The shape of the sum and difference beams can be severely distorted if nulls in jammer directions are formed. The usual monopulse estimation can then show a large bias, especially for mainbeam jammers. The previously developed correction formulas for the monopulse ratio are generalised to antennas with low sidelobe patterns and digital beamforming at subarray outputs. The low sidelobe sum beam is assumed to be formed by suitable element tapering and the low sidelobe difference beams by subarray output weighting. The new correction values are simply calculated from scalar products of the adapted beamforming vectors with planewave or steering vectors. The bias can be further reduced by switching the beams at subarray level to the estimated direction and repeating the procedure, which is called the multistep monopulse procedure.
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