Multipath spread-Doppler clutter mitigation for over-the-horizon radar

This paper discusses two adaptive spatial processing approaches that have been recently proposed for mitigating spread-Doppler clutter in skywave over-the-horizon (OTH) radar. The first is slow-time MIMO (SLO-MO) STAP which uses conventional waveforms that are phase-coded so as to be orthogonal after Doppler processing at the receiver, i.e. in ldquoslow-time.rdquo SLO-MO STAP is proposed as a means of mitigating transmit array sidelobes without costly redesign of legacy transmit or receive OTH radar hardware. The second approach is wavefront adaptive sensing (WAS) which uses a horizontally stratified ionospheric model to motivate a new application of blind source separation (BSS) methods for discriminating targets of interest from spatially distributed Doppler spread clutter. Comparison of these two approaches suggests they each may offer significant performance gains under different ionospheric propagation conditions.