ISAR Imaging of Multi-target
|School||Harbin Institute of Technology|
|Course||Electronics and Communication Engineering|
|Keywords||Inverse Synthetic Aperture Radar Multi-target Motion Compensation Time-frequency representation|
Inverse Synthetic Aperture Radar (ISAR) is a microwave imaging system，whichused the technique of synthetic aperture and wide signal to get the high-resolution. Themotion of ISAR target can be decomposed into two parts, which are the motion of thetarget center relative to the radar and rotational motion of the different target pointsrelative to the target center.The motion of the target center relative to the radar makesnocontribute to the imaging,and it will result in imaging blur. To eliminate the influenceof the translational motion of the imaging is the key to the ISAR imaging. The processof eliminate the impact of this translational motion is called motion compensation.The thesis has a comprehensive study on the ISAR imaging of multi-target.If thetarget is formation or intensive objects, the distance between each targets is often a fewmeters to tens of meters. Therefore, there are two or more targets in the radar antennalobe.For some reasons, the targets cannot make the exactly same movement.So themulti-target cannot be regarded as rigid body.If the multi-target in the radar antennalobe is regarded as one target to be processed. Since the multi-target has differentmovement, using the motion compensation for single target will result in blur or evennot imaging.So we need to study on the multi-target imaging.Firstly, ISAR imaging principle and the model of ISAR echo is introduced. Thenthe motion compensation principle is introduced from the range alignment and phasecompensation. Among the main range alignment methods, we mainly introduce thecross-correlation method of range alignment and the minimum entropy method. Amongthe phase compensation methods, we mainly introduce the the Doppler centroidtracking method.And the PGA algorithm is also be introduced.Secondly,the method of ISAR imaging based on image field segmentation isintroduced in detail,that at first we make compansating to the multi-target as awhole;then separate it into single target in image field;then make fft to each target tochange it to radar echo;finally make compansating to each single target.We use thismethod to make simulation experiments,which proves the method effective.Besides,some methods to separate image is introduced and the method K-means used by thisthesis is introduced in detail.Finally,the method of ISAR imaging based on time-frequency representation isintroduced in detail.To some multi-targets which are overlapped in range domain,wecannot use the method based on image field segmentation.So we have to use the methodof imaging based on time-frequency representation to separate the multi-targetsignals.Then in each range cell,the signals is used STFT to get the time-frequence representation.Since the speeds of the targets are different,there wil be a few time-frequency segments.These segments can be separated.Then the separated segments aretransformed back to the radar signals.Arranging the signals in order of range cells,wecan get the single target signal.Then using the method of compensation and imaging tosingle target,the image of target will be presented. We use this method to makesimulation experiments, which proves the method effective.Besides,some methods toget the time-frequency representation is introduced,too.