A 3-D spatially-FIR RF frustum digital filter with microwave channelization for FPAs

Focal plane arrays (FPAs) find applications in dish-antenna based receivers having multiple wideband beams. Such beams have a plurality of off-axes directions from the main beam. Maximally-decimated multirate 3-D digital FIR frustum filterbank can be employed in an FPA receiver to reduce directional jamming/clutter and other interference, noise, mutual electromagnetic coupling effects, and out-of-system noise/interference from warm bodies close to the antenna. A 3-D frustum filter requires high arithmetic complexity in the DSP hardware and sophisticated wide-band RF-front ends featuring high dynamic range. The temporal channelization of FPA elements using microwave triplexers achieves frequency channelization in continuous-time. Channelization is moved before the LNA stage, thereby allowing considerable improvement in dynamic range requirements for the RF-front end. The channelization reduces LNA bandwidth for each channel. The signals within the microwave channelizer subbands can either be down-converted through mixers, or directly sub-sampled by means of bandpass sampling A/D converters. Integration of multi-dimensional signal processing theory - which, traditionally is built around DSP methods - with microwave engineering, yields mixed-mode microwave-digital realizations of 3-D frustum filters having applications in FPA receivers. Simulation results of 3-D microwave-digital FIR mixed-domain three-channel frustum filters show SNR improvement of 21.5 dB and SIR improvement for 24.2 dB, for wideband applications in the range 1-4 GHz using an FPA having 32 × 32 elements with a dish of aperture 5m and focal length 7m.

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