Adaptive antenna configuration for unambiguous signal reconstruction in dual-channel SAR systems

In a dual-channel SAR (synthetic aperture radar) system, two different approaches have been proposed in order to obtain at the same time wide range swath and high spatial azimuth resolution. The first one, based on the classical DPC (displaced phase centers) technique (Currie and Brown, 1992), requires a rigid selection of the PRF (pulse repetition frequency) value in order to guarantee uniform sampling of the SAR signal from the two receiving channels. The second approach, proposed in the work of Krieger et al. (2004) and Gebert et al. (2005) permits to correctly reconstruct the SAR signal even for nonuniform sampling. However the two approaches are able to completely suppress the signal of an ambiguous target having a Doppler centroid equal to PRF only if working with "uniform" PRF. This results in a degradation of the focused image quality that gets higher as the PRF moves away from its uniform value. This paper, starting from the approach proposed in the work of Krieger et al. (2004), describes how, in addition to a correct signal reconstruction, it is possible to make available different uniform PRFs for a complete suppression of the azimuth ambiguity. Through an adaptive selection of the dual-receive antenna configuration, it is possible to vary the phase centers displacement and, consequently, to vary the correspondent uniform PRF value. Using a phased array, the adaptive selection of the antenna configuration of either receiving channels, obtainable through a proper amplitude tapering, directly determines the level of accuracy achievable in the choice of the PRF. Such an antenna configuration adaptivity can be simply realized on board, hence permitting to real time reconfigure the system. This is particularly suitable in those SAR which need to operate with different PRF values. In this paper, for a given physical antenna, the performances of several tapering configurations are evaluated in terms of achievable uniform PRF and azimuth ambiguity level.