We consider sidelobe reduction and resolution enhancement in synthetic aperture radar (SAR) imaging via an
iterative adaptive approach (IAA) and a sparse Bayesian learning (SBL) method. The nonparametric weighted
least squares based IAA algorithm is a robust and user parameter-free adaptive approach originally proposed
for array processing. We show that it can be used to form enhanced SAR images as well. SBL has been used as
a sparse signal recovery algorithm for compressed sensing. It has been shown in the literature that SBL is easy
to use and can recover sparse signals more accurately than the l 1 based optimization approaches, which require
delicate choice of the user parameter. We consider using a modified expectation maximization (EM) based SBL
algorithm, referred to as SBL-1, which is based on a three-stage hierarchical Bayesian model. SBL-1 is not only
more accurate than benchmark SBL algorithms, but also converges faster. SBL-1 is used to further enhance
the resolution of the SAR images formed by IAA. Both IAA and SBL-1 are shown to be effective, requiring
only a limited number of iterations, and have no need for polar-to-Cartesian interpolation of the SAR collected
data. This paper characterizes the achievable performance of these two approaches by processing the complex
backscatter data from both a sparse case study and a backhoe vehicle in free space with different aperture sizes.
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