The design and development process for the Square Kilometre Array (SKA) radio telescope's Low Frequency Aperture Array component was progressed during the SKA pre-construction phase by an international consortium, with the goal of meeting requirements for a critical design review. As part of the development process a full-sized prototype SKA Low 'station' was deployed -the Aperture Array Verification System 1 (AAVS1). We provide a system overview and describe the commissioning results of AAVS1, which is a low frequency radio telescope with 256 dual-polarisation log-periodic dipole antennas working as a phased array. A detailed system description is provided, including an in-depth overview of relevant sub-systems, ranging from hardware, firmware, software, calibration, and control sub-systems. Early commissioning results cover initial bootstrapping, array calibration, stability testing, beam-forming, and on-sky sensitivity validation. Lessons learned are presented, along with future developments.

We describe the APERture Tile In Focus (Apertif) system, a phased array feed (PAF) upgrade of the Westerbork Synthesis Radio Telescope that transforms this telescope into a high-sensitivity, wide-field-of-view L-band imaging and transient survey instrument. Using novel PAF technology, up to 40 partially overlapping beams are formed on the sky simultaneously, significantly increasing the survey speed of the telescope. With this upgraded instrument, an imaging survey covering an area of 2300 deg 2 is being performed that will deliver both continuum and spectral line datasets, of which the first data have been publicly released. In addition, a time domain transient and pulsar survey covering 15 000 deg 2 is in progress. An overview of the Apertif science drivers, hardware, and software of the upgraded telescope is presented, along with its key performance characteristics.

The low frequency array (LOFAR) is a phased array interferometer currently consisting of 13 international stations across Europe and 38 stations surrounding a central hub in the Netherlands. The instrument operates in the frequency range of ~10–240 MHz and is used for a variety of astrophysical science cases. While it is not heliophysics or space weather dedicated, a new project entitled “LOFAR for Space Weather” (LOFAR4SW) aims at designing a system upgrade to allow the entire array to observe the Sun, heliosphere, Earth’s ionosphere, and Jupiter throughout its observing window. This will allow the instrument to operate as a space weather observing platform, facilitating both space weather science and operations. Part of this design study aims to survey the existing space weather infrastructure operating at radio frequencies and show how LOFAR4SW can advance the current state-of-the-art in this field. In this paper, we survey radio instrumentation and facilities that currently operate in space weather science and/or operations, including instruments involved in solar, heliospheric, and ionospheric studies. We furthermore include an overview of the major space weather service providers in operation today and the current state-of-the-art in the radio data they use and provide routinely. The aim is to compare LOFAR4SW to the existing radio research infrastructure in space weather and show how it may advance both space weather science and operations in the radio domain in the near future.

Aperture array technology is one of the candidate technologies for the 500 MHz to 1500 MHz frequency range of the SKA. The feasibility and low noise potential of aperture arrays have been demonstrated with small test systems before, e.g. with a 50 K system noise temperature, measured on a 1 m² prototype tile in 2010. However, further reduction of the array noise temperature is essential to optimize the ratio of effective collecting area and system noise temperature. This is made possible by applying new, lower noise, technology to the LNA design. Thus the sensitivity requirement for the Mid Frequency Aperture Array of the SKA could be satisfied at lower cost. Results of a step by step approach to reduce the system noise temperature to below 40 K, giving at least 20% improvement, are presented.

No abstract