The Radio Array of Portable Interferometric Detectors (RAPID) is a new radio array with a flexible architecture. The instrument uses per element software defined radios and a software signal processing architecture to enable the flexible study of a wide range of natural phenomena using radio imaging techniques. The array will be used for investigations of ionospheric phenomena, solar radio emission, the Galactic synchrotron background, and ultra-high energy cosmic rays via air-shower emission. The array will consist of ~100 small, low gain antennas operating over a frequency range of 48 to 450 MHz. RAPID is designed to make flexible and coherent radio observations, capturing the amplitude and phase of the electric field across a user-defined aperture with easily reconfigurable spatial sampling. Key technical elements include a novel absolute broadband antenna calibration method, elimination of a clock distribution network with a compact, low power chip scale atomic clock in each unit, state-of-the-art high performance voltage data recording, and low power consumption, via use of the latest low-power A/D converters and digital processing chips. By minimizing the power per element the RAPID system will be able to use compact, portable solar panels and batteries. Unlike existing arrays, RAPID will be operated without any cabling between the antennas and a central location, and can be shipped, deployed and physically reconfigured quickly and easily with zero site infrastructure. This creates a unique capability to locate and configure an imaging radio interferometer array, highly customized to the specific science goal of any given field campaign, thereby supporting science investigations that have not before been feasible. When used in conjunction with existing incoherent scatter radar transmitters or other transmitters of opportunity the array will provide a flexible capability for radar imaging of coherent and enhanced backscatter (e.g. E and F-region irregularities; naturally or artificially enhanced ion acoustic lines). The RAPID system architecture is based on voltage data capture with all processing performed in software, simplifying field operations and reducing equipment complexity. Data and work-flow management for the system will exploit distributed messaging, cloud technologies for scalable processing, and be implemented using open source Object Oriented Data Technology (OODT) software.

This paper is the first in a series of papers describing the impact of antenna instrumental artefacts on the 21 cm cosmology experiments to be carried out by the low frequency instrument (SKA1-LOW) of the Square Kilometre Array telescope (SKA), i.e. the Cosmic Dawn (CD) and the Epoch of Reionization (EoR). The smoothness of the passband response of the current log-periodic antenna being developed for the SKA1-LOW is analysed using numerical electromagnetic simulations. The amplitude variations over the frequency range are characterized using low-order polynomials defined locally, in order to study the impact of the passband smoothness in the instrument calibration and CD/EoR Science. A solution is offered to correct a fast ripple found at 60 MHz during a test campaign at the SKA site at the Murchison Radio-astronomy Observatory, Western Australia in 2015 September with a minor impact on the telescope's performance and design. A comparison with the Hydrogen Epoch of Reionization Array antenna is also shown demonstrating the potential use of the SKA1-LOW antenna for the delay-spectrum technique to detect the EoR.

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.

This paper describes the important design aspects of an array antenna for the low frequency instrument of the SKA telescope (SKA-low). The most important considerations to meet the telescope performance requirements are discussed. Finally, a plot of the expected sky brightness sensitivity for phase I of the SKA using log-periodic antennas is presented.

This memo presents a feasibility study of a software correlator for SKA Phase 1 (SKA1). It sets out a generic parametric and platformindependent description of the processing and data-flow requirements of an FX correlator. These are then quantified for SKA1 Low and SKA1 Mid using the draft specifications presented in the SKA Phase 1 Preliminary System Description (SKA Memos 125 and 130) and compared against a real processing architecture–NVIDIA’s Tesla platform–to design a model system. We present estimate of the number of processing nodes needed, and their purchase cost and power consumption. We project that the processing nodes needed for this model would cost 3.1 million euros in 2017 and dissipate around 520 kW; we go on to indicate how this performance might be improved by up to a factor of two.

Aperture phased arrays operating at mid-frequencies from 400MHz to 1.4 GHz are a very exciting receiver technology being developed for the Square Kilometre Array, SKA.In many respects they enable the original concept of the SKA: to survey hydrogen in the universe out to a high redshift.The capabilities of a telescope using phased array stations brings major scientific opportunities, including very high survey speeds, flexibility for searching for transient phenomena, and multi-beaming capability which cannot be realized using any other technology.The very high level of control over each receiver element enables exquisite calibration as a function of frequency and pointing direction.The technological requirements to implement high frequency, astronomically capable phased arrays are severe in terms of power and cost due to the large numbers of channels and the amount of digital processing required.However, technology roadmapping shows that forthcoming technical developments make a large system deployment realistic from 2020 onwards.An aperture array covering this frequency range is the only instrument able to perform some of the most challenging science experiments planned for the SKA and is likely to make transformational discoveries.

Aperture array (AA) technology is at the forefront of new developments and discoveries in radio astronomy. Currently LOFAR is successfully demonstrating the capabilities of dense and sparse AA's at low frequencies. For the mid-frequencies, from 450 to 1450MHz, AA's still have to prove their scientific value with respect to the existing dish technology. Their large field-of-view and high flexibility puts them in an excellent position to do so. The Aperture Array Verification Program is dedicated to demonstrate the feasibility of AA's for science in general and SKA in particular. For the mid-frequency range this has lead to the development of EMBRACE, which has already demonstrated the enormous flexibility of AA systems by observing HI and a pulsar simultaneously. It also serves as a testbed to demonstrate the technological reliability and stability of AA's. The next step will put AA technology at a level where it can be used for cutting-edge science. In this paper we discuss the developments to move AA technology from an engineering activity to a fully science capable instrument. We present current results from EMBRACE, ongoing tests of the system, and plans for EMMA, the next step in mid-frequency AA technology.

The medium of RF signal transfer adopted for 2PAD was twisted pair differential signal cabling.While intended to demonstrate a low cost solution, the technique has brought with it several challenges, not least in terms of the losses and phase skew introduced.Some interesting engineering challenges have been faced along the way to delivering usable signals to the DSP Engineers.Faced with an aggressive RFI environment, with strong TV and GSM broadcast signals, a small, reasonably quiet band was exploited.A review of the RFI shielding policy has been required to maintain stability in the gain stages of the analogue system.An effective cabinet RFI barrier has been successfully demonstrated.Future work through PrepSKA will explore alternative cabling solutions, such as coaxial and optical fibre, with the intention of evaluating the main contenders against the cost, power, and performance requirements for SKA.

This document describes software-based architectures which could provide an FX correlator for SKA Phase 1. It provides an assessment of the feasibility of implementing such a correlator on the current generation of NVIDIA general-purpose graphics processing unit (GPGPU) cards, showing that the performance delivered by this line of processors is considerably more competitive than that of the current generation of x86-based processors. It also provides a forecast of how we expect the performance metrics derived from this implementation to evolve between now and the construction of SKA Phase 1 in 2016-2019 (Garrett et al. 2010, Dewdney et al. 2010), making reference to the digital signal processing (DSP) technology roadmap (Turner 2011). Reasonable GPGPU performance expectations by 2016 show that the SKA Phase 1 correlator can be implemented economically using this platform.

The SKADS Benchmark Scenario is an overall SKA concept which aims to meet as many as possible of the SKA requirements presented in the SKA reference design. The key element of the system design is the use of aperture array technology on all baselines below a frequency of 1 GHz which gives a field of view of 250 square degrees in the key mid-frequency band. At higher frequencies comparatively low-cost, small (6.1 m) antennas are proposed each equipped with a single wide-band feed. The detailed design of high frequency dishes and wide-band, single pixel feeds is likely under a highly complementary US TDP programme and elsewhere. This Scenario is presented in detail, concentrating in particular on the design of the key mid-frequency aperture array and drawing on the work of other projects for elements of the system outside of the expertise and scope of the SKADS project. Detailed costing of the design suggests strongly that the Benchmark Scenario is a practical and achievable implementation which delivers the scientific performance for the SKA. The “worst case” cost is estimated to be€ 1.91 Billion with an uncertainty of 9% costed for 2011. Further development of the Benchmark Scenario will include detailed scientific and astronomical evaluation and simulation together with cost optimisation and cost/performance tradeoffs.