A new encoding transponders for SAR calibration

A transponder can encode the signal transmitted by synthetic aperture radar (SAR). The reflected signal from the encoding transponder to SAR can be imaged with the background signals suppressed. One type of encoding transponder is to make the linear frequency modulation (LFM) signal transmitted by SAR inverted. To realize this aim, there are the analog mixing method and the digital undersampling method, which is put forward in this paper. The error models of these two methods are studied. Simulation experiments about an input LFM signal are carried out. The results prove that the precision of the digital undersampling method is better than that of the analog mixing method.