Research On Principles Of Bistatic Inverse Synthetic Aperture Radar Imaging

Inverse synthetic aperture radar (ISAR) imaging is one of the hot topics in radar imaging processing and signal processing. In this paper, we mainly discuss bistatic ISAR imaging research with a focus on the model and algorithms of rotation-induced imaging and translation compensation.Traditionally, ISAR is monostatic, that is, one antenna is used for both transmitting and receiving signals. This configuration has several disadvantages. For example, a high pulse repetition frequency (PRF) is expected in order to avoid the aliasing in azimuth, but a high PRF may cause the overlap between different echoes. Besides, monostatic ISAR is vulnerable in electronic warfare. These disadvantages can be overcome by bistatic ISAR due to the separation of the transmitter and the receiver. This paper addresses the principles of bistatic ISAR imaging. After carefully introducing the history, principles and algorithms of ISAR and the geometry of bistatic radar system, we come to the mathematic model of bistatic ISAR. Then, an expression of the signal from a scatterer is derived by appropriate approximation, and we also provide a mathematic deduction here.According to this expression, we show that the ideas and the methods for monostatic ISAR imaging, can be generalized to bistatic ISAR imaging under some conditions. Firstly, we consider the rotation-induced imaging, where the Doppler frequency of scatter echoes can be converted to a variable related to azimuth information by appropriate approximation. Therefore we can apply mature techniques of monostatic ISAR to bistatic situation. We also make simulation experiments which fully prove our theory.Then we focus on translation compensation, because the arbitrary motion makes the Doppler frequency of scatter echoes no longer a constant. So we have to remove the effect of translation before taking the Fourier Transform to avoid the image blurring. Finally, several sets of data, corresponding to an arbitrarily-moving target, are generated by computer simulation. Here we use maximum-correlation method for range alignment, minimum-entropy method for phase adjustment and the Fourier Transform. The processing results justify our analysis that the ideas and the methods for monostatic ISAR imaging can be generalized to bistatic ISAR imaging. Besides, we also realize that the images blur when the speed of arbitrary movement increases, so we make experiments to observe the effects of two main factors leading to image blurring.I am sure the study of bistatic ISAR imaging algorithms will have definite reference and application value for radar imaging techniques.