Use of adaptive non-causal transmit beamforming in OTHR: Experimental results

We report results from an experiment that applied multiple-input multiple-output (MIMO) waveform techniques to over-the-horizon radar (OTHR). The experiment objective was to demonstrate that adaptive transmitter beamforming could be used to reject spatially discrete radar clutter. In MIMO radar architectures, conventional or adaptive transmitter beamforming occurs following waveform transmission, propagation, scatter from targets and clutter sources, return propagation and finally signal reception. We have successfully rejected spatially discrete clutter to the noise floor of the radar return with rejection in excess of 35 dB achieved using common adaptive algorithms and straightforward training data selection. As part of this we estimated the transmitted waveform direction-of-departure from the transmitter array to the target and used the estimate as the preserved steer direction in the adaptive beamformer. The direction-of-departure estimates agreed well with the true values.