Study On Shorebase-shipborne Bistatic ISAR Imaging Of Ship Target At Sea

As a kind of inverse synthetic aperture radar, Shorebase-Shipborne Bistatic ISARsystem can overcome the weakness of monostatic ISAR system. Besides, it has manyother advantages than monostatic ISAR. Bistatic ISAR configuration has better security,concealment, larger operation range and hence indispensable for modern warfare andcoastal construction. In this paper, we are focusing on Shorebase-Shipborne BistaticISAR imaging of ship targets at sea and the key technologies of non-real-time imaging,in order to obtain ISAR images for identification and classification of the targets.First, a resolution model of Shorebase-Shipborne Bistatic ISAR based onambiguity function method is proposed, which explain the space-varying andtime-varying characters of its spatial resolution. Besides, the results of simulation provethe space-varying and time-varying characters, and illustrate the region conducive toimaging.Secondly, the Shorebase-Shipborne Bistatic ISAR is proposed and the imagingmodel of ship target is build. Based on the proposed model, the Doppler frequency ofthe received signal is analyzed in three different movement cases. In this paper， themodel when the receiver ship is constant，the target and the receiver ship only havetranslation and the target and the receiver ship only have3-dimensional rotation isderived and the Doppler frequency of the received signal is analyzed, aiming to providea theoretical basis for the azimuth resolution. Finally, the results of simulation verify thetime-varying character of the Doppler frequency and illustrate the variation of Dopplerfrequency caused by bistatic spatial geometry changes.Third, we study the RID algorithm based on the real time-delay time-frequencydistribution and complex time-delay time-frequency distribution, and the expressions ofthem are derived. Besides, the reasonability of RID algorithm applied to tShorebase-Shipborne Bistatic ISAR is proved here. In this paper, two kinds of newtime-frequency distributions named the2nd and4th order time-frequency distributionwith complex-lag are proposed, and their optimality are proved theoretically. The signalsimulations illustrate the performance of the distributions and prove the optimality ofthe proposed time-frequency distribution. After that, the RID algorithm is applied toShorebase-Shipborne Bistatic ISAR imaging. The results show that the quality of theimage obtained by the time-frequency with complex-lag is the best, which is a goodbistatic ISAR imaging method for target identification and classification.Finally, the main three synchronization problems of bistatic ISAR system isstudied. The reasons as well as the solution of synchronization problems are analyzed.In this paper, the main focus is the phase synchronization for bistatic ISAR system. The received signal model is derived when phase error is existed, and the linear, quadraticand cubic distortion of the system caused by the phase synchronization error and spatialbistatic geometry are analyzed. Finally, the simulation results show the effects ofdistortion on azimuth resolution and prove that the relationship between the systemdistortions are caused by the phase synchronization error and spatial bistatic geometry.