Marco Schiaffino

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 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).

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.

Design and modeling of an optimized sensor for atmospheric electric field measurement

In this work an optimized version of the field-mill sensor structure for atmospheric electric field measurements was presented. Both the mechanical structure and the electronic front-end, acquisition and control system are optimized in order to reduce the power consumption and to enhance the instrument metrological performance in term of sensitivity and frequency band. A solar power operated system was realized and tested. The developed system is also equipped with a GPS receiver, allowing data synchronization. This feature enables the implementation of a distributed measurement system for the monitoring of the atmospheric electric field.

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.

A low power measurement system for the atmospheric electric field

In this work an optimized version of the field-mill sensor structure for atmospheric electric field measurements is presented. Both the hardware components, i.e. the mechanical structure, the electronic front-end, the acquisition and control systems, and the data processing software, are optimized in order to reduce the power consumption and to enhance the instrument metrological performance in term of accuracy, sensitivity and frequency band.

A Photosensor-Based Measuring System for Precision Mechanics

In this short paper we describe a general measurement method for quality control of curved surfaces, obtained by means of machine-tools. Such control can be performed by measuring the surfaces in correspondence to a discrete number of adjacent points. Our system is based on a matrix of analog position transducers using commercially available photocouplers, microprocessor controlled by appropriate programs. To avoid the time variability of the displacement voltage transfer function, the characteristics of the photocouplers are stored in a digital memory by measuring a convenient number of reference elements or surfaces (initial calibration). These stored characteristics are then utilized for the evaluation of the unknown surface (measurement). As a result, we obtain with economical components an instrument having a remarkable precision which depends on the photocoupler stability and on the time interval between calibration and measurement.