Pietro Bolli, Giuseppe Pupillo, Fabio Paonessa, Giuseppe Virone, Stefan J. Wijnholds and Andrea Maria Lingua, "Near-Field Experimental Verification of the EM Models for the LOFAR Radio Telescope,", IEEE Antennas and Wireless Propagation Letters, V17, no. 4, pp613-616, April 2018.
Modern radio astronomical facilities in the Very High-Frequency band (VHF, 30-300 MHz) consist of large antenna arrays with digital beamforming. The calibration of these instruments requires accurate models of their electromagnetic behavior. Numerical models covering the full telescope field-of-view are nowadays effectively computed by means of full-wave solvers. However, their experimental verification is still an open and challenging task. This letter proposes a verification strategy based on near-field scans. An unmanned aerial vehicle carrying a test source is used to excite the array from a limited set of spatial points, located in the radiating near-field region. The collected data are directly used to verify the telescope electromagnetic model without additional postprocessing. This exploits the capability of full-wave solvers to predict near-field patterns from the same geometrical and electrical model used to compute far-field patterns. The application of the proposed technique to the Low Frequency Array (LOFAR) radio telescope verified the predictions with residuals below 0.5 dB.
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