Issues in ultra-wideband, widebeam SAR image formation

The formation of low-frequency, ultra-wideband/widebeam (UWB/WB) SAR imagery faces inherent challenges not present in conventional SAR systems operating at higher frequencies. Small angle approximations and other shortcuts taken in conventional SAR processors may be inappropriate for the UWB/WB SAR processor. The severe range migration associated with fine resolution UWB/WB SAR poses a significant problem for the image formation algorithm. The combination of a long synthetic aperture and a wide azimuth beamwidth has important implications for motion compensation implementation and performance. We survey the major challenges to UWB/WB SAR image formation. The emphasis is on the formation of fine resolution digital imagery from low frequency UWB/WB data collected in the stripmap mode by an airborne SAR system. We examine the differences in image formation and data processing between UWB/WB systems and conventional SAR systems. We illustrate aspects of UWB/WB image formation with imagery from the P3 ultra-wideband radar system-a 0.3 m resolution SAR which operates in the VHF/UHF frequency bands.