Spatial-spectral processing for imaging systems: Multibeam RF imaging and radar systems using spectral hole burning materials

Abstract

Systems which form many spatial beams (beamformers) for the RF and microwave spectral bands output either a few simultaneous spatial beams across a wide bandwidth—using true-time-delay beamformers—or many simultaneous spatial beams across a moderate bandwidth—using digital aperture synthesis imagers. The simultaneous spatial beams in true-time-delay beamformers require parallel hardware while digital aperture synthesis imagers requires both high speed digitizers and huge digital processors. Moreover; each output beam is typically processed further by a spectrum analyzer or a radar processor. Simultaneous formation and processing of all spatial beams is intractable for wide bandwidths and many beams. This dissertation develops and demonstrates a new class of photonic processing architectures which form and process many simultaneous, wide bandwidth spatial beams. These photonic architectures modulate RF signals from an emulated array of antennas onto an array of coherent optical carriers. I show the theory, the methods, and the results for systems which use Fourier optics and spectral hole burning (SHB) crystals; the demonstrated applications are: wideband RF imaging, Doppler radar, and multi-static radar applications. Proof-of-concept results show 20-beam RF images across a 1 GHz bandwidth and 20-beam radar correlations across bandwidths up to 150 MHz, but these systems can be scaled to process antenna arrays with thousands of beams across bandwidths up to 20 GHz. While these systems can process wide bandwidths for large antenna arrays, I also show an analysis that claims these systems can offer sensitivity levels comparable to other digital or analog beamformers.