Bisector angle estimation in a nonsymmetric multipath radar scenario

The performance of any bearing estimation scheme is dependent on the phase difference between the direct and specular path signals at the centre of the array. The beamspace domain maximum likelihood (BDML) bearing estimator is a recently developed three-beam extension of the sum and difference beam technique employed in conventional radar. Nonsymmetric BDML breaks down when the phase difference is either 0° or 180°. In contrast, symmetric BDML, in which the point angle of the centre beam is the bisector angle between the two ray paths, can theoretically handle any phase difference, with the 0° case giving rise to the best performance. A simple, closed-form bisector angle estimator is developed based on characteristic features of the 3×3 forward-backward averaged beamspace correction matrix when the centre pointing angle is the true bisector angle. Simulations are presented assessing the performance of the new bisector angle estimator and comparing the performance of symmetric BDML employing the new estimator with other ML based bearing estimation schemes in a simulated low-angle radar tracking environment