The presence of at least one target (120) within a single range cell (111)...The presence of at least one target (120) within a single range cell (111) is detected.The term monopulse refers to the fact that the echo from a single transmitted pulse returning from a target is used to measure the angle of the target. Monopulse processing may be implemented for a linear array of N antenna elements which provides respective signals x(0),...,x(N-l) to a beamforming network.The output signals of the beamforming network are the sum, Σ, and difference, Δ, signals which are processed to generate an output signal, θ, representing the estimated direction of arrival.The sum beam pattern has a symmetrical amplitude profile with respect to its maximum at the boresight, and the difference beam pattern has an antisymmetrical amplitude profile with respect to a zero response at the boresight.
In this case the sum and difference signals represent sum and difference signals for angles in elevation and azimuth.SUMMARY OF THE INVENTION  The present invention is a method and system for identifying a number of targets within a main beam of an antenna array that transmits the main beam and receives echo returns from the main beam.The presence of at least one target within a single range cell is detected.In the missile defense scenario, the problem is compounded by the possibility that closely spaced re-entry vehicles, decoys, and/or debris may be present. The failure to identify multiple threats within a single range cell can cause under-commitment of engagement measures.
An updated covariance matrix (170, 374) is estimated each time the echo signal is sampled.