Maximum likelihood estimator approach to determine the target angular co-ordinates in presence of main beam interference: application to live data acquired with a microwave phased array radar

This paper illustrates the application of the maximum likelihood estimation (MLE) technique to determine the target direction of arrival (TDoA) in presence of main beam directional interference (MBI). Application to target plus noise-like interference live data are also considered. MLE technique, which is the best in terms of achievable performance, is a possible candidate as an alternative to the more conventional monopulse usually implemented in multifunctional and surveillance radar. Multifunctional radars are required to detect, locate and track targets in presence of natural (clutter) and intentional RF directional interference. The interference might impinge on the side lobes as well as on the main beam of the antenna pattern. A possible definition of side lobes (SLI) and main beam (MBI) or skirt (SKI) interference is given. Concerning the location capabilities of the radar, the requirements can be summarized as follows: (1) the estimation of the Target Direction of Arrival (TDoA) has to be unbiased; and (2) the accuracy of the angular co-ordinates has to be a suitable fraction of the -3 dB beamwidth depending on the target and the interference conditions. The paper contains the derivation of an algorithm to estimate the TDoA, via the MLE technique, against side lobes as well as MBI. To test the validity of the MLE approach, data have been recorded in the recent years with a ground based microwave phased array test-bed radar equipped with the conventional three high gain beams: the sum, the difference in azimuth and the difference in elevation. The experimental set-up is described and the achieved TDoA estimation in presence of a MBI is presented; in addition to this, the estimation of the target power and Doppler frequency is also presented.