High-Latitude OTHR Adaptive Beamforming: Preserving Angle-Doppler Coupled Clutter

Over-the-horizon radars (OTHRs) often operate in the presence of interference that is nonstationary over the coherent processing interval (CPI). In this case, effective adaptive beamforming requires intra-CPI updates to the spatial weight vector to track changes in the interference spatial structure. However, these weight vector changes must be constrained to prevent modulating the clutter signal and drastically reducing subclutter visibility. These additional constraints require a model of the clutter signal. Existing adaptive beamforming algorithms either explicitly or implicitly rely on a scalar multivariate autoregressive (MVAR) model, which is based on typical observations made by mid-latitude OTHRs. However, high-latitude OTHRs often observe angle-Doppler coupled clutter, for which the scalar MVAR model does not apply. This article investigates the ramifications of angle-Doppler coupling for spatial adaptive processing (SAP), which results in the proposal of a new SAP algorithm. The efficacy of the new algorithm is compared to existing methods through simulation.