Recursive super-resolution algorithm for low-elevation target angle tracking in multipath

Abstract

Conventional methods of tracking a target using monopulse radar are severely limited in the presence of multipath, particularly at low-elevation angles. A technique using recursive eigendecomposition together with frequency-agile waveforms for tracking low-elevation targets in multipath has been developed. Frequency agility decorrelates the coherence of the direct and specular components on a pulse-to-pulse basis. This frequency agility also provides some robustness to the severe signal cancellation that arises when the direct and specular components are 180 degrees out of phase. The proposed high-resolution, eigenstructure-based algorithm for solving the low-angle tracking problem can be implemented in three steps: (i) updating the covariance matrix, (ii) updating the eigenvalue decomposition of the covariance matrix, and (iii) updating the angle estimates by searching for the peaks of the updated MUSIC spectrum, or solving the zeros derived by the minimum-norm polynomial coefficient. In addition, a phased-array implementation using three orthogonal simultaneous beams placed at half null-beamwidth apart has been developed. The angles can be determined by explicit computation or by a calibration curve in a lookup table such as in monopulse processing for angle estimation using two simultaneous beams.