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Moving-target detection in ultrawideband (UWB) synthetic aperture radar (SAR) is associated with long integration time and must accommodate azimuth focusing for reliable detection. This paper presents the theory on detection of moving targets by focusing and experimental results on single-channel SAR data aimed at evaluating the detection performance. The results with respect to both simulated and real data show that the ability to detect moving targets increases significantly when applying the proposed detection technique. The improvement in signal-to-clutter noise ratio, which is a basic requisite for evaluating the performance, reaches approximately 20 dB, using only single-channel SAR data. This gain will be preserved for the case of multichannel SAR data. The reference system for this study is the airborne UWB low-frequency SAR Coherent All RAdio BAnd Sensing II. Index Terms-CoherentAll RAdio BAnd Sensing (CARABAS)-II, detection, fast backprojection, fast factorized backprojection (FFBP), moving target, multichannel, single channel, synthetic aperture radar (SAR), ultrawideband (UWB), UWB chirp scaling (UCS). I. INTRODUCTIONO VER the last decades, synthetic aperture radar (SAR) has attracted considerable interest as the number of applications in geoscience, remote sensing, surveillance, and reconnaissance increases. The ability to effectively collect data in severe conditions, such as rain, clouds, and/or darkness, is considered to be the main advantage of SAR systems as compared to other imaging sensors. Ultrawideband (UWB) SAR is understood as SAR systems utilizing either a large absolute bandwidth or a large fractional bandwidth signal and a wide antenna beamwidth. Examples of experimental UWB SAR systems are Coherent All RAdio BAnd Sensing (CARABAS)-II operating in the lower very high frequency (VHF) band from 20 to 90 MHz [1], LORA in the VHF and UHF bands from 200 to 800 MHz [2], P-3 with a bandwidth of 515 MHz in the VHF/UHF bands at 215-900 MHz [3], ground-based BoomSAR with a spectral response extending from 50 to

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