Test-Driven Design of an Active Dual-Polarized Log-Periodic Antenna for the Square Kilometre Array

Abstract

An active dual-polarized Log-Periodic antenna has been designed to meet the requirements of the low-frequency (50-350 MHz) radio telescope of the Square Kilometre Array (SKA). The integration of antenna and low noise amplifier has been conceived in order to achieve a high degree of testability. This aspect has been found to be crucial to obtain a smooth frequency response compatible with the SKA science cases. The design has also been driven by other factors such as the large-volume production (more than 130 000 antennas will be built) and the environmental conditions of the harsh Australian desert. A specific verification approach based on both wideband radiometric spectral and spatial measurements in relevant laboratory and in-situ conditions has been developed. Electromagnetic analyses and experimental results exhibit a very good agreement. In December 2019, this antenna was part of the reference solution for the System Critical Design Review of the SKA.

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

“…For frequencies ≥70 MHz, self calibration with the Sun was also applied by selecting subsets of snapshots in the LST ranges corresponding to Sun elevations ≥ þ 45°, to avoid calibration inaccuracies related to the "naturally" degraded sensitivity of the antenna at low elevations. 24 The sensitivities derived through self calibration are consistent with those obtained through calibration using a single snapshot at the Sun transit (in the common LST intervals) for all frequencies ≤160 MHz, suggesting a good system calibration stability over several hours (see also Ref. 6).…”

“…Among the brightest "A-team" radio sources, we selected those with an elevation ≥60°at their culmination. This criterion allows for analysis of the fluxes ≈1 h across the source transit, avoiding the sensitivity losses due to the poor SKALA4.1 antenna response at lower elevations (which is related to the natural drop off in the antenna design trade-off 24 ). Only Centaurus A, Fornax A, and Pictor A met this selection criterion.…”

Computational electromagnetics for the SKA-Low prototype station AAVS2

“…[16][17][18] The version selected as reference antenna during the SKA System Critical Design Review in December 2019 is the so-called SKALA4.1. 3 The SKALA antenna consists of two identical orthogonal LPDAs to receive both linear polarizations of the electromagnetic waves emitted by the Universe. For AAVS2, the North-South polarization is labeled "Y," and the orthogonal East-West polarization "X;" this nomenclature is used throughout this paper.…”

“…All these systems shared a quasi-random distribution of antenna elements; the elements themselves are log-periodic dipoles known as the Square Kilometre Array log-periodic antenna (SKALA) and these have also evolved with the various deployments; the elements in AAVS2 are SKALA4.1 antennas. 3 A key part of the AAVS effort has been to provide reliable simulations of the detailed antenna pattern, including the effects of mutual coupling, to support comparison of the antenna designs proposed and installed in the various AAVS prototype stations, as well as preliminary astronomical tests. The groups in Italy [National Institute for Astrophysics (INAF)] and Australia [International Centre for Radio Astronomy Research-Curtin (ICRAR-Curtin)] performed Computational Electromagnetic (CEM) simulations on AAVS1.5 and AAVS2.…”

Measurement of the LOFAR-HBA beam patterns using an unmanned aerial vehicle in the near field

“…The SKA will become the biggest and most sensitive radio telescope in the world. Aperture arrays are envisioned for both SKA1-LOW (50 to 350 MHz, random configuration) 2,3 and possibly SKA1-Mid phase 2 (400 to 1.45 GHz, regular configuration). [4][5][6] Dishes will be adopted for higher frequencies up to 14 GHz.…”