Fast ISAR motion compensation algorithm and ISAR imaging technique for search radar systems

Abstract

Along with high resolution range profile (HRRP) and jet engine modulation (JEM) signals, inverse synthetic aperture radar (ISAR) images are widely used in radar target recognition. A motion compensation process is essential for ISAR image acquisition, but this compensation process takes a long time. In addition, ISAR images can be currently obtained from the tracking radar. It is necessary to expand the image acquisition technique to a search radar that is widely used compared to a tracking radar. In this thesis, the author proposes an algorithm that solves the shortcomings of the processing time of the existing motion compensation process, and also an algorithm that acquires ISAR images from discontinuous and insufficient received signals of a search radar. The fast motion compensation algorithm is divided into two parts: the rough optimization and the precise optimization. In the rough optimization process, the entropy envelope value is used as the fitness function instead of the entropy used as the fitness function in the existing SSA algorithm. Using a small number of phase samples, it is possible to quickly reach the point where the entropy is minimum. Since the proposed algorithm significantly reduces the number of phase samples, the processing time of the motion compensation process can also be significantly reduced. The performance of the proposed algorithm was evaluated from the received signal obtained through simulation and measurement, and it was confirmed that the processing time of the proposed algorithm is reduced by 8.7 times compared to the existing algorithm. Therefore, real-time ISAR image acquisition is possible using the proposed algorithm. In the proposed algorithm for ISAR image acquisition in search radar, it is essential to reconstruct the received signal in the time domain that the search radar cannot observe. In the received signal in the visible region, information of scattering centers is obtained using a scattering center extraction technique, and the received signal in the invisible region is reconstructed using the information. The reconstructed signal has a similarity to that of the tracking radar, and if it is compensated using the ISAR motion compensation algorithm, it is possible to acquire the ISAR image from the search radar. The simulation showed that it is possible to acquire ISAR images from the received signal of the search radar.