Eloy de Lera Acedo

Hydrogen Epoch of Reionization Array (HERA)

The Hydrogen Epoch of Reionization Array (HERA http://reionization.org) is a staged experiment that uses the unique properties of the 21-cm line from neutral hydrogen to probe the Epoch of Reionization (EOR). During this epoch, roughly 0.3-1 billion years after the Big Bang, the first galaxies and black holes heated and reionized the early Universe. Direct observation of the large scale structure of reionization and its evolution with time will have a profound impact on our understanding of the birth of the first galaxies and black holes, their influence on the intergalactic medium (IGM), and cosmology. This paper will provide an overview of the project and describe the design of the HERA receiving element.

Low frequency aperture array developments for phase 1 SKA

Aperture Arrays (AA) mark a new era in radio astronomy combining high sensitivity with a large field-of-view, enabling very high survey and imaging speeds. This paper describes the development of low frequency aperture arrays leading up to SKA phase 1 within the Aperture Array Verification Program (AAVP) as part of the SKA program.

A Global-Local Synthesis Approach for Large Non-Regular Arrays

A method is proposed for the synthesis of large planar non-regular arrays assuming constant magnitude for the excitation of the elements. The approach, which combines global and local optimization, is based on distinguishing aperture-type and non-coherent parts of the array factor. The following constraints are considered: minimal separation of the antennas, maximum size of the array and fixed mainbeam width. The level of the sidelobes is reduced via the minimization of a new type of flexible averaging cost function based on an Lp-norm. Possible applications of this model lie in the field of radio astronomy, satellite communications and radar systems. The proposed optimization strategy consists of three successive steps designed to be independent of each other. Starting with an equivalent continuous aperture, the first two steps act as global transformations of the radial and azimuthal positions of the elements in the initial array, while the third step performs a local optimization of individual elements of the array. This last step heavily relies on computations of the gradient of the cost function, which can be done quickly using an FFT-based procedure. The method is illustrated for several large-scale examples by considering as inputs four different types of non-regular arrays.

Non-periodic arrays for radio-astronomy applications

The exploitation of non-periodic antenna arrays for next-generation radio-telescopes is evaluated in the present work. More precisely, the radiation properties and the mutual coupling effects in such structures are studied. A special-purpose Method-of-Moments (MoM) simulation technique allows us to obtain all the Embedded Element Patterns (EEP) and the array impedance matrix, while estimating the effects of mutual coupling in very large arrays. The level of averaging of mutual-coupling effects is analyzed in terms of array patterns and the more difficult case of deterministic nulling in presence of mutual coupling is exposed.

Fast MBF based method for large random array characterization

The array pattern obtained for the example proposed in the previous section is shown in Fig. 4. The result for a 7λ radius of convergence is compared with the pattern obtained considering only the isolated element pattern, which can also be seen as the embedded element pattern for a radius of influence set to 0. A difference of 0.45 dB is observed at broadside direction between both approaches. It is striking that this difference is much more than what one would expect assuming that the effects of mutual coupling behave like a centered random variable. This bias, as well as more elaborate techniques for the fast array solution will be the focus of further research.

The hydrogen epoch of reionization array dish. II. Characterization of spectral structure with electromagnetic simulations and its science implications

Author(s): Ewall-Wice, Aaron; Bradley, Richard; Deboer, David; Hewitt, Jacqueline; Parsons, Aaron; Aguirre, James; Ali, Zaki S; Bowman, Judd; Cheng, Carina; Neben, Abraham R; Patra, Nipanjana; Thyagarajan, Nithyanandan; Venter, Mariet; Acedo, Eloy de Lera; Dillon, Joshua S; Dickenson, Roger; Doolittle, Phillip; Egan, Dennis; Hedrick, Mike; Klima, Patricia; Kohn, Saul; Schaffner, Patrick; Shelton, John; Saliwanchik, Benjamin; Taylor, H. A; Taylor, Rusty; Tegmark, Max; Wirt, Butch

UAV-based pattern measurement of the SKALA

A novel antenna pattern measurement technique has been recently developed exploiting the capabilities of a micro Unmanned Aerial Vehicle (UAV) as a far-field test-source. This technique is suitable for characterizing VHF antennas such as those for low-frequency radio astronomy. This paper presents some of the measurements recently performed on the Square Kilometer Array Log-periodic Antenna (SKALA), which has been selected as the receiving element for the Low Frequency Aperture Array (LFAA).

Analysing the impact of far-out sidelobes on the imaging performance of the SKA-LOW telescope

This work used the Wilkes GPU cluster at the University of Cambridge High Performance Computing Service (http://www.hpc.cam.ac.uk/), provided by Dell Inc., NVIDIA and Mellanox, and part funded by STFC with industrial sponsorship from Rolls Royce and Mitsubishi Heavy Industries.

Mutual coupling analysis in non-regular arrays of SKALA antennas with the HARP approach

Wideband arrays devoted to radio-astronomy are analyzed. The Macro Basis Functions (MBFs) approach is used and improvements on the interpolatory approach are proposed for the fast interaction between MBFs: application to wire-antennas, DFT approach for the harmonic decomposition and modeling specific to extremely small distances between antennas.

Radio Array of Portable Interferometric Detectors (RAPID): Development of a deployable multiple application radio array

The Radio Array of Portable Interferometric Detectors (RAPID) is an advanced radio designed for multi-role applications. The system implements a spatially diverse sparse array technology and can be deployed and reconfigured easily. Data are captured at the raw voltage level using the system in the field and processed post-experiment. Signal processing for the system is software defined and uses a scalable Cloud computing architecture. The system builds upon the Square Kilometer Array Low Frequency Aperture antenna (SKALA) in combination with custom hardware for data acquisition on a per antenna basis. The instrument uses physically disconnected elements, a high performance direct digitization receiver, hot swap solid state storage, solar and battery power, and wireless control for interconnection. Schedule based operation can also be used in radio quiet locations or to enable minimally attended operation. RAPID is intended for application as both an Astronomical radio telescope and a Geospace imaging radar system. The high degree of mobility a orded by the system enables a wide variety of interferometric configurations and allows deployment of the instrument at locations which are optimal for specific scientific goals.