Federico Perini

Antenna Pattern Verification System Based on a Micro Unmanned Aerial Vehicle (UAV)

This letter presents a radiation pattern verification system for low-frequency antennas in their operative conditions, e.g., on the ground, next to other elements, etc. It is a far-field setup using a properly equipped micro unmanned aerial vehicle (UAV) as a test source. The micro UAV can perform an autonomous flight. Its absolute position is measured with a remote topographic instrument. By data processing, the received power pattern along the UAV flying path is reconstructed. The proposed setup has been validated on two standard wire antennas at 150 and 408 MHz with an estimated accuracy of 1 dB.

Low frequency aperture array developments for phase 1 SKA

Aperture Arrays (AA) mark a new era in radio astronomy combining high sensitivity with a large field-of-view, enabling very high survey and imaging speeds. This paper describes the development of low frequency aperture arrays leading up to SKA phase 1 within the Aperture Array Verification Program (AAVP) as part of the SKA program.

A VLBI experiment using a remote atomic clock via a coherent fibre link

We describe a VLBI experiment in which, for the first time, the clock reference is delivered from a National Metrology Institute to a radio telescope using a coherent fibre link 550 km long. The experiment consisted of a 24-hours long geodetic campaign, performed by a network of European telescopes; in one of those (Medicina, Italy) the local clock was alternated with a signal generated from an optical comb slaved to a fibre-disseminated optical signal. The quality of the results obtained with this facility and with the local clock is similar: interferometric fringes were detected throughout the whole 24-hours period and it was possible to obtain a solution whose residuals are comparable to those obtained with the local clock. These results encourage further investigation of the ultimate VLBI performances achievable using fibre dissemination at the highest precision of state-of-the-art atomic clocks.

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.

A coherent fiber link for very long baseline interferometry

We realize a coherent fiber link for application in very long baseline interferometry (VLBI) for radio astronomy and geodesy. A 550-km optical fiber connects the Italian National Metrological Institute (INRIM) to a radio telescope in Italy and is used for the primary Cs fountain clock stability and accuracy dissemination. We use an ultrastable laser frequency- referenced to the primary standard as a transfer oscillator; at the radio telescope, an RF signal is generated from the laser by using an optical frequency comb. This scheme now provides the traceability of the local maser to the SI second, realized by the Cs fountain at the 1.7 × 10-16 accuracy. The fiber link never limits the experiment and is robust enough to sustain radio astronomical campaigns. This experiment opens the possibility of replacing the local hydrogen masers at the VLBI sites with optically-synthesized RF signals. This could improve VLBI resolution by providing more accurate and stable frequency references and, in perspective, by enabling common- clock VLBI based on a network of telescopes connected by fiber links.

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.