This correspondence shows that resonance signatures in ultra-wideband synth
etic aperture radar (SAR) images, which are smeared out due to their late a
rrival time, can be focused and extracted by postfiltering the SAR images w
ith special two-dimensional (2-D) allpass filters. A design algorithm for F
IR approximations to the desired allpass filters based on radial slice appr
oximations (RSA) is presented.