5,283 research outputs found
Mapping our Universe in 3D with MITEoR
Mapping our universe in 3D by imaging the redshifted 21 cm line from neutral
hydrogen has the potential to overtake the cosmic microwave background as our
most powerful cosmological probe, because it can map a much larger volume of
our Universe, shedding new light on the epoch of reionization, inflation, dark
matter, dark energy, and neutrino masses. We report on MITEoR, a pathfinder
low-frequency radio interferometer whose goal is to test technologies that
greatly reduce the cost of such 3D mapping for a given sensitivity. MITEoR
accomplishes this by using massive baseline redundancy both to enable automated
precision calibration and to cut the correlator cost scaling from N^2 to NlogN,
where N is the number of antennas. The success of MITEoR with its 64
dual-polarization elements bodes well for the more ambitious HERA project,
which would incorporate many identical or similar technologies using an order
of magnitude more antennas, each with dramatically larger collecting area.Comment: To be published in proceedings of 2013 IEEE International Symposium
on Phased Array Systems & Technolog
Future Developments in Low Temperature Detectors for CMB and Submm Astronomy
We summarize the wide range of current and upcoming developments in low temperature detectors for CMB and submillimeter astronomy. We discuss work in sensor development, photon coupling and filtering architectures, and polarimetry and how these tie to applications requirements
The Precision Array for Probing the Epoch of Reionization: 8 Station Results
We are developing the Precision Array for Probing the Epoch of Reionization
(PAPER) to detect 21cm emission from the early Universe, when the first stars
and galaxies were forming. We describe the overall experiment strategy and
architecture and summarize two PAPER deployments: a 4-antenna array in the
low-RFI environment of Western Australia and an 8-antenna array at our
prototyping site in Green Bank, WV. From these activities we report on system
performance, including primary beam model verification, dependence of system
gain on ambient temperature, measurements of receiver and overall system
temperatures, and characterization of the RFI environment at each deployment
site.
We present an all-sky map synthesized between 139 MHz and 174 MHz using data
from both arrays that reaches down to 80 mJy (4.9 K, for a beam size of 2.15e-5
steradians at 154 MHz), with a 10 mJy (620 mK) thermal noise level that
indicates what would be achievable with better foreground subtraction. We
calculate angular power spectra () in a cold patch and determine them
to be dominated by point sources, but with contributions from galactic
synchrotron emission at lower radio frequencies and angular wavemodes. Although
the cosmic variance of foregrounds dominates errors in these power spectra, we
measure a thermal noise level of 310 mK at for a 1.46-MHz band
centered at 164.5 MHz. This sensitivity level is approximately three orders of
magnitude in temperature above the level of the fluctuations in 21cm emission
associated with reionization.Comment: 13 pages, 14 figures, submitted to AJ. Revision 2 corrects a scaling
error in the x axis of Fig. 12 that lowers the calculated power spectrum
temperatur
Hybrid Simulation-Measurement Calibration Technique for Microwave Imaging Systems
This paper proposes an innovative technique to calibrate microwave imaging (MWI) systems combining available measured data with simulated synthetic ones. The introduced technique aims to compensate the variations of the antenna array due to unavoidable manufacturing tolerances and placement, in comparison to the nominal electromagnetic (EM) scenario. The scheme is tested virtually and experimentally for the MWI of the adult human head tissues. The virtual EM analysis uses a realistic 3-D CAD model working together with a full-wave
software, based on the finite element method. Meanwhile, the real implementation employs a single-cavity anthropomorphic head phantom and a custom brick-shaped antenna array working at around 1 GHz
On the calibration of a multistatic scattering matrix measured by a fixed circular array of antennas
International audienceThe calibration of the multistatic scattering matrix plays an important part in the construction of a quantitative microwave imaging system. For scattering measurement applications, the calibration must be performed on the amplitude and on the phase of the fields of interest. When the antennas are not completely identical, as for example with a multiplexed antennas array, a specific calibration procedure must be constructed. In the present work, we explain how a complex calibration matrix can be defined which takes advantage of the geometrical organization of the antennas. Indeed, for arrays of antennas positioned on a circle, the inherent symmetries of the configuration can be fully exploited by means of an adequate reorganization of the multistatic scattering matrix. In addition, the reorganization permits to detect antenna pairs which are not properly functioning and to estimate the signal-to-noise ratio. Experimental results obtained within a cylindrical cavity enclosed by a metallic casing are provided to assess the performance of the proposed calibration procedure.This calibration protocol, which is described here in detail, has already been applied to provide quantitative images of dielectric targets [1, 2]
Hydrogen Epoch of Reionization Array (HERA)
The Hydrogen Epoch of Reionization Array (HERA) is a staged experiment to
measure 21 cm emission from the primordial intergalactic medium (IGM)
throughout cosmic reionization (), and to explore earlier epochs of our
Cosmic Dawn (). During these epochs, early stars and black holes
heated and ionized the IGM, introducing fluctuations in 21 cm emission. HERA is
designed to characterize the evolution of the 21 cm power spectrum to constrain
the timing and morphology of reionization, the properties of the first
galaxies, the evolution of large-scale structure, and the early sources of
heating. The full HERA instrument will be a 350-element interferometer in South
Africa consisting of 14-m parabolic dishes observing from 50 to 250 MHz.
Currently, 19 dishes have been deployed on site and the next 18 are under
construction. HERA has been designated as an SKA Precursor instrument.
In this paper, we summarize HERA's scientific context and provide forecasts
for its key science results. After reviewing the current state of the art in
foreground mitigation, we use the delay-spectrum technique to motivate
high-level performance requirements for the HERA instrument. Next, we present
the HERA instrument design, along with the subsystem specifications that ensure
that HERA meets its performance requirements. Finally, we summarize the
schedule and status of the project. We conclude by suggesting that, given the
realities of foreground contamination, current-generation 21 cm instruments are
approaching their sensitivity limits. HERA is designed to bring both the
sensitivity and the precision to deliver its primary science on the basis of
proven foreground filtering techniques, while developing new subtraction
techniques to unlock new capabilities. The result will be a major step toward
realizing the widely recognized scientific potential of 21 cm cosmology.Comment: 26 pages, 24 figures, 2 table
A Sensitivity and Array-Configuration Study for Measuring the Power Spectrum of 21cm Emission from Reionization
Telescopes aiming to measure 21cm emission from the Epoch of Reionization
must toe a careful line, balancing the need for raw sensitivity against the
stringent calibration requirements for removing bright foregrounds. It is
unclear what the optimal design is for achieving both of these goals. Via a
pedagogical derivation of an interferometer's response to the power spectrum of
21cm reionization fluctuations, we show that even under optimistic scenarios,
first-generation arrays will yield low-SNR detections, and that different
compact array configurations can substantially alter sensitivity. We explore
the sensitivity gains of array configurations that yield high redundancy in the
uv-plane -- configurations that have been largely ignored since the advent of
self-calibration for high-dynamic-range imaging. We first introduce a
mathematical framework to generate optimal minimum-redundancy configurations
for imaging. We contrast the sensitivity of such configurations with
high-redundancy configurations, finding that high-redundancy configurations can
improve power-spectrum sensitivity by more than an order of magnitude. We
explore how high-redundancy array configurations can be tuned to various
angular scales, enabling array sensitivity to be directed away from regions of
the uv-plane (such as the origin) where foregrounds are brighter and where
instrumental systematics are more problematic. We demonstrate that a
132-antenna deployment of the Precision Array for Probing the Epoch of
Reionization (PAPER) observing for 120 days in a high-redundancy configuration
will, under ideal conditions, have the requisite sensitivity to detect the
power spectrum of the 21cm signal from reionization at a 3\sigma level at
k<0.25h Mpc^{-1} in a bin of \Delta ln k=1. We discuss the tradeoffs of low-
versus high-redundancy configurations.Comment: 34 pages, 5 figures, 2 appendices. Version accepted to Ap
Application-Specific Broadband Antennas for Microwave Medical Imaging
The goal of this work is the introduction of efficient antenna structures on the basis of the requirement of different microwave imaging methods; i.e. quantitative and qualitative microwave imaging techniques. Several criteria are proposed for the evaluation of single element antenna structures for application in microwave imaging systems. The performance of the proposed antennas are evaluated in simulation and measurement scenarios
Eliminating stray radiation inside large area imaging arrays
With increasing array size, it is increasingly important to control stray
radiation inside the detector chips themselves. We demonstrate this effect with
focal plane arrays of absorber coupled Lumped Element microwave Kinetic
Inductance Detectors (LEKIDs) and lens-antenna coupled distributed quarter
wavelength Microwave Kinetic Inductance Detectors (MKIDs). In these arrays the
response from a point source at the pixel position is at a similar level to the
stray response integrated over the entire chip area. For the antenna coupled
arrays, we show that this effect can be suppressed by incorporating an on-chip
stray light absorber. A similar method should be possible with the LEKID array,
especially when they are lens coupled.Comment: arXiv admin note: substantial text overlap with arXiv:1707.0214
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