Microwave Imaging of Small Scatterers: Linking and Comparing the Beam-Forming and the Orthogonality Sampling Method

Advancements in sensor array technology and radar imaging applications continue to trigger the research towards the development of new imaging algorithms. The orthogonality sampling method is one among the most recently proposed imaging method in the literature. In this paper, we are concerned with studying how the orthogonality sampling method is linked to and compares with classical beam-forming methods. In particular, herein we consider two versions of the beam-forming algorithm: the windowed and the non-windowed schemes. This goal is pursued in the framework of small scatterer imaging, by considering a multiview/multistatic/multifrequency configuration. We succeed in analytically estimating the point-spread functions of the methods under comparison and this allows to establish a clear connection between the different methods in terms of the achievable resolution and, at the same time, to highlight the link between the configuration parameters and the performance. The role of noise, of the cross-terms, of the multiple scattering and of uncertain antenna frequency response are also addressed by a combination of analytical and numerical arguments. It is shown that the non-windowed beam-forming scheme exhibits the best trade-off between achievable performance and robustness against the noise and antenna uncertainties.