Computational electromagnetics for the SKA-Low prototype station AAVS2

Bolli, Pietro; Davidson, David; Bercigli, M.; Ninni, Paola Di; Labate, Maria Grazia; Ung, D.; Virone, G.

doi:10.1117/1.jatis.8.1.011017

Cited by 29 publications

(24 citation statements)

References 40 publications

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“…For instance, the full-wave analysis of 256 SKALA4.1 antennas by means of the multilevel fast multipole method along with the method of moment technique requires on the order of days for each frequency point on a multicore workstation. 13 Alternative techniques to accelerate the solution of Maxwell equations in the context of SKA1-Low were proposed in Ref. 14.…”

Section: Introductionmentioning

confidence: 99%

Impact of mutual coupling between SKALA4.1 antennas to the spectral smoothness response

Bolli

Bercigli

Ninni

et al. 2022

J. Astron. Telesc. Instrum. Syst.

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One of the advantages of arrays with aperiodic distributed elements is their ability to mitigate the detrimental mutual coupling effects on the radiation pattern. However, we show that the mutual coupling inside a random array can still generate undesired structures in the frequency response although the single antenna features a spectral smooth response. For small subsets (a couple of SKALA4.1 antennas and a 16-element array) of a low-frequency instrument station of the Square Kilometre Array, the combination of large mutual coupling and antenna geometry creates systematic distortions in the element frequency responses. This phenomenon compromises the station spectral smoothness response versus frequency. However, we demonstrate that it is possible to partially mitigate these frequency structures by reconfiguring the antenna distribution based on exclusion zones.

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Section: Introductionmentioning

confidence: 99%

Impact of mutual coupling between SKALA4.1 antennas to the spectral smoothness response

Bolli

Bercigli

Ninni

et al. 2022

J. Astron. Telesc. Instrum. Syst.

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“…The Galactic plane has a more pronounced morphological difference, particularly at 55 MHz for the XX polarization and close to the horizon (panels C, left side). This discrepancy may be due to mutual coupling from the antennas, 5,15 which is more prominent near the horizon and is not accounted for in our simulations. We also note that our simulated images do not include the station uv coverage and this can also cause slight differences between observed and simulated images, although a more quantitative comparison is left for the future.…”

Section: Observations and Data Processingmentioning

confidence: 85%

“…We rather fixed the absolute flux density scale by multiplying each flux density and noise measurement of our analysis (see Sections 3.1,4.1, 4.2) by the primary beam response corresponding to the Sun position in the snapshot observation used for calibration, normalized to zenith. We assumed that all the antennas have the same primary beam, the average embedded element pattern (hereafter EEP) 5,15 .…”

Section: Observations and Data Processingmentioning

confidence: 99%

“…The peak brightness values of the Sun and the corresponding uncertainties was extracted for the snapshots in the 21.7 < LST < 22.7 h range (≈ 1 h around transit) using the IMFIT task, and corrected for the normalized mean EEP 5,15 in the direction of the Sun. We found the apparent flux density of the Sun to be sufficiently constant in time (see Fig.…”

Section: Calibration At 55 Mhzmentioning

confidence: 99%

“…All the flux measurements and their uncertainties were finally corrected for the primary beam, taking into account the antenna response both in the direction of the Sun (calibrator) and of each radio source (excluding measurements at 55 MHz, already corrected for the primary beam, see Section 3.1). The average EEP 5,15 per frequency and linear polarization was used in this correction.…”

Section: Consistency Checks On Radio Sources Flux Densitiesmentioning

confidence: 99%

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Characterization of the SKA1-Low prototype station Aperture Array Verification System 2

Macario¹,

Pupillo²,

Bernardi³

et al. 2021

Preprint

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The low frequency component of the Square Kilometre Array (SKA1-Low) will be an aperture phased array located at the Murchison Radio-astronomy Observatory (MRO) site in Western Australia. It will be composed of 512 stations, each of them consisting of 256 log-periodic dual polarized antennas, and will operate in the low frequency range (50 MHz -350 MHz) of the SKA bandwidth. The Aperture Array Verification System 2 (AAVS2), operational since late 2019, is the last full-size engineering prototype station deployed at the MRO site before the start of the SKA1-Low construction phase. The aim of this paper is to characterize the station performance through commissioning observations at six different frequencies (55, 70, 110, 160, 230 and 320 MHz) collected during its first year of activities. We describe the calibration procedure, present the resulting all-sky images and their analysis, and discuss the station calibratability and system stability. Using the difference imaging method, we also derive estimates of the SKA1-Low sensitivity for the same frequencies, and compare them to those obtained through electromagnetic simulations across the entire telescope bandwidth, finding good agreement (within 13%). Moreover, our estimates exceed the SKA1-Low requirements at all the considered frequencies, by up to a factor of ∼2.3. Our results are very promising and allow an initial validation of the AAVS2 prototype station performance, which is an important step towards the upcoming SKA-Low telescope construction and science.

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What is the SKA-Low sensitivity for your favourite radio source?

Sokołowski

Tingay

Davidson

et al. 2022

Publ. Astron. Soc. Aust.

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The Square Kilometre Array (SKA) will be the largest radio astronomy observatory ever built, providing unprecedented sensitivity over a very broad frequency band from 50 MHz to 15.3 GHz. The SKA’s low frequency component (SKA-Low), which will observe in the 50–350 MHz band, will be built at the Murchison Radio-astronomy Observatory (MRO) in Western Australia. It will consist of 512 stations each composed of 256 dual-polarised antennas, and the sensitivity of an individual station is pivotal to the performance of the entire SKA-Low telescope. The answer to the question in the title is, it depends. The sensitivity of a low frequency array, such as an SKA-Low station, depends strongly on the pointing direction of the digitally formed station beam and the local sidereal time (LST), and is different for the two orthogonal polarisations of the antennas. The accurate prediction of the SKA-Low sensitivity in an arbitrary direction in the sky is crucial for future observation planning. Here, we present a sensitivity calculator for the SKA-Low radio telescope, using a database of pre-computed sensitivity values for two realisations of an SKA-Low station architecture. One realisation uses the log-periodic antennas selected for SKA-Low. The second uses a known benchmark, in the form of the bowtie dipoles of the Murchison Widefield Array. Prototype stations of both types were deployed at the MRO in 2019, and since then have been collecting commissioning and verification data. These data were used to measure the sensitivity of the stations at several frequencies and over at least 24 h intervals, and were compared to the predictions described in this paper. The sensitivity values stored in the SQLite database were pre-computed for the X, Y, and Stokes I polarisations in 10 MHz frequency steps, $\scriptsize{1/2}$ hour LST intervals, and $5^\circ$ resolution in pointing directions. The database allows users to quickly and easily estimate the sensitivity of SKA-Low for arbitrary observing parameters (your favourite object) using interactive web-based or command line interfaces. The sensitivity can be calculated using publicly available web interface (http://sensitivity.skalow.link) or a command line python package (https://github.com/marcinsokolowski/station_beam), which can also be used to calculate the sensitivity for arbitrary pointing directions, frequencies, and times without interpolations.

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Computational electromagnetics for the SKA-Low prototype station AAVS2

Cited by 29 publications

References 40 publications

Impact of mutual coupling between SKALA4.1 antennas to the spectral smoothness response

Impact of mutual coupling between SKALA4.1 antennas to the spectral smoothness response

Characterization of the SKA1-Low prototype station Aperture Array Verification System 2

What is the SKA-Low sensitivity for your favourite radio source?

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