Low-frequency arrays represent the new generation of radio astronomical facilities capable to expand the frontiers of the Universe observation from the Earth. The most important example is the Square Kilometre Array (SKA), which will become the world’s largest radio telescope upon its completion in the 2020s. Several arrays and thousands of antennas operating from 50 MHz to 20 GHz will compose the SKA, producing a total collecting area of several square kilometers. Besides the outstanding performance in terms of resolution and sensitivity, the advantage of antenna arrays is the great flexibility. In fact, the signals of all the array elements can be digitally combined and treated in different ways, e.g. from only one large group to multiple smaller ones. Moreover, a digital beam-forming system controls the observation direction that can be rapidly steered across the sky. These complex instruments require advanced procedure to test their front-end electronics. In addition, the electromagnetic characterization and the array calibration are challenging tasks especially at lower frequencies. The strong interaction between the array elements, and with the surrounding environment as well, produces effects that can be difficult to predict during the design stage. Therefore, advanced in-situ measurement procedures are required to validate the facility. In the context of the Aperture Array Verification Program (AAVP) of the SKA telescope, a test-source mounted on an Unmanned Aerial Vehicle (UAV) has been conceived in Italy within a collaboration between the Institute of Electronics, Computer and Telecommunication Engineering (IEIIT) of the Italian National Research Council (CNR), the Department of Environment, Land and Infrastructure Engineering (DIATI) of the Polytechnic of Turin and the Italian National Institute for Astrophysics (INAF). In this thesis work, the concept of a UAV-based VHF/UHF far-field test-source to perform in-situ antenna array measurements has been developed into a real system that has been used in several measurement campaigns around the world on some of the SKA pathfinders. Several relevant aspects such as measurement strategies, data processing, system design, modeling, integration and test have been addressed in great detail. A detailed data analysis has been performed after all the above mentioned campaigns. The obtained results demonstrate that the UAV-system provides good accuracy and effectiveness to characterize the radiation pattern and the polarization properties of the single antennas, the embedded elements and the whole array. The provided data are already being used by the radio astronomical scientific community to improve both the data set of the existing telescopes and the design of the new ones. The UAV has been also used as calibration source for the digital beam-forming system, providing a direct solution with a higher signal-to-noise ratio with respect to the exploitation of astronomical sources. The versatility and the transportability of the system open up a wide variety of possibilities for antenna measurement in many other applications.

VHF/UHF Antenna Array Measurements with a UAV-based Test Source / Paonessa, Fabio. - (2017).

VHF/UHF Antenna Array Measurements with a UAV-based Test Source

PAONESSA, FABIO
2017

Abstract

Low-frequency arrays represent the new generation of radio astronomical facilities capable to expand the frontiers of the Universe observation from the Earth. The most important example is the Square Kilometre Array (SKA), which will become the world’s largest radio telescope upon its completion in the 2020s. Several arrays and thousands of antennas operating from 50 MHz to 20 GHz will compose the SKA, producing a total collecting area of several square kilometers. Besides the outstanding performance in terms of resolution and sensitivity, the advantage of antenna arrays is the great flexibility. In fact, the signals of all the array elements can be digitally combined and treated in different ways, e.g. from only one large group to multiple smaller ones. Moreover, a digital beam-forming system controls the observation direction that can be rapidly steered across the sky. These complex instruments require advanced procedure to test their front-end electronics. In addition, the electromagnetic characterization and the array calibration are challenging tasks especially at lower frequencies. The strong interaction between the array elements, and with the surrounding environment as well, produces effects that can be difficult to predict during the design stage. Therefore, advanced in-situ measurement procedures are required to validate the facility. In the context of the Aperture Array Verification Program (AAVP) of the SKA telescope, a test-source mounted on an Unmanned Aerial Vehicle (UAV) has been conceived in Italy within a collaboration between the Institute of Electronics, Computer and Telecommunication Engineering (IEIIT) of the Italian National Research Council (CNR), the Department of Environment, Land and Infrastructure Engineering (DIATI) of the Polytechnic of Turin and the Italian National Institute for Astrophysics (INAF). In this thesis work, the concept of a UAV-based VHF/UHF far-field test-source to perform in-situ antenna array measurements has been developed into a real system that has been used in several measurement campaigns around the world on some of the SKA pathfinders. Several relevant aspects such as measurement strategies, data processing, system design, modeling, integration and test have been addressed in great detail. A detailed data analysis has been performed after all the above mentioned campaigns. The obtained results demonstrate that the UAV-system provides good accuracy and effectiveness to characterize the radiation pattern and the polarization properties of the single antennas, the embedded elements and the whole array. The provided data are already being used by the radio astronomical scientific community to improve both the data set of the existing telescopes and the design of the new ones. The UAV has been also used as calibration source for the digital beam-forming system, providing a direct solution with a higher signal-to-noise ratio with respect to the exploitation of astronomical sources. The versatility and the transportability of the system open up a wide variety of possibilities for antenna measurement in many other applications.
2017
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11583/2687180
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