Practical Issue Analyses and Imaging Approach for Hypersonic Vehicle-Borne SAR With Near-Vertical Diving Trajectory

As a frontier technology in radar imaging, hypersonic vehicle (HSV)-borne synthetic aperture radar (SAR) has several practical issues to be dealt with, namely, ground resolution capability, pulse repetition frequency (PRF) selection, and beam pointing description, especially for the near-vertical diving trajectory because of the extremely small angle between the velocity and slant range vectors. Moreover, its focusing approach design is greatly challenged by very large cross-couplings and spatial variations. Considering these practical problems, the constraints between system performance and parameter selection are analyzed first to obtain the parameter optimization procedure and avoid system design deviation. Then, a frequency radius/angle algorithm (FRAA) is devised, which is an extension of the radius/angle algorithm (RAA) performed in the 2-D frequency domain. In the FRAA, the new range equation and 2-D frequency interpolation function are reconstructed with high accuracy by quadratic fitting and 3-D expansion. Compared with RAA, FRAA is more suitable for the HSV SAR with near-vertical diving trajectory. Simulation results verify the effectiveness of the proposed approach.