All-Pass Filter-Based 2-D IIR Filter-Enhanced Beamformers for AESA Receivers

Recent advances in multidimensional systems and signal processing: An overview

“…Multi-beam digital array processing architecture proposed in [11] was based on MD wave-digital filters that lead to improved sensitivity properties for fixed-point quantization effects. Applications of MD IIR filters to significantly improve the spatial selectivity of conventional phased/timed array beamformers both in the analog and the digital domains have been recently investigated in [12]. The proposed approach employs 2-D/3-D IIR filters as a pre-filtering stage to existing array processing algorithms -thereby mathematically modifying the conventional zeroonly array manifold functions to contain MD pole-manifolds at guaranteed p-BIBO stability -in order to obtain reduced side-lobe levels without compromising the array size.…”

An overview of multi-dimensional RF signal processing for array receivers

“…One possible approach of designing continuous-time domain network-resonant beam filters is to employ first-order all-pass filter based transfer function synthesis [13]. That is, by replacing unit-sampled time delays function is obtained as…”

“…Moreover, the use of first-order all-pass filters in place of sampled time delays removes the bilinear frequency warping effect along temporal frequencies [13].…”

“…2), where a cascade of M ≥ 1 all-pass filters is used to approximate element time delays required at each antenna [13]. Delay-sum beamformer 2-D transfer function for such all-pass filter based implementation is given by [13] …”

“…For beam direction ψ from array broadside, τ = Δx c sin ψ, where Δx is the ULA inter-antenna spacing. The all-pass filter cascade length M should be appropriately selected based on the required beam direction and beam pointing accuracy as described in [13].…”