Optimization and Evaluation of Physical Complementary Radar Waveforms

In high dynamic-range environments, matched-filter radar performance is often sidelobe-limited with correlation error being fundamentally constrained by the TB of the collective emission. To contend with the regulatory necessity of spectral containment, the gradient-based complementary-FM framework was developed to produce complementary sidelobe cancellation (CSC) after coherently combining responses from distinct pulses from within a pulse-agile emission. In contrast to most complementary subsets, which were discovered via brute force under the notion of phase-coding, these comp-FM waveform subsets achieve CSC while preserving hardware compatibility since they are FM. Although comp-FM addressed a primary limitation of complementary signals (i.e., hardware distortion), CSC hinges on the exact reconstruction of autocorrelation terms to suppress sidelobes, from which optimality is broken for Doppler shifted signals. This work introduces a Doppler-generalized comp-FM (DG-comp-FM) framework that extends the cancellation condition to account for the anticipated unambiguous Doppler span after post-summing. While this framework is developed for use within a combine-before-Doppler processing manner, it can likewise be employed to design an entire coherent processing interval (CPI) to minimize range-sidelobe modulation (RSM) within the radar point-spread-function (PSF), thereby introducing the potential for cognitive operation if sufficient scattering knowledge is available a-priori. 

Some radar systems operate with multiple emitters, as in the case of Multiple-input-multiple-output (MIMO) radar. Whereas a single emitter must contend with the self-inflicted autocorrelation sidelobes, MIMO systems must likewise contend with the cross-correlation with coincident (in time and spectrum) emissions from other emitters. As such, the determination of "orthogonal waveforms" comprises a large portion of research within the MIMO space, with a small majority now recognizing that true orthogonality is not possible for band-limited signals (albeit, with the exclusion of TDMA). The notion of complementary-FM is proposed for exploration within a MIMO context, whereby coherently combining responses can achieve CSC as well as cross-correlation cancellation for a wide Doppler space. By effectively minimizing cross-correlation terms, this enables improved channel separation on receive as well as improved estimation capability due to reduced correlation error. Proposal items include further exploration/characterization of the space, incorporating an explicit spectral