Research On Missile-borne Dual-antenna Forward-looking SAR Imaging Algorithm

Synthetic Aperture Radar(SAR)is a kind of imaging radar that can work in all-weather and all-weather.It can obtain high-resolution radar images like similar optical radiographs under very low weather conditions.So it is widely used.Combining SAR imaging with missile navigation,SAR image information can be compared with inertial navigation system positioning information to correct the navigation error and improve the combat efficiency.However,the SAR of the missile-borne platform has the features of forward vision and non-uniform linear motion,which makes the traditional imaging methods unable to obtain high-resolution radar images.Therefore,in this paper,the forward-looking SAR imaging method is studied from the two trajectories of flat-flight trajectory and sub-ballistic trajectory,according to the motion characteristics of the missile.For the forward-looking missile-borne SAR in the flat flight trajectory,blind area exists because of the change of Doppler frequency is small.What's more,since the target in each side produces the same Doppler frequency,there is problem of left and right ambiguity.Firstly in this paper,based on the geometrical relationship between the missile and the target,the target echo signal model is built for forward-looking missile-borne SAR.According to the model built,Taylor approximation formulas of instantaneous slant range are deeply analyzed.Then an extended range-Doppler imaging algorithm for the missile-borne forward-looking SAR based on double antenna under flat-flight trajectory is proposed.And the left and right ambiguity is solved by using the wave-path difference between different antenna signals in the dual-antenna mode.Finally,the feasibility of the algorithm is verified by simulation experiments.In the subduction ballistic,because of the relative motion between the missile and the target,the echo signal will has serious range migration,and also makes the Doppler frequency slope changes constantly.Which can cause serious azimuth focus depth problem,the imaging resolution is greatly reduced.By analyzing the movement features of the missile-borne platform under the subduction ballistic trajectory,the target echo signal model of the forward-looking SAR imaging is constructed and the expression of the two-dimensional echo signal is deduced.Then a modified nonlinear chirp scaling(NLCS)imaging algorithm for dual-antenna single-platform forward-looking SAR imaging system is proposed from the viewpoint of frequency domain.According to the analysis above,linear range walk correction(KRWC)and a bulk RCMC are employed to compensate the coupling between range and azimuth direction.The secondary range compression(SRC)is adopted to achieve the range focusing.Then,the azimuth dependent Doppler FM rate can be corrected by using NLCS operation,and the azimuth focusing can be achieve in range frequency domain.Finally,the simulation results show that the algorithm is feasible.Based on the forward-looking SAR of the flat-flight trajectory and the submarine trajectory,this paper puts the corresponding imaging algorithms.And the simulation experiment proves the feasibility of the imaging algorithm.So this paper has a certain theoretical reference value.