G. Pupillo

From MAD to SAD: The Italian experience for the Low Frequency Aperture Array of SKA1‐LOW

This paper describes two small aperture array demonstrators called Medicina and Sardinia Array Demonstrators (MAD and SAD, respectively). The objectives of these instruments are to acquire experience and test new technologies for a possible application to the low-frequency aperture array of the low-frequency telescope of the Square Kilometer Array phase 1 (SKA1-LOW). The MAD experience was concluded in 2014, and it turned out to be an important test bench for implementing calibration techniques based on an artificial source mounted in an aerial vehicle. SAD is based on 128 dual-polarized Vivaldi antennas and is 1 order of magnitude larger than MAD. The architecture and the station size of SAD, which is along the construction phase, are more similar to those under evaluation for SKA1-LOW, and therefore, SAD is expected to provide useful hints for SKA1-LOW.

UAV-based pattern measurement of the SKALA

A novel antenna pattern measurement technique has been recently developed exploiting the capabilities of a micro Unmanned Aerial Vehicle (UAV) as a far-field test-source. This technique is suitable for characterizing VHF antennas such as those for low-frequency radio astronomy. This paper presents some of the measurements recently performed on the Square Kilometer Array Log-periodic Antenna (SKALA), which has been selected as the receiving element for the Low Frequency Aperture Array (LFAA).

UAV-based radiation pattern verification for a small low-frequency array

The Unmanned Aerial Vehicle (UAV) technology has been recently used to develop a pattern measurement system for low-frequency arrays in their real installation conditions. This paper presents the most important results that have been obtained on the Italian Medicina Array Demonstrator (MAD).

Antenna pattern characterization of the low-frequency receptor of LOFAR by means of an UAV-mounted artificial test source

Low frequency aperture array technology requires advanced ad-hoc tools for performing antenna and array pattern characterization and instrumental calibration. A micro Unmanned Aerial Vehicle (UAV) mounting a radio-frequency transmitting system developed in Italy has demonstrated to satisfy the challenging characteristics of these tasks. Therefore, a measurement campaign by means of this UAV system has been planned to one Dutch station of the Low Frequency Array (LOFAR) with the main goal to improve the LOFAR antenna and array models. In preparation for this campaign, some initial tests applying the UAV system to one low-frequency antenna of LOFAR were performed in Italy. This contribution describes this measurement session and shows that the measured antenna gain patterns at different frequencies between 40 and 70 MHz agree very well with the electromagnetic models.

UAV-aided calibration for commissioning of phased array radio telescopes

Calibration of antenna positions and instrumental response is a crucial step in the commissioning of a phased array radio telescope. The Low Frequency Aperture Array system of the Square Kilometre Array (SKA) is envisaged to consist of about 131,000 antennas. In this paper, we propose a strategy to efficiently conduct commissioning calibration of such a large phased array radio telescope using a near-field probe mounted on an Unmanned Aerial Vehicle (UAV). We demonstrate the effectiveness of the proposed method using simulations. This indicates that potentially cost-saving relaxation of requirements on placement accuracy is possible. We also propose to validate this method in practice using the Low Frequency Array (LOFAR).

Sardinia Array Demonstrator: Instrument overview and status

In the framework of the Square Kilometer Array (SKA) project, the Italian Institute for Astrophysics (INAF) has addressed several efforts in the design and prototyping of aperture arrays for low-frequency radio astronomical research. The Sardinia Array Demonstrator (SAD) is a national project aimed to develop know-how in this area and to test different architectural technologies and calibration algorithms. SAD consists of 128 prototypical dual-polarized Vivaldi antennas designed to operate at radio frequencies below 650 MHz. The antennas will be deployed at the Sardinia Radio Telescopes site with a versatile approach able to provide two different array configurations: (i) all antennas grouped in one large station or (ii) spread among a core plus few satellite stations. This paper provides an overview of the SAD project from an instrumental point of view, and illustrates its status after 2 years from its start.

Sardinia aperture array demonstrator

We present a project aimed at realizing an Italian aperture array demonstrator constituted by prototypical Vivaldi antennas designed to operate at radio frequencies below 500 MHz. We focus on an array composed of a core plus a few satellite phased-array stations to be installed at the Sardinia Radio Telescope (SRT) site. The antenna elements are mobile and thus it will be possible to investigate the performance in terms of both uv-coverage and synthesized resolution resulting from different configurations of the array.

UAV-based antenna and field measurements

This paper overviews the emerging antenna and EM field measurement strategies based on the modern Unmanned Aerial Vehicle (UAV) technology. UAVs are currently being exploited as source/probe antenna positioners in various applications from HF to microwaves. Several contributions from all-over the world will be discussed in terms of measurement approach, RF setup and positioning strategies. A measurement example at 350 MHz highlights the importance of position and orientation accuracy in the post-processing chain.

The Digital Signal Processing Platform for the Low Frequency Aperture Array: Preliminary Results on the Data Acquisition Unit

A signal processing hardware platform has been developed for the Low Frequency Aperture Array component of the Square Kilometre Array (SKA). The processing board, called an Analog Digital Unit (ADU), is able to acquire and digitize broadband (up to 500MHz bandwidth) radio-frequency streams from 16 dual polarized antennas, channel the data streams and then combine them flexibly as part of a larger beamforming system. It is envisaged that there will be more than 8000 of these signal processing platforms in the first phase of the SKA, so particular attention has been devoted to ensure the design is low-cost and low-power. This paper describes the main features of the data acquisition unit of such a platform and presents preliminary results characterizing its performance.

The UAV-based test source as an end-to-end verification tool for aperture arrays

A UAV-mounted radio-frequency transmitter is proposed as a known reference field source to perform a set of functional tests on aperture arrays. The experimental results obtained on complete prototypes (end-to-end) and sub-assemblies provide good confidence on both amplitude and timing verification.