Recursive eigenstructure-based technique for low-angle tracking using frequency agile waveforms

The author outlines a technique for solving the low-elevation target angle tracking problem. The technique involves frequency-agile waveforms together with recursive eigenstructure-based algorithms. Frequency agility decorrelates the coherence between the direct signal and specular component as well as provides some robustness to the fading phenomena. Fast algorithms for updating the eigenvalue decomposition as well as for tracking the corresponding minimum-norm polynomial zeros can be used for efficient implementation of the recursive eigenstructure-based high-resolution algorithm. The algorithm is illustrated for tracking a low-flying target as it pops up from the horizon. Fading occurs for monopulse processing for the entire tracking duration when the direct and reflected angles are out of phase. The recursive minimum-norm algorithm smooths out the fading by using snapshots within a sliding window for covariance matrix estimation. Simulation verifies that the technique works well in resolving and tracking the direct signal and the specular component, even though the separation between the signal components incident on the array may be a small fraction of a beamwidth