The nonlinearity correction and GMTI issues in FMCW SAR have been discussed in this chapter. As a new scheme of SAR, FMCW SAR acquires high range and azimuth resolutions by continuously transmit and receive signals. The small-size, low-cost, and high resolution characters make FMCW SAR highly suitable for UAV platforms, which is a hotspot in the military applications.
The nonlinearity correction is the prior problem to be solved in the FMCW SAR signal processing. The impact of nonlinearity is not negligible since the foundation of the following signal processing operations. Therefore, a novel nonlinearity correction algorithm based on homomorphic deconvolution has been introduced in this chapter. The advantages of this algorithm are: first, this algorithm is a theoretically unbiased algorithm compared with the traditional derivative algorithm; second, this algorithm does not rely on the length of the delay line.
After the nonlinearity correction, the signal model of a moving target in FMCW SAR has been established in Sect. 5.4. By extract the additional RWM with Hough transform, the along-track moving target can be indicated, and the motion parameters can be estimated.
The research on FMCW SAR signal processing in this chapter is still in theory and simulation stage. The algorithms introduced in this chapter are validated by mathematics and simulations, however, real FMCW SAR data are needed to further demonstrate the effectiveness of these algorithms.