A Compact Polarimetric CTLR Mode Calibration Method Immune to Faraday Rotation Using Two Dihedral Reflectors

This paper proposes a compact polarimetric CTLR mode calibration method using only two dihedral reflectors. The method leverages the property that the dihedral scattering matrix is unaffected by double-pass Faraday rotation, effectively eliminating the interference of Faraday rotation on distortion parameter estimation. By selecting any two from four dihedral reflectors rotated at 0°, 22.5°, 45°, and 67.5°, the system distortion parameters can be estimated. To resolve the two-fold solution ambiguity inherent in the estimation process, two ambiguity elimination methods are proposed: Method I selects the solution with equivalent crosstalk magnitude less than 0 dB based on the prior knowledge that the transmit antenna is dominated by right-hand circular polarization; Method II employs cross-validation using different dihedral combinations with distinct product constants, applicable when the prior knowledge does not hold. Through simulation analysis, the algorithm’s sensitivity to receive crosstalk levels, signal-to-noise ratio, and polarization orientation angle shift is evaluated. The results demonstrate that to maintain residual receive imbalance amplitude within ±1 dB, phase within ±10°, and residual equivalent crosstalk below −30 dB, the system received crosstalk must be lower than −25 dB, the signal-to-noise ratio must exceed 35 dB, and polarization orientation angle shift should be controlled within ±1°. The effectiveness of the proposed algorithm is validated using fully polarimetric calibrated GaoFen-3 satellite data, achieving root mean square errors of 0.10 dB, 1.13°, and 0.42 dB for amplitude imbalance, phase imbalance, and equivalent crosstalk amplitude, respectively. Comparative analysis demonstrates that the proposed method achieves significantly higher calibration accuracy than existing approaches, with substantial improvements in parameter estimation precision.