In this paper, a fast time domain imaging for the bistatic synthetic aperture radar (BSAR) including the motion errors is presented. This method is called the fast factorized backprojection (FFBP) algorithm, which not only precisely handles the large spatial-variance, serious range-azimuth coupling and complicated motion errors, but also greatly improves the imaging efficiency compared with the backprojection (BP) algorithm. In addition, it requires the local beamforming from radar echoes as an intermediate processing in the slant range plane instead of the ground plane, which can be accurately referenced to tracks of the transmitter and receiver considering the platform altitudes. Moreover, it analyzes the bistatic range error considering motion errors to derive the requirement for selecting sizes of the subaperture and subimage, which can offer a near-optimum tradeoff between imaging precision and efficiency. Experiment results prove that the proposed method outperforms the BP algorithm in the terms of the efficiency improvement.
Low frequency ultrawideband (LF UWB) bistatic synthetic aperture radar (BSAR) is able to provide the high-resolution BSAR image and obtain more information of the scene. Here, an imaging experiment of the LF UWB BSAR using the fixed-receiver configuration is presented in the paper. In August 2015, based on the monostatic LF UWB SAR system, a LF UWB BSAR imaging experiment was carried out, and the then LF UWB BSAR raw data was collected. This BSAR system has a LF UWB SAR system as the moving transmitter and the other LF UWB radar system as a fixed-receiver. The aim was to investigate the imaging property of the LF UWB BSAR system. One pulse per second (1PPS) signal in combination with the global position system (GPS) disciplined 100MHz oscillator from the GPS receivers were used to implement the time and frequency synchronization in this BSAR system. LF UWB BSAR image was obtained using the fast factorized back projection (FFBP) algorithm integrated with the subaperture-based spectrum equilibrium method. The excellent results are shown to prove the validity of the imaging experiment of the LF UWB BSAR system.
Compared with the traditional narrowbeam–narrowband (NB) synthetic aperture radar (SAR), the large fractional signal bandwidth and wide azimuth beamwidth of the low frequency (LF) ultrawidebeam–ultrawideband (UWB) SAR induce serious coupling between the azimuth and range wave numbers of the echo data, which might influence the behavior of the spatial resolution in the SAR imaging. The spatial resolution considering the system wave number coupling and radar squint angle for the LF UWB SAR system is proposed based on the wave number domain support (WDS) of the echo data. First, the SAR imaging geometry is built and then the spatial wave number of the echo data for the LF UWB SAR is analyzed. Second, based on the WDS of the echo data, the spatial resolution of the LF UWB SAR is derived. Moreover, the narrowing/broadening factor defined as the ratio of the proposed spatial resolution to the traditional spatial resolution is presented, which indicates the effects of the fractional bandwidth and associated integration angle as well as the squint angle on the spatial resolution. Finally, simulation results are given to prove the correctness of the theory analysis and validity of the proposed spatial resolution.
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