Compensational Clutter Mitigation for Periodic Modified BFSK Waveforms in HF OTHR

The use of FSK-coded waveforms has been previously shown to potentially allow for target detection when the target Doppler is ambiguously aligned to a Doppler offset that is a multiple of the waveform repetition frequency (WRF) and therefore obscured by clutter sidelobes. This has been demonstrated, for example, with pseudo-random coded BFSK waveforms with the thumbtack ambiguity function. Detecting Doppler-ambiguous targets is of particular importance in HF over-the-horizon radar (OTHR), where blind zones due to clutter and/or clutter sidelobe masking is frequently encountered in the detection of high-speed targets. The need to suppress the ambiguous clutter sidelobes is of particular importance in applications with these waveform classes. The considered mismatched processing has been proven in earlier works to have two strictly equivalent realizations, as the optimum mismatched filter and also as compensational processing (the CLEAN technique) with optimum a posteriori clutter estimation. While the computational demands associated with forming these filters can be significant, it is shown here that filters can be largely pre-computed, allowing for real-time applications. We examine target processing losses associated with various perturbations of this clutter filtering technique.