Maximum likelihood beamforming in the presence of multipath and refraction effects

The authors present a method of performing accurate tracking of low-altitude flying targets in the presence of multipath and refraction effects. The method applies maximum likelihood (ML) beamforming to an array radar having frequency agility in combination with a computational method for predicting interference patterns which are affected by atmospheric refraction. Tracking errors obtained when using the current ML technique under ducting conditions are shown. Then, the proposed method is described and examples of tracking improvement under ducting are given using experimental data in the X-band