Transponder with undersampling method

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 clutters suppressed. One type of encoding transponder inverts the chirp slope of a linear frequency modulation (LFM) signal transmitted by the SAR. Two methods exist by which the transponder can invert the chirp slope of a LFM signal from the SAR: the analog mixing method and the digital undersampling method. I put forth the latter method in this paper as being the superior approach. I have applied this method in the design of a RadarSat-1 SAR transponder.