It should be the ultimate goal of the adaptive antenna that not only the magnitude of the variable weights but also their number should be adaptively determined. It is shown that the beamspace adaptive antenna system is most appropriate to realise it. Next, the beam weight control based on the eigen/analysis technique is described, together with a simple and accurate method to discriminate the signal subspace from the noise subspace. When the constraint for the desired signal direction contains some pointing error, the conventional system tends to suppress the desired signal, taking it for an unwanted interference, but the authors' algorithm proves to be a robust system which guarantees the protection of the desired signal.