Adaptive main beam nulling using array antenna auxiliary patterns

Abstract

Without use of separate auxiliary antennas, adaptive nulling automatically reduces jamming or other interference affecting a radar or IFF system. A primary beam forming network utilizes four-port directional coupler devices, each having an ancillary port which would have been resistively terminated in the absence of the invention. Signals from ancillary ports are coupled to an auxiliary beam forming network to form auxiliary beam patterns which are orthogonal to and track steered main beam patterns. Auxiliary signals are received via the auxiliary beam patterns. Least mean square (LMS) control loops operate on a feedback basis to derive weighted auxiliary signals responsive to jamming signals. The weighted auxiliary signals are combined with the primary received signals (which may be sum and difference signals) in reverse polarity, so as to be additively destructive of the jamming signals. Multiple LMS control loops enable nulling of jamming signals simultaneously in sum and difference channels. Multiple control loops may be implemented on a time share or multiplexed basis.