The 21-cm absorption profile is detected in the sky-averaged radio spectrum, but is much stronger than predicted, suggesting that the primordial gas might have been cooler than predicted. As the first stars heated hydrogen in the early Universe, the 21-cm hyperfine line—an astronomical standard that represents the spin-flip transition in the ground state of atomic hydrogen—was altered, causing the hydrogen gas to absorb photons from the microwave background. This should produce an observable absorption signal at frequencies of less than 200 megahertz (MHz). Judd Bowman and colleagues report the observation of an absorption profile centred at a frequency of 78 MHz that is about 19 MHz wide and 0.5 kelvin deep. The profile is generally in line with expectations, although it is deeper than predicted. An accompanying paper by Rennan Barkana suggests that baryons were interacting with cold dark-matter particles in the early Universe, cooling the gas more than had been expected. After stars formed in the early Universe, their ultraviolet light is expected, eventually, to have penetrated the primordial hydrogen gas and altered the excitation state of its 21-centimetre hyperfine line. This alteration would cause the gas to absorb photons from the cosmic microwave background, producing a spectral distortion that should be observable today at radio frequencies of less than 200 megahertz1. Here we report the detection of a flattened absorption profile in the sky-averaged radio spectrum, which is centred at a frequency of 78 megahertz and has a best-fitting full-width at half-maximum of 19 megahertz and an amplitude of 0.5 kelvin. The profile is largely consistent with expectations for the 21-centimetre signal induced by early stars; however, the best-fitting amplitude of the profile is more than a factor of two greater than the largest predictions2. This discrepancy suggests that either the primordial gas was much colder than expected or the background radiation temperature was hotter than expected. Astrophysical phenomena (such as radiation from stars and stellar remnants) are unlikely to account for this discrepancy; of the proposed extensions to the standard model of cosmology and particle physics, only cooling of the gas as a result of interactions between dark matter and baryons seems to explain the observed amplitude3. The low-frequency edge of the observed profile indicates that stars existed and had produced a background of Lyman-α photons by 180 million years after the Big Bang. The high-frequency edge indicates that the gas was heated to above the radiation temperature less than 100 million years later.

An absorption profile centred at 78 megahertz in the sky-averaged spectrum

The techniques and technologies currently being investigated to detect weapons and contraband concealed on persons under clothing are reviewed. The basic phenomenology of the atmosphere and materials that must be understood in order to realize such a system are discussed. The component issues and architectural designs needed to realize systems are outlined. Some conclusions with respect to further technology developments are presented.

Standoff Detection of Weapons and Contraband in the 100 GHz to 1 THz Region

Author(s): DeBoer, David R; Parsons, Aaron R; Aguirre, James E; Alexander, Paul; Ali, Zaki S; Beardsley, Adam P; Bernardi, Gianni; Bowman, Judd D; Bradley, Richard F; Carilli, Chris L; Cheng, Carina; Acedo, Eloy de Lera; Dillon, Joshua S; Ewall-Wice, Aaron; Fadana, Gcobisa; Fagnoni, Nicolas; Fritz, Randall; Furlanetto, Steve R; Glendenning, Brian; Greig, Bradley; Grobbelaar, Jasper; Hazelton, Bryna J; Hewitt, Jacqueline N; Hickish, Jack; Jacobs, Daniel C; Julius, Austin; Kariseb, MacCalvin; Kohn, Saul A; Lekalake, Telalo; Liu, Adrian; Loots, Anita; MacMahon, David; Malan, Lourence; Malgas, Cresshim; Maree, Matthys; Martinot, Zachary; Mathison, Nathan; Matsetela, Eunice; Mesinger, Andrei; Morales, Miguel F; Neben, Abraham R; Patra, Nipanjana; Pieterse, Samantha; Pober, Jonathan C; Razavi-Ghods, Nima; Ringuette, Jon; Robnett, James; Rosie, Kathryn; Sell, Raddwine; Smith, Craig; Syce, Angelo; Tegmark, Max; Thyagarajan, Nithyanandan; Williams, Peter K. G; Zheng, Haoxuan

https://iopscience.iop.org/article/10.1088/1538-3873/129/974/045001/pdf

Hydrogen epoch of reionization array (HERA)

The Murchison Widefield Array 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: detection and characterization of three-dimensional brightness temperature fluctuations in the 21 cm line of neutral hydrogen during the epoch of reionization (EoR) at redshifts from six to ten; 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 broadband active dipoles, arranged into 512 ldquotilesrdquo comprising 16 dipoles each. The tiles are quasi-randomly distributed over an aperture 1.5 km in diameter, with a small number of outliers extending to 3 km. All tile-tile baselines are correlated in custom field-programmable gate array based hardware, yielding a Nyquist-sampled instantaneous monochromatic uv coverage and unprecedented point spread function 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.

/pdf/the-murchison-widefield-array-design-overview-1op0axbp6l.pdf

The Murchison Widefield Array: Design Overview

Cooperating Organizations American Astronomical Society (United States) • Netherlands Institute for Radio Astronomy (ASTRON) (Netherlands) • Ball Aerospace & Technologies Corporation (United States) Canadian Astronomical Society (CASCA) (Canada) • European Astronomical Society (Switzerland) • ESO—European Southern Observatory (Germany) • International Astronomical Union • Korea Astronomy and Space Science Institute (KASI) (Republic of Korea) • National Radio Astronomy Observatory • POPSud (France) • TNO (Netherlands)

/pdf/ground-based-and-airborne-telescopes-iii-2e6sjio423.pdf

Ground-based and Airborne Telescopes III

We have constructed an 810 GHz receiver system incorporating a HIFI Band-3 superconductor-insulator-superconductor (SIS) mixer developed for Herschel space observatory and a wide-band SiGe low noise amplifier (LNA) designed at Caltech. The instrument is currently installed at the RLT telescope (elevation 5500 m) in northern Chile. Hot/cold (280K/72K) load measurements performed at the telescope yield noise temperatures of 225 K (Y-factor = 1.7) including receiver optics. First-light observations indicate that the receiver is highly sensitive and functions stably. We present details of the receiver system, its performance at the telescope, and first-light observations with a Herschel mixer.

/pdf/a-field-deployed-810-ghz-receiver-incorporating-a-2nda26la1f.pdf

A field-deployed 810 GHz receiver incorporating a superconducting mixer developed for herschel space telescope and a SiGe low noise amplifier

A dual beam, dual polarization, low noise receiver has been installed at a Cassegrain focus of the NASA 70m antenna near Canberra, Australia. It operates in five pairs of 1GHz bands from 17 to 27GH...

The 17–27 GHz Dual Horn Receiver on the NASA 70 m Canberra Antenna

High Electron Mobility Transistors (HEMTs) play a crucial role in receivers for millimeter and submillimeter astrophysical observations. Low noise HEMTs are used extensively in low noise receiver front ends, for coherent direct detection and intermediate frequency (IF) amplification in heterodyne detection. Power amplifiers are becoming widely used for local oscillator (LO) subsystems in heterodyne receivers. We will describe the state-of-the-art in low noise amplifier technology stressing recent results at frequencies 1-110 GHz, with a focus on TRW’s InP HEMT devices. We will describe the potential for performance improvements with a focus on proposed astrophysics applications.

Amplifier Technology for Astrophysics

This paper presents a novel ultra-low-loss high-pass filter with 3 dB cutoff frequency of 890 MHz for astronomical receiver radio frequency interference mitigation application. The filter consists of three series capacitors, four shunt inductors, and microstrip circuit board. Specially, 4 shunt inductors are actualized by fabricating air-core short-circuit coaxial cable inductors in the filter box body, and the quality factor of these cable inductors is up to 762.2 and 1046, respectively, at 1.4 GHz. In the expected passband of 1.1–1.9 GHz, S parameters measurement show that insertion loss is lower than 0.16 dB and two-port return loss is larger than 20 dB; noise measurement show that filter noise temperature is lower than 8 at 300 K ambient temperature. Noise sources of this filter are analyzed by simulation and measurement.

Ultra-low-loss high-pass filter with air-core short-circuit coaxial cable

Thecharacterization oftheintensity fluctuations oftheCosmicMicrowave Background (CMB)will befollowed by themappingofthepolarization fluctuations oftheCMB. Measurement ofthepolarization fluctuations requires highly sensitive instruments thatareonlypossible byincreasing the numberofreceivers. We aredeveloping alarge receiver arrayfor theQ,U Imaging Experiment (QUIET)bybuilding individual receivers thathavenoise temperatures close tothephysical limit andthataresimple, andlowcosttobuildandoperate. We developed theseplanarpolarimetry receivers forQ-bandby designing InPMMIC amplifiers withnoise below20K,lowloss andhighly balanced phaseswitches andan entirely planar hybrid thinfilmcircuit forthedetection oftheStokes parameters Q andU.Ourreceivers achieve 25K noise temperature over8 GHz bandwidth andprovide theI,Q andU parameters simultaneously. Theseplanar moduleshavea simple plugin architecture thatenables automated production ofa large numberofreceivers andsimple integration oflargearrays of receivers. IndexTerms- Polarimetry, Millimeter waveradiometry, Millimeter wave phaseshifters, MMICs,Millimeter wave imaging, Cosmic Microwave Background (CMB).

http://ieeexplore.ieee.org/iel5/4014788/4014789/04014826.pdf

Sander Weinreb

Papers

A field-deployed 810 GHz receiver incorporating a superconducting mixer developed for herschel space telescope and a SiGe low noise amplifier

The 17–27 GHz Dual Horn Receiver on the NASA 70 m Canberra Antenna

Amplifier Technology for Astrophysics

Ultra-low-loss high-pass filter with air-core short-circuit coaxial cable

Planar Polarimetry Receivers forLargeImaging Arrays atQ-band