A radar transponder was constructed, which modifies the received signal such that its complex conjugate is returned to the radar, qualities of the conjugate mirror used in optics and acoustics. For a monostatic synthetic aperture radar (SAR), a perfect conjugate mirror will reflect a signal back to the radar with no phase shift due to the propagation path. The signal received by the transponder is also decorrelated from other targets, enhancing the transponder signal in the SAR image. This letter describes a transponder operated as a SAR conjugate mirror and an experiment with the European Remote Sensing 1 satellite, demonstrating the feasibility and characteristics. The significance for transponder design is addressed and possible applications discussed
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