Range-resolution improvement for spaceborne/airborne bistatic synthetic aperture radar using stepped-frequency chirp trains

In this paper, a stepped-frequency spaceborne/airborne bistatic synthetic aperture radar (SFSA-BiSAR) configuration is proposed to show to improve the range resolution of BiSAR. First, the geometry and the signal model of SFSA-BiSAR are formulated, and then an analytical bistatic point target reference spectrum (BPTRS) is derived. Second, based on the developed BPTRS, two imaging algorithms called combination-before-focusing algorithm (CBFA) and combination-after-focusing algorithm (CAFA) are proposed to obtain BiSAR images with improved range resolution. CBFA uses sub-band combination to obtain synthetic BPTRS, and then uses a new bistatic frequency-domain algorithm (BFDA) to obtain the improved BiSAR image, whereas CAFA first uses the BFDA to focus all the sub-pulses, and then uses sub-image combination to obtain the improved BiSAR image. Both of the two algorithms can focus the SFSA-BiSAR signal well and comparison simulations are performed to verify the authors´ conclusion. Computation loads are also calculated to compare the two algorithms and show that CAFA uses less floating-point operations than CBFA. Besides, some important parameters of SFSA-BiSAR are analysed both theoretically and numerically to provide a reference for system design.