Bearing Accuracy Improvement of the Amplitude Direction Finding Method for LFM Radar’s in Multipath Environments in the ECM Systems

Electronic Warfare Support Systems (ESM/ELINT) receive, process, analyze and direction finding signals sent by radars. Direction Finding and determining the Direction of Arrival (DOA) is one of the most important radar parameters that plays an important role in the operations of processing, de-interleaving, Clustering, classification and location of radars. Various techniques are used to direction finding (DF) and estimate the angle of Arrival. Among the methods, amplitude comparison direction finding (ADF) is one of the most common techniques due to its high speed and low computational complexity. Multipath fading degrades the performance of Direction Finding systems. In hilly and suburban environments, the direction finding accuracy of ELINT systems can change under the influence of various factors. One of the factors influencing the accuracy of DF is the Multipath factor. In this paper, a new method is presented to reduce the effect of multipath on the pulses received from the LFM radars and improve DF accuracy in ESM/ELINT systems. The amplitude of the received pulses fluctuates and distorts due to the existence of multipath effects. The proposed method is to first convert the signal into a two-dimensional Short-Time Fourier Transform (STFT) and wavelet and using the SOBEL edge finding algorithm, two Time of Arrivals (TOA) are detected. The first TOA corresponds to the start of the main pulse (raise time of the pulse received from the direct path) and the second TOA is related to the reflected pulse (multi-path effect). Then the time interval between the first and second TOA is considered as a signal without a multi-path effect which this time, the pulse has not fluctuated or distorted. In other words, the main pulse is not merged with the reflected pulses. Therefore, the amplitude detecting is implemented for main pulse after eliminated the multi-path effect. The average value of the signal amplitude is measured in this time range. Then Direction finding is performed using the mono-pulse Direction finding technique for an array of 8 antennas. Therefore, the proposed method improves the Amplitude Direction Finding (ADF) accuracy in multi-path conditions.