Research On Imaging Algorithms For Bistatic Forward-looking SAR

Bistatic forward-looking synthetic aperture radar(BFSAR)is a special working mode of bistatic synthetic aperture radar.Because the transmitter and receiver platform of BFSAR are separated,the problem of low Doppler resolution and range ambiguity in forward-looking imaging of monostatic SAR is effectively solved.BFSAR also can break through the limitations of linear array SAR,whose Doppler resolution is limited by the length of linear array and the flight altitude.However,BFSAR gains these advantages by increasing the system complexity.BFSAR system introduces a large squint angle,which makes the echo data have severe coupling between range and azimuth frequency,high range cell migration(RCM),and large range walk.At the same time,the separation of the transceiver platform leads to the dual-root form of the range history,which makes the principle of stationary phase(POSP)for monostatic SAR unable to obtain the formula of the bistatic point target reference spectrum(BPTRS).Therefore,most of the proposed algorithms for bistatic SAR can not be directly used for BFSAR.Aiming at the above problems,this paper mainly focus on the imaging algorithms of BFSAR.The main contents of this paper can be summarized as follows:(1)According to the characteristics of one stationary BFSAR,a modified CS algorithm based on squint minimization is proposed.The squint minimization method is used to preprocess the large squint data to low squint data.Compared with the traditional algorithm,this method can effectively improve the orthogonality of range and azimuth and the focus depth in the case of large squint.Then,a modified CS algorithm is derived based on the squint minimization data to image one stationary BFSAR.CS algorithm adopts Chirp Scaling operation instead of interpolation operation in RD algorithm,which reduces the computation amount and makes the phase calculation more accurate.Finally,the effectiveness of the algorithm is verified by numerical simulation.(2)An improved hyperbolic approximating method is proposed to obtain the twodimensional spectrum of BFSAR.The main idea of this method is to transform the two square roots bistatic range into monostatic range,which has only one squre root.In order to make a complete equivalence of phase terms which are under the third order in the Taylor expansion of BFSAR range,we add a new equivalent paremeters in the improved hyperbolic approximating method,which makes the the two-dimensional spectrum of BFSAR more accurate.Then,the Omega-k algorithm for the parallel BFSAR is derived based on the two-dimensional spectrum.Finally,the validity of the algorithm is verified by the simulation of BFSAR.