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  • IEEE Xplore  (7)
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  • 1
    Language: English
    In: IEEE Transactions on Microwave Theory and Techniques, August 2016, Vol.64(8), pp.2631-2639
    Description: This paper introduces a one-port method for estimating model parameters of vector network analyzer calibration standards. The method involves measuring the standards through an asymmetrical passive network connected in direct mode and then in reverse mode, and using these measurements to compute the S-parameters of the network. The free parameters of the calibration standards are estimated by minimizing a figure of merit based on the expected equality of the S-parameters of the network when used in direct and reverse modes. The capabilities of the method are demonstrated through simulations, and real measurements are used to estimate the actual offset delay of a 50-Ω calibration load that is assigned zero delay by the manufacturer. The estimated delay is 38.8 ps with a 1 σ uncertainty of 2.1 ps for this particular load. This result is verified through measurements of a terminated airline. The measurements agree better with theoretical models of the airline when the reference plane is calibrated using the new estimate for the load delay.
    Keywords: Standards ; Transmission Line Measurements ; Calibration ; Delays ; Scattering Parameters ; Ports (Computers) ; Extraterrestrial Measurements ; Delay ; Impedance ; Reflection Standards ; Scattering Parameters ; Vector Network Analyzer (Vna) ; Engineering
    ISSN: 0018-9480
    E-ISSN: 1557-9670
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  • 2
    Language: English
    In: 2014 United States National Committee of URSI National Radio Science Meeting (USNC-URSI NRSM), January 2014, pp.1-1
    Description: Summary form only given. Significant effort has recently been turned to the problem of detecting and characterizing intergalactic hydrogen prior to its complete ionization by stars, occurring sometime before t=950Ma (z=6). The distribution of HI, visible in redshifted 21cm radio emission, is one of the few observables into the onset of non-linear structure leading to the birth of the first stars and galaxies. Before it was ionized by stellar UV radiation, HI was found throughout the universe, roughly tracing out the underlying matter distribution and temperature. HI 21cm emission from this epoch (6 〈; z 〈; 12) is redshifted into the VHF radio band (100 〈; f 〈; 200 MHz) and with a observer frequency depending on redshift/distance provides a fully three dimensional view. The emission is expected to have surface brightness of ~25mK with a non-gaussian distribution and most power occurring on scales of 10cMpc. Here we describe how data from PAPER and MWA have significantly tightened our constraints on bright foregrounds, and through comparison, identified some of the most likely sources of error in foreground removal steps. In addition we present early results of an exploration of the redshift and spatial dependence of fainter foreground components identified in the deep PAPER data which has so far given the tightest constraints. Comparing with new MWA observations we seek to separate possible faint foreground contamination from equally likely systematic corruption.
    Keywords: Pollution Measurement ; Educational Institutions ; Contamination ; Jacobian Matrices ; Earth ; Space Exploration ; Hydrogen
    Source: IEEE Conference Publications
    Source: IEEE Xplore
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  • 3
    Language: English
    In: 2015 USNC-URSI Radio Science Meeting (Joint with AP-S Symposium), July 2015, pp.296-296
    Description: Removal of the sky foreground is critical to the success of the Experiment to Detect the Global Epoch of reionization Signature (EDGES) program. We evaluate terrestrial locations for the ease of removing the sky foreground from the convolution of the antenna beam with the frequency scaled Haslam skymap. We use two dipole antennas: 1) a ½-wavelength dipole whose beam can be expressed in a closed-form equation and 2) the EDGES dipole antenna, both over ground planes.
    Keywords: Communication, Networking and Broadcast Technologies ; Fields, Waves and Electromagnetics ; Photonics and Electrooptics;
    Source: IEEE Conference Publications
    Source: IEEE Xplore
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  • 4
    Language: English
    In: 2015 USNC-URSI Radio Science Meeting (Joint with AP-S Symposium), July 2015, pp.295-295
    Description: The Experiment to Detect the Global EoR Signature (EDGES) is attempting to place constraints on parameters that characterize the Epoch of Reionization (EoR). This is an important period of the Universe in which the intergalactic medium, mostly atomic Hydrogen (HI), transitioned from a neutral to an ionized state. Models and observations suggest that the EoR occurred between redshifts 13 and 6. There are predictions for the average evolution of HI in this period in the form of a characteristic signature of 21-cm radiation as a function of redshift. This radiation (emitted originally at about 1.4 GHz) needs to be measured in the 100-200 MHz range due to cosmological expansion. The goal of EDGES is to detect this signature using an extremely well characterized spectrometer.
    Keywords: Communication, Networking and Broadcast Technologies ; Fields, Waves and Electromagnetics ; Photonics and Electrooptics;
    Source: IEEE Conference Publications
    Source: IEEE Xplore
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  • 5
    Language: English
    In: 2018 2nd URSI Atlantic Radio Science Meeting (AT-RASC), May 2018, pp.1-1
    Description: The 21-cm spectral line emitted by neutral hydrogen in the intergalactic medium (IGM) at redshifts 〉 6, can be used to characterize the first generations of stars, galaxies, and black holes in the Universe. Due to redshift, the 21-cm signal is expected at frequencies 〈 200 MHz for z 〉 6. The Experiment to Detect the Global EoR Signature (EDGES) measures the sky-average, or global, brightness temperature spectrum in the frequency range 50-200 MHz, with the objective of characterizing the cosmological 21-cm signal. The EDGES instruments are single-antenna, absolutely-calibrated, total-power radiometers. They conduct observations from the Murchison Radio-astronomy Observatory in Western Australia.
    Keywords: Instruments ; Image Edge Detection ; Data Mining ; Observatories ; Frequency Measurement ; Calibration ; Receivers
    Source: IEEE Conference Publications
    Source: IEEE Xplore
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  • 6
    Language: English
    In: 2014 United States National Committee of URSI National Radio Science Meeting (USNC-URSI NRSM), January 2014, pp.1-1
    Description: Recent interest in high redshift cosmology observations with the redshifted 21cm line has rekindled exploration of the VHF radio band (50-200MHz) for radio astronomy. Single antenna instruments like the ground-based EDGES and the proposed lunar orbiting DARE have the goal of characterizing the global HI signal and extracting astrophysical and cosmological information. One limitation over much of the band is strong man-made and naturally occurring interference, which DARE avoids by observing as it orbits the far side of the moon. Another advantage of space-based observing is avoidance of the ionosphere which becomes increasingly reflective at the lower end of the VHF band. Technical challenges to this type of mission include development of lower power wide-band spectrometers, better mapping of Earth originating interference, and incorporation of lessons learned from ongoing ground-based experiments. One of the main challenges faced by EDGES, observing the narrower but clean stretch of bandwidth found in Western Australia, is calibrating the spectral response of the antenna at the required 0.01dB level.
    Keywords: Space Vehicles ; Antennas ; Interference ; Bandwidth ; Educational Institutions ; Earth ; Propulsion
    Source: IEEE Conference Publications
    Source: IEEE Xplore
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  • 7
    Description: The Murchison Widefield Array (MWA) is a dipole-based aperture array synthesis telescope designed to operate in the 80-300 MHz frequency range. It is capable of a wide range of science investigations, but is initially focused on three key science projects. These are detection and characterization of 3-dimensional brightness temperature fluctuations in the 21cm line of neutral hydrogen during the Epoch of Reionization (EoR) at redshifts from 6 to 10, solar imaging and remote sensing of the inner heliosphere via propagation effects on signals from distant background sources,and high-sensitivity exploration of the variable radio sky. The array design features 8192 dual-polarization broad-band active dipoles, arranged into 512 tiles comprising 16 dipoles each. The tiles are quasi-randomly distributed over an aperture 1.5km in diameter, with a small number of outliers extending to 3km. All tile-tile baselines are correlated in custom FPGA-based hardware, yielding a Nyquist-sampled instantaneous monochromatic uv coverage and unprecedented point spread function (PSF) quality. The correlated data are calibrated in real time using novel position-dependent self-calibration algorithms. The array is located in the Murchison region of outback Western Australia. This region is characterized by extremely low population density and a superbly radio-quiet environment,allowing full exploitation of the instrumental capabilities. Comment: 9 pages, 5 figures, 1 table. Accepted for publication in Proceedings of the IEEE
    Keywords: Astrophysics - Instrumentation And Methods For Astrophysics ; Astrophysics - Cosmology And Nongalactic Astrophysics ; Astrophysics - Solar And Stellar Astrophysics
    ISSN: 00189219
    E-ISSN: 15582256
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