Monopulse DOA Estimation for High-Speed Targets in Frequency Agile Radar With Phase Shifter Mismatch

The frequency agile radar (FAR) is widely recognized for its robust anti-jamming capabilities in complex electromagnetic environments. However, achieving accurate monopulse direction-of-arrival (DOA) estimation with FAR remains challenging, particularly under short dwell times where phase shifter mismatch (PSM) exacerbates the issue. This paper proposes a targeted procedure to monopulse DOA estimation for FAR that considers the impact of PSM. Initially, we introduce a modified FAR-Radon Fourier Transform (FAR-RFT) algorithm to enhance the extraction of matched filtering samples for high-speed targets, laying the groundwork for subsequent DOA estimation procedures. We then present two distinct methods for monopulse DOA estimation with FAR. The modified monopulse method facilitates rapid DOA estimation at low beam pointing angles, while the Maximum Likelihood Estimation (MLE) method ensures high accuracy across all beam pointing angles. Furthermore, we discuss fast implementation techniques tailored to the MLE method. Additionally, leveraging extensive simulation experiments based on real-world electromagnetic data and rigorous theoretical analyses, we explore critical aspects such as the Cramer-Rao Lower Bound (CRLB) for ´ DOA estimation under FAR with PSM and the theoretical computational complexities of our algorithms. Our results demonstrate the superior performance of the proposed methods in diverse scenarios. Particularly noteworthy is the accuracy achieved by the modified monopulse and MLE methods, which closely approach the CRLB at medium to high signal-to-noise ratios.