Holographic Radar Signal Processing

ABSTRACT: This STTR Phase I feasibility study is a collaboration between Chiaro Technologies LLC (Chiaro) and the University of Colorado (CU). The program assesses the feasibility of a prototype holographic range-Doppler signal processor with a code-name"HORUS". The HORUS processor can take element signals from a large linear phased array to produce simultaneous range-Doppler maps across many angles of arrival (AOAs). This processor can operate with arbitrary waveforms and across wide bandwidths, offer enhanced Doppler processing for extended dynamic range, and electronically switch between active radar or passive radar modes. To produce such performance, HORUS takes advantage of a recently-developed pulse-shaping-method where RF signals and an RF array can be scaled down to the size of an optical pulse and an optical array; this enables an optical system to use a single hologram to perform beamforming and range-Doppler processing across the three dimensions of a 1-inch hologram. The dynamic, compact, high performance HORUS system offers processing for both active and passive radar systems. BENEFIT: Unlike any previous holographic radar processors, HORUS can be used in either a multibeam ubiquitous radar system or a passive multistatic radar system. A radar system equipped with HORUS could use a stealthy passive multistatic radar when operating in densely populated areas with many illuminators of opportunity or jammers, and it could use an active, monostatic radar when operating in remote areas with no illuminators of opportunity. A fully-functional HORUS system could offer all of these properties within a single implementation using COTS equipment. Other range-Doppler processors, including previous holographic and CCD-based interferometric approaches can produce 1000 range bins and 1000 Doppler bins. To this capability, the HORUS system adds the capability for parallel multi-beam TTD beamforming with up to 1000 parallel beams and an additional 30 dB of beamformer processing gain. This is enabled by harnessing the third dimension of a volume hologram for signal processing, and not just for multiplexing, as in holographic optical data storage. This range-Doppler processing across 1000 simultaneous AOA beams allows an active radar system to monitor up to 1000 regions on the ground with enormous dwell times and sensitivities. In a multistatic radar system, the system can perform parallel Doppler correlations for up to 1000 different transmitters, a feature which can have a dramatic impact on the detection and resolution of the system. A third feature is that these correlations are performed on arbitrary optically-upconverted RF signals without an RF receiver. Arbitrary waveform processing allows monostatic radars to transmit dynamic radar pulses without reconfiguring the receiver, and even more significantly it allows passive multistatic radars to use whatever signals are available without reconfiguring the receiver. Thus, the passive radar could conceivably work with the entire spectrum of FM broadcasters, TV broadcasts, and cellular phone transmitters simultaneously if the RF signals could be collected. And finally, the HORUS system can process RF bandwidths of 100 MHz or more using detectors and digitizers of 1 MHz or less not the 200 MHz digitizers required by DSP systems. Slower digitizers are available with higher dynamic range, so the HORUS system could use 16-bit, or even 2024-bit, digitizers instead of 812-bit digitizers; this improves the detector dynamic range to 96 dB or more. Moreover, the HORUS system performs the Doppler signal processing and beamforming before it digitizes the signal on a high dynamic range detector. This dramatically enhances the clutter-limited dynamic range and the direct-transmitters-limited dynamic range of the active and passive radars, respectively.