Beamforming and aberration correction in HF radar

A combined array beamforming and channel equalization technique for mitigating the effect of external interferences and signal phase aberrations associated with an HF radar is presented. The aberration correction scheme is a nonmodel-based technique which makes use of the statistical randomness in the clutter region. It is capable of correcting phase distortions due to frequency dispersion incurred in the ionospheric propagation paths. Simulation shows that with this technique the phase distorted signal can be restored to within 1 dB loss of the undistorted signal. In order to retain the possibility of correcting phase aberration at the array element level, a two-step beamforming technique has been implemented by providing a spatial filter to exclude the strong RFI and jammers at the element level and by applying conventional beamforming on the receiver residue which contains only clutter return and local noise. The phase aberration technique is applied between the two steps after the major interferers are canceled.<>