Adaptive clutter suppression for airborne phased array radars

The problem of clutter suppression is more serious for airborne than for ground-based radars because the ground returns become Doppler coloured owing to platform motion. Therefore the clutter power depends on both the azimuth and the Doppler frequency. Such two-dimensional spectra can only be suppressed by two-dimensional filters, which require sampling of the echo field in both space and time. This is verified by a phased array radar using coherent pulse trains. The platform motion causes the clutter background to change with time, and any change of the platform velocity results in a change of the Doppler characteristics of the clutter returns. Therefore two-dimensional filter has to be adpative. The paper presents some new results on optimum adaptive clutter supression. For comparison, a suboptimum approach (beamformer plus adaptive temporal filter) is presented. It turns out that the favourable properties of the optimum space-time clutter filter can hardly be achieved by any suboptimum substitute.