Active adaptive antennas for Radio Astronomy; results for the R&D program toward the Square Kilometre Array

Various unique concepts are studied for the Square Kilometer Array expected to be operational between 2010 and 2015. We compare telescopes in operation to day with the SKA requirements and among these concepts, emphasize the active adaptive aperture antenna. This electronic concept for aperture synthesis has intrinsic capabilities that may widen avenues of new astronomical research with SKA even further and is topic of active R & D within NFRA. Within the program, technology demonstrators are built with increasing complexity. As desirable side effect of the ongoing studies for SKA, new albeit smaller telescopes are coming into operation earlier. Of these, a new generation low frequency array to be operational in 2005 may result with close ties to the exploration of new technologies in our R & D program together with firm scientific push from the US and Holland. Experience gained with this telescope are relevant for SKA's mainstream development and in particular the electronic array. Results of these and other research aspects of the R & D program are presented.