Il progetto SKA: misure di campo elettromagnetico mediante UAV

Transcription

1 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

2 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

3 Square Kilometer Array (SKA) Low-frequency instrument Frequency band MHz More than one hundred thousand elements (Phase 1) Dual-polarized elements 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

4 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

5 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

6 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

7 Directivity (dbi) Directivity (dbi) Test Source Patterns E-plane 50 MHz 150 MHz 250 MHz 350 MHz H-plane MHz 150 MHz 250 MHz 350 MHz Nadir angle (Deg) Nadir angle (Deg)

8 SKA AAVS0.5 Array pattern at 350 MHz September 2014 Cartesian Raster measurement Analog Power Combiner Mullard Radio Astronomy Observatory (UK) Courtesy of

9 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) MHz LBAouter: 48 dual-pol elements (random sparse) MHz HBA: 48 tiles having 16 dual-pol bow-ties (dense) MHz

10 Element Pattern (dbi) Measured Element Patterns at 57 MHz 30 NE-oriented Elements Element 0 Element 3 Element 15 Element 16 Element Zenith Angle (Deg) The distrorted behavior of the Elements 0 and 3 explains the anomalies in the astronomical observations

11 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 GHz

12 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

13 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