A. Farina et al., NONLINEAR NONADAPTIVE SPACE-TIME PROCESSING FOR AIRBORNE EARLY WARNING RADAR, IEE proceedings. Radar, sonar and navigation, 145(1), 1998, pp. 9-18
The paper deals with the cancellation of clutter echoes in modern airb
orne early warning radar systems equipped with digital beamforming. Pe
rformance is compared of the following two-dimensional filters that op
erate in the angle and Doppler frequency domains: (i) fully adaptive l
inear filter, (ii) partially adaptive linear filter, (iii) linear filt
ers with displaced phase centre antenna weights and with fixed Chebysh
ev tapering, and (iv) the recently conceived nonlinear filter which ta
kes the minimum among the outputs of few linear filters that process t
he same radar signals with properly selected weights. The fully adapti
ve filter requires the highest computational burden and a large region
of homogeneous clutter to estimate the clutter covariance matrix. Fil
ter (ii) alleviates these drawbacks at the expense of a reduced cancel
lation. Filters (iii) are the simplest but offer limited performance.
The nonlinear filter is a compromise solution, since its computational
requirement is slightly higher than filter (iii), but much less than
(i) and (ii), and its performance is comparable to filters (i) and (ii
). Moreover, since it requires a limited form of adaptation, it shows
much higher robustness to nonhomogeneous clutter. Further, the filters
are compared against the live data recorded by the experimental radar
adaptive array flight test equipment of NRL. The set of real data, wh
ich relates to the sea-to-ground transition, allows demonstration of t
he robustness of the new nonlinear detector to nonhomogeneous conditio
ns.