Radio frequency interference mitigation in radio astronomy

Abstract The next generation of radio telescopes is expected to be one to two orders of magnitude more sensitive than the current generation. Examples of such new telescopes are the Low Frequency Array (LOFAR), currently under constructionin the Netherlands, and the Square Kilometer Array (SKA), currently in a concept study phase. Another trend is that technological advances in the fields of electronics and communications systems have led to a vast increase in radio communication applications and systems, and also to an increasing demand for radio spectrum. These two trends, more sensitive telescopes and a much denser spectrum use, imply that radio astronomy will become more vulnerable to interference from radio transmitters. Although protection criteria exist for radio astronomy, it becomes increasingly difficult to keep the radio astronomy frequency bands free from interference.In order to mitigate interference in radio astronomical data, filtering techniques can be used. In this thesis, modern array signal processing techniques have been applied to narrow-band multichannel interference detection and excision, and to narrow-band spatial interference filtering. By investigating the subspace structure of the telescope array output covariance matrices, new results were found, such as upper limits on interference residuals after excision and spatial filtering. The effect of bandwidth, extendedness of the interfering sources, and multipath effects on the detection andspatial filter effectiveness were studied as well. The advantage of a multichannel approach over a single telescope approach was demonstrated by using experimental data from the Westerbork Synthesis Radio Telescope (WSRT). As the performance of mitigation algorithms can be improved by calibration of the telescope gains and noise powers, calibration algorithms were developed. These algorithms were verified both for single and dual polarised arrays. Finally, a LOFAR interference mitigation strategy was developed.