Analysis and Calibration of Crossed-Loop Antenna for Vessel DOA Estimation in HF Radar

High-frequency surface wave radar equipped with a crossed-loop/monopole antenna has been applied to estimate vessel direction of arrival (DOA). However, unavoidable distortion of the antenna pattern and complicated channel calibration are challenges for achieving high angular accuracy when the multiple signal classification (MUSIC) algorithm that relies on the antenna pattern is employed. Although various methods of pattern measurement and calibration have been proposed, high system complexity and considerable time cost are still troublesome problems, especially for the temporary use of radar. In this letter, we first analyze the characteristics of measured pattern and then rapidly calibrate the crossed-loop antenna using sea echoes and the automatic identification system data. Finally, vessels' DOAs are estimated using MUSIC algorithm and the calibrated loop-only patterns. The high accuracy of DOA estimation is validated at an angle range of less than 180 degrees. This method effectively reduces the system complexity and time cost when compared with the conventional method. A simulation and two field experiments are conducted. Both the rapid pattern calibration for 115 min and the comparison of processing results demonstrate the validity of this proposed method.