<title>Performance of uniform and nonuniform subband constrained adaptive beam forming under broadband correlated arrivals</title>

Abstract

Several array processing architectures have been devised for mitigation of multipath interference. Those algorithms have focused on rejection of terrain scattered interference, sidelobe and mainlobe clutter, and hot clutter. Two adaptive array architectures for rejection of broadband coherent interference are developed in this paper. Both techniques involve uniform subbanding using the Discrete Fourier transform (DFT) or non-uniform subbanding using the wavelet transform (WT). In the first approach, adaptation and weight computation is performed independently in each subband, and in the second technique the Frost constrained LMS algorithm is applied to all subbands in the transform domain. Due to the correlated nature of the jamming signal, spatial averaging is utilized in both cases. The mitigation performance of both algorithms is compared for various scenarios of coherent broadband interference. This paper also focuses on evaluating and rejecting multipath interference due to propellers or rotor of the radar receiver aircraft or helicopter (see Figure 5). This type of interference is characterized by an induced doppler spread proportional to the angular velocity of the propeller or the rotor. Furthermore the reflected signal represents the near-field component of the propeller scattering signatures. Spatial averaging followed by a transform-domain adaptive beamformer based on the Frost algorithm is used to reject this type of propeller generated multipath interference.