A CALIBRATION TECHNIQUE FOR POLARIMETRIC COHERENT-ON-RECEIVE RADAR SYSTEMS

A new technique for calibrating a coherent-on-receive polarimetric rad ar system is proposed. A coherent-on-receive polarimetric radar is cap able of measuring the Mueller matrix of point or distributed targets d irectly by transmitting at least four independent polarizations and me asuring the vertical and horizontal components of the backscatter sign al simultaneously. The technique requires the use of two calibration t argets, a target with known scattering matrix (such as a metallic sphe re or a trihedral corner reflector) and any depolarizing target (for w hich knowledge of its scattering matrix is not required) to determine the system distortion parameters. The system distortion parameters, wh ich include the channel imbalances, the cross-talk factors of both the transmit and the receive antennas, and the phase shifts and amplitude variations of the transmitter polarizers, are determined by measuring the calibration targets for four different transmit polarizations. Th e validity of the new calibration technique is examined by measuring t he scattering matrices of spheres and cylinders as test targets using a coherent-on-receive radar operating at 34.5 GHz. Excellent agreement between the theoretical and the measured scattering matrices for the test targets are obtained.