Research On Shipborne ISAR Imaging Algorithm For Air Target

The shipborne ISAR is an important means of information detection in the field of coastal defense.Due to the 3-D rotation of radar-borne ship,the imaging mechanism of the shipborne ISAR is complicated.As a result,the imaging mechanism and algorithm have not been broken through yet.In this paper,the shipborne active/passive ISAR imaging algorithm is studied.Firstly,the basic theory of the shipborne ISAR imaging is studied.After the active shipborne ISAR imaging model is established,the range profile acquisition algorithm,the envelope alignment algorithm,the phase correction algorithm are studied.On this basis,the model of the passive shipborne ISAR imaging is deduced.After establishing the geometry model,the echo signal model is established when the DVB-T signal is used to form the ISAR image.Then the range resolution and the Doppler frequency of the target scattering point are derived.Then the bandwidth synthesis of multiple DVB-T channels in the frequency domain is studied in order to obtain the high range resolution.Then the classical Range-Doppler(RD)imaging algorithm is studied.All the algorithms are verified by simulation experiments.Since the shipborne ISAR echo signal is likely to be non-stationary,the shipborne ISAR RID 2-D imaging algorithm is studied in this paper.As for the nonparametric RID imaging algorithm,this paper focuses on analyzing the performance of the double adaptive Chirplet transform(DACT)and its improvement to make it applicable to the RID imaging.As for the parameterized RID imaging algorithm,this paper studies three commonly used parameter estimation algorithms.In order to solve the problem caused by the spectral gaps of the multiple DVB-T channels and the nonstationarity of echo signal,a novel approach for shipborne-passive bistatic ISAR imaging with DVB-T signals based on MIAA-RID technique is proposed in this paper.In the proposed algor ithm,the MIAA technique is used to recover the spectral gaps of the range profile and the RID technique is used to form the instantaneous ISAR image.All the algorithms are verified by the simulation experiments.Finally,the shipborne 3-D ISAR imaging algorithm is studied.After analyzing the difference between this 3-D ISAR imaging algorithm and 2-D RID imaging algorithm,the specific content of the active 3-D ISAR imaging algorithm is studied which includes the relationship between the echo parameters of the target scattering point and its 3-D coordinates when the target moves in a uniform velocity and the radar-borne ship has a maneuvering motion both in high and low sea condition.Then the 3-D resolution and the height dimension coordinate reconstruction errors caused by the principle of the algorithm are analyzed.Furthermore,the shipborne passive ISAR 3-D imaging algorithm is proposed in this paper,in which the relationship between the echo parameters of the target scattering point and its 3-D coordinates is established in both high and low sea condition.Finally,the effectiveness of all the algorithms is verified by the simulation results.