Ron Beresford

Australian SKA Pathfinder: A High-Dynamic Range Wide-Field of View Survey Telescope

The Australia SKA Pathfinder (ASKAP) is a new telescope under development as a world-class high-dynamic-range wide-field-of-view survey instrument. It will utilize focal plane phased array feeds on the 36 12-m antennas that will compose the array. The large amounts of data present a huge computing challenge, and ASKAP will store data products in an archive after near real-time pipeline processing. This powerful instrument will be deployed at a new radio-quiet observatory, the Murchison Radio-astronomy Observatory in the midwest region of Western Australia, to enable sensitive surveys of the entire sky to address some of the big questions in contemporary physics. As a pathfinder for the SKA, ASKAP will demonstrate field of view enhancement and computing/processing technology as well as the operation of a large-scale radio array in a remote and radio-quiet region of Australia.

The Australian Square Kilometre Array Pathfinder: System Architecture and Specifications of the Boolardy Engineering Test Array

This paper describes the system architecture of a newly constructed radio telescope - the Boolardy Engineering Test Array, which is a prototype of the Australian Square Kilometre Array Pathfinder telescope. Phased array feed technology is used to form multiple simultaneous beams per antenna, providing astronomers with unprecedented survey speed. The test array described here is a 6-antenna interferometer, fitted with prototype signal processing hardware capable of forming at least 9 dual-polarisation beams simultaneously, allowing several square degrees to be imaged in a single pointed observation. The main purpose of the test array is to develop beamforming and wide-field calibration methods for use with the full telescope, but it will also be capable of limited early science demonstrations.

Design and implementation of the 2 nd Generation ASKAP Digital Receiver System

The Second Generation Digital Receiver (DRX) is the new digitisation platform for the Australian Square Kilometre Array Pathfinder (ASKAP). The DRX is the result of the ASKAP Design Enhancement (ADE) project which was undertaken to improve the manufacturability of the prototype ASKAP hardware. The DRX is a 16 port optically fed direct sampled digitiser operating between 700MHz and 1800MHz. It processes up to 768MHz of instantaneous bandwidth and allows the selection of an arbitrary 384MHz to be transmitted to the beamformer.

Shielding requirements for ADE receivers

A single focal plane array receptor element in the ASKAP design enhancement (ADE) receiver system typically has a 40K LNA input noise temperature. For nominal conditions this is amplified by 70dB before RF over single mode fibre transmission to the central building for digitization and digital beam-forming. Shielding requirements for the ADE receivers are determined by three factors, these being unconditional gain stability over the 700MHz to 1800MHz band, very low cross talk between PAF elements and EMC susceptibility issues in the unlikely event a strong transient transmission presents. The crosstalk specification can be related to the phased array co-variance matrix (ACM). Measuring the shielding attenuation performance of very small electronics enclosures and subassemblies is particularly challenging. We use a number of test configurations including RF over fibre to electrically short radiators to replicate in-module emissions and enable realistic estimates of module shielding. This paper will briefly discuss the derivation of the specifications and the empirical techniques used to validate the prototype ADE receiver design.

Gain calibration of phased array feeds

Phased array feeds can greatly increase the field of view of interferometric radio telescope arrays. High dynamic range imaging with these arrays requires compensation for drifts in the many receiver-chain gains. A calibration system using surface radiators is proposed for the Australian Square Kilometre Array Path Finder. Design considerations and a proposed system are discussed.

New instrumentation for EMC work in radio astronomy

Both conventional swept frequency spectrum analyser based instrumentation and dedicated integrating spectrometers, based on high sample rate DSP, continue to serve admirably in helping to characterize and maintain the integrity of the radio spectrum quality at current radio astronomy facilities. Increasingly, impulsive, often sporadic transmissions are becoming the interference of most importance. Monitoring of both impulsive and continuous interference is important for ensuring the quality of observatory spectrum and also provides a critical role in determining the RF and DSP signal processing dynamic range headroom requirements for new radio astronomy receiver designs. The only way to ensure 100% probability of intercept (POI) is to ensure entire RF bands are sampled at the Nyquist rate. Our equipment uses a remote wideband 0dBi non-directional antenna isolated several hundred metres from the DSP to minimise self interference and maximize sensitivity. The antenna is connected by a high dynamic range RF over single-mode fibre. This paper summarises the CSIRO developed DSP based RFI monitoring system capable of real time nanosecond timescale transient event capture, combined with traditional integrating spectrometer spectrum capture.

Pre-compliance EMC measurements for MRO equipment

The establishment of Australias newest radio astronomy observatory, the Murchison Radio-astronomy Observatory (MRO), in the remote Mid West region of Western Australia offers very low ambient radio frequency interference (RFI) levels and is an ideal location for high sensitivity large collecting aperture instrumentation operating between 70MHz and 25GHz. Unlike previous radio astronomy (RA) facilities, all plant, electrical, electronic equipment and subsystems are required to meet, or better, rigorous MIL-STD 461F EMC standards for radiated emissions prior to deployment at the site. The site is regarded as a common infrastructure platform for several users and systems with disparate operational frequencies and antenna technologies distributed over several kilometres. A common requirement is radio quietness. A main building facility housing the MRO digital signal processing systems has achieved a shielding effectiveness (SE) design goal in excess of 160dB at 5GHz. This paper discusses the test protocol and measurement apparatus used at the CSIRO for equipment EMC compliance in the ASKAP project.

Radio astronomy L-band phased array feed RFoF implementation overview

The Australian Square Kilometre Pathfinder ASKAP Design Enhancement (ADE) is the second generation architecture based on a distributed antenna system (DAS) with radio over fiber transmission (RFoF) from planar phased array feed (PAF) to the central site digital signal processing (DSP). With 36 × 12m reflector antennas and 188 elements per PAF, there are 6840 ports with signal and conversion (SAC) paths. Low cost implementation is key for phased array systems comprising thousands of elements. The implementation and component choices are critical to provide a viable project delivery; balancing component availability, RF performance, power consumption, maintenance and whole of life aspects. In this paper we mention discrete components used, basic subassembly performance and fiducial end to end compliance measurements.

Low cost RF over fiber distribution for radio astronomy phased arrays

Arguably RFoF has found wide application in broadband cable TV (CATV) systems and more recently in wireless cell applications. The use of RFoF also has a history in Radio Astronomy (RA) instrumentation. Typically in the distribution of high quality Local Oscillator reference signals to reflector antennas. On the scale of a small number of reflector antennas there are several examples where Directly Modulated (DM) laser diodes or Externally Modulated (EM) RFoF links have been used for wideband RF or IF transmission of the radio astronomy signal bandpass from the receiver package back to a centralized digital signal processing rack. In the last decade the radio astronomy community has developed an appetite for wide field of view, large N phased arrays, essentially N element distributed antenna systems (DAS). The Square kilometre Array (SKA), the Murchison Widefield Array (MWA) and the Australian Square Kilometre Array Pathfinder (ASKAP) all have thousands of receptors. ASKAP in particular is already demonstrating a 6840 RFoF link based DAS architecture with 36 remotely located 12m reflector antennas and RFoF spans up-to 6km. Each reflector having a 188 element L-Band phased planar array feed (PAF) at the prime focus. In this paper we report our development of the low cost RFoF “building block” for the generic RA signal transmission application.

A radio astronomy L-band phased array feed system using RF over fiber distribution

This is an overview of the system level RF design for the second generation architecture used in the Australian Square Kilometre Array Pathfinder (ASKAP) [1] design enhancement (ADE). ADE is a distributed antenna system (DAS) of 36 reflector antennas each 12m in diameter. Each antenna has a planar Phased Array Feed (PAF) at the prime focus. The PAF contains 188 broadband 700–1800MHz receptors. Inside a PAF the radioastronomy (RA) signals are amplified, band selected and converted to 188 individual broadband RF over (singlemode optical) fiber (RFoF) lightwaves [2]. The entire ADE array has 6840 RFoF links, this includes transmission line delay metrology for each reflector. The longest RFoF span is 6km. Optical to RF demodulation of the RF sky signal at the central site Digital Signal Processing (DSP) shielded building is direct sampled in 12bit analog to digital convertors (ADCs). Digital beamforming provides 36 pencil beams, each of 384MHz bandwidth. The scale of ADE represents a leap forward in applied RF and photonic techniques to enable a simpler, lower cost, more modular, EMC compliant, phased array receiver architecture. ADE will provide unprecedented high speed sky surveys with an instantaneous widefield of view (30deg2 at 1420MHz) capability for a new generation of radio astronomers.