Synthesis of sum and difference patterns possessing common nulls for monopulse bearing estimation with line arrays

In conventional monopulse radar, the bearing of a single target within the main lobe of the transmitted beam is estimated via a maximum likelihood (ML) procedure based in a 2-D beamspace defined by sum and difference beams. The authors show that if the sum and difference beams have all but a few nulls in common, the ML estimate of the target bearing may be determined via a simple trigonometric expression which is exact in the case of no noise. It is shown that sum and difference beams exhibiting both the common nulls property as well as low sidelobe levels can be synthesized via linear combinations of phase-only steered beams formed in the receive mode. For proper operation in the presence of interference, a procedure is developed for synthesizing adaptive-adaptive sum and difference beams for which the set of common nulls includes nulls aligned with the bearings of strong interferences. The procedure works to maintain low sidelobe levels as best as possible under the interference null constraints. Sample patterns demonstrating the efficacy of the method are presented