Improved Single Target Calibration Technique for Polarimetric Radars

In this article, an algorithm for calibrating polarimetric radar systems that ensures accurate measurements of complex scattering matrices of point targets in the backscatter direction is presented. In this approach, only a single target, namely, a metallic sphere, is needed as the calibration target, which significantly simplifies the calibration procedure and improves the accuracy. The error model for the polarimetric radar is based on an exact physics-based channel model for radars with dual-channel passive single antennas (Sarabandi and Ulaby, 1990). This article improves upon (Sarabandi and Ulaby, 1990) by allowing the crosstalk distortion matrices for the transmit and receive antennas to be different, thereby enabling polarimetric calibration of monostatic polarimetric radars with different transmit and receive antennas. The closed-form expressions for the calibrated elements of the scattering matrix of the unknown target in terms of the uncalibrated (measured) scattering matrices of both the unknown target and the calibration sphere are derived. The proposed calibration algorithm is validated experimentally using three different polarimetric radar systems operating at X-, W-, and J-bands and using different point targets with known scattering matrices. Excellent agreements between the measurements and the expected theoretical/numerical results are demonstrated.