Bistatic Synthetic Aperture Radar Imaging of Moving Targets Using Ultra-Narrowband Continuous Waveforms

We consider a synthetic aperture radar (SAR) system that uses ultra-narrowband continuous waveforms (CWs) as an illumination source. Such a system has many practical advantages, such as the use of relatively simple low-cost and low-power transmitters, and in some cases, using the transmitters of opportunity, such as television and radio stations. Additionally, ultra-narrowband CW signals are suitable for motion estimation due to their ability to acquire high resolution Doppler information. In this paper, we present a novel synthetic aperture imaging method for moving targets using a bistatic SAR system transmitting ultra-narrowband CWs. Our method exploits the high Doppler resolution provided by ultra-narrowband CW signals both to image the scene reflectivity and to determine the velocity of multiple moving targets. Starting from the first principle, we develop a novel forward model based on the temporal Doppler induced by the movement of antennas and moving targets. We form the reflectivity image of the scene and estimate the motion parameters using a filtered-backprojection technique combined with a contrast optimization method. Analysis of the point spread function of our image formation method shows that reflectivity images are focused when the motion parameters are estimated correctly. We present analysis of the velocity resolution and the resolution of reconstructed reflectivity images. We analyze the error between the correct and reconstructed positions of targets due to errors in velocity estimation. Extensive numerical simulations demonstrate the performance of our method and validate the theoretical results.