Bistatic, fully polarimetric radar cross-section calibration techniques and measurement error analysis

Accurate polarimetric radar cross-section (RCS) measurements require effective calibration procedures and strict attention to possible sources of error. The development of a detailed computer simulation of bistatic, fully polarimetric RCS measurements allowed determination of principal error sources and their relative effect on measurement accuracy. The computer simulation divides the measurement process into five distinct phases: transmission, propagation from the transmit antenna to the target, scattering from the target, propagation from the target to the receive antenna, and reception. The transmission and reception phases model the respective antenna patterns, and the propagation phases model antenna alignment and the geometric differences between the polarization definitions of the antennas and the target.; The simulation indicates that poor antenna cross polarization purity produces significant error when trying to measure scattering in one polarization when comparable strength scattering is present in the orthogonal polarization. Fortunately, proper calibration can effectively reduce this type of error to acceptable levels. Additionally, the simulation predicts that approaching into the near-field of an extended target causes considerable measurement error and that azimuthal averaging, when possible, significantly reduces this type of error.; Numerous calibration techniques exist in the literature, with the 12-term error model forming the basis for most of them. These existing procedures are critically analyzed and experimentally verified. The logical extension of these existing techniques resulted in the development of two new calibration techniques. One of these techniques uses a conducting cylinder in various orientations as the known reference target. Since moment method techniques can be used to calculate the theoretical response of a cylinder for any measurement configuration, the calibration technique is equally applicable to both monostatic and bistatic calibrations. In addition, a limited amount of cylinder misalignment can be detected and corrected during the calibration; however, this misalignment correction procedure is not robust enough to ensure success in field calibrations where precise target alignment is difficult.; Actual laboratory measurements demonstrate the differences in accuracy between the various calibration techniques. A computer program implementing these different calibration techniques is presented, which conveniently permits the user to calibrate the same set of raw measured data using a number of different calibration techniques.