Spatially Diverse Radar Techniques - Emission Optimization and Enhanced Receive Processing

Radar systems perform 3 basic tasks: search/detection, tracking, and imaging. Traditionally, varied operational and hardware requirements have compartmentalized these functions to distinct and specialized radars, which may communicate actionable information between them. Expedited by the growth in computational capabilities modeled by Moore’s law, next-generation radars will be sophisticated, multi-function systems comprising generalized and reprogrammable subsystems. The advance of fully Digital Array Radars (DAR) has enabled the implementation of highly directive phased arrays that can scan, detect, and track scatterers through a volume-of-interest. Conversely, DAR technology has also enabled Multiple-Input Multiple-Output (MIMO) radar methodologies that seek to illuminate all space on transmit, while forming separate but simultaneous, directive beams on receive.

Waveform diversity has been repeatedly proven to enhance radar operation through added Degrees-of-Freedom (DoF) that can be leveraged to expand dynamic range, provide ambiguity resolution, and improve parameter estimation.  In particular, diversity among the DAR’s transmitting elements provides flexibility to the emission, allowing simultaneous multi-function capability. By precise design of the emission, the DAR can utilize the operationally-continuous trade-space between a fully coherent phased array and a fully incoherent MIMO system. This flexibility could enable the optimal management of the radar’s resources, where Signal-to-Noise Ratio (SNR) would be traded for robustness in detection, measurement capability, and tracking.

Waveform diversity is herein leveraged as the predominant enabling technology for multi-function radar emission design. Three methods of emission optimization are considered to design distinct beams in space and frequency, according to classical error minimization techniques. First, a gradient-based optimization of the Space-Frequency Template Error (SFTE) is applied to a high-fidelity model for a wideband array’s far-field emission. Second, a more efficient optimization is considered, based on the SFTE for narrowband arrays. Finally, a suboptimal solution, based on alternating projections, is shown to provide rapidly reconfigurable transmit patterns. To improve the dynamic range observed for MIMO radars employing pulse-agile quasi-orthogonal waveforms, a pulse-compression model is derived that manages to suppress both autocorrelation sidelobes and multi-transmitter-induced cross-correlation. The proposed waveforms and filters are implemented in hardware to demonstrate performance, validate robustness, and reflect real-world application to the degree possible with laboratory experimentation.