Robust adaptive beamforming with mainlobe maintenance of monopulse beams

Abstract

Adaptive monopulse approaches for angularly localising a main-beam target in jamming are usually based on variations of the concept of optimising the sum (Σ) beam via standard adaptation and then optimising the delta (Δ) beam subject to maintain the monopulse slope. These methods have some deficiencies: they do not address target self-nulling issues; they lack tapering, leading to high sidelobes; they introduce multiple point constraints, which may result in target leakage; and they assume linearity of the monopulse ratio curve, something valid only in a small region close to the beam steering direction. The method of this study addresses these and other concerns by maintaining tapered Σ and Δ beams and fully preserving their mainlobes while adaptively suppressing jammers. This approach provides the added bonus of enabling operating in the monopulse curve's non-linear region at wider beamwidths, hence also increasing the efficiency of radar searching and tracking functions. It is shown that such approach is extremely robust and flexible, as it avoids target self-nulling effects due to beam mispointing, it is immune to target and interference dithering effects, and it can be easily extended for super-resolving multiple main-beam targets.