Phased array feeds (PAFs) are an active research area in radio astronomy, as they offer potential advantages over traditional single-pixel feeds. Their key advantage is increased field of view and survey speed, however they also permit tailoring the antenna beam for <i>A<sub>e</sub>=T<sub>sys</sub></i>, or other objectives such as attenuating strong radio frequency interference (RFI). A primary research goal is to improve the noise temperature performance of a PAF over comparable single-pixel feeds. <p> </p>In this work we have constructed a small 16-element digital beamformer with 384 MHz of bandwidth to evaluate the performance of NRCs Advanced Focal Array Demonstrator (AFAD) operating from 750 to 1500 MHz. We compare measured sensitivity results to previous measurements made with an analog beamformer. The digital beamformer is implemented using NRCs Kermode platform, a Virtex6-based compute blade. We take a standards-based approach, using the AdvancedTCA (ATCA) form factor for the Kermode board, ANSI/VITA-49.0 framing for all chip-to-chip and chip-to-host communications, and AXI4-Stream format for all internal datapaths. The Kermode system can be expanded with a standard ATCA full-mesh backplane to support up to 128 inputs with over 1 GHz of bandwidth.<p> </p> This expanded capability will ultimately be used to evaluate the performance of the full 96-element AFAD PAF mounted on a re ector antenna. To achieve this goal, we are well into developing a digitizer system that will handle at least 96 elements with up to 1.5 GHz of bandwidth per element. We present an overview of the digitizer system in the context of the PAF beamformer system, and provide an update on the progress to date.
The Square Kilometre Array (SKA) Project is a global science and engineering project realizing the next-generation radio telescopes operating in the metre and centimetre wavelengths regions. This paper addresses design concepts of the broadband, exceptionally sensitive receivers and reflector antennas deployed in the SKA1-Mid radio telescope to be located in South Africa. SKA1-Mid (350 MHz – 13.8 GHz with an option for an upper limit of ~24 GHz) will consist of 133 reflector antennas using an unblocked aperture, offset Gregorian configuration with an effective diameter of 15 m. Details on the unblocked aperture Gregorian antennas, low noise front ends and advanced direct digitization receivers, are provided from a system design perspective. The unblocked aperture results in increased aperture efficiency and lower side-lobe levels compared to a traditional on-axis configuration. The low side-lobe level reduces the noise contribution due to ground pick-up but also makes the antenna less susceptible to ground-based RFI sources. The addition of extra shielding on the sub-reflector provides a further reduction of ground pick-up. The optical design of the SKA1-Mid reflector antenna has been tweaked using advanced EM simulation tools in combination with sophisticated models for sky, atmospheric and ground noise contributions. This optimal antenna design in combination with very low noise, partially cryogenic, receivers and wide instantaneous bandwidth provide excellent receiving sensitivity in combination with instrumental flexibility to accommodate a wide range of astronomical observation modes.
With two large deformable mirrors with a total of more than 7000 actuators that need to be driven from the measurements of six 60x60 LGS WFSs (total 1.23Mpixels) at 800Hz with a latency of less than one frame, NFIRAOS presents an interesting real-time computing challenge. This paper reports on a recent trade study to evaluate which current technology could meet this challenge, with the plan to select a baseline architecture by the beginning of NFIRAOS construction in 2014. We have evaluated a number of architectures, ranging from very specialized layouts with custom boards to more generic architectures made from commercial off-the-shelf units (CPUs with or without accelerator boards). For each architecture, we have found the most suitable algorithm, mapped it onto the hardware and evaluated the performance through benchmarking whenever possible. We have evaluated a large number of criteria, including cost, power consumption, reliability and flexibility, and proceeded with scoring each architecture based on these criteria. We have found that, with today’s technology, the NFIRAOS requirements are well within reach of off-the-shelf commercial hardware running a parallel implementation of the straightforward matrix-vector multiply (MVM) algorithm for wave-front reconstruction. Even accelerators such as GPUs and Xeon Phis are no longer necessary. Indeed, we have found that the entire NFIRAOS RTC can be handled by seven 2U high-end PC-servers using 10GbE connectivity. Accelerators are only required for the off-line process of updating the matrix control matrix every ~10s, as observing conditions change.
NFIRAOS, the Thirty Meter Telescope’s first adaptive optics system is an order 60x60 Multi-Conjugate AO system with two deformable mirrors. Although most observing will use 6 laser guide stars, it also has an NGS-only mode. Uniquely, NFIRAOS is cooled to -30 °C to reduce thermal background. NFIRAOS delivers a 2-arcminute beam to three client instruments, and relies on up to three IR WFSs in each instrument. We present recent work including: robust automated acquisition on these IR WFSs; trade-off studies for a common-size of deformable mirror; real-time computing architectures; simplified designs for high-order NGS-mode wavefront sensing; modest upgrade concepts for high-contrast imaging.
The TMT first light Adaptive Optics (AO) facility consists of the Narrow Field Infra-Red AO System (NFIRAOS) and the associated Laser Guide Star Facility (LGSF). NFIRAOS is a 60 × 60 laser guide star (LGS) multi-conjugate AO (MCAO) system, which provides uniform, diffraction-limited performance in the J, H, and K bands over 17-30 arc sec diameter fields with 50 per cent sky coverage at the galactic pole, as required to support the TMT science cases. NFIRAOS includes two deformable mirrors, six laser guide star wavefront sensors, and three low-order, infrared, natural guide star wavefront sensors within each client instrument. The first light LGSF system includes six sodium lasers required to generate the NFIRAOS laser guide stars. In this paper, we will provide an update on the progress in designing, modeling and validating the TMT first light AO systems and their components over the last two years. This will include pre-final design and prototyping activities for NFIRAOS, preliminary design and prototyping activities for the LGSF, design and prototyping for the deformable mirrors, fabrication and tests for the visible detectors, benchmarking and comparison of different algorithms and processing architecture for the Real Time Controller (RTC) and development and tests of prototype candidate lasers. Comprehensive and detailed AO modeling is continuing to support the design and development of the first light AO facility. Main modeling topics studied during the last two years include further studies in the area of wavefront error budget, sky coverage, high precision astrometry for the galactic center and other observations, high contrast imaging with NFIRAOS and its first light instruments, Point Spread Function (PSF) reconstruction for LGS MCAO, LGS photon return and sophisticated low order mode temporal filtering.
Adaptive Optics Real-Time Control systems for next generation ground-based telescopes demand significantly higher
processing power, memory bandwidth and I/O capacity on the hardware platform than those for existing control systems.
We present a FPGA based high-performance computing platform that is developed at Dominion Radio Astrophysical
Observatory and is very suitable for the applications of Adaptive Optics Real-Time Control systems. With maximum of
16 computing blades, 110 TeraMAC/s processing power, 1.8Terabyte/s memory bandwidth and 19.5 Terabit/s I/O
capacity, this ATCA architecture platform has enough capacity to perform pixel processing, tomographic wave-front
reconstruction and deformable mirror fitting for first and second generation AO systems on 30+-meter class telescopes.
As an example, we demonstrate that with only one computing blade, the platform can handle the real time tomography
needs of NFIRAOS, the Thirty-Meter Telescope first light facility Multi-Conjugate Adaptive Optics system. The High-
Performance FPGA platform is integrated with Board Software Development Kit to provide a complete and fully tested
set of interfaces to access the hardware resources. Therefore the firmware development can be focused on unique, userspecific