This book is a contribution to observation improvements for phased array radio telescopes, in the presence of radio frequency interferers (RFIs). The originality of the study is the use of the cyclostationarity property, in order to improve the spatial separation between cosmic sources and telecommunication signals. This book is part of the European SKADS project, which aims to improve RFI mitigation techniques for future instruments in radio astronomy. We have proposed three spatial processing techniques: detection, estimation and subtraction and spatial filtering. The performance of the techniques presented have been evaluated through simulations on synthetic and/or real data, and compared to existing approaches.