Wideband mixed microwave-digital 2-D IIR beam filters for nested uniform linear array processing

The synthesis of approximately frequency independent array factors at low hardware complexity using 2-D infinite impulse response (IIR) digital beam filters and nested uniform linear arrays is proposed. The array is designed to have multiple levels of nesting. Each level consists of a uniform linear array (ULA) covering a separate subband of the incident wideband signal. The use of nested arrays allows the required aperture size albeit using a significantly smaller number of elements compared to using a single ULA to capture the entire wideband signal. The use of different levels of nesting further allows the operation of the digital processor for each sub-band at different clock rates. This is a hierarchical approach which saves both digital VLSI hardware and power consumption. The 2-D IIR digital beam filters that process each subband signal from each of the nested subarray achieves wideband beamforming. Frequency domain simulations have been carried out to illustrate the concept of generating approximately frequency independent fan-shaped beam passbands as required in wideband beamforming.