Phased Array Feed Research Articles

A Cryogenic SiGe Low-noise Amplifier Optimized for Phased-array Feeds

The growing number of phased-array feeds (PAF) being built for radio astronomy demonstrates an increasing need for low-noise amplifiers (LNA), which are designed for repeatability, low noise, and ease of manufacture. Specific design features that help to achieve these goals include the use of unpackaged transistors (for cryogenic operation); single-polarity biasing; straight plug-in radio frequency (RF) interfaces to facilitate installation and re-work; and the use of off-the-shelf components. The focal L-band array for the Green Bank Telescope (FLAG) is a cooperative effort by Brigham Young University and the National Radio Astronomy Observatory using warm dipole antennae and cryogenic Silicon Germanium Heterojunction Bipolar Transistor (SiGe HBT) LNAs. These LNAs have an in band gain average of 38 dB and 4.85 Kelvin average noise temperature. Although the FLAG instrument was the driving instrument behind this development, most of the key features of the design and the advantages they offer apply broadly to other array feeds, including independent-beam and phased, and for many antenna types such as horn, dipole, Vivaldi, connected-bowtie, etc. This paper focuses on the unique requirements array feeds have for low-noise amplifiers and how amplifier manufacturing can accommodate these needs.

The Detection of an Extremely Bright Fast Radio Burst in a Phased Array Feed Survey

Abstract We report the detection of an ultra-bright fast radio burst (FRB) from a modest, 3.4-day pilot survey with the Australian Square Kilometre Array Pathfinder. The survey was conducted in a wide-field fly’s-eye configuration using the phased-array-feed technology deployed on the array to instantaneously observe an effective area of 160 deg2, and achieve an exposure totaling 13200 deg2 hr . We constrain the position of FRB 170107 to a region in size (90% containment) and its fluence to be 58 ± 6 Jy ms. The spectrum of the burst shows a sharp cutoff above 1400 MHz, which could be due to either scintillation or an intrinsic feature of the burst. This confirms the existence of an ultra-bright ( Jy ms) population of FRBs.

Observing Pulsars with a Phased Array Feed at the Parkes Telescope

AbstractDuring 2016 February, 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 receiver system on the 64-m diameter Parkes radio telescope. Here, we demonstrate that the phased array feed can be used for pulsar observations and we highlight some unique capabilities. We demonstrate that the pulse profiles obtained using the phased array feed can be calibrated and that multiple pulsars can be simultaneously observed. Significantly, we find that an intrinsic polarisation leakage of −31 dB can be achieved with a phased array feed beam offset from the centre of the field of view. We discuss the possibilities for using a phased array feed for future pulsar observations and for searching for fast radio bursts with the Parkes and Effelsberg telescopes.

One Year of Monitoring the Vela Pulsar Using a Phased Array Feed

AbstractWe have observed the Vela pulsar for 1 year using a phased array feed receiver on the 12-m antenna of the Parkes Test-Bed Facility. These observations have allowed us to investigate the stability of the phased array feed beam weights over time, to demonstrate that pulsars can be timed over long periods using phased array feed technology and to detect and study the most recent glitch event that occurred on 2016 December 12. 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 phased array feeds on single dish telescopes.

Spectral-Line Observations Using a Phased Array Feed on the Parkes Telescope

AbstractWe present first results from pilot observations using a phased array feed (PAF) mounted on the Parkes 64-m radio telescope. The observations presented here cover a frequency range from 1 150 to 1 480 MHz and are used to show the ability of PAFs to suppress standing wave problems by a factor of ~10, which afflict normal feeds. We also compare our results with previous HIPASS observations and with previous H i images of the Large Magellanic Cloud. Drift scan observations of the GAMA G23 field resulted in direct H i detections at z = 0.0043 and z = 0.0055 of HIPASS galaxies J2242-30 and J2309-30. Our new measurements generally agree with archival data in spectral shape and flux density, with small differences being due to differing beam patterns. We also detect signal in the stacked H i data of 1 094 individually undetected galaxies in the GAMA G23 field in the redshift range 0.05 ⩽ z ⩽ 0.075. Finally, we use the low standing wave ripple and wide bandwidth of the PAF to set a 3σ upper limit to any positronium recombination line emission from the Galactic Centre of <0.09 K, corresponding to a recombination rate of <3.0 × 1045 s−1.

An Active Ka-Band Shared-Aperture Antenna With 50 dB Isolation for Satellite Communication

An active hybrid shared-aperture concept (employing both active and passive circuits) is presented. This active shared aperture realizes the required isolation level of 48 dB between transmit (TX) (30 GHz) and receive (RX) (20 GHz) channels of a ground terminal for two-way satellite communication. It can be applied in very small aperture terminals. The dual-frequency shared aperture can be used as a building block for a linearly or circularly polarized phased-array feed in a focal-plane array system. It includes a 20-GHz low-noise amplifier with on-chip notch filtering realized in a 0.25- μ m SiGe:C BiCMOS technology. The on-chip filter achieves 30 dB of attenuation at 30 GHz with only 0.4 dB noise figure degradation. The isolation is further enhanced by a novel dual-frequency shared-aperture concept based on defected ground structures in the printed circuit board. Experimental results from the prototype show an overall isolation between TX and RX channel of more than 50 dB at 30 GHz.

Random Feeding Networks for Reducing the Number of Phase Shifters in Limited-Scan Arrays

A new phased-array feeding network that results in low sidelobe levels (SLLs) over a limited scan region is demonstrated. The proposed concept groups the individual phased-array elements into random sequences of nonuniform subarrays and employs a single phase shifter (PS) for each subarray. When these random sequences are optimized, the resulting phased array can scan over a wide angle with low SLLs. A methodology for analyzing the random arrays is provided, multiple cases with different numbers of PSs and subarray groups are optimized, and design guidelines are presented. The performance of the random arrays is compared with conventional uniform subarrays and it is shown that random arrays reduce the number of PSs by up to 40% while preserving the same performance. A random array is demonstrated at 7.9 GHz for a 30-element linear design (scan in one direction) with 12 PSs and results in a half-power beamwidth of 4.1° with a scan angle up to ±14° and SLLs less than −15 dB. It is also shown that random arrays can be used in 2-D phased arrays with up to 60% reduction in the number of PSs. Application areas are in low-cost phased arrays with limited scan angles such as automotive radars or landing systems.

On the Bandwidth Gap Between the Array-Feed and Cluster-Feed Regimes for Broadband Multifeed Systems

For reflector antennas with broadband multiple feed systems, under optimal beamforming conditions, the feed operates at low frequencies as a phased array feed (PAF), with multiple elements contributing to a synthesized illumination pattern, whereas at high frequencies, each element forms a single independent beam. There is a frequency range between these two regimes where it is difficult to achieve high aperture efficiency, which limits the ultimate performance of broadband multifeed systems. We show that this bandwidth gap is largely independent of the formed beam angle, number of array elements, array layout, and element radiation patterns. We use simulation and modeling to study the origin and nature of this physical effect, develop an upper bound on the sensitivity bandwidth of a high-efficiency array feed, and consider several possible methods for improving the efficiency of multifeed systems in the bandwidth gap.

Wide-field broad-band radio imaging with phased array feeds: a pilot multi-epoch continuum survey with ASKAP-BETA

The Boolardy Engineering Test Array is a 6 x 12 m dish interferometer and the prototype of the Australian Square Kilometre Array Pathfinder (ASKAP), equipped with the first generation of ASKAP's phased array feed (PAF) receivers. These facilitate rapid wide-area imaging via the deployment of simultaneous multiple beams within a 30 square degree field of view. By cycling the array through 12 interleaved pointing positions and using 9 digitally formed beams we effectively mimic a traditional 1 hour x 108 pointing survey, covering 150 square degrees over 711 - 1015 MHz in 12 hours of observing time. Three such observations were executed over the course of a week. We verify the full bandwidth continuum imaging performance and stability of the system via self-consistency checks and comparisons to existing radio data. The combined three epoch image has arcminute resolution and a 1-sigma thermal noise level of 375 micro-Jy per beam, although the effective noise is a factor 3 higher due to residual sidelobe confusion. From this we derive a catalogue of 3,722 discrete radio components, using the 35 percent fractional bandwidth to measure in-band spectral indices for 1,037 of them. A search for transient events reveals one significantly variable source within the survey area. The survey covers approximately two-thirds of the Spitzer South Pole Telescope Deep Field. This pilot project demonstrates the viability and potential of using PAFs to rapidly and accurately survey the sky at radio wavelengths.

High-Sensitivity Phased Array Receivers for Radio Astronomy

Phased arrays have a long history in radio astronomy. Large, sparse synthesis arrays have been in use for decades to capture high-resolution images of deep space objects. More recent work has extended the range of applications to other types of arrays, including aperture arrays (AAs) and phased array feeds (PAFs) for multibeam reflector antennas. The extreme sensitivity required for astronomical instrumentation is driving advances in numerical electromagnetic modeling, design optimization of large arrays, low noise amplifiers, minimization of receiver noise, cryogenic PAFs, array calibration, optimal beamforming, interferometric imaging, and array signal processing algorithms for radio-frequency interference mitigation. We give an overview of research progress, current and planned array-based instruments, and open challenges in these areas related to the new generation of sparse arrays, PAFs, and AAs that are in development for astronomical observatories around the world.

The sensitivity of past and near-future lunar radio experiments to ultra-high-energy cosmic rays and neutrinos

Various experiments have been conducted to search for the radio emission from ultra-high-energy (UHE) particles interacting in the lunar regolith. Although they have not yielded any detections, they have been successful in establishing upper limits on the flux of these particles. I present a review of these experiments in which I re-evaluate their sensitivity to radio pulses, accounting for effects which were neglected in the original reports, and compare them with prospective near-future experiments. In several cases, I find that past experiments were substantially less sensitive than previously believed. I apply existing analytic models to determine the resulting limits on the fluxes of UHE neutrinos and cosmic rays (CRs). In the latter case, I amend the model to accurately reflect the fraction of the primary particle energy which manifests in the resulting particle cascade, resulting in a substantial improvement in the estimated sensitivity to CRs. Although these models are in need of further refinement, in particular to incorporate the effects of small-scale lunar surface roughness, their application here indicates that a proposed experiment with the LOFAR telescope would test predictions of the neutrino flux from exotic-physics models, and an experiment with a phased-array feed on a large single-dish telescope such as the Parkes radio telescope would allow the first detection of CRs with this technique, with an expected rate of one detection per 140 h.

Design of an L-Band Cross-Dipole Phased Array Feed for FAST

The Five-Hundred-Meter Aperture Spherical Telescope (FAST) is a Chinese megascience project that aims to build the largest single dish radio telescope in the world. Given its multiple simultaneous beam formation, phased array feed (PAF) is widely used to extend the field of view and enhance the survey speed of the radio telescope. In this study, a broadband and low cost PAF element using cross-dipole antenna at L-band is designed based on the requirement of the FAST. The antenna is fed by two microstrip baluns which have high performance and is easy to manufacture compared to the traditional coaxial balun. A simple system model is also introduced to evaluate the PAF performance. The measured results of the fabricated element and the simulations of the system performance validate the effectiveness of element design.

The Australian Square Kilometre Array Pathfinder: Performance of the Boolardy Engineering Test Array

AbstractWe describe the performance of the Boolardy Engineering Test Array, the prototype for the Australian Square Kilometre Array Pathfinder telescope. Boolardy Engineering Test Array is the first aperture synthesis radio telescope to use phased array feed technology, giving it the ability to electronically form up to nine dual-polarisation 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 Boolardy Engineering Test Array’s performance: sensitivity, beam characteristics, polarimetric properties, and image quality. We summarise the astronomical science that it has produced and draw lessons from operating Boolardy Engineering Test Array that will be relevant to the commissioning and operation of the final Australian Square Kilometre Array Path telescope.

平方公里阵中国验证天线光学设计

The SKA (Square Kilometer Array) will be the world's largest synthesis radio telescope and will address many fundamental questions about our universe. The SKA has now entered the preconstruction phase. Many countries, including China, are involved in the development of its key technology, such as dish prototyping, phased array feed, and wideband single pixel feed. The Dish Veri cation Antenna-China (DVA-C) is a prototype being built to most closely meet the requirements of the SKA scienti c goals. In this paper, the details of the optical design of the DVA-C are presented, including the dish optics and feeds. Although the DVA-C is designed for optimal performance of bore sight, it is also potentially employed for multibeam observation. Hence, the multibeam performance of the DVA-C is also analyzed.

A Fully Cryogenic Phased Array Camera for Radio Astronomy

We have developed a fully cryogenically cooled phased array feed (PAF) prototype camera and tested it on the Arecibo Radio Telescope in the summer of 2013. The camera consists of 19 dual-polarized elements on a hexagonal grid. The array elements are modified sleeve dipoles specially designed to be reinsertable, to include a noise injection coupling port and to operate at 18 K. Experimental results for observations on the Arecibo Telescope demonstrate performance of the cryogenic amplifiers, digital beamforming, and sensitivity over the PAF field of view, and provide an important proof of concept for a full-scale PAF receiver.

Optical design of the Dish Veri cation Antenna-China (DVA-C) for the square kilometer array

The SKA (Square Kilometer Array) will be the worlds largest synthesis radio telescope and will address many fundamental questions about our universe. The SKA has now entered the preconstruction phase. Many countries, including China, are involved in the development of its key technology, such as dish prototyping, phased array feed, and wideband single pixel feed. The Dish Veri cation Antenna-China (DVA-C) is a prototype being built to most closely meet the requirements of the SKA scienti c goals. In this paper, the details of the optical design of the DVA-C are presented, including the dish optics and feeds. Although the DVA-C is designed for optimal performance of bore sight, it is also potentially employed for multibeam observation. Hence, the multibeam performance of the DVA-C is also analyzed.

Reducing Relative Gain and Noise Response Variations for Phased-Array Feed Imaging of Radio Astronomical Sources

In comparison to a single horn-feed system, single dish radio astronomical imaging with a phased-array feed (PAF) has additional noise due to variations in the responses of the various beams used in the creation of the image. This increased noise may obscure weak sources of interest and discredit the ability of a PAF to increase sky survey speed. In order to reduce the beam-to-beam variations, we introduce several new PAF beamforming strategies. A dual constraint beamformer is designed to simultaneously satisfy uniform main beam and noise response constraints, eliminating one aspect of the variation. A rim constraint beamformer that relies on calibrator sources on the rim of the reflector dish to control the spillover pattern variations among beams with eigenvector constraints is introduced and shown to reduce beam-to-beam variations. Finally, by combining the dual constraint and rim constraint beamformers, we are able to construct a beamformer that provides spillover pattern control while meeting specified gain and noise response constraints to reduce the beam-to-beam variations and improve PAF imaging.

Hybrid Analog–Digital Antenna Array With Built-in Image Injection Calibration

This study presents a hybrid receiving array architecture that combines analog and digital beamforming to offer a solution for the phased-array feed and other multifunction receive-only applications. This architecture is capable of handling multiple beams forming simultaneous and precision beam steering. To further reduce the hardware counts of the online performance monitoring, a calibration method is proposed in which none of the transmitters or the dedicated distribution network are used. The hybrid architecture concept and built-in calibration are validated experimentally via a prototype. The system performance, including the statistical results of the baseband measurement, phase error, and radiation patterns under various array configurations, are illustrated. An effective phase tuning step of 0.1 ° , as well as a steering resolution at the subdegree level, is achieved, and the measured aperture distribution is in good agreement with that derived from the proposed online calibration.

Fast and Accurate Analysis of Reflector Antennas With Phased Array Feeds Including Multiple Reflections Between Feed and Reflector

Several electrically large phased array feed (PAF) reflector systems are modeled to examine the mechanism of multiple reflections between parabolic reflectors and low- and high-scattering feeds giving rise to frequency-dependent patterns and impedance ripples. The PAF current is expanded in physics-based macro domain basis functions (CBFs), while the reflector employs the physical optics (POs) equivalent current. The reflector-feed coupling is systematically accounted for through a multiscattering Jacobi approach. An FFT expands the reflector radiated field in only a few plane waves, and the reflector PO current is computed rapidly through a near-field interpolation technique. The FEKO software is used for several cross validations, and the convergence properties of the hybrid method are studied for several representative examples showing excellent numerical performance. The measured and simulated results for a 121-element Vivaldi PAF, which is installed on the Westerbork Synthesis Radio Telescope, are in very good agreement.

Focal Field Analysis and Phased Array Feed Design

摘要: 该文介绍了焦面场的计算方法及其与反射面焦径比的关系，分析了焦面场与馈源口径场的联系，并建立了基于焦面场分析进行相控阵馈源设计的方法，包括确定单元间距、阵列规模以及实现目标方向图所需要的激励。按照这一方法，分别以未赋形卡塞格伦天线和前馈抛物面天线为对象，设计了各自的相控阵馈源以实现赋形波束的效果，并在后者上验证了波束扫描性能。通过仿真，天线性能实现了预定目标，证明了设计方法的有效性。 关键词: 反射面天线 / 多波束 / 焦面场 / 相控阵馈源