On the use of the ideal filter concept for improving SAR image quality

Abstract

The conventional matched filter forms the basis for SAR image generation. Although the impulse response function obtained by the matched filter approach has the best achievable signal-to-noise ratio, high sidelobes, paired echoes and azimuth ambiguities will appear in the impulse response function (IRF) for severe phase and amplitude errors. This paper considers two types of error: 1) SAR transceiver chain errors and instabilities which influence the range IRF and 2) azimuth signal aliasing which leads to azimuth ambiguities. In order to suppress these errors and to improve the SAR image quality, an ideal filter concept is used which provides, in addition to the matched filtering, the deconvolution of the phase and amplitude errors. Several simulation results are presented concerning the improvement of the range and azimuth IRFs. In the case of range compression, the sidelobes can efficiently be suppressed if the replica of the transmitted signal is known with sufficient accuracy. For azimuth processing, the Doppler parameters' accuracy and the azimuth fading limits the efficiency of ambiguity suppression. The results of the image quality analysis show that the sidelobes of the IRF obtained by matched filtering are attenuated by more than 10 dB when using the ideal filter concept.