented with essential experimental data. The array is low-profile, suitable for conformal mounting on a platform. It has an omnidirectional coverage with a unidirectional Beam that generally aims at a moderate directivity of 6 to 15 dBi. It consists of a center driven element and parasitic surface waveguide elements in the periphery for Beam steering. This array can achieve ultra-wideband multiband performance and low-profile conformability unattainable by conventional array approaches. In addition, its cost is an order of magnitude lower than that of conventional Beam-steering array. At present, its broadband/multiband performance is only limited by its surface waveguide elements since its driven element has achieved continuous 10:1 bandwidth.
Guohui Zhao - One of the best experts on this subject based on the ideXlab platform.
-
study of rectangular Beam folded waveguide traveling wave tube for terahertz radiation
Physics of Plasmas, 2017Co-Authors: Changqing Zhang, Yong Wang, M Grieser, Guohui ZhaoAbstract:To gain higher power with a lower cathode current density and a simpler structure, a novel rectangular Beam folded waveguide traveling-wave tube (RB-FW-TWT) operating at 220 GHz is proposed and analyzed in this paper and compared with the normal Circular Beam (CB) FW TWT. The dispersion characteristic was investigated based on an equivalent circuit model. The interaction impedance and the S-parameter of a RB-FW traveling-wave tube were analyzed by numerical simulations. A 3-D particle-in-cell code CST particle studio was introduced to analyze the performance of RB-FW TWT. The influence of the initial electron energy, frequency, input power, guiding magnetic field, and aspect ratio of the RB tunnel on the circuit performance was observed, and physical explanations were given. It reveals that the output power of RB-FW can reach 51.1 dBm, 8.4% dBm higher than a CB-FW, with a 3 dB bandwidth of 35 GHz when the Beam voltage and current are set to 14.25 kV and 140 mA, respectively. An aspect ratio of 0.4 is reco...