Seminars & Colloquia----National Astronomical Observatories, Chinese Academy of Sciences

Abstract: The radio astronomy community is transitioning from single feed antennas to a new generation of instruments based on phased array technology. Major international development efforts include multi-pixel phased array feeds for large reflectors, low frequency aperture arrays，e.g.，LOFAR in the Netherlands, and the Square Kilometer Array (SKA). These instruments will have a significantly larger field of view than conventional single-pixel telescopes. Wide field instruments will enable fundamentally new astronomical observations such as rapid sky surveys and radio transient searches. Phased array feeds also allow electronic beam pattern control and adaptive interference mitigation to cancel manmade radio signals that would otherwise obscure extremely week deep space sources. Phased array research efforts have opened up a broad range of new and interesting challenges for antenna design, microwave systems, and multichannel signal processing. This presentation will highlight these challenges and survey recent developments including impedance matching and noise minimization for active arrays, measurement techniques for system noise and efficiencies, calibration methods, and stable beamforming algorithms. Experimental results for the BYU/NRAO L-band Phased Array Feed on the Green Bank 20-Meter Telescope will be shown, including some of the first radio images produced with a phased array.