Applied Electromagnetics and Electronic Devices group Il progetto SKA: misure di campo elettromagnetico mediante UAV in collaboration with POLITECNICO DI TORINO Environment, Land and Infrastructures Department National Institute for Astrophysics
Square Kilometer Array (SKA) KEY FEATURES Largest radio telescope array ever constructed Interferometric Configuration More than 10 countries South Africa, High-Frequency SKA KEY SCIENCE Strong-field test of gravity Galaxy evolution, cosmology and dark matter Cosmic Magnetism Cosmic Dawn (Epoch of reionization) Transients/Pulsar Cradle of Life Solar physics and Space Weather https://www.skatelescope.org/
Square Kilometer Array (SKA) Low-frequency instrument Frequency band 50-350 MHz More than one hundred thousand elements (Phase 1) Dual-polarized elements https://www.skatelescope.org/ Murchinson Area Australia How can we measure low-frequency antennas in their operative conditions? Full-scale models On the soil, with or without a metallic ground plane In the array configuration
Flying Far-field Test Source A micro hexacopter is used as far-field RF source flying over the AUT RF transmitter UAV equipped with a continuous-wave RF transmitter and a dipole antenna The received power at the AUT port is measured during the flight The UAV autonomously performs quasi-rectilinear, constant height paths (GPS navigation) e.g. E-plane or H- plane cuts Dipole antenna co-/cross-polar measurements by setting the UAV compass angle e.g. 0 or 90
Adopted Methodologies Scan strategy Path loss and source gain are not constant Received signal (AUT) depends also on the test-source pattern and the path loss they must be computed and removed Both test-source orientation and accurate position data are needed z UAV position data: a differential GNSS with a rover and a master station provides centimeter accuracy UAV orientation data: Onboard Inertial Measurement Unit (IMU) is exploited to correct the effect of the test-source orientation and avoid pattern distortion
The Test Source Geometry A set of dipoles with different lengths is used to cover a large frequency range Hexacopter alluminum arms mainly work as a ground plane The balun is also embedded in a metal box
Directivity (dbi) Directivity (dbi) Test Source Patterns 10 5 0 E-plane 50 MHz 150 MHz 250 MHz 350 MHz 10 5 0 H-plane -5-10 -5-10 50 MHz 150 MHz 250 MHz 350 MHz -15 0 50 100 150 Nadir angle (Deg) -15 0 50 100 150 Nadir angle (Deg)
SKA AAVS0.5 Array pattern at 350 MHz September 2014 Cartesian Raster measurement Analog Power Combiner Mullard Radio Astronomy Observatory (UK) Courtesy of
LOFAR campaign March 2016 in collaboration with Dr. Stefan Wijnholds Aerial View of a LOFAR station (The Netherlands) UAV to perform an end-toend system verification LBA inner Three Arrays in Three Days with Multi-frequency TX HBA half LBA outer Embedded Element Patterns Array Calibration and Pattern Antenna positions Courtesy of LBAinner: 48 dual-pol elements (random quasi-dense) 10-80 MHz LBAouter: 48 dual-pol elements (random sparse) 10-80 MHz HBA: 48 tiles having 16 dual-pol bow-ties (dense) 120-240 MHz
Element Pattern (dbi) Measured Element Patterns at 57 MHz 30 NE-oriented Elements 25 20 15 10 5 Element 0 Element 3 Element 15 Element 16 Element 38 0-60 -40-20 0 20 40 60 Zenith Angle (Deg) The distrorted behavior of the Elements 0 and 3 explains the anomalies in the astronomical observations
Q-band Polarimeter Calibration in-situ STRatospheric Italian Polarimeter (Low-Frequency Instrument of the Large-Scale Polarization Explorer) University of Rome, La Sapienza, and University of Milan Funded by Italian Space Agency Recently converted to a ground-based instrument (Tenerife) Q-band receiver cluster Flying Test Source @ 38-50 GHz
EM environmental monitoring In-situ performance can be very different from nominal RF Emission evaluation Health Quality of service A few research groups and small companies are already working on this problem
IEEE CAMA 2016 Conference on Antenna Measurement and Applications 2016, Syracuse, New York October 23-27, 2016 First Special Session ever organized on «UAV-based Antenna and Field Measurements» With contribution from Europe, US, Australia and South Africa