ISAR Imaging For Monopulse Stepped-frequency Radar

Stepped-frequency radar is one kind of important high resolution radars. Recently, this kind of radar system has attracted wide attention as it can effectively solve the limitation between range resolution and system hardware or instantaneous bandwidth. Moreover, ISAR imaging is an important method in target recognition, which can effectively obtain intuitive 2D image and size of the target and greatly reduce the difficulty of target recognition. As a result, applying the stepped-frequency radar to ISAR imaging can not only reduce the instantaneous bandwidth for 2D imaging system, but also improve the information acquisitioning power of the stepped-frequency radar. This paper has summarized the procedure of ISAR imaging for monopulse stepped-frequency radar in detail, made a deep research on the phenomenon of range-doppler coupling and the method of cross-range scaling in ISAR imaging combined with stepped-frequency signal, and proposed an algorithm of target selection and an algorithm of cross-range scaling based on monopulse estimation. The imaging procedure and algorithm are verified by simulation experiments and real data. This paper can be divided into three parts which are listed as follows.The first part mainly introduces the related theory and principle of the stepped-frequency signal and ISAR imaging. In this part, the scheme of obtaining high resolution range profile of the stepped-frequency radar and the range profile stitching alignment based on multiple scattering centers are mainly introduced.In the second part, the range-doppler coupling phenomenon caused in the application of stepped-frequency signal to ISAR imaging is particularly studied. And a scheme of the imaging target selection in multi-targets scene with clutter background is proposed, which is based on the velocity sensitivity of the stepped-frequency signal. After the selection step, the 2D image of the interested target can be obtained by HRRP extraction, translation compensation and focusing. Results of simulation and real data are finally shown to demonstrate the validity of the proposed procedure.In the third part, the algorithm of cross-range scaling of the ISAR imaging for monopulse stepped-frequency radar is particularly studied. A cross-range scaling algorithm is proposed, which is based on the target trajectory measured by monopulse estimation. Furthermore, a goniometric method based on the HRRP from sum and difference channel in monopulse stepped-frequency radar is presented. Finally, this cross-range scaling algorithm is proved to be effective by simulation and real data.