Signal Errors Analysis of Active Calibration via Transponder

Quantitative analysis of SAR signatures require an absolute radiometric calibration of the complete SAR system. The active reflector named as transponder is an effective SAR calibration device that can yield a larger radar cross section than a corner reflector, and decouple the transponder from the background scatterers, which can be used to calibrate the SAR for radiometry, polarimetry, and interferometry. This paper concentrates on the signal error analysis of active calibration via transponder. The system configuration and possible signal processing algorithms are briefed. The most essential element of this transponder, a X-band wideband voltage controlled attenuator (VCA) is developed. As any ripple on the control line will result in AM sidebands on the VCA output, this paper details the various kinds of signal error and their impacts on calibrating high resolution SAR.