Polarimetric calibration of a coherent radar with application at 94 GHz
Publish date: 2001-01-01
Report number: FOI-R--0161--SE
Pages: 77
Written in: Swedish
Abstract
The report describes the application of a method for calibration of a polarimetric radar, published by the Sandia National Laboratories, USA. The method has been used with a coherent monostatic mm-wave radar at the FOI, operating at 94 GHz, intended for use in polarimetric measurements of static objects. The method reflects an increasing demand for accurate, polarimetric target cross section determinations, including both amplitude and phase. It involves calibration measurements of known reference reflectors from which the polarization distortion of the system is determined, both in the transmitter and receiver parts. The method requires in the implemented general form three calibration measurements: one measurement of a sphere (alternatively flat plate, or trihedral) and two of a dihedral with different tilt angles with respect to the horizontal. If the transmitter and receiver parts have equal, symmetric transformation properties the requirement for independent measurements is reduced to only one, e.g. of a trihedral. The result shows that with a careful calibration it is possible to correct measurements with a system, which is far from ideal, neither with respect to polarization purity nor low distortion. Hence a precise determination of the polarization properties of a target can be obtained, which raises possibilities of its recognition and measurement of the orientation from polarization analysis. This will be described in more detail in a future report.