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We describe the performance of the Boolardy Engineering Test Array (BETA), the prototype for the Australian Square Kilometre Array Pathfinder telescope ASKAP. BETA is the first aperture synthesis radio telescope to use phased array feed technology, giving it the ability to electronically form up to nine dual-polarization beams. We report the methods developed for forming and measuring the beams, and the adaptations that have been made to the traditional calibration and imaging procedures in order to allow BETA to function as a multi-beam aperture synthesis telescope. We describe the commissioning of the instrument and present details of BETA's performance: sensitivity, beam characteristics, polarimetric properties and image quality. We summarise the astronomical science that it has produced and draw lessons from operating BETA that will be relevant to the commissioning and operation of the final ASKAP telescope., Accepted for publication in PASA

Apertif is the phased array feeds (PAFs) system operational on the Westerbork Synthesis Radio Telescope. This paper will cover various aspects of the system describing how the instrument is operated on a daily basis. Focus will be given to the use of new technology adopted for the hardware monitoring, automation of operational routines, calibration of the instrument and the results and lessons learned by operating it.

The scientific capability of an astronomical phased array feed receiver can be quantified by combining the bandwidth, sensitivity, and field of view into the overall survey speed of the instrument. The authors investigate the relationships between survey speed and reflector geometry, array layout, element spacing and element configuration using numerical simulations, to determine the values of these parameters that lead to optimal system performance. They characterise the array element spacing that leads to maximum survey speed as a function of the reflector f/D. To further improve survey speed in relation to the overall number of array elements, the authors explore the possibility of using elements with modest levels of superdirectivity to sample more of the focal plane Airy pattern and increase optimal spacing for survey speed figure of merit. The results explain how optimal survey speed is controlled primarily by the influence of element type and array layout on the peak achievable aperture efficiency.

In this paper we describe the system design and capabilities of the Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope at the conclusion of its construction project and commencement of science operations. ASKAP is one of the first radio telescopes to deploy phased array feed (PAF) technology on a large scale, giving it an instantaneous field of view that covers 31 square degrees at 800 MHz. As a two-dimensional array of 36x12m antennas, with baselines ranging from 22m to 6km, ASKAP also has excellent snapshot imaging capability and 10 arcsecond resolution. This, combined with 288 MHz of instantaneous bandwidth and a unique third axis of rotation on each antenna, gives ASKAP the capability to create high dynamic range images of large sky areas very quickly. It is an excellent telescope for surveys between 700 MHz and 1800 MHz and is expected to facilitate great advances in our understanding of galaxy formation, cosmology and radio transients while opening new parameter space for discovery of the unknown., 38 pages, 24 figures, accepted for publication in PASA

We describe the beamforming strategy and the preliminary laboratory characterization results of the beam pattern synthesized by the PHAROS2 Phased Array Feed (PAF), a 4-8 GHz PAF with digital beamformer for radio astronomy application. The PAF is based on an array of 10×11 dual-polarization Vivaldi antennas cryogenically cooled at 20 K along with low noise amplification modules (LNAs) cascaded with a multi-channel Warm Section (WS) receiver. We present the beamforming and test procedures used to, respectively digitally synthesize and characterize the PHAROS2 antenna array beam pattern at 6 GHz. The tests of the array were carried out at room temperature by directly connecting 24 antenna elements to the WS and iTPM digital beamformer in a laboratory measurement setup.

In order to improve the prediction accuracy of the pattern of the reflector antenna with phased array feed, a high-precision semi-physical pattern prediction method based on the combination of the electric field and circuit priori measurement data is proposed in this paper. Combined with the differential evolution algorithm, the proposed method is applied to the beam optimization of the reflector antenna with phased array feed. For a given configuration of the reflector antenna with phased array feed, several examples are optimized efficiently and accurately. The proposed method greatly improves the accuracy of the optimization of the reflector antenna with phased array feed.

In this article, two new ultra‐wideband (UWB) dual‐polarized Bowtie antennas are investigated as the elements for a phased array feed for reflectors. In addition to its UWB impedance matching characteristic, the Bowtie antennas have stable large beam‐width and a low cross‐polar level over a wide frequency band with a compact size, which is an essence for phased array applications. The simulated and measured results state a low ohmic loss, good impedance matching (S11 below −15 dB) and good radiation performance, with a simple structure for easy manufacturing. The proposed antennas can be good candidates for phased array feed (PAF) in FAST and the SKA (square kilometer array) pathfinder PHAROS2 projects, and massive MIMO antennas in wireless communication systems.

Modern and upcoming radio telescopes at low frequencies are often characterized by hundreds or thousands of antenna elements operating at wide bandwidths up to about 0.5[Formula: see text]GHz. A spectral correlator for such an array is required to estimate the cross-power spectrum of the response of each element with that of every other element with a high spectral resolution. The resulting all-to-all connectivity between signals from the entire array poses a serious bottleneck. In this paper, we propose a simple digital receiver architecture that interfaces the digitized time series from a large number of antenna elements to a High-Performance Computing (HPC) cluster through a communication switch to overcome the data ingest bottleneck. Each HPC node can then perform wideband processing in steps of finite but significant time-slices for the entire array. We explain in detail the implementation of our architecture for the proposed expansion of the Ooty Wide Field Array (OWFA) into a 1056 element array. Since the proposed digital receiver is based on Field Programmable Gate Array (FPGA), it can be reconfigured for different applications. This is illustrated by considering the case of Phased Array Feeds (PAF) for the proposed expanded Giant Metrewave Radio Telescope (eGMRT).

PHased Arrays for Re°ector Observing Systems (PHAROS) is a C-band (4–8 GHz) Phased Array Feed (PAF) receiver designed to operate from the primary focus of a large single-dish radio astronomy antenna. It consists of an array of 220-element Vivaldi antennas (10 11 2 polarization), cryogenically cooled at roughly 20K along with low noise ampli¯ers (LNAs), and of analogue beamformers cryogenically cooled at roughly 80 K. PHAROS2, the upgrade of PHAROS, is a PAF demonstrator developed in the framework of the Square Kilometer Array Advanced Instrumentation Program (SKA AIP) with the goal of investigating the potential of the PAF technologies at high frequencies in view of their possible application on the SKA dish telescopes. The PHAROS2 design includes new cryogenically cooled LNAs with state-of-the-art performance, a digital beamformer capable of synthesizing four beams from a sub-array of 24 single-polarization antenna elements, and a C-band multi-channel Warm Section receiver capable of analogue ¯ltering and down-converting the signals from the antennas to a suitable frequency range at the input of the digital backend, providing an instantaneous bandwidth of 275MHz for each signal. In this paper, we describe the design and performance of the PHAROS2 digital backend/beamformer, based on the Italian Tile Processing Module (ITPM) hardware, which was initially developed for the SKA Low Frequency Aperture Array (LFAA). The backend was adapted to perform the beamforming for our PAF application. We describe the implementation of the beamformer on the Field Programmable Gate Arrays (FPGAs) of the ITPM and how the backend was successfully used to synthesize four independent beams, both in the laboratory (across the entire 275MHz instantaneous bandwidth) and during on-¯eld observations at the BEST-2 array (across 16MHz instantaneous bandwidth), which is a subset of the Northern Cross Radio Telescope (located in the district of Bologna, Italy). The beamformer design allows re-scaling to a greater number of beams and wider bandwidths., peer-reviewed

For large reflector radio telescopes, cryogenic phased array feed (PAF) has the great potential on enhancing the telescope’s performance and thus PAF becomes one of the research frontiers in the field of radio astronomy. The Joint Laboratory for Radio Astronomy Technology (JLRAT) team has been studying on PAF theories and key technologies and developing a cryogenic prototype for the Five hundred meter Aperture Spherical Telescope (FAST). This paper is to present the current progress on the frontend signal processing devices including the signal processing framework design, the system integration and key components development.

This paper presents an ultra-wideband Phased Array Feed (PAF) based on novel flat bend crossed dipole fed by 50Ohm coaxial line. The PAF is dual-polarized and made from all-metal to minimize Ohmic losses and simplify cryogenic integration. It is optimized for 1-2 GHz band and can be good PAF candidate for the Five hundred meter Aperture Spherical Telescope (FAST) and Qi Tai Telescope (QTT) as well as other radio telescopes.

Brigham Young University (BYU), in collaboration with Cornell University, is developing the Advanced Cryogenic L-band Phased Array Camera for Arecibo (ALPACA) as a user provided facility instrument on the Arecibo 305 m radio telescope. This instrument will consist of a fully cryogenic 69-element phased array feed (PAF) and real-time digital beamformer back end capable of producing 40 simultaneous dual polarized beams with approximately 305 MHz of instantaneous bandwidth at 1.4 GHz. The target design goal is to operate with a system noise temperature of 25 K. We report on simulation results and a preliminary overview of the design and progress of the instrument’s development.

Here we outline the development techniques used to design a millimeter-wave lens antenna that is fed by a single chipset phased array feed. The lens significantly increases the gain and retains the scanning capability of the array. The resulting system is only slightly more expensive than the array alone but has the directivity of a system with many more elements.

We report results from a neutral hydrogen (HI) intensity mapping survey conducted with a Phased Array Feed (PAF) on the Parkes telescope. The survey was designed to cover ~ 380 deg^2 over the redshift range 0.3 < z < 1 (a volume of ~ 1.5 Gpc^3) in four fields covered by the WiggleZ Dark Energy Survey. The results presented here target a narrow redshift range of 0.73 < z < 0.78 where the effect of radio frequency interference (RFI) was less problematic. The data reduction and simulation pipeline is described, with an emphasis on flagging of RFI and correction for signal loss in the data reduction process, particularly due to the foreground subtraction methodology. A cross-correlation signal was detected between the HI intensity maps and the WiggleZ redshift data, with a mean amplitude of = 1.32 \pm 0.42 mK (statistical errors only). A future Parkes cryogenic PAF is expected to detect the cross-correlation signal with higher accuracy than previously possible and allow measurement of the cosmic HI density at redshifts up to unity., Comment: 16 pages, 11 figures, accepted by Research in Astronomy and Astrophysics

Phased array feeds (PAFs), which illuminate the dish with digitally synthesized beams instead of separated horns, provide the capability for wider and continuous field-of-view surveys. As a promising technology for next generation radio telescopes, PAFs will provide the Qi Tai Telescope (QTT), which will be next world-class fully steerable radio telescope, an opportunity of reaching several cutting-edge science goals. This paper presents a brief introduction of the wideband PAF for QTT, and the detailed design and simulation of the cryogenic system. Based on this design, a scaled prototype of the spherical vacuum window, which is the key part of the cryogenic system, has been built and the performance is verified.

We describe the development of a multi-channel “warm receiver section” (WS) and of a digital beamformer for the PHAROS2 Phased Array Feed (PAF), a PAF demonstrator for radio astronomy application across the 4-8 GHz radio frequency (RF) band. The PAF is based on an array of 10×11 dual-polarization Vivaldi antennas cryogenically cooled at 20 K along with low noise amplification modules (LNAs). The WS receiver can process the signals from a subset of 24 antenna elements of the array by downconverting them to an intermediate frequency (IF) range, 375-650 MHz, suitable for digitization by the digital beamformer. The latter is based on the iTPM (Italian Tile Processing Module), developed for the Square Kilometer Array (SKA) Low Frequency Aperture Array (LFAA). We modified the iTPM firmware to synthesize four independent beams across the 275 MHz instantaneous IF bandwidth in the iTPM FPGAs (Field Programmable Gate Arrays). The 24 signals are sent from the WS to the iTPM through analogue IFoF (IF over fiber) optical links. In this paper we present the design and performance of the WS and of the digital bemaformer for PHAROS2.

Phased Array Feed (PAF) is an emerging technology to increase the field of view for the radio telescopes based on reflector antennas. The Lovell Telescope has been used for over 50 years for investigating cosmic phenomena. This work reports a low profile circular PAF design for the Lovell antenna based on the experience from the antenna design for the Mid-Frequency Aperture Array of Square Kilometre Array. The objective is to provide a low profile and cost effective PAF design suitable for cryogenically cooling of the entire front-end to improve noise performance. The EM performance of the proposed PAF design and its characteristics are reported in this paper.

A wide-field receiver for the Arecibo Telescope is currently in development, the Advanced L band Phased Array Camera for Arecibo (ALPACA). The Arecibo optical system provides a new challenge for design optimization of phased array feeds. We report on results from a simulation and design optimization study aimed at determining the element layout and geometry that maximizes the receiver sensitivity, field of view, and survey speed.

This paper describes the design, fabrication, and test results of a room temperature multi-channel heterodyne receiver operating across the 2.3&ndash, 8.2 GHz radio frequency (RF) band. Such a &ldquo, Warm Section&rdquo, (WS) receiver is part of phased arrays for reflector observing systems 2 (PHAROS2), a C-band phased array feed (PAF) demonstrator with digital beamformer for radio astronomy application. The WS receiver is cascaded to the PHAROS2 cryostat, which includes an array of Vivaldi antennas with low noise pre-amplification stages. The WS can handle up to 32 RF signals and, for each of them, realizes the operations of filtering, RF amplification and down-conversion from the RF to the 375&ndash, 650 MHz intermediate frequency (IF). Also, the WS incorporates an IF-to-optical signal conversion through analogue wavelength division multiplexing IF over fiber (IFoF) and fiber-optic transmitters (OTXs). The 32-channel WS receiver consists of four eight-channel WS RF/IF modules, one local oscillator (LO) splitter module and one monitoring and control module, all hosted in a standard 6U &times, 19-inch rack.

Apertif; the next stage Chapter 15.1: - Observing Perspectives with Apertif Exploring the time-varying Universe Chapter 15.2: - ARTS, the Apertif Radio Transient System Apertif; the next stage Chapter 15.3: - From Multi-frequency to Widefield; the System - An overview of the Apertif Phased Array Feed principles

Phased array feed is a small two-dimension phased array located at the focal plane of a reflector antenna and acts as the feed, which can offer the capability for multiple simultaneous beam formation and wide field-of-view. This paper presents the development of a phased array feed at Ku-band, including the design, optimization, and prototyping. The test results of the prototype are given, which match the simulation reasonably well, validating a successful development and effective way of calibration.

We present three recent receiver designs and the challenges in their development: a phased array feed (PAF), a multibeam system for FAST and an “ultra-wideband” feed for the Parkes telescope. A significant driver in the development of these receivers is the radio astronomy focus on surveys. In general terms

We have conducted a search for bright repeating Fast Radio Bursts in our nearby Universe with the Australian Square Kilometer Array Pathfinder (ASKAP) in single-dish mode. We used eight ASKAP 12-m dishes, each equipped with a Chequerboard Phased Array Feed forming 36 beams on the sky, to survey $\sim$30,000 deg$^{2}$ of the southern sky ($-90^{\circ} < ��< +30^{\circ}$) in 158 antenna days. The fluence limit of the survey is 22 Jyms. We report the detection of FRB 180515 in our survey. We found no repeating FRBs in a total mean observation of 3hrs per pointing divided into one-hour intervals, which were separated in time ranging between a day to a month. Using our non-detection, we exclude the presence of a repeating FRB similar to FRB 121102 closer than $z=0.004$ in the survey area --- a volume of at least $9.4 \times 10^4$Mpc$^3$ --- at 95% confidence., 7 pages, 8 figures, accepted in MNRAS

Based on a novel composite right/left-handed unit cell, a wideband frequency-scanning network with a large scanning angle ranging towards both negative and positive elevation angles is proposed. The measured results show that the insertion loss variation of the designed frequency-scanning network is 7.2 ± 1 dB when the frequency ranges from 4.33 to 8.53 GHz and the phase differences of adjacent output ports scan from −50° to 50° when the frequency ranges from 4.76 to 8.26 GHz (53.8%). The proposed network can be used in wideband systems that require a large scanning angle range.

We present results from a first attempt to mitigate radio frequency interference in real-time during astronomical measurements with a phased array feed on the 64 m Parkes radio telescope. Suppression of up to 20 dB was achieved despite errors in estimating the interference spatial signature. Best results were achieved in the clean excision of a narrowband and stationary clock signal that originates from the receiver's digital back-end system. We also contribute a method to interpolate valid beamformer weights at interference-affected channels. Correct initial beam weights are required to avoid suppressing the desired signal., 4 pages, 6 figures, 1 table, accepted for publication in Electromagnetics in Advanced applications (ICEAA), 2017 International Conference on

An overview of ASKAP phased array feed (PAF) development is presented. New analytical and experimental techniques devised for ASKAP are described. Dedicated engineering test facilities are shown to be invaluable for system verification. Experience gained from PAF manufacture is compared with forecasts, and the importance of routine engineering demonstrated.

We have observed the Vela pulsar for one year using a Phased Array Feed (PAF) receiver on the 12-metre antenna of the Parkes Test-Bed Facility. These observations have allowed us to investigate the stability of the PAF beam-weights over time, to demonstrate that pulsars can be timed over long periods using PAF technology and to detect and study the most recent glitch event that occurred on 12 December 2016. The beam-weights are shown to be stable to 1% on time scales on the order of three weeks. We discuss the implications of this for monitoring pulsars using PAFs on single dish telescopes., Comment: 6 pages, 4 figures, 2 tables. Accepted for publication in PASA

During February 2016, CSIRO Astronomy and Space Science and the Max-Planck-Institute for Radio Astronomy installed, commissioned and carried out science observations with a phased array feed (PAF) receiver system on the 64m diameter Parkes radio telescope. Here we demonstrate that the PAF can be used for pulsar observations and we highlight some unique capabilities. We demonstrate that the pulse profiles obtained using the PAF can be calibrated and that multiple pulsars can be simultaneously observed. Significantly, we find that an intrinsic polarisation leakage of -31dB can be achieved with a PAF beam offset from the centre of the field of view. We discuss the possibilities for using a PAF for future pulsar observations and for searching for fast radio bursts with the Parkes and Effelsberg telescopes., 10 pages, 8 figures, 2 tables. It has been accepted for publication in PASA

Phased array feeds (PAFs) for large diameter single dish radio telescopes offer the capability for multiple simultaneous beam formation and wide field-of-view surveys. An L-band PAF front end design is presented for the Five-hundred-meter Aperture Spherical Telescope (FAST), which is currently under construction and when complete will be the largest single dish radio telescope in the world. A broadband PAF element at L-band was designed in conjunction with the FAST optics and focal plane field distribution, fabricated, and tested. The simulated performance of the array meets the FAST PAF performance requirements for field of view, efficiency, sensitivity, and other key parameters. A unique aspect of the FAST PAF is the need for feed cabin vibration compensation. A study of the use of adaptive beamforming to compensate for lateral movement is given.

The SKA (Square Kilometer Array) will be the world’s largest synthesis radio telescope, which will address many fundamental questions about our universe. Scientists and Engineers from 67 institutions in 20 countries have joined the pre-study of the SKA since 1993. China has been playing an important role, from various SKA concepts in the early years, to the current site selection as well as the technical development. The SKA has now entered the pre-construction phase, and many countries including China are involved into the key technology development, such as antenna prototyping and Phased Array Feed. With China’s continuous participation into the SKA, including the establishment of a science team aiming at limited scientific objectives, technical studies and designs of high-precision light antennas and broadband wide-field receivers, the Chinese Astronomy and related technologies will be greatly promoted. The SKA will provide a great opportunity for China to play an active role in international mega-science projects.

A real-time spatial RFI mitigation experiment has been conducted with an ASKAP test array in Australia at GPS L2 frequencies. The goal of the study was to observe and image a bright astronomical source in a corrupted environment. The RFI spatial information was estimated in real-time with Phased Array Feed sample Array Covariance Matrices in order to update a spatial filter based on subspace projection. The resulting images show a clear improvement in the filtered data compared to the unprocessed data. This paper describes the instrument and the RFI mitigation strategy implemented. Possible limitations and improvements of the algorithms employed are suggested after analyzing and interpreting the results.

The Australian Square Kilometre Array Pathfinder (ASKAP) will be the fastest dedicated cm-wave survey telescope, and will consist of 36 12-meter 3-axis antennas, each with a large chequerboard phased array feed (PAF) receiver operating between 0.7 and 1.8 GHz, and digital beamforming prior to correlation. The large raw data rates involved (~100 Tb/sec), and the need to do pipeline processing, has led to the antenna incorporating a third axis to fix the parallactic angle with respect to the entire optical system (blockages and phased array feed). It also results in innovative technical solutions to the data transport and processing issues. ASKAP is located at the Murchison Radio-astronomy Observatory (MRO), a new observatory developed for the Square Kilometre Array (SKA), 315 kilometres north-east of Geraldton, Western Australia. The MRO also hosts the SKA low frequency pathfinder instrument, the Murchison Widefield Array and will host the initial low frequency instrument of the SKA, SKA1-Low. Commissioning of ASKAP using six antennas equipped with first-generation PAFs is now complete and installation of second-generation PAFs and digital systems is underway. In this paper we review technical progress and commissioning to date, and refer the reader to relevant technical and scientific publications.

Phased array feed (PAF) is an emerging technology which can greatly improve the survey speed of telescopes. As a world-class radio telescope, the Five-hundred-meter Aperture Spherical radio Telescope (FAST) is also trying to enhance its observation capability and open up new scientific studies at several frequency bands by PAFs. At the first partof this paper, the blue print of the FAST PAFs development and corresponding scientific goals are introduced, as well as the progress has been made in these PAFs.

We present the first installation and characterization of a phased array feed (PAF) on the 64 m Parkes radio telescope. The combined system operates best between 0.8 GHz and 1.74 GHz where the beamformed noise temperature is between 45 K and 60 K, the aperture efficiency ranges from 70% to 80%, and the effective field of view is 1.4 deg$^2$ at 1310 MHz. After a 6-month trial observing program at Parkes, the PAF will be installed on the 100 m antenna at Effelsberg. This is the first time a PAF has been installed on a large single-antenna radio telescope and made available to astronomers., 4 pages, 7 figures, 1 table, accepted for publication in Electromagnetics in Advanced applications (ICEAA), 2016 International Conference on

The overview of a Phased Array Feed (PAF) system and the early results with it on the 100 m diameter telescope at Effelsberg are presented in the paper.

Since the first light of the 2.4-m Thai National Telescope in 2013, Thailand foresees another great leap forward in astronomy. A project known as “Radio Astronomy Network and Geodesy for Development” (RANGD) by National Astronomical Research Institute of Thailand (NARIT) has been approved for year 2017-2021. A 40-m radio telescope has been planned to operate up to 115-GHz observation with prime-focus capability for low frequency and phased array feed receivers. The telescope’s first light is expected in late 2019 with a cryogenics K-band and L-band receivers. RFI environment at the site has been investigated and shown to be at reasonable level. A 13-m VGOS telescope is also included for geodetic applications. Early single-dish science will focus on time domain observations, such as pulsars and transients, outbursts and variability of maser and AGN sources.

The challenges of detecting and localising Fast Radio Bursts in real time can be met with the use of Phased Array Feeds. One such system, capable of creating up to 36 simultaneous beams, is currently being commissioned at the Effelsberg radio telescope in Germany following testing at the 64 m Parkes radio telescope. The PAFINDER (Phased Array Feed FRB Finder) pipeline will be used with this receiver to enable real–time single–pulse detection and localisation.

We have observed the Vela pulsar for 1 year using a Phased Array Feed (PAF) receiver on the 12-m antenna of the Parkes Test-Bed Facility (PTF). These observations have allowed us to investigate the stability of the PAF beam weights over time, to demonstrate that pulsars can be timed over long periods using PAF technology and to detect and study the most recent glitch event that occurred on 12 December 2016. The beam weights are shown to be stable to 1% on time scales on the order of three weeks.