Hybrid Random FM Waveforms for Enhanced Range Sidelobe Performance

Recent work has examined optimization of frequency modulated (FM) waveforms to improve matched filter range sidelobes, while maintaining continuous phase attributes and spectral containment amenable to high power amplification. Through autocorrelation sidelobe minimization of each pulse independently, the range characteristics of a traditional nonlinear FM (NLFM) can be further enhanced. However, the resulting waveforms no longer exhibit the monotonic instantaneous frequency features of NLFM. Here, random phase perturbations are incorporated into each NLFM prior to optimization - resulting in marginally diverse waveforms. The ensuant waveforms are similar to NLFM (though never explicitly enforced), revealing per-pulse autocorrelation performance resembling that of NLFM. Importantly, because each waveform is distinct from the others, slow time processing results in incoherent range sidelobes as observed for random FM (RFM). This hybrid random FM (HRFM) class demonstrates reduced range sidelobes relative to NLFM. As a consequence of pulse-to-pulse diversity, Doppler sidelobes slightly increase due to range mainlobe modulation (RMM) in trade for the improved range performance.