Angle-Tracking Adaptive Array -- Adaptive-Adaptive Array Processing

The optimal array, which maximizes the signal to interference plus noise ratio (SINR), is beam-formed by the following weigh vector: W = c[R-1s(ϕ)]* whereRis the covariance matrix of interference and receiver noise, and wheres(ϕ)is the steering vector from a desired directionϕ. The optimal array is well known and fundamental in the literature of adaptive array and signal processing but has not been actually applied to real radar because of huge computation burden for invertingR, which is on the order ofN3/Δτ. HereNis the number of sensors in an array andΔτis the update interval. Typically, N = 1,000 in a planar array andΔτ= 1 μs. In order to reduce the computational burden, Brookner and Howells proposed [1] the technique of adaptive-adaptive array, which transforms the large array of N sensors to a small array of M+1 beams of pointing to M interference sources and the desired directionΔ. The optimal array based on M+1 beams requires a computation burden only on the order ofM3/Δτ. The adaptive-adaptive array in [1] is an ingenious conjecture rather than a solid technique, because no solid method for tracking the directions of M interference sources is given. In this paper, the angle-tracking adaptive array (ATAA) in [2] is introduced to implement the adaptive-adaptive array processing. The ATAA offers an even higher SINR than the well-known optimal array at a computational burden only on the order ofN·M2/Δτ. The ATAA is providing a solid basis for the adaptive-adaptive array and is superior over the well known optimal array in both SINR and computation burden, suggesting a remarkable new direction to the adaptive array processing in the eve of digital beam-forming era.