Cognitive radios are a promising technology for future wireless networks due to their ability to change behaviour according to their operating context. These radios require a platform which offers high performance while also being highly reconfigurable. This paper proposes a novel design methodology, along with a flexible software/hardware system and associated high-level tools for the implementation of cognitive radios on modern field programmable gate arrays (FPGAs). The platform presented can be used by wireless communication engineers with no hardware design experience. We present an initial case study demonstrating the use of the platform for a real application.