Angle measurement accuracy analysis of sum-difference amplitude-comparison monopulse in onshore or shipborne ISAR

The effect of antenna rotation on the angle measurement accuracy in onshore or shipborne Inverse Synthetic Aperture Radar (ISAR) is investigated in this paper. The main monopulse ratio after coherent integration is approximately the amplitude and phase weighted sum of all the instantaneous monopulse ratios, which may affect the azimuth estimation. In order to reduce this impact, a non-coherent integration monopulse model is established. Furthermore, based on the experimental data, a method using the amplitude and phase to calculate the azimuth error and its polarity respectively is proposed, which is verified for different signal-to-noise ratio (SNR). In addition, for the extreme case with low SNR, the azimuth output is set by the use of the two basic antenna beams, where the deviation is depicted to be less than the angle measurement precision. The method proposed would be of advantage to the application of azimuth measurement in onshore or shipborne ISAR.