Subretrograde Geosynchronous SAR: Parameter Design and Performance Analysis

In recent years, geosynchronous synthetic aperture radar (GEO SAR) has attracted many scientists to carry out relevant research. Its research is in-depth and gradually maturing. However, conventional GEO SAR has the problems of great influence by the Earth's rotation, complex timing design, uneven flight speed in the whole orbit, nonorthogonal range, and azimuth resolution, which limits its application. A new concept of subretrograde geosynchronous synthetic aperture radar is proposed in this article. Compared with traditional GEO SAR, the satellite has the advantages of less influence by the Earth's rotation, simple timing, uniform motion speed in the whole orbit, shorter revisit time, better resolution, and small space-variant in azimuth and range. The radar parameters of subretrograde GEO SAR are designed. Through the research, it is found that the system sensitivity and resolution no longer change with the orbit position, and its timing design does not need to consider the range migration variation. In addition, the imaging characteristics of subretrograde GEO SAR are investigated. The results show that the range model can meet the imaging requirements as long as it is expanded to the fourth order. After that, the influence of orbit perturbation error in subretrograde GEO SAR is given for the first time. Last, two ways to solve the observation blind area of subretrograde GEO SAR are proposed, one is to change the orbit inclination, and another way is to use the bistatic mode.