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Register a new user1.2 Meter Shielded Cassegrain Antenna for Close-Packed Radio Interferometer
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Interferometric millimeter observations of the cosmic microwave background and clusters of galaxies with arcmin resolutions require antenna arrays with short spacings. Having all antennas co-mounted on a single steerable platform sets limits to the overall weight. A 25 kg lightweight novel carbon-fiber design for a 1.2 m diameter Cassegrain antenna is presented. The finite element analysis predicts excellent structural behavior under gravity, wind and thermal load. The primary and secondary mirror surfaces are aluminum coated with a thin TiO$_2$ top layer for protection. A low beam sidelobe level is achieved with a Gaussian feed illumination pattern with edge taper, designed based on feedhorn antenna simulations and verified in a far field beam pattern measurement. A shielding baffle reduces inter-antenna coupling to below $sim$ -135 dB. The overall antenna efficiency, including a series of efficiency factors, is estimated to be around 60%, with major losses coming from the feed spillover and secondary blocking. With this new antenna, a detection rate of about 50 clusters per year is anticipated in a 13-element array operation.
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PUMA is a proposal for an ultra-wideband, low-resolution and transit interferometric radio telescope operating at $200-1100,mathrm{MHz}$. Its design is driven by six science goals which span three science themes: the physics of dark energy (measuring the expansion history and growth of the universe up to $z=6$), the physics of inflation (constraining primordial non-Gaussianity and primordial features) and the transient radio sky (detecting one million fast radio bursts and following up SKA-discovered pulsars). We propose two array configurations composed of hexagonally close-packed 6m dish arrangements with 50% fill factor. The initial 5,000 element petite array is scientifically compelling, and can act as a demonstrator and a stepping stone to the full 32,000 element full array. Viewed as a 21cm intensity mapping telescope, the program has the noise equivalent of a traditional spectroscopic galaxy survey comprised of 0.6 and 2.5 billion galaxies at a comoving wavenumber of $k=0.5,hmathrm{Mpc}^{-1}$ spanning the redshift range $z = 0.3 - 6$ for the petite and full configurations, respectively. At redshifts beyond $z=2$, the 21cm technique is a uniquely powerful way of mapping the universe, while the low-redshift range will allow for numerous cross-correlations with existing and upcoming surveys. This program is enabled by the development of ultra-wideband radio feeds, cost-effective dish construction methods, commodity radio-frequency electronics driven by the telecommunication industry and the emergence of sufficient computing power to facilitate real-time signal processing that exploits the full potential of massive radio arrays. The project has an estimated construction cost of 55 and 330 million FY19 USD for the petite and full array configurations. Including R&D, design, operations and science analysis, the cost rises to 125 and 600 million FY19 USD, respectively.
Following the selection of The Gravitational Universe by ESA, and the successful flight of LISA Pathfinder, the LISA Consortium now proposes a 4 year mission in response to ESAs call for missions for L3. The observatory will be based on three arms with six active laser links, between three identical spacecraft in a triangular formation separated by 2.5 million km. LISA is an all-sky monitor and will offer a wide view of a dynamic cosmos using Gravitational Waves as new and unique messengers to unveil The Gravitational Universe. It provides the closest ever view of the infant Universe at TeV energy scales, has known sources in the form of verification binaries in the Milky Way, and can probe the entire Universe, from its smallest scales near the horizons of black holes, all the way to cosmological scales. The LISA mission will scan the entire sky as it follows behind the Earth in its orbit, obtaining both polarisations of the Gravitational Waves simultaneously, and will measure source parameters with astrophysically relevant sensitivity in a band from below $10^{-4},$Hz to above $10^{-1},$Hz.
This paper summarizes the design process and metrics for the latest antenna design for 2 radio telescopes, SKALA4 for the SKA1-LOW instrument and the V-feed for the HERA telescope. In the paper we briefly describe the main features of the antenna element design and the most important figures of merit for both instruments. Finally, we show the response of both designs against some of these figures of merit.
The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is a transit interferometer currently being built at the Dominion Radio Astrophysical Observatory (DRAO) in Penticton, BC, Canada. We will use CHIME to map neutral hydrogen in the frequency range 400 -- 800,MHz over half of the sky, producing a measurement of baryon acoustic oscillations (BAO) at redshifts between 0.8 -- 2.5 to probe dark energy. We have deployed a pathfinder version of CHIME that will yield constraints on the BAO power spectrum and provide a test-bed for our calibration scheme. I will discuss the CHIME calibration requirements and describe instrumentation we are developing to meet these requirements.
We report development of a simple and affordable radio interferometer suitable as an educational laboratory experiment. With the increasing importance of interferometry in astronomy, the lack of educational interferometers is an obstacle to training the future generation of astronomers. This interferometer provides the hands-on experience needed to fully understand the basic concepts of interferometry. The design of this interferometer is based on the Michelson & Pease stellar optical interferometer, but operates at a radio wavelength (~11 GHz; ~2.7cm); thus the requirement for optical accuracy is much less stringent. We utilize a commercial broadcast satellite dish and feedhorn. Two flat side mirrors slide on a ladder, providing baseline coverage. This interferometer resolves and measures the diameter of the Sun, a nice daytime experiment which can be carried out even in marginal weather (i.e., partial cloud cover). Commercial broadcast satellites provide convenient point sources for comparison to the Suns extended disk. We describe the mathematical background of the adding interferometer, the design and development of the telescope and receiver system, and measurements of the Sun. We present results from a students laboratory report.
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