An antenna system has N antenna units stacked on a mast. Each unit has elements for responding to, e.g., GPS signals, and a phasing network that produces mutually orthogonal primary and auxiliary pattern modes at corresponding mode ports of the unit. A number of power dividers are each associated with a different mode, and each divider has N input ports coupled to the associated mode port of a corresponding antenna unit. The power divider associated with the primary pattern mode produces a reference beam and an auxiliary beam, and remaining power dividers produce different auxiliary beams. All beams have approximately both a common phase center and a common group delay center. An adaptive processor combines the reference and selected auxiliary beams to obtain a composite antenna reception pattern in which nulls are inserted at certain angles to suppress interfering signals, without degrading authentic signals arriving at other angles.